# Grinding Cams - Will this Work?



## dsage (Jan 3, 2013)

I'll ask this question here because I'm sure you are all aware of this method of making a cam:
Take a cam blank,hold it horizontally in a rotory table,
Rotate it a number of degrees, lower the cutter a pre-determined amount, 
Take a flat cut across the side of it, turn it again, lower the cutter some more (or less), take another flat cut across it etc. etc. 
In the end you have a rough cam shape with small steps instead of a smooth surface and you then file it to remove the steps.
The amount to turn and the depth of cut can be calculated from a program called CamCalc which is free.
Hopefully you know what I'm talking about.

How about this idea:
Hold the cam blank horizontally in a rotory table (as above).
Arrange a fixed grinder at the back of the milling table with a stone the width of the cam lobe. instead of a cutter (as above).
Advance the table Y axis into the grinding wheel the same amount (as above). The result being you get the flat spot in one touch without having to move across the lobe with a small cutter. No difference from above really.

Now the new idea:
Instead of backing out when you rotate, keep the wheel where it is and rotate the cam blank (as above) the prescribed amount.
BUT if you do this with a CNC machine and GCODE program you can put the rotation AND the depth of cut command (A and Y) on the same GCODE line and you'll get a (somewhat smooth move in both rotation AND depth of cut (Y) at the same time.
This should produce a smooth surface joining the individual points requiring little or no filing instead of rough steps.

Sounds reasonable to me but I can't figure a couple of things and I need some help getting this straight in my mind:

As with any outside profile milling the path taken depends on the diameter of the cutter (I think). Also I know that real cam grinders use master cams that don't look anything like the finished cams and you have to use a follower the same diameter as the grinding wheel.
In this case we have a wheel that is say 4" in diameter. Does that matter?

On the other hand the wheel is only touching the side of the cam blank at one point so does the diameter of the wheel really matter.

I need help getting this straight in my head.

I'm about to try it. I have the Gcode figured out but am I wasting my time?

Sage


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## Jasonb (Jan 4, 2013)

You would treat the edge of the wheel like any other cutting tool and touch down to set a starting point.

May be better to rough out the cam first and then finish with the grinder as taking a large cut off will heat the part and wear the wheel


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## MuellerNick (Jan 4, 2013)

Yes, that works. Works like any CNC Cam-grinder.
The diapeter of the wheel does make a difference.


Nick


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## thayer (Jan 4, 2013)

Pretty sure that is how the Sherline cam grinder works.

http://www.sherline.com/8650pg.htm


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## canadianhorsepower (Jan 4, 2013)

MuellerNick said:


> Yes, that works. Works like any CNC Cam-grinder.
> The diapeter of the wheel does make a difference.
> 
> 
> Nick


Hi  The diameter of the wheel *does  or does not* make a difference.
I don't think is does if your using a follower cause the ratio doesn't change


look at the pictures

cheers


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## MuellerNick (Jan 4, 2013)

> I don't think is does if your using a follower cause the ratio doesn't change



But he intends to use a CNC. And there too, the diameter of the wheel and of the follower have to match. Difference is, with CNC the follower is made in math.
In the picture you posted, "Ds" is diameter of the grinding wheel. You see that both at the wheel and the follower.


I don't know why my iPad made "diapeter" out of diameter. But better than diaper. 


Nick


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## mu38&Bg# (Jan 4, 2013)

As stated above the actual diameter of the grinding wheel doesn't matter as long as the program is properly written with tool radius compensation. The important part is to adjust  the tool radius every time you true the grinding wheel. It all depends on how accurate you want to be. Plenty of engines work fine with rough milled cams filed to final shape. A simple cam shape is easy enough to program for simultaneous 4th axis motion.


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## MuellerNick (Jan 4, 2013)

> As stated above the actual diameter of the grinding wheel doesn't matter as long as the program is properly written with tool radius compensation.



So the diameter does matter.


Nick


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## Jasonb (Jan 4, 2013)

Diameter does not matter

What matters is the distance from the axis of the cam to the cutting surface, its just like putting any tool in your mill you don't worry about how far it sticks out the collet you just touch down the end of the cutter.


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## MuellerNick (Jan 4, 2013)

> What matters is the distance from the axis of the cam to the cutting surface, its just like putting any tool in your mill you don't worry about how far it sticks out the collet you just touch down the end of the cutter.



I must have misunderstood the initial posting. I understood, that he wants to grind at the circumference of the grinding wheel. And then, the diameter matters.


Nick


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## mu38&Bg# (Jan 4, 2013)

MuellerNick said:


> So the diameter does matter.
> 
> 
> Nick



Yes, Nick, the tool radius is important, just like any other CNC process, not only CAM grinding.

Nick, you very well understand that Gcode can be written such that any diameter cutter could be used to mill a part which has no inside corners. The machine just needs to know the diameter of the cutter in order to perform the correct moves. Tool diameter, 3", 28m, whatever, is not related to the part itself in anyway in the case of the cam assuming radius compensation.

Now, it's also possible to program and use offset to adjust the feature size. In this case the radius of the grinding wheel is ignored and the offset is adjusted to achieve the correct cam dimensions. The reality is that the wheel does influence the form of the cam. However, assuming the program was written for a tool radius near what is being used to grind, the offset will only cause a small error. Writing code for a 4" wheel and using offset to correct for a wheel that is 1" or 10" without correcting for tool radius will result in a different cam form. The larger the wheel, the less influence using offset will have on the finished cam.


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## MuellerNick (Jan 4, 2013)

If you are working with facets (that's what the OP described) and do not use cutter compensation but try to do it by yourself by just adding an offset to each segment &#8230; that will not work. That only works at the base circle and then it gets off. Right at the tip's highest point, you are OK again, then you are off again until the base circle.

That is also true if you use G02/G03 in the YZ-plane (without cutter compensation, would not work anyhow). Works with the base circle and the very tip of the tip radius.
The reason is, that the center of the chest radius and of the tip radius are not at the rotational axis.

If you use the setup described by the OP, with the rotational axis (A-axis) along X and the wheel's axis along X, you would have to redefine all axes on your CNC, or the cutter compensation will not work. The setup without changing axes would be a C-axis.


Nick


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## Jasonb (Jan 4, 2013)

Have a watch of this

As you can see the guy does not take any notice of wheel dia, he sets the program to start when the edge of the wheel contacts a known point, the program is just set to move the cutting edge of the wheel in and out relative to the rotation of the cam.

[ame]http://www.youtube.com/watch?v=OIWyGtXEgR4[/ame]

Now if you had a known distance between cam axis and grinder axis then you would need to know wheel dia. Really depends on how you write the program and what equipment you have.


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## MuellerNick (Jan 4, 2013)

> Really depends on how you write the program and what equipment you have.



Well, that IS wrong. You need to know the diameter of the wheel. If it is wrong, you get distortions.
It doesn't matter if you have wear or dress the wheel and just feed in a bit to get the right lift/base circle.
If you use a follower, it has to have the same diameter (within limits) as the wheel.

If you use the multi-facets-method like in milling, but just with a wheel instead of the cutter, the wheel's effective diameter gets infinite.


Need a drawing?


Nick


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## mu38&Bg# (Jan 4, 2013)

I assumed the correct spindle axis setup would be obvious, Spindle parallel to X. What I missed is that it's not a milling machine setup, it's actually a lathe with live tool and C axis. Nick is absolutely correct that CNC cam grinding is a C axis setup. Just because the Sherline setup produces a cam, doesn't mean it's what was actually designed. I don't know if the Sherline is a real C axis with polar interpolation. A wheel large enough will produce a cam that's relatively similar to the programmed part, even if it's not a real C axis. The indexed method using flat milling is essentially the same idea with an infinite radius tool, so only offset matters.


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## Charles Lamont (Jan 4, 2013)

Jasonb said:
			
		

> Now if you had a known distance between cam axis and grinder axis then you would need to know wheel dia. Really depends on how you write the program and what equipment you have.


Remember that the contact line between the finished cam and the follower sweeps across the face of the follower as the cam
rotates. It is the same when machining the cam. The contact point between cam and wheel only lies on the centre-line joining the cam and wheel axes at points where the cam slope is zero - at maximum lift and round the clearance arc. At all other points you are off the centreline. Unless the wheel diameter is infinite, it has a curvature. That is why the wheel diameter does make a difference.


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## dsage (Jan 4, 2013)

Wow !!

First off let me thank all of you for responding. I didn't expect such a response. I think I see about a 50/50 split on whether this is going to work or not.
 I spent today making the mount for my minigrinder. But I never got a chance to try it. Might not for another 3 days.
I guess a picture would be useful but basically the mount just fastens the grinder to the column at the back of my mill drill (SOLID) with the edge of the wheel in the Y direction (axis parallel to the table X) and the height so the axis of the wheel is the same as the height of the center of my rotary table.

It could be used exactly like the facet method by turning the rotory table - moving in, in the Y direction the prescribed amount according to the CamCalc program. In this case the cutter would be the grinding wheel.

What I propose to add to the process is, instead of moving the grinding wheel back out, rotating the blank and then back in to a new prescribed depth I would drive the rotory AND the Y axis at the same time by putting the new angle and the new depth on the same line of G-code.
 By having the A and Y moves on the same line in the program, it is the nature of Mach 3 (or any CNC) to drive both axis' at the same time to the new location thereby blending what would normally have been steps.

No special programming is undertaken i.e cutter compensation etc. I'm using the angle and Z axis data exactly as it comes from CamCalc except I'm swapping the Z axis (depth of cut per facet) for Y - still depth of cut. And the rotory stays the same as in the CamCalc requirements.
 I'm fastening the grinder to the column and using the Y table movement (instead of Z) because I couldn't figure a good way to fasten the grinder to the quill solidly. Too many obstructions.

I hope this helps clarify what I'm doing and that someone can help me figure out if these moves between facets will work.

I can't see it being much different than blending facets with a file. But then if I were sure about that I wouldn't be asking.

PS> I had previously looked at the Sherline video and wasn't sure what he was doing with the Y axis (in out). You can't really see it in the video. He doesn't say much except that "the program is very complex" and that it took him a couple of months to write it. Something about problems when you grind the peak of the cam and the axis' changing. It didn't answer my questions.
Somehow I think he's right but I can't see why. Or perhaps what I'm plannning to so is fundamentally different.




Thanks

Sage


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## MuellerNick (Jan 4, 2013)

Sage, your method works, but not the way you think. It is more complicted.
Charles described it very well in words why you need to compensate for the wheel's diameter. But words can be very abstract!
I do understand where you don't understand. 
Sure, you can rotate and move in/out at the same time. But the problem is, that the wheel doesn't cut where you think it cuts.
The method you intend to use is good, but it is complicated from a mathematical POV. If you would use a C-axis, the math will be very simple, but the setup gets a bit funny (tailstock).

I think I'll draw a picture tomorrow that shows what Charles wrote. I'm in bed and writing this on my iPad.

Nick


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## dsage (Jan 4, 2013)

Some added information. Remember I'm grinding a model cam not a full sized one. The cams lift is only .074 and I'm using a 4.5" diamter grinding wheel. If that makes any difference in terms of an (relatively anyway ) infinite sized grinding wheel.

Sage


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## gus (Jan 4, 2013)

Hi Fellow HMEM Members,

Will be bookmarking this thread as there a possibliity when my IC engine building prowess grows, four engine building can be made possible.With a basic machineshop limited by space,I can only rely on simplest methods as threaded.

Gus,now recovered from food poisoning last nite. I was one of the 200 at a function.Sure great to have a Nursing Officer as wife.


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## dman (Jan 4, 2013)

OK guys I'm no math genius. my highest math was trig. but I use it a lot. I'm very good with geometry.... the whell diameter does matter but not by much. on a model engine you can overlook it and get good results. biggest factor being that it doesn't change too much from start to Finnish on a multi cylinder engine. even then you are not likely to know the difference. 

if you want absolute repeatability then worry about the wheel size but the relationship between the cam diameter and the wheel diameter makes the wheel look like a nearly flat surface. if you have a 1/2" can diameter and a ~4" wheel the worst case scenario puts the contact from the lobe to the wheel in a range that could never deviate from the centerline more than 1/4" drawing a 1/2" chord on a 4inch diameter gives a height of about .008" that's a good amount but its not the significant value we are looking for... if you swamped in a 50% larger wheel the chord height would change but it only drops to .005 a .003 difference so a massive change in wheel diameter made a noticeable but still small difference in the chord. remember this is a worst case scenario. the chord you are worried about in reality would be much much less than the cam diameter, in fact to avoid the lifter from scraping the lobe off the cam lift needs to be slow enough that the contact point always lands in an area smaller than the lifter diameter which on a pushrod american engine is often smaller than the camshaft. as the wheel gets bigger and bigger the change to the chord height gets smaller and smaller and thus the effects on geometry. remember the rocker ratio is not constant or linear, the lifter radius can vary, and the thing will wear, not to mentioned lash. a .003 change in lash will change timing more than a 50% change in wheel diameter if the cam is small enough. 

the important part is that the valve accelerates open decelerates to the max lift and does the same closing so it doesn't release energy on direction changes and bounce or jump. the lift curve on a well engineered cam should resemble a section of a sine wave. the cam may look different from a sine wave wrapped around a radius because of how the contact point of the lifter moves across the lifter surface but if you have flat lifters and a large grinding wheel and you plot a single sine wave in g-code across a section of rotation equal to the advertised duration you will be in good shape. if you use roller lifters you can't ignore the difference in wheel radius to lifter radius when you design the lobe and a lobe design becomes mathematically complex to translate into g-code but if you are going off a blueprint that describes the lobes dimensions you can treat the wheel like a flat surface as long as the wheel is large enough. 

even if you don't exactly match the ideal cam as the blueprint or your own design sees it, it's not the end of the world. I mean people successfully do this with a file and never plot the valve lift curve on the assembled engine or check that the lifters aren't binding.. its only a model after all.


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## Jasonb (Jan 5, 2013)

Charles Lamont said:


> Remember that the contact line between the finished cam and the follower sweeps across the face of the follower as the cam
> rotates. It is the same when machining the cam. The contact point between cam and wheel only lies on the centre-line joining the cam and wheel axes at points where the cam slope is zero - at maximum lift and round the clearance arc. At all other points you are off the centreline. Unless the wheel diameter is infinite, it has a curvature. That is why the wheel diameter does make a difference.


 
Charles, that explains the issue in a way that I understand and can now see that the wheel dia does come into it.

Thanks, jason


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## canadianhorsepower (Jan 5, 2013)

OK. here's the answer to this delema
use your micrometer

the diameter of the grinding wheel is important IF USING  CNC PROGRAM
BUT NOT IF YOUR USING A FOLLOWER

a very simple explanation your "zero setting for your Z axes using an end mill" is set you run your program. When your done let's assume that your program says that you remove 250 thousand you take your micrometer and man your only at 200 thousand what is the next step 
reset your "zero" to compensate for your end mill that change height or in our case the grinding wheel worn out a bit and that's it no rocket science there.
Now if you listen to the next video Joe Martin founder of Sherline does mention at 5:53 minutes in the video that the dimension of the grinding disk is important and then at 6:57 he takes mesurement and has to give a few more thousands to compensate for the disk warring out.
I' in the process of building a follower and the only reason I'm going to use a 5inch disk it will take longer to ware out:fan:




[ame]http://www.youtube.com/watch?v=PlZDg0rpIi8[/ame]


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## dsage (Jan 5, 2013)

Charles and Nick:
(and everyone else)

I'm starting to see the issue with machining the cam this way, especially with the explanation of the changing axis produced by the changing lifter contact point during rotation. I've seen this before in a diagram and it's certainly easy enough to see it in operation on a real cam and lifter.
 But I didn't really relate it to the process I'm planning to follow making the cams - which is a modified facet operation.
How much of an error it's goint to create I guess remains to be seen.
 I guess the proof will be in the results. I hope to grind something soon and I'll let you know if it works out.
 I can measure the lift, duration etc easily by putting a dial indicator with a dummy lifter pad on it in the (unused) Z-axis quill. Since I have the rotory axis I can measure the timing as well.

I'll let you know in a few days.

Thanks

Sage


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## mu38&Bg# (Jan 5, 2013)

Nobody is disputing that the method described by Sage will produce a cam.

The question is what will the actual machined profile of the cam look like? It will not be what is expected based on the output from Ron's Camcalc data. It will be something different. How different? I see about 0.04mm more material adjacent to the nose radius for a 2mm lift on a 5mm base circle if cut with a 4" wheel. If you've been conservative with follower size it should not run the edge to the follower into the cam.

Will it matter for a model engine? Probably not. If I was making a cam for a high performance engine that was actually intended to drive a load at high power and high speed, I'd be concerned about many things in addition to the actual cam geometry. I'm sure the Sherline unit does all the proper calculations to account for grinding wheel diameter. The dressing of the wheel has such a small impact, it's negligible for our purposes.

Don't worry about valve acceleration rates if you're making simple cams. Without ramps and smoothing, it's going to jerk. Unfortunately, high performance cam design is a black art and those in the know keep the secrets close. Software for engine cam design runs in the thousands of dollars.

Luc, if you are using a follower machine you can compensate with the proper follower shape. That is not in question here this is how cams have been made since the beginning of time, it's simple geometry. The mechanical interface of the cam pattern and follower will take care of the issues at hand. Gcode for a cam grinder is also simple geometry, but the Gcode needs to be calculated either before making gcode if using a simple machine control, or the machine control must be able to calculate what's called polar interpolation on a C-axis, to use relatively simple input data.


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## canadianhorsepower (Jan 5, 2013)

I'm sure the Sherline unit does all the proper calculations to account for grinding wheel diameter. The dressing of the wheel has such a small impact, it's negligible for our purposes.
Hi Greg, I agree with you 100% but if you look at the video at the 6:57 you see Joe mesuring the cam total hight
it didn't match the program and he says that he have to remove 3.5 thousand to be good. I think that this will only
work if someone can figure out hte % of ware on the stone itself and compensate with it in the program. 
Joe says it took him nearly 3 years to come out with a good cam profile using his set up


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## mu38&Bg# (Jan 5, 2013)

I don't think the Sherline is fully automated. It's up to you to set the offsets manually to get the finished base circle size. It seems to perform the tool path once, and you have to feed the wheel for each pass manually. On a stepper motor pushing the motor through a few steps manually is easier and faster than changing the offsets. I've never investigated their cam grinder. I'll build one long before I put down that sort of cash on something appearing so crude.


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## canadianhorsepower (Jan 5, 2013)

this is my next project, It was originaly German and got it translate

should be fun and usefull for cam and cranks
what  do you think


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## canadianhorsepower (Jan 5, 2013)

canadianhorsepower said:


> this is my next project, It was originaly German and got it translate
> 
> should be fun and usefull for cam and cranks
> what do you think


oups forgot the picture:wall::wall:


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## dsage (Jan 5, 2013)

Well All I can say is it works !!
And it works REALLY Well.

I didn't have much time so I made the first cam out of a wood dowell. That way I could take big cuts and not have to worry (Except for a little smell of burnt wood). Also if I got mixed up in the feed directions I wouldn't prang up the works.

The surface finish is smooth albeit a bit blackened.
Measurements are a bit hindered by the metal lifter not sliding on the wood so well but using the proper diameter lifter on the end of an indicator here are the results:

The lift programmed was .074" I got .075"
Base circle diameter programmed was .274 I got .272
(This is under my control and I probably fed in too much. I think this is what the guy from Sherline was measuring to tell when he was done. I went in a couple of thou. too much It's also tough to measure and avoid including the the sloped part  of the cam)

The duration was programmed as 135deg. I got 133.5deg
(I measured that duration at .002" of lift. The program does not specify a lift. I'm sure there would be at least a couple of degrees extra if measured as soon as the indicator came off zero instead of waiting for .002" .)

So I'm going to say that this method works. All of the important parameters are there. It is possible due to the axis issue that the peak of the cam may not be exactly at the 0deg point but if it's shifted it will make no difference I don't have to put a cam lobe on anything pre-existing. Also if I make another lobe next to this one it will be shifted by an equal amount eliminating any problems. The whole shaft will just need to be rotated one way of the other.
(I don't even know if this is a problem)


This is certainly a LOT easier than any other method I've ever tried. And it's certainly good enough for a model engine. I hope I'm as successful with a steel version.


Picture of the setup to follow

I'll try a steel one soon.

Sage


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## dsage (Jan 5, 2013)

A picture of the Cam griding setup. Grinding a wood dowel. Cam is black part.

Sage


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## mu38&Bg# (Jan 5, 2013)

I'm sure you'd find that the nose radius is actually larger than designed. If you use a reasonable flank radius there will be no problems. A large flank radius (flat) will actually result in a negative flank radius (roughly equal to wheel radius) using this method.


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## dsage (Jan 6, 2013)

I'm not sure what you mean by choosing a "reasonable" flank radius
The flank radius was certainly reasonable in the design. I'd have to try to measure it and see if it is significantly different than designed. 
You've surmised that the nose radius would be wider. I can section one and use a radius gauge to check. If that's true then I guess the flank radius must be a bit steeper or flatter? The curve still has to come from the base circle and join up with the nose in a smooth fashion.

But you know something; it really doesn't matter. The results of using this method are so much better than hand filing from the facet method surely nobody can complain. The results are right on the design figures. It's not like it milled a rectangle or a circle instead of a teardrop shape. Almost anything will work in a model but we do strive for perfection moderated by simplicity and this sure meets those requirements.

It's going to be so easy now to index the intake and exhaust separation by simply rotating the shaft the desired amount using the rotory table, zeroing the angle reading and grind the other cam.

I'm going to have to make a steel one now so I can get a really good look at it. (In a couple of days).

If anyone can do the math to quantify the errors from the design values it might be nice to see where the problems lie. That's way beyond me. Perhaps there is some sort of distortion that is not visible.
Remember these values are entered into the CamCalc program to give depth of cut vs. degrees rotation for the facet milling method. The only change I made was to join the facets with a smooth move between facets.


Cam Open Angle (degrees): 135.0
Valve Lift (thous): 74
Flank Radius (inches): 0.542
Base Radius (inches): 0.137
Engine Speed (RPM): 10000
Nose Radius (inches): 0.056
Tang follower width min (inches): 0.235 
Max acceleration (g): 285 
Min acceleration (g): -108 
Lift Area (inch degrees): 5.803 
Nose Transition delay (degrees): 17.11




Sage


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## petertha (Jan 6, 2013)

dsage said:


> The amount to turn and the depth of cut can be calculated from a program called CamCalc which is free.
> Sage


 
Can you elaborate on what website you are using/downloading Camcalc. 
Once upon a time this worked for me, but not sure why not anymore. Its either broken or my PC isnt allowing something necessary to install.
http://modelenginenews.org/design/CamTable.html


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## Art K (Jan 6, 2013)

Luc
You posted a photo of a cam grinding device in the tread as your next project. I failed in my attempt to look it up in google. Can you post more info on this grinder or send me a private message if this would be considered taking over the thread
Art


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## canadianhorsepower (Jan 6, 2013)

Art K said:


> Luc
> You posted a photo of a cam grinding device in the tread as your next project. I failed in my attempt to look it up in google. Can you post more info on this grinder or send me a private message if this would be considered taking over the thread
> Art


Hi Art, I'm not completely done with scaling all the cad drawings and
their are some stuff that I will modified so I can use it for Crank and Cam'S

Can you post more info on this grinder or send me a private message if this would be considered taking over the thread

what does this quote nean I dont understand
cheers


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## mu38&Bg# (Jan 6, 2013)

http://www.homemodelenginemachinist.com/f13/another-cam-grinder-10361/


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## dsage (Jan 6, 2013)

Petertha:

You have the correct link to Model Engine News and the Cam Calculator. It should work right there on the web page if you enter the data. See the note below the entry form. He says it has only been tested on certain Browsers. Works for me on IE 8. (Which I don't think is on the list but works for me). I think it uses Javas script. Do you have Java installed?

Sage


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## dman (Jan 7, 2013)

dsage said:


> I'm not sure what you mean by choosing a "reasonable" flank radius
> The flank radius was certainly reasonable in the design. I'd have to try to measure it and see if it is significantly different than designed.
> You've surmised that the nose radius would be wider. I can section one and use a radius gauge to check. If that's true then I guess the flank radius must be a bit steeper or flatter? The curve still has to come from the base circle and join up with the nose in a smooth fashion.
> 
> ...



my assumptions are there will be distortion but too little to notice. it won't be visable and may be difficult to measure without a scaled up print out and a comparator. it will likely be more acurate than the facets and file

I may be able to make up a spread sheet to figure it all out but it will take me time since I'm not really that familiar with spread sheets.. depends also on how in depth I want to go with plotting the curves. but lash will affect the critical timing events more so than the wheel diameter. wheel diameter would be critical if it was closer in scale to the cam lobe like a 1" wheel would need much more compensation the get ideal results. 

if you use cam software and make it aware of the grinder geometry then problem solved. I believe master cam 8 and maybe 9 have been opened up for educational use and no longer need dongles or keys to use. its old software but will more than serve the purpose. there is more modern free software available as well but Im not familiar with them and find them lacking in features I like. makes me adjust my drafting style too much.....


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## canadianhorsepower (Jan 7, 2013)

dieselpilot said:


> http://www.homemodelenginemachinist.com/f13/another-cam-grinder-10361/


Hi Greg thanks for posting this link being a fairly new member didn't know it exist.
This is what I'm using but I have the original "German" version.Theirs a few mod
that I want to do to it but I think that it will do Crank and Cam when done


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## mu38&Bg# (Jan 7, 2013)

Finally, found Achim's website, couldn't locate it in my bookmarks. http://metallmodellbau.de/

As for cam error using Dave's method. I actually drew the stuff in CAD and traced a path as described by the method using a 4" grinding wheel. There was no guessing involved. Yes, it will work fine in most cases, but don't pretend it's exactly as you'd expect it to be. If the discrepencies don't bother you, proceed.


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## dsage (Jan 7, 2013)

Well Im going to have to declare a TOTAL success in metal.
I prepared everything for using coolant but I didnt have to use any - BONUS
There was so much air blowing out of the mini-grinder fan that it actually blew the sparks sideways and kept the metal cool too.
I made a little cardboard duct anyway to make sure all the air was directed at the grinding.
After each 5thou pass the metal was warmish to the touch but you could hold your finger on it ( so maybe 130deg F?)
By the time I got the next pass dialed in the metal was cool.

If you get the light just right you can see faint facet lines in the surface finish but you cant feel them. With a flat lifer in place there is no sign of wavering in the readings as the cam turns. The surface finish is perfect even with the coarse wheel. I wont change that. Not sure what the camera is picking up. It shows some radial lines that I dont see on the real thing.

WOW.!! I never thought this was going to work out so well.

I measured the results:

The program assumes full contact for the lifter. I measured duration at the .002 lift points. The design of the exhaust lobe was 135deg duration, I got 122.5 Im sure eliminating the .002 at each end would easily get back several of the missing degrees of duration. From experience probably all of it. About the same error for the intake cam I ground.
The lift is a  few thou shy of the design at .071 instead of .074

I could go measure the duration at the zero points but thats not how the engine will be operated. It would be easy enough to fudge the input numbers a bit to tune the result if I had to. Im leaving it. Im more concerned with overlap which I have total control over now because I just have to dial in the number of degrees and then zero the CNC reading and grind the next lobe.

So, bottom line for anyone with a CNC mill this is the cats meow for making cams.

Im going to try to automate the machining passes a bit more. I have to do a bit of fiddling to get each pass set up. (about 5 seconds) as it is.

Now all I have to make is 16 lobes plus some spares.


Sage


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## dsage (Jan 7, 2013)

Greg:

I'd be interested in what you found to be wrong with the profile when you drew it in CAD.
It measures better and was easier to made than any cam I've ever made.

Sage


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## mu38&Bg# (Jan 10, 2013)

The greatest deviation from the desired profile occurs where the flank meets the nose radius. There is excess material left behind. This is more prominent if a small grinding wheel or a large flank radius is used.

Why do you think the lift is smaller than intended? There is no error using this method at the apex of the nose radius. The results do look good however.


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## canadianhorsepower (Jan 10, 2013)

How many lines og Gcode did you need for this
great work


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## dsage (Jan 10, 2013)

Greg and Luc:

I measured everything to do with the profile. The base diameter I made right on by tweeking the last path and the lift comes out only a couple of thou short at most. The duration is a bit short but I haven't measured it at zero lash. My engine needs about .002 of lash so I measured it there. It was about 10deg short at that lash. I suspect all of that will be made back if I measure it at zero lash as the program calculates for.

Luc:

The number of lines will vary I suspect based on the profile. I just took the output of CamCalc and converted the numbers to Gcode.
In this case there were 135 lines. There will basically one line for each degree of rotation so a maximum of 360. But when you get around the base circle a lot of degrees are zero cut so it becomes one line to move from one degree setting to the next with the same cut setting. No need for a new line until the depth of cut changes.

Having said that there are about 15 passes required of 5 thou each of the same code. If you were to make that all one program you'd have 15x135 lines. I've been setting the offset manually and running the same code over.


Sage


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## dsage (Jan 12, 2013)

I've ground a couple of more cams and with careful attention to the base circle diameter in the final grinding pass the lift comes out only about 1 thou short. I also measured the duration at zero lash and it is right on for both the intake and exhaust cams I ground.
So I guess the bottom line is that this method works perfectly and produces the cam specified in the CaCalc program.$

I can't explain why except for perhaps one thing:
The lifter is already considered in the calculations. So perhaps the offsets in axis' and shifted point of grinding as you rotate are already figured into the calculations for depth of cut. 
If you draw a 4.5" grinding wheel next to the cam lobe drawing, the grinding wheel is pretty much flat like a lifter.

Maybe this is why the cam turns out exactly as spec'd.

Sage


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## dman (Jan 12, 2013)

dsage said:


> I've ground a couple of more cams and with careful attention to the base circle diameter in the final grinding pass the lift comes out only about 1 thou short. I also measured the duration at zero lash and it is right on for both the intake and exhaust cams I ground.
> So I guess the bottom line is that this method works perfectly and produces the cam specified in the CaCalc program.$
> 
> I can't explain why except for perhaps one thing:
> ...



been trying to say that.... the missing thou can be a number of factors but isn't the radius. most likely it is because the narrow radius on the nose of the cam gives less contact and the wheel cuts it more aggressively due to less pressure and deflection where there is more. you may also have a thou of backlash in the lead screw or if you have steppers they do lag behind because of lack of feedback. the driver can only output steps and micro steps that would give an ideal position under zero load. they do deviate from that under load.


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## mu38&Bg# (Jan 12, 2013)

I can assure you the cams deviate from design where the flank meets the nose radius. Whether or not this is enough to cause problems with followers depends on the factors I've already mentions. They are not as designed though. Simple cams for display engines are not demanding of profile or accuracy so it won't matter 99% of the time. Real cams are much more than just duration and lift.


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## dman (Jan 12, 2013)

dieselpilot said:


> I can assure you the cams deviate from design where the flank meets the nose radius. Whether or not this is enough to cause problems with followers depends on the factors I've already mentions. They are not as designed though. Simple cams for display engines are not demanding of profile or accuracy so it won't matter 99% of the time. Real cams are much more than just duration and lift.



again it is a little difficult to calculate the entire profile by hand but you can easily see that the geometry dictates it is impossible for it to deviate more than .005 at any point based on the distance of max lift from the axis of rotation. if you run it through the Pythagorean theorem you get a difference of .005 and that's in an impossible situation. the actual deviation of the contact point from the centerline is likely no more than a 1/3 of that and at that point the error is .001 or so.

i know exactly what the concern is, but i can estimate how much of a problem it is and the normal problems of deflection and such are a bigger concern.


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## MuellerNick (Jan 13, 2013)

> I measured everything to do with the profile.



I'm sorry, but you didn't. If the lift is as intended and your timing angle is off, the rest will be off even more.
Stating your measured everything, only shows you didn't understand the physics of a cam that well.
Are you sure, the acceleration/deceleration isn't completely off or are you just guessing?


Nick


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## dsage (Jan 13, 2013)

You're right. I never pretended to understand cams to any great extent. That's why I titled this thread "Will this work".
 I'm only interested in producing something easily. But that's not to say I'd be happy with something whittled out of a metal bar either.
I really appreciate all or your input (everyone).

Explain what you mean about timing angle.
If you mean is the lobe shifted around the shaft from where it is intended?
I doubt it (see last paragraph) but it might be.  If so it makes no difference.
The lobes are ground in pairs (intake and exhaust) and assembled onto a shaft with bearing and spacers in between.
If I grind the pairs in one setup then both of them are shifted the same amount but relative to each other they will be exactly at the Lobe center angle I chose. It makes no difference, I just have to rotate the pair on the shaft at assembly time.
For each pair I intend to measure where the TDC point I want is and mark it. Then I will assemble it on the shaft which will be rotated to the cylinders TDC point and rotate the pair to the mark and pin it in place.

As for acceleration and deceleration being right or wrong:
I have no idea. I know that the base circle is right on diameter and (in case I didn't mention it) I used some radius gauges and best I can tell the tip radius is VERY close to expected. So I figure there are a limited number of ways to join those two circles with the flank. It could be the flank is flatter than desired (as eluded to by one of you) but it certainly isn't concave or bulging out. I can attempt to measure it to see if it has a radius of (can't remember off hand) someting like 0.56" as designed.

I don't want to disrespect anyone that grinds cams for real engines but I don't think whatever errors that are there are significant or will make any difference to the model engines operation. They are certainly leaps and bounds better than a hand filed cam and have abetter finish than the side milled cams I made previously.

I will go back to one thing. The CamCalc program that generated the data for the cam lists the acceleration G-forces etc. for each degree of rotation along with the cutting data. It is what it is, and I have to assume it is correct.
 I remind all that I have simply added a slight modification on getting from one facet to the other to avoid the filing. The intermediate points (facets) are the same no matter the process used to join them.


Sage


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## dman (Jan 13, 2013)

before somebody catches me i made an error on my last rough ass guestimation. i used the wheel diameter instead of the radius when trying to figure out chord height, well i did some more estimating, i can run precise numbers if i look up a few formula that i forgot or i can draft it in cad (i don't have it installed.) but by my new estimations the max offset of the contact point to the wheel is probably ~60-70degrees from the lobe being vertical and the error is .0025-.0035" again, just an estimation. if i play with cad i can give precise numbers but i really think the op has absolutely nothing to worry about.


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## mu38&Bg# (Jan 13, 2013)

If one is happy with this method that's fine. If one understands what the downfalls are and is still happy that's even better. If one doesn't understand it's time to ask questions. I'm giving up on forums left and right because you talk talk as much as you want but people only listen to what they want to hear.


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## canadianhorsepower (Jan 14, 2013)

I was under the impression that these forums were to exchange knowledge 
that would allow any of us to build better engine

Right now this post looks like it's a fight that someone end out winning

I'm disapointed seeing so much knowledge bying over run by typical personality


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## canadianhorsepower (Jan 14, 2013)

canadianhorsepower said:


> I was under the impression that these forums were to exchange knowledge
> that would allow any of us to build better engine
> 
> Right now this post looks like it's a fight that someone end out winning
> ...


beeing over run


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## dman (Jan 14, 2013)

yeah no more arguing from me.. dsage congrats on a beautiful part.


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## dsage (Jan 15, 2013)

Thanks - to everyone.
I guess I've insulted some for not listening to reasons why these cams may not be "correct". But in the end, I have several in my hand and I can't see (or measure) enough wrong with them to be rejected.

BTW I attempted to measure the flank radius which is supposed to be 0.56" radius. The best I can say is that it is NOT flat because a straight edge rocks on it, and my 0.5" radius gauge shows a bit of light in the center of the arc so it must be slightly over 0.5". Not very precise I know but worth something.


Yup - may be crap theoretically but practically they're more than good enough for my purposes.


Thanks again

Sage


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## MuellerNick (Jan 15, 2013)

> I guess I've insulted some for not listening to reasons why these cams may not be "correct".



Accepted!



> Yup - may be crap theoretically but practically they're more than good enough for my purposes.



I can't argue against that. When you are happy with them, you are happy with them!


Nick


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## dsage (Mar 21, 2013)

I just thought I'd throw in an update on this cam grinding approach. Yes I'm still at it.

First off I have to apologize to a couple of you who said there would be something (not exactly defined) wrong with the shape of the cams. There does appear to be a problem but I previously had no way to prove it and the cams I've ground appear pretty good but then they are small and difficult at best to measure.
 A friend of mine devised an excellent method of seeing exactly what the grinding wheel is producing. He suggested drawing a REALLY large cam on cardboard and then input that data into the Cam Calc program. Then install the cardboard template in the rotary table and set it up like I would a cam blank. Then I run the program a step (1 degree) at a time and trace the profile of the grinding wheel for each step to show the path of the grinding wheel to see how it deviates from the profile on the cardboard.
 To be sure the method is correct I first used a straight edge in place of the grinding wheel to simulate the way the program was supposed to work which is to turn the blank, take a pass across it with a milling cutter, rotate the blank, take another pass, etc. etc.
 Using that method the straight edge follows the profile perfectly so I know the Cam Calc program and the testing method is correct.

See attached picture of the path produced by the grinding wheel. Sorry, there is parallax in the picture I couldn't get the camera straight on so it looks like the wheel is way off the line.
 The shaded area is the pencil lines from tracing the grinding wheel at each step so you can see where it actually grinds vs. the proper path CAD line on the cardboard. I have to admit that none of the cams I have actually ground look this far off. Of course the errors are magnified about 20 times (best I can figure).
 Someone once mentioned that the problem is that for most of the profile you are not grinding where you would expect i.e on a line from the axis of the grinding wheel and that the point of grinding moves as you rotate the blank. This is true but using the straight edge test like the program expects it become obvious that the program needs for the grinding (or cutting) point to move. If you look at the straight edge setup (next post) the cutting takes place (on this enlarged mockup) as much as 2" off the centerline and this is exactly what is required to produce the correct profile. In this respect an infinitely large grinding wheel would be best. Anything smaller and some of the grinding is missed because of the curvature of the wheel.

Hmmm maybe I'll make a little belt sander instead of using the grinding wheel. 

Another issue came into view as well. If you look carefully at the picture, down near the bottom of the tracing you'll see the grind path is separated from the proper path slightly whereas at the same point on the other side of the cam the grind path is right on the line. At first I thought his might be some eccentricity in the cardboard template but although there was some it was not this much.  I've also noticed on the real ground metal cams that the lifter was not returning to the closed position at exactly the same zero point I had set at opening. It was about 2 thou off on the steel cams and is probably 20 times that in this test setup. So that gap appears to be real. I can't explain that. I guess it's a problem in the calculations.

So, I'm abandoning this method of making cams for the time being. The upshot of this exercise is that my friend who is a good programmer got interested and he seems to think he can fix this problem with a new program which will compensate for the off axis grinding and the diameter of the grinding wheel. I hope he's right. 


Sage


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## dsage (Mar 21, 2013)

Here's the picture of the straight edge setup emulating passing a milling cutter across the blank. Note that the point of contact is (properly) a couple of inches off the center line. This produces the correct profile.

Sage


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## mu38&Bg# (Mar 21, 2013)

This is what we were expecting. The offset is curious. A problem with the math would be obvious in the coordinates supplied by Camcalc. The numbers from Camcalc are symmetric so I don't think that's the issue.


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## dsage (Mar 21, 2013)

After checking, Yes, it appears the data is symmetric so I guess it comes down to eccentricity in the rotary table chuck. It was just odd to see it show up exactly where I've seen it in some of my test cams when I make no special effort to put parts in the chuck in a particular place. I just zero it wherever it lands. That error is minor. For now this method of grinding cams is on the back burner due to the apparent errors in the flank. Even though, like I said, you'd be hard pressed to see (visually) as much error as shows up in the test piece. As well, the duration, lift and as best I can measure, the radii come out correct. It may not be fair to magnify the errors like this. Sort of like using an optical comparator. Minor issues can be made to look excessive But I guess errors are errors and I'd like to make them the best they can be.
 I'll have to see what my programmer friend comes up with for a new program.
It's all been an interesting experiment.
I just thought it best to update this thread in case someone thought this method of grinding cams was a done deal and worked properly.
At the moment I'd say it's a far cry better than using cam calc to rough them out and then hand file them. I'll leave it at that for now.

" I'll be back "


Sage


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## dman (Mar 21, 2013)

dsage said:


> After checking, Yes, it appears the data is symmetric so I guess it comes down to eccentricity in the rotary table chuck. It was just odd to see it show up exactly where I've seen it in some of my test cams when I make no special effort to put parts in the chuck in a particular place. I just zero it wherever it lands. That error is minor. For now this method of grinding cams is on the back burner due to the apparent errors in the flank. Even though, like I said, you'd be hard pressed to see (visually) as much error as shows up in the test piece. As well, the duration, lift and as best I can measure, the radii come out correct. It may not be fair to magnify the errors like this. Sort of like using an optical comparator. Minor issues can be made to look excessive But I guess errors are errors and I'd like to make them the best they can be.
> I'll have to see what my programmer friend comes up with for a new program.
> It's all been an interesting experiment.
> I just thought it best to update this thread in case someone thought this method of grinding cams was a done deal and worked properly.
> ...



if the radius of the grinding wheel is not in the same proportion to the cam that you used while grinding then the error will be exagerated and not scaled to the cams you made. i an be wrong but that wheel in the mockup looks less than scale. 

if you want to  be 100% precise you can move the wheel up and down as well as the table in and out as it turns and then wheel radius wont matter. 

if i have time tomorrow i can try to draft something up in draftsight to show how to find all the points as a visual aid and maybe come up with a spreadsheet to crunch the numbers.


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## dsage (Mar 21, 2013)

Most of you guys are so smart. (compared to me).
 Why didn't I think of that. Yes the size of the grinding wheel is far from scale. It's 7" diameter and it's what I used to grind the cams which are about .430 dia as a blank. For this test setup the grinding wheel would need to be 16 times the cardboard size or about 100" in dia. to be in the proper scale. (the cardboard cam is 6.25 base to tip)
I'm glad you caught that because I was dismayed at the amount of error showing up. It certainly was not indicative of what my steel cams were coming out like but I couldn't pinpoint the source of the error.
Certainly a properly scaled wheel would appear more flat (like the program is expecting and works fine with) and a lot of what shows as error would be removed.
Now I'm curious as to what effect that will have. I should be able to do that by drawing a 100" circle and use a portion of it in place of the 7" wheel. I'll try that tomorrow.

Thanks for that insight. 

I had rejected the idea of moving the grinding wheel up and down early on because it would then need to be mounted on the quill of the machine (unless you had some other idea I've missed). There is too much "stuff" on the head and quill to get a setup rigid enough (I expect). If I were going to use the quill I would generate a cam program specifying a 7" diameter tool and effectively  "side mill" the cams with a grinder.
 Side milling is how I did my first set of cams and it worked just alright but your cutter needs to be factory sharp and holding cam blanks vertically is problematic. I had a lot of rejects with chatter etc. from flexure.

I had thought to model the whole thing in 3D CAD so it will be easier to visualize the geometry but it's probably quicker and easier to just keep making cardboard models. But if you know of a way to accomplish that I'd be interested in your results.Thanks for the offer on the analysis. 

My friend reported back that he has corrected his program to take care of the tip geometry but he has to do other things for a day or so before he can get back to figuring out the flank.

This is all very interesting. I hope it works out in the end.

Sage


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## dsage (Mar 22, 2013)

OK, so here's the latest.
Yes, in fact using a properly scaled up grinding wheel - in this case 108" in diameter does get rid of most of the error. See the two pictures below.
I also figured out what the gap I mentioned before was on the one side. The card with the template on it was rotated slightly i.e a line from tip to base circle was not precisely level so obviously the outline scribed by the program was not going to follow the drawing. I decided to eliminate that distraction by tracing the path using a blank card and overlay the template after to fit inside the shaded area to observe the differences.
 The first picture is the tracing on a blank card. The second picture is with the template overlaid. It can be seen that there is a slight error on both sides of the tip. The rest of the trace is right on. 

I'm not sure all of the error is real though. Drawing a cam in AutoCad is difficult. I drew the cam using all the same radii used to program camcalc. But I measure the duration of the cardboard cam and it is 125deg whereas the data was for 138deg. I'm sure that comes down to my ability to line up all the curves in CAD and print and cut out the template. It appears the program is scribing something with more duration so it's probably closer to correct.
  But for sure there will be some error using the large radius instead of a flat because a surprising amount of the grinding takes place off the centerline and the curve instead of a flat will affect that. No grinding is going to take place where there is a curve instead of a flat and that's what the template shows - a lack of material removal at the tip.
 Considering I'm using about the largest wheel I can swing and the largest practical diameter wheel at 7" I'm going to have to live with the error.
 The error as far as I can see is only about .050 on each side of the cardboard lobe. Scaled down that's only .003". Some of it might disappear if I could perfect drawing a cam with the 138deg of duration.

So, I'm back to thinking this method is pretty darn good considering the simplicity and accuracy of grinding over hand filing the output of CamCalc.
I'm glad I was able to prove it.

Have I missed anything (else) ?? 

Sage


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## dsage (Mar 22, 2013)

Oh. BTW
Dieselpilot. You win the prize. I went back through the posts and you have long maintained that there would be a problem exactly where the test shows. Had you posted the cad drawing you said you created to show the problem I might have understood what you were getting at earlier. Sorry I was so slow.
 Dman was also onto important considerations to do with the point of grinding etc..
Sorry I didn't listen earlier but seeing is believing I guess. A picture is worth a thousand words as they say.

Thanks to both of you for your help. And to everyone else for for that matter for keeping the discussion going.

Unless someone can come up with where I've gone wrong on this I'm going to go ahead and grind some cams. I understand where they are wrong now and I'm happy to live with the slight errors in favour of making superior cams in an easy fashion.

(I reserve the right to change my mind on all if this - again) 


Thanks

Sage


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## dman (Mar 22, 2013)

dsage said:


> Most of you guys are so smart. (compared to me).
> Why didn't I think of that. Yes the size of the grinding wheel is far from scale. It's 7" diameter and it's what I used to grind the cams which are about .430 dia as a blank. For this test setup the grinding wheel would need to be 16 times the cardboard size or about 100" in dia. to be in the proper scale. (the cardboard cam is 6.25 base to tip)
> I'm glad you caught that because I was dismayed at the amount of error showing up. It certainly was not indicative of what my steel cams were coming out like but I couldn't pinpoint the source of the error.
> Certainly a properly scaled wheel would appear more flat (like the program is expecting and works fine with) and a lot of what shows as error would be removed.
> ...



ok, if you are using cam then you can do that. if you did it by hand it could be easier to offset the wheel as it goes round. i haven't come up with a way to analyze it without actually offsetting, i have some concept of what would have to be done but it would be complex for sure, would take more time and energy than i have. maybe if i knew some computer programming or was better with spreadsheets and had no job i could come up with some way eventually but why when the cam programmers already have ways built into the software?. 

i thought your fixture used the quill. but since it doesn't and especially since you have cam available then that's the way to go.  but just to throw it out there you could turn the grinding wheel horizontal and the cam vertical and use the x and y. but enough being silly. sounds like you got the picture. 

if there is a problem with symmetry or timing make certain that the wheel and cam are exactly on center height of each other as measured perpendicular to the y. if you project the motion of the cam it should line up with the center of the wheel exactly. 

i haven't made a cam yet but i have put a lot of thought into the subject. i used to want to try this on full scale but it's really not worth it. if the oem's didn't know what they were doing the aftermarket would have certainly proved something weird works better by now. cam choice isn't as much of a mystery as they want you to think. david vizard has it pretty much to a science. while you can do as well or better with other methods or rigorous dyno testing the difference often isn't enough to matter and if you want to do better it's atleast a good starting point. his rules are simple enough to be understood by anyone.


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## dsage (Mar 23, 2013)

dman:

Just to clarify a few thing because I know a few of them have been buried with all the discussion on the profile:

One of the unique things about the way I'm doing this is that I have the A-axis and Y-axis move commands on the same line of G-code. This way it describes an arc (tiny) between the two facets. The facets are 1 degree apart and the cut depths are accurate to tenths of a thou. No additional work is required on the cam after it's ground. I've improved considerably on the finish posted in the early pictures by using tenths. It takes a keen eye and very good light at the right angle to see the facets. In fact if I didn't tell you they were there you wouldn't notice them.

It's all automated so I just go watch TV or do other things while it's busy. It pauses about 10 thou short of the final base circle diameter. Then I measure what's left to remove and  adjust the final cuts to bring it exactly to size. This is necessary because the wheel is wearing slightly as you go.

I don't use the quill for the reasons mentioned. You'll need to go back to the earlier posts to the first picture I posted. The grinder is fixed. Although I'm not using the mini-grinder any more. I made a proper grinding spindle and I'm using a proper 7" wheel.

I don't understand your proposed setup using X and Y. They are both on the table. I guess you could put the grinder on the table to move the wheel to the right position but then where would the cam go? It also needs to move slowly around it's axis.

As mentioned I could arrange the grinder like a big milling cutter and just side "mill" them. I use Mach 3. Apparently cutter compensation doesn't work properly and that would be necessary to use that method with a grinder since the wheel wears. I side milled my first set of cams with a fixed program of cuts and a carbide end mill. A good number of them had chatter marks. Holding the cam vertical is problematic since it's so small. Might be worth another try though since the tool pressures are almost nill with a grinder.

My grinding wheel is right on center. This is one of the reasons I'm limited to a 7" wheel. My rotory table center is about 4" above the table. Holding everything solid is key to success and mounting to the mill column helps considerably in that respect.

Thanks

Sage


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## dman (Mar 23, 2013)

dsage said:


> dman:
> 
> Just to clarify a few thing because I know a few of them have been buried with all the discussion on the profile:
> 
> ...



sometimes i just say thing that are hypothetical. not actually suggesting them. but what i meant about the arrangment was to tip the rotary fixure on it's side so the axis was vertical and parallel to the z.. you could call that an auxiliary "c" axis though if you already have indexing on the spindle then c might not be available, you could still call it "a" for your own purposes. then you could mount the grinder so it's axis was vertical and the wheel would be horizontal. in that case you could use x and y. but it's all hypothetical. without a tailstock things might get difficult. i have ideas on how to deal with that too but i don't want to get carried away. you have a good setup, you just may want to tweak the program for the sake of accuracy. or you might be satisfied... 

i'm not always critisizing nor suggesting, sometimes my mind just wanders into hypothetical land when i type.... don't take me too seriously.


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## dsage (Mar 23, 2013)

I'm not sure I've seen a C-axis, I assume that's on a lathe? I'l have to look that up to fully understand what you're describing.

So, you're saying hang the grinder from above (i.e. the quill or head) with the wheel horizontal, rotate the cam which is standing vertical in a rotory table and move the table in one (or two?) axis' to correct for the off axis grinding? 

Is that correct?

Interesting. I guess that does add an extra dimension of flexibility to move around and get rid of the off-axis grinding problem. But I'd have to think hard what the program would look like. I'm not a mathematician.

I think in that case it would be just as easy to set the grinder horizontal over the table (fixed) and consider it a really big tool bit and write a CNC program to generate a cam shaped outside profile and side mill it. The CNC program would take care of the position to correct the point of grinding. The program would be easy as well. Just draw the cam and send it through a CAM processor and specify a 7" tool bit. (already done it with a milling cutter). Yes a tail stock would not be possible in this arrangement and as I found out before it would help things considerably. 

Sage


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## dman (Mar 23, 2013)

dsage said:


> I'm not sure I've seen a C-axis, I assume that's on a lathe? I'l have to look that up to fully understand what you're describing.
> 
> So, you're saying hang the grinder from above (i.e. the quill or head) with the wheel horizontal, rotate the cam which is standing vertical in a rotory table and move the table in one (or two?) axis' to correct for the off axis grinding?
> 
> ...



technically a is parallel to x, b is parallel to y though one may change based on the other and go in line with the z. and c would be parallel to the z but i think it sometimes used for actual spindle orrientation rather than used as an auxiliary axis but spindle orientation can also be set with m19. you never hear of it because there is little need for it. 5 axis is enough to hit any side of the part from any angle so c is never really used. 

if you didn't need such a large wheel it would be possible to hold the part rigidly and move the part around the grinding wheel. 

again i was being hypothetical. you are much better off using a tailstock. cam software will crunch the numbers for you, just program it as side milling as you suggested, it's a good idea.


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## dsage (Mar 24, 2013)

>>> if you didn't need such a large wheel it would be possible to hold the part rigidly and move the part around the grinding wheel. 

That's exactly what I've already described. It's a standard side milling setup. I described it several times, once in my last post. You could use any sized wheel with no errors. The rigidity of holding the cam vertical is problematic (at least it was with a standard milling cutter. May be a non issue with the low tool pressures exerted by a grinder. I also mentioned a few other reasons why I abandoned it.

Sage


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## dsage (Jun 15, 2013)

We've finally come up with a program to grind cams properly. I started a new thread at:

http://www.homemodelenginemachinist.com/f26/grinding-cams-cnc-program-beta-test-21127/#post223130


Sage


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