Cam Grinder questions / suggestions

[Jasonb]

For one cam on a hit and miss engine, I would probably hand-grind that cam.

You don't even need to grind them, milling and possibly a bit of file work will be fine for hit & miss engines. Consider a lot just ran on a cast cam profile at full size, you could even replicate that.

Don't worry about the mud when there is no need to step into it for what you want to make

 

[GreenTwin]

Don't worry about the mud when there is no need to step into it for what you want to make

Yes, but knowledge propagates to similar things, and so while it may not be directly applicable, mathematical exercises can often be applied to many other things. There is no compelling reason for me to dumb myself down.

"Knowledge is power" as they say.

Edit:
Perhaps this has already been stated, but the cam that is being ground is swinging in an arc, and so as it swings towards the grinding wheel, it would tip down a bit, ie: the cam being ground is not moving in a linear motion towards the grinding wheel, and its centerline is not remaining on the centerline of the grinding wheel. Ditto for the enlarged guide cam pattern.
If the grinding wheel was also on a swinging shaft that pivoted with the camshaft support, then it could swing in parallel with the camshaft being ground, and they would rise and fall together.

I will start a new "Cam Grinding Hypothetical Design Concepts" thread, so we can ponder cam design and grinding machine geometery design in 2D and 3D.
.

 

[Charles Lamont]

Yes, but knowledge propagates to similar things, and so while it may not be directly applicable, mathematical exercises can often be applied to many other things. There is no compelling reason for me to dumb myself down.

"Knowledge is power" as they say.

Edit:
Perhaps this has already been stated, but the cam that is being ground is swinging in an arc, and so as it swings towards the grinding wheel, it would tip down a bit, ie: the cam being ground is not moving in a linear motion towards the grinding wheel, and its centerline is not remaining on the centerline of the grinding wheel. Ditto for the enlarged guide cam pattern.
If the grinding wheel was also on a swinging shaft, then it could swing in parallel with the camshaft being ground, and they would rise and fall together.
.

Jason - I don't think we are talking about actually making cams. The thread subject is cam grinders, and seems to be about understanding their geometry at the moment.

Green Twin - Again thinking about the scaled up master design, you are right about the cam moving in an arc over the wheel, but if the scaled up master cam is moving in an equally scaled up arc over an equally scaled up follower it all works as it should. This is why I keep banging on about 'similarity'.

Petertha - Your diagram in post #40 is incomplete without the pivot point. (And I suspect you may be overthinking it.) Sure, other geometries are feasible with compensation in the profile of the master cam, but I have never felt much desire to chase that particular hare.

 

[Jasonb]

Charles, that is why I only quoted the one line of Pat's statement about making cams for hit and miss engines.

Nothing wrong with expanding your knowledge but knowing when to apply it is a different matter.

 

[werowance]

folks, i am happy with all the information that is coming in, im fine if you keep it in this thread but also fine if you want to start another one, either way i can follow along and learn. i keep going back and re-reading everything, seems once i understand one part then i go back and look at other bits and then that makes sense to me so with all the information i am piecing it all together ib my head and starting to understand more and more. i do want to say that i do know how to mill a cam and have done so. this is more of learning and fun to me. so dont let my questions cause anyone any stress or anything. and again, i will be asking alot of stupid questions that i should already know so just tell me to shut up or say "whats wrong with you boy" have you been sniffing the glue again.....

 

[peterl95124]

No. As explained in post #29, the follower is radiused (though it is not really discernible in the view). The master cam scaling factor is five, and the radius of the follower is therefore five times the radius of the grinding wheel. Anything else would introduce errors.

Charles, thanks for the correction !, in the CAD drawing it *looks* flat !

 

[Charles Lamont]

This is how it the follower acquired a radius

 

[minh-thanh]

folks, i am happy with all the information that is coming in, im fine if you keep it in this thread but also fine if you want to start another one, either way i can follow along and learn. i keep going back and re-reading everything, seems once i understand one part then i go back and look at other bits and then that makes sense to me so with all the information i am piecing it all together ib my head and starting to understand more and more. i do want to say that i do know how to mill a cam and have done so. this is more of learning and fun to me. so dont let my questions cause anyone any stress or anything. and again, i will be asking alot of stupid questions that i should already know so just tell me to shut up or say "whats wrong with you boy" have you been sniffing the glue again.....

Hi @werowance !!
Lobe grinder ???? : It's just a grinder !!!!. It grinds the lobes to the lobe profile template you give it . Add an angle index and you'll be able to grind the lobes to the angle you want : 105 , 110 , 117...
Lobe template !??? : You have a running engine , from the camshaft of that engine that you find best , just size it up with the grinder you will and did , and you'll have a lobe template good enough for other engines

 

[petertha]

Petertha - Your diagram in post #40 is incomplete without the pivot point. (And I suspect you may be overthinking it.) Sure, other geometries are feasible with compensation in the profile of the master cam, but I have never felt much desire to chase that particular hare.

Yes & no, requires explanation. I inserted the wrong screen grab. I have a couple versions of these defining some parameters & leaving others to float, meaning they become determined to an exact value when drawing is fully defined. In this version the dimension going towards the pivot point (now X-d out) is meaningless. It was a remnant of another drawing overlay where I was confirming a dimension.

Here I have defined an arbitrary 10-deg angle between tangent of grind wheel to cam & same angle template to follower. It could be any value but just translates into same proportional contact position. Also the link distance between wheel centers is defined. So the extension of these dash axis lines will intercept somewhere off the page to the right & will be the pivot point. So its there, just not on the sketch. The noteworthy thing here is the follower has a calculated radius = 2.020" (grey color vs defined is a black color). Change the grind wheel radius results in changed follower radius all other things equal which is more what this sketch was about. As I mentioned previously, we could just as easily define a different collection of parameters based on practicalities of the actual build & some other parameter would become calculated as a result. Its just a generic model that could be specified to whatever dimensions were desireable.

 

[Jasonb]

A quick look at that image and my mind is saying that although the 2" ctr distance of the blank/master and the 2" follower/grinding wheel remain constant there will be some change in the distance between contact points, try it with the lobe at 45deg and 315 deg and see where the tangents end up.

But I'm not sure if that will affect the profiles or not.

 

[petertha]

You might be right Jason. I'm going to work on this some more. I want to make the cam & template as sketch blocks, rotate them phased together with a belt mate. Then make the follower ride tangent on the template only constrained by the lever/pivot point & see how the grind wheel OD line compares to the target cam zoomed in. TBC