Cam lobe development chart

[gbritnell]

Gentlemen,
I have a long distance friend in North Carolina. I have been helping him by phone with his engine building problems for several years. He recently contacted me asking me if I could help him with a cam design for a typical 2 valve pushrod operated I.C. engine. To this point he has only done hit and miss engines. The chart I created for him was from his specifications.
I thought it might be of some value to the builders on this forum to see how I develop my cam lobes so I am including the chart that I made up for him.
This is for machining a cam on a milling machine using a horizontal rotary table.
gbritnell

View attachment CAM LAYOUT DRAWING.pdf

 

[Charles Lamont]

You seem to have a flat cam flank and a flat faced tappet?

 

[gbritnell]

You're correct Charles. Although automotive engineering dictates a curved flank to slowly accelerate the lifter in all the years of model making I've never found a need for it. I have a drawing of a full sized camshaft from when I worked as a metal patternmaker and the radius is extremely minimal for the size of the lobe. I think that when fellows design model cams they have gone to the extreme to add the flank radius. My 302 V-8 engine has more than 50 hours of running time on it and the cam is still like new. With my layout one could put a flank radius on the lobe and just add a few more numbers to the step-off chart.
gbritnell

 

[artist334]

Just about flat cams. Seems like the designer of this engine didnt hesitate with flats. Engine is from a T-72 tank.

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Henri

 

[digiex-chris]

why 8 degree steps? If I use 9, I can use my 40:1 dividing head always going back to the same hole.

 

[Jasonb]

8 degrees suits a rotary table as its two turns of the handle, more people have rotary tables with a 90:1 ratio than dividing heads.

 

[digiex-chris]

ah gotcha. Same kind of deal. Thanks!

 

[RichD]

That's a lot of information on a single page. Very clear and to the point. Thank you George for sharing not only the moves, but the logic behind the profile. Valve timing included!

I'm saving a copy for myself.

And to the point of the 8 degree subject, you could recalculate the moves by following George's method using a different divisor of your choosing and some trig similar to Marv Klotz's ball turning program. The important information George has provided is the start and stop points for the different radii involved and the actual cam profile development process.

Rich

 

[Jasonb]

Or use Camcalc and enter the increments that you want to suit your equipment .

But don't forget the bigger the steps the more hand blending that will be required

 

[windy]

My high speed flash steamer uses a similar cam with a curved cam follower and is a two stroke with no load 15,000rpm plus.
I use only quality materials i.e. Stellite tipped cam follower and this is also burnished.
Lubrication is by solid lubrication.
The wear is very limited after many years of high speed competition.

 

[gus]

Hi gbritnell,

Thanks for the drawing and info. From now on,my cam lobes will be cut to model engine requirement. As a young kid,I watched in awe at the pattern makers next door at work making patterns for another next door C.I. foundry. Further down the street we have machineshops and boilermakers' shop and even spring shops. Wish I could bring all that back to learn from these master tradesmen. Looks like 71 young Gus will spend his remaining active years building gas engines. Take care.

 

[Holt]

Just saw this and remembered when I was toying with a BMW K1200 16V motorcycle head on a classic Mini engine, the BMW cams was with flat flanks as well, and it was possible to run the cams in opposite direction without problems.



I'm afraid this was the best picture I could find.
The engine is developed at BMW motorsports division, they should know a thing or two about the correct shape of a cam.


Holt