Cam Machining

[tds11223]

I am having an difference in opinions. We have an old blueprint of a cam. We need to make a master for the cam. The drawing shows the cam being cut with the dimensions of the profile being off the center of a cutter.

Others that I talk to say that the master must be built using the cutter specified in the drawing.

I say we can subtract half the cutter width and use whatever size end mill we want. In a cam system we could shrink the drawing by a percentage, offset it or something to that matter.

If I am not correct could someone please explain why? The agruement is that the dwells and rises will not be the same without using the exact cutter specified.

[Geof]

I think you are correct. You say In a cam system we could shrink the drawing by a percentage, offset it or something to that matter.
I guess you mean a CAD/CAM system.

Surely you can do a CAM program using the original profile and tool diameter and also draw it changed in scale with a smaller or larger cutter then superimpose a plot of the path traced by the tool periphery in each case to demonstrate that it is or is not the same.

[RICHARD ZASTROW]

A problem comes up where you incur fast rise and fall rates. Ex. in a fast rise, the cam follower isn't normal to the center of the cam. It is normal to the angle tangent to the radius on the rising "bump".

That's why us old timers with manual machines used cutters ground to the same diameters as the cam followers.

The master were laid out by laying out circles the diameter of the followers at the angle of rotation of the master. The center of the circle were drilled out undersized then bored out to the correct follower diameter. The "cusps" were then removed and blended with German Mills (AKA files) This kept two toolmakers busy full time after the cam engineer designed the cams.

I'm sure somebody has CAD/CAM software to be able to machine these cams with variable cutter diameters.

Either study history or you'll get stuck with repeating it. LOL

Dick Z

[tds11223]

I can use the software to "shrink" the cam contour as needed. I just can't get anyone to agree with me that we do not need an end mill 2.55" in order to machine it properly. The only problem I see would be if the rise or fall radius was smaller than the 2.55" diameter cutter the print calls out.