How to make a cam grinder?

[j45acp]

Does anyone out there know where I can get a GOOD set of plans to make my own cam grinder for some model engine projects I would like to start.

I would try to design one but i have never used one so the working theory of the machine is non-existent at this point.

[motordude]

If you have a CNC mill you can use that as a grinder. Put a grindingwheel in the spindle and program a path it can go around. If it is a vertical mill, set the camshaft vertically. When working on a ship engine factory I saw an old setup that worked quite well. They milled the cams with dividing heads (not for small cams) then ground them by having a "floating" grinding wheel with a pneumatic cylinder to keep a uniform pressure. The grindingwheel then followed the profile, just as a cam follower.

John

[NeoMoses]

A CNC lathe with something as simple as a bench grinder on the cross-slide would work. You'll likely want to do this process wet, too.

[j45acp]

Sorry guys forgot to mention no cnc equipment in my shop, just manual lathes, mill and shaper. I saw that strictly IC has some back issues with a cam grinder in it however I dont know if it's for copying existing cams or making new ones.

[Swede]

That Strictly IC article is for a machine to grind cams from scratch. I have the entire SIC library, which is a real wealth of information and a boon to IC hobbyists. Before you order those issues, tell me what the dates/nums are of the cam grinder series and I'll look at it for you in detail, and answer any questions about it that you might have.

IIRC it is for traditional, inline cams, not a radial engine cam ring.

Swede

[j45acp]

Sounds like what i'm looking for. The issue numbers were 82, 83, 84 according to SIC's web page. Just out of curiosity how do you make a cam ring for a radial??

[Swede]

I didn't find any cam grinding in the issues that you mentioned, but did find one in issues 39, 40, and 41. There is also a very simplified cam "jig" in issue 6. The more complex cam grinder looks pretty capable, with its own grinding head.

Really, the "jig" setup should be more than adequate for anything except production. The jig consists of a hand-cranked rig with a master cam pattern and uses a regular 6" bench grinder.

Strictly IC serialized the creation of a 1/6 scale deHavilland Cirrus which I built a few years ago. This is an inline 4, requiring an 8-lobe tiny cam shaft perhaps 5" long. The author described a way to make the camshaft with an EXTREMELY simple cam jig using a slotted hand-wheel setup with a dowel pin to restrict the rotation of the handwheel through a predetermined arc. The entire assembly is placed in the mill beneath a regular mill cutter, and the lobes are roughed out by feeding slightly, then rotating the camshaft with the handwheel through the arc limited by the dowel pin. It looked crude as hell but I did it, and amazingly it worked fine! All that was required was a little hand smoothing at the end, and polishing of the cam.

The really "funny" part was after I had this pretty little camshaft, I was putting the engine together partially and checking the valve timing to be sure all was OK, and noticed that the cam was backwards, and would have caused the engine to run in reverse. I wrote the magazine pointing this out, and the response was "No way. But I'll forward your letter to the author". The author, Eric Whittle, confirmed my observation, and they posted a correction later. Yes I had to start over with the cam. I point this out because it is one additional way to make a camshaft, simple but functional. Get the deHavilland Cirrus 1/6 issues if you want to pursue it.

Don't let commercial cams for racing engines throw you. They expend big $$ on R&D to tweak the last Newton out of their engines. It is very easy to make a cam that will reliably run the engine if you are not after power. All you need is valve lift. Blend the peak with the flanks and the base circle, and your engine will run.

The one radial engine cam ring I've made was simple. 4340 steel round with two cam "peak" circles turned on the perimeter. Chucked in a R/T on the mill, and a keyway cutter is used to mill away the correct portions of the cam down to the base circle. The flanks are then blended with a dremel sanding drum to a roughly correct shape. The cam was heat treated to Rc 43. Like I said, not rocket science, get some valve lift at the correct points and the engine will run fine.

HTH

[richard tuns]

thera's an article series on a cam grinder in the uk's Model Engineer magazine
starting a few weeks ago.

[ViperTX]

Check out the Nov/Dec 2004 issue of Home Shop Machinist, one is actually built in the mag.

[Hiredgun]

why not cut lobes out one by one on cnc and put a set screw recessed opposite of the lobe. then you could degree in each lobe with a degree wheel on the crank and get it dead on. It would be easy to experiment with cam profiles that way to. you could also make a roller cam profile and make a roller lifter.

[Swede]

That is a valid way to produce model cams for small engines. I have read of guys who have used nothing except sleeve loctite to keep the lobes in place! Apparently it works fine. I think you could set it up as you proposed, gently tightening the set screws once you are happy with the timing; then, remove the lobes, and file or mill a small flat on the mark from the set screw. Combine the small flats, set screws, and loctite, and you're probably good to go!

[Holmes_ca]

E.T.Westbury who designed the cams for his 4 cylinder sealion shows how you can machine the camshaft in a jig and complete it on a lathe between centres from a solid round bar