Simple cam grinder

[Johno1958]

Hello all.
Nearly completed this grinder. Please watch . This gentleman takes you through his grinder and how it works. If you read the comments you see I asked a question to get a scale of things. Mine differs that I used cheap cnc rails and aluminum extrusion and all in all its quite rigid. The motor I have used is a cheap 550 Chinese watt brush less sewing machine motor which speed control is done via foot pedal.I have done away with the foot control and used a pivoting bolt on top of the controller. You just screw it down and up goes the speed. I did it that way as I am electronically challenged .I can move the tail stock frame for different sized shafts to help with rigidity and a floating tail stock if I find alignment slightly out. I'll make a video of it in operation when I make a couple more clamps and make sure it is calibrated 4 x master cam to shaft.
Cheers
John

 

[Charles Lamont]

He has introduced an error in the 4:1 scaling geometry by using a small roller for the master cam to ride against. To have the correct geometry the roller would need to be scaled up 4 times too. That is to say 4 times the diameter of the grinding wheel! Not doing this can introduce considerable errors in the cam flanks. The error could be compensated for by making the master cam the 'wrong' shape deliberately, but working out exactly the right wrong shape would be an 'interesting' exercise.

 

[Johno1958]

Hi Charles. That is very interesting and something I would not have thought of in a million years. I am trying to get my head around this .
I will have to have a play and see if I can measure the difference.First I will make a 40mm disk as a master and adjust the roller, mine is adjustable up, down, in and out so I
have 10mm at the shaft. I will have to make a cam shape that I can easily as possible check the difference of the output ......Yep play time.
John

 

[Charles Lamont]

John. If you have not seen it, you may find this thread of interest. It includes my own effort.

https://www.homemodelenginemachinist.com/threads/cam-grinder-on-the-go.25362/

 

[Johno1958]

Thanks Charles I will be studying that post quite eagerly .
I was thinking try the roller first and see if I can measure the difference but I can make a section of ( don't know the words) skid plate with the correct diameter .
Nicely polished steel or a bit of bronze plate. It would almost appear flat. Do you think this may work to correct the problem?
Cheers
John

 

[Charles Lamont]

Yes, that is what both I and Brian-in-Oz did with our grinders. I used a piece of delrin.

Watch the chap in the video grinding. You can clearly see the nose of the master cam hanging over the roller. This will result in the ground cam flanks being too flat and concentrating all the acceleration towards the nose. On the other hand, a flat shoe for the master cam results in a cam lobe that is a shade too fat, concentrating the acceleration in the early part of the lift.

I consider getting the scaling geometry theoretically correct to be quite a tricky design problem, involving a number of subtle traps for the uninitiated. It took me quite a while to figure it out, and I have a degree in this stuff.

In the end though, the chap in the video probably made a camshaft that worked fine. Hell, hand filed cams can be made that will work.

 

[Shopgeezer]

Just found this thread. Fascinating stuff, thanks to everyone who provided info. I have had a cam grinder lurking in my brain for a while now. These designs have given me some ideas.

The importance of the shape of the follower on the master cam is new to me. Making it the same profile as the grinding wheel is a new piece of info I would never have thought of.

The distance from the pivot point of the camshaft fixture to the camshaft itself dictates the ratio of the master cam to the actual cam. This would have to be adjustable for different cam sizes. The first video of the fellow grinding with his setup doesn’t seem to allow this. Looks like he is locked into a 1:4 ratio.

The need to turn the master cam in relation to a index of some sort on the camshaft (ultimately related to the cam gear) is important and not immediately apparent in the photos of the various projects. Easy enough to rig up. They all have degree wheels.

These designs beg modification for grinding the crankshaft. Replacing the master cam with a circle would work for the crank bearings. You would need a fixture to offset the crank for the rod pin (or journals on a multicylinder). This would be doable with these designs.

Great information. Beautiful work on the rigs shown in all the threads.

 

[Johno1958]

Thanks Charles. I have a 90mm disk of delrin on order now from Ebay that I will machine up. Not easy to get flat here in Australia in small quantities .
I see lot more clearly now what you are talking about, the over hang of the master cam to the roller. Once again thank you.

Hi Shopgeezer .
I don't know of anyone who has modified one of these machines to do crankshafts, interesting. There is one fellow on this forum that completely cut
his crankshaft with a tool post grinder on his lathe. I think from memory it was for an air driven V8.
Cheers
John

 

[Charles Lamont]

The distance from the pivot point of the camshaft fixture to the camshaft itself dictates the ratio of the master cam to the actual cam. This would have to be adjustable for different cam sizes. The first video of the fellow grinding with his setup doesn’t seem to allow this. Looks like he is locked into a 1:4 ratio.

Mine is fixed a 1:5. A different camshaft demands different master cams.