The Craftmans Shop > Model Engineering
Side Valve i.c. engine from Bar stock
Brian Rupnow:
Yowzahhhhhhhhhhhhhh!!
philf:
Hi Brian,
I thought I'd replied last night but it must be stuck in the ether somewhere. (We're on holiday in our touring caravan and the wireless broadband connection has been very dodgy until 2 BT OpenReach engineers turned up this morning.)
I drew out your cam on Autocad using your figures of 0.24 base radius, 0.08 lift and 0.64 flank radius and it comes out with 0.08 nose radius. So, how the program generated a profile with such a huge nose rad I don't know. (It wouldn't display anything on my PC complaining of a Java Security issue.)
By the way - the speed has nothing to do with the profile the program generates. It's only used if you need to know accelerations.
For your 3d model why couldn't you just extrude the profile?
A very simple machining job for a CNC mill!
Phil.
Brian Rupnow:
Philf--I did exactly that (extruded the profile) on the green cam. On the grey cam, I used the machining sequence generated by CamCalc to create the profile. That is why you see the side facets in the grey cam. It is a rotary table job with a cut taken every two degrees of rotation.---Brian
Brian Rupnow:
I have had a crazy busy week, and haven't had a chance to play machinist very much. I did come home last night from the factory where I've been consulting for a couple of weeks, and got a good start on the tappets. I figure that if I have to set the rotary table up on the mill to do the cam anyways, I might as well cut the hex shapes on the tappets, which are being made from 1/2" 01 drill-rod. I hope to get the cams done this weekend as well. You are probably right about the shape of the cams not being all that critical. They are very "not critical" if using a follower wheel on the tappet, but for a flat bottomed tappet, if you don't get the curve right on the cam flank, they will 'slap' the bottom of the tappet on every revolution.----At least that's what the books say.-----Brian
Brian Rupnow:
This morning I made the tappets from drill rod, which is a "water hardening steel". The machining went reasonably well, until I realized that I had tapped the wrong end of the larger diameter which rides on the cam!!! After remaking the large ends and getting it right the second time around, I carefully fit everything, then took the pieces out to my big garage for hardening. I heated the pieces one at a time with my oxy acetylene torch until they were bright orange, then tipped them into a can of water. I hoped that I wouldn't get much heat distortion which would have buggered up either the internal or external threads, but I must have lived right this week, because everything went back together fine. The outer diameter of one of the large parts may have grown a little, as it was a tight fit into the bronze guide block and I had to set it up in the lathe and polish it a tiny bit with some 280 grit paper. I decided at the last moment to use mild steel #10-24 locknuts, because it was less work, and I figured when used as a jam nut the mild steel would grip better and not back off while the engine was running. In the picture, one valve is open and one is closed, but the cams are still not made. That will be tomorrows job. The blob of stuff on top of the left hand tappet is some oil I had used when assembling things and then forgot to wipe off before taking the picture.
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