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- Jun 24, 2010
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Ive been sporadically working on cylinder parts to the point I think I can replicate 5, so now I'm proceeding to the center guts, specifically the crankcase. I havent done this sort of work before & figured there would probably be some learning's.... And there were 
Actually the operations went quite smooth, so I figured I was going to be 'that guy' who broke his tap off in the proverbial last hole. Turns out I had a more fundamental problem.
I was concerned the donut might rotate in my holding fixture while machining so I incorporated a small pin. Unfortunately the CC faces get inundated with tapped hole patterns so I had to pick a spot where it wouldnt interfere. But that now meant having to clock the donut relative to this pin position which I accomplished by indicating across a small mill flat. I thought about temporarily gluing the donut to the jig but chickened out.
So I dialed the donut block in longitudinally/square & CYL-1 clock orientation, but completely mind blanked to check concentricity with RT axis. My chuck is a 3-jaw with centering plate & jaws presumably pretty accurate. Never assume! I'm not sure if the plate shifted and/or the typical 3-jaw clamping runout. Anyway some of the milled deck facets are off by max ~ 4-5 thou depending on the cylinder. Actually I could tell something was up when the internal master rod groove started breaking through unequally, which I wishfully hoped was just out-of-round internal grooving induced back at the lathe stage.
Unfortunately this bad geometry translates into each cylinder sitting at slightly different deck heights resulting in different compression ratios per head. I don't want to mess with custom cylinders, heads or modified pistons. That just gets nutty. So.... #1 is a Binner! No Biggy actually, now I feel quite confident about producing #2 and having a spare tester is for other operations is nice.
I told myself if I can get traction on the internals, Ill start a build post. Right now Im just focusing on making parts when I have time J
My New Tooling Opinion:
I've never been super keen on my 6" 3-jaw on 6" RT combo. Its big & heavy & extended stack length. More importantly it really doesn't lend itself to dialing in. I tried re-shimming after the fact & its a PITA. Even good 3-jaw chucks can have 2-3 thou runout & I suspect may vary by part diameter as a function of the scroll. This particular sub-plate assembly relies on a centering do-dad & nestled registration bosses. Seemed like a good idea at the time for convenience, but also sources of collective error creep. So, I've ordered a smaller 4-jaw chuck (offshore Asian, fingers crossed) and will have to make an adapter plate. But if it goes according to plan I'll have an assembly that is much easier to mount, adjust & zero part concentricity. Plus 4-jaws can hold irregular stock..
Comments welcome.
Actually the operations went quite smooth, so I figured I was going to be 'that guy' who broke his tap off in the proverbial last hole. Turns out I had a more fundamental problem.I was concerned the donut might rotate in my holding fixture while machining so I incorporated a small pin. Unfortunately the CC faces get inundated with tapped hole patterns so I had to pick a spot where it wouldnt interfere. But that now meant having to clock the donut relative to this pin position which I accomplished by indicating across a small mill flat. I thought about temporarily gluing the donut to the jig but chickened out.
So I dialed the donut block in longitudinally/square & CYL-1 clock orientation, but completely mind blanked to check concentricity with RT axis. My chuck is a 3-jaw with centering plate & jaws presumably pretty accurate. Never assume! I'm not sure if the plate shifted and/or the typical 3-jaw clamping runout. Anyway some of the milled deck facets are off by max ~ 4-5 thou depending on the cylinder. Actually I could tell something was up when the internal master rod groove started breaking through unequally, which I wishfully hoped was just out-of-round internal grooving induced back at the lathe stage.
Unfortunately this bad geometry translates into each cylinder sitting at slightly different deck heights resulting in different compression ratios per head. I don't want to mess with custom cylinders, heads or modified pistons. That just gets nutty. So.... #1 is a Binner! No Biggy actually, now I feel quite confident about producing #2 and having a spare tester is for other operations is nice.
I told myself if I can get traction on the internals, Ill start a build post. Right now Im just focusing on making parts when I have time J
My New Tooling Opinion:
I've never been super keen on my 6" 3-jaw on 6" RT combo. Its big & heavy & extended stack length. More importantly it really doesn't lend itself to dialing in. I tried re-shimming after the fact & its a PITA. Even good 3-jaw chucks can have 2-3 thou runout & I suspect may vary by part diameter as a function of the scroll. This particular sub-plate assembly relies on a centering do-dad & nestled registration bosses. Seemed like a good idea at the time for convenience, but also sources of collective error creep. So, I've ordered a smaller 4-jaw chuck (offshore Asian, fingers crossed) and will have to make an adapter plate. But if it goes according to plan I'll have an assembly that is much easier to mount, adjust & zero part concentricity. Plus 4-jaws can hold irregular stock..
Comments welcome.
