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Turbo,
How did you measure the holes? What size drill bit did you use for drilling the 0.156 dia. holes? Using a test pin would be nice, but since I have the pins I could just drill a test hole with the same size bit you used and test it that way here. I too am having trouble holding tol., I checked dia. on the lathe, after I let it cool down and checked again when off the lathe and got 0.002 less in dia. I guess I will just have to machine 0.002 bigger and let it go as that. We are sending parts (less one) for yourself to David U. Maybe you can use one of your drill bit tops to measure the holes and see what you come up with that way instead of a test pin, there should be one that should come close to the required dimension needed.
Paul
 
Couple of things. Check the diameter of the drill shank before using it as a gage pin. Also, careful of chuck marks if it is a used bit. And, if the size or number is stamped on the shank, it usually raises the surface to the point it affects the size hole that will accept it.

On lathe work, it is usually best to cool the part before taking the final cuts and measurements. If it is a part of job, be mindful that if the material immediately behind the part is solid, the size of the parted of piece may surprise you. I often bore well beyond the depth of the piece I am making to minimize the effect. Not all materials exhibit this behavior, but many do. This can affect roundness as well.


Hey TD.....did you power tap those big old 2-56's?
 
Was just kidding, but if you have the rigid tapping cycle on a CNC, 1000 rpm is about right, if you can stop and reverse quick enough.

Glad the taps worked out for you.
 
Turbo,
The pin should rotate in the hole with no side slop is ideal. I dought if we can get it that close though. It still bothers me about the 0.002 tol. of parts on and off the lathe, will have to do a temp. probe to see if that is the problem. I just did some stainless small dia. parts and it was ok, but the brass pins might be more prone to temp. change than stainless. When I worked in a machine shop years ago we did some plastic parts and temp. was a big factor on parts as plastic expands more than steel on temp. .00005 vs .000055/in./deg. F if I remember right. What I am trying to say is always machine and measure at room temp. on close tol. parts.
Paul
 
Turbo,
I believe you mean #20 drill bit which is 0.161. My #20 drill bit measures 0.161.
Paul
 
I've been a little indisposed as of late but I'm trying to make headway between mad dashes. Today the only thing I got done was to take a pic. :eek:
Here are the crank discs. :p I'm ready to turn it down to size. I had been waiting to get a part for my grinder so that I can make a new cutting tool for the job. That came in yesterday so I am getting closer. Once it's to size I'm planning on drilling the center hole undersize then use one of the nifty new reamers I got from JGedde to finish it to size. Then I'll use a parting tool to slice off donuts (I'll bevel the edges as I do so). Any comments or things you'd do differently? I won't be offended as I am still trying to learn here. :biggrin:

-Ron
 
I was pretty much planning on doing just what you suggested, with the exception of drilling it out first. The only reason for that is the live center I am using. As it sits the countersink in the end of the stock conforms to the point on the live center very nicely. If I were to drill it out first then I would only have a "square" edge contact with the center. While it would probably still keep it fairly stable I don't think it would be quite as solid as it is now. Just going on instinct here, I've been known to be "off" at times, just ask my wife. :p :biggrin:

-Ron
 
Ron,
I would finish the O.D. first, then drill undersize hole pass the last piece. If your spindle hole is big enough I would drill closer to the chuck. The reamer should be used about half way then start your chamfer and cutoff, or maybe you could use the reamer on the cutoffs one at a time if you can set it up easy. You can also make a fixture to drill the .125 holes on the drill press, if you have one. Just adding my opion and you can take it with a grain of salt if you like.
Paul
 
pjf134 said:
Ron,
I would finish the O.D. first, then drill undersize hole pass the last piece. If your spindle hole is big enough I would drill closer to the chuck. The reamer should be used about half way then start your chamfer and cutoff, or maybe you could use the reamer on the cutoffs one at a time if you can set it up easy. You can also make a fixture to drill the .125 holes on the drill press, if you have one. Just adding my opion and you can take it with a grain of salt if you like.
Paul
Click to expand...

That's pretty much the plan, including using a fixture on the drill press for the .125 holes. The spindle hole is big enough (well, sort of. It's only 7/8" but big enough for a .25" hole) but the piece is long enough where I don't think it's necessary to drill that deep to have enough for all the pieces. I'll do all the center reaming in one procedure as I think the fewer operations I do the less chance there is to introduce error. Of course, I could bugger it ALL up in one fell swoop. :faint: I'm "prepared" for that eventuality (kind of an old habit of mine to have a fallback) and have plenty of extra material to do the job over if that's the case. :biggrin:

-Ron
 
pity about the jig! That's a mighty fine looking plate!

I'm with EdK on the surface grinder :drool: but don't have enough use for one.
Or is that Because I don't have one?:huh:

Jason
 
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