Need to make a measuring fixture for some turnings

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TDubs

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Hi Everyone,

I need to turn 48 pieces out of .375" 6061 round. Overall length is 3.564". The part has a shoulder on each end that is .417" long, turned down to .250" diameter. I did this using a right hand index tool to face the ends and cut the shoulders. I'm looking for a faster method to turn these parts. I have a SB 10K lathe with the micrometer stop. The problem is that I was told that I should only extend a part through a collet 3x's the diameter. In this case 1.125" would stick out. My micrometer won't allow the carriage to move in that close because the gearbox limits how far in the stop can move to the left on the way. I can set the part so that more extends from the collet but this makes me wonder about too much force against the stock and not getting a good cut.

Does anyone have any suggestions how to do this part given the constraint of the micrometer stop?

I had thought of just turning the shoulder down to .417" x .250" and making somewhat of a go/no go block out of some plastic tooling board. I would face it down to .417" on the Z, followed by drilling a .375" hole to use in marking the line with a scribe. I would also add a .250" hole to check the shoulder length after the cut. These holes would probably be .005" to .010" oversize to allow for easy placement of the stock and machined part into both holes without a tight grip.

Does any of this make sense? I'm open to any ideas that you folks may have.

Thanks!
 
Perhaps batch processing them?

Assuming your starting with something like 1/2" stock,

First operation, cut each part about a half inch too long, to leave a work-holding stub, then face and center drill the other end of each part.

Second op, put the parts in a 1/2" collet,
supporting the other (center drilled) end in a live center, turn them to 3/8" diameter, except obviously the work-holding stub the collet grips.

Third op, cut off all the 1/2" workholding stubs.

Fourth op, face them all to the correct length.

Fifth op, seat them as deep as needed into a 3/8" collet and turn the shoulders.


I've done this in the past, and used a parallel and 1-2-3 block as a work stop, to set the depth of parts in the collet consistently. If accuracy isn't a big issue, a 3 jaw chuck and spider type work stop is hard to beat for speed.
 
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Thanks Ken!

I understand all five steps. Can you give me a better understanding of the parallel/block combination?
 
Here are a couple techniques to get quick, repeatable depths while batch processing parts. Put the blocks/parallel against a face, then pull the part out till touching.

I didn't wanna put my collet chuck on, but you get the idea.





This is a 3d printed depth stop for my 3 jaw. I made some in different sizes to allow various depths.



It wouldn't be too hard to rig something to use as a depth stop, be it 1-2-3 blocks, parallels, gauge blocks or whatever you happen to have. For large quantities of the same part, sometimes it pays to make a custom fixture, like maybe boring a soft emergency collet with an internal shoulder for depth control, or something similar like a custom made split bushing.

I have an entire drawer full of custom split bushings from years of batch processing jobs, kept on the off chance they'll be useful again someday.
 
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Can you set up a dial indicator on the carriage so you can work closer to the collet without the stop? You can put the micrometer on the right side of the carriage if necessary (on a mag base, for example).

That would let you face, set zero, then cut the first end.

Joe Pi has a video about parting with a depth stop bayou might be able use use a similar technique for the length of the first shoulder.

Do you have a collet depth stop? That would be useful for the second operation, once flipping the parts. You again need the dial indicator on z travel.
 
Is your micrometer stop close to working? You may have enough wiggle room on the tooling side to make it happen. Some possibilities include shifting the T nut in the slot, running the compound out, or setting the tool differently in the toolholder.

Alternately, do you have clearance for a thinner carriage stop?
 
The order of operations depends upon which dimensions are critical as there will be tolerance stacking at play.Are the .317" shoulders the critical dimension or is it the 2.730" distance between the shoulders.

If the former, I have approached it this way. First cut the parts to the exact overall length. Second, make a spacer block .417" long. Set up the carriage stop to a convenient position. Mount the part in the collet such that the turning tool just touches the end of the part while touching the carriage stop plus the spacer. Remove the spacer and turn the .250" shoulder to the carriage stop.

If the 2.530" dimension is the critical dimension, it gets more complicated. I would use a spindle stop to reference the opposite end of the part. First, I would use it to face all the work pieces to length and then to cut the first shoulder.. I would reverse the part and use a modified stop with a 1/4" clearance hole so the stop referenced the first shoulder.

There is a gotcha when using a collet stop in that a slightly different diameter on the part will result in a different seating depth as the collet is closed. The seating depth is also affected by the amount of torque used to close the collet. Joe Pieczynski made a great video on these sources of error. I use a spindle stop so the work is referenced to the lathe spindle rater than the collet. With care you can keep parts to within +/- .001".
 
Thanks everyone!! Looks like I have a number of good ideas to try out. I'll put up pics of the finished parts.
 
If you post a pic of the part and what size had to be maintained it would help .
And do you have a steady rest?
 
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