Parting off spacer on lathe question

[DanH]

This might be a pretty basic question for some of you but here goes.

I needed to make 2 spacers .300" long on the lathe. After turning the OD and drilling the bolt hole I used a parting tool to get the .300" thickness. What's the best way to set the parting tool position to get an accurate thickness? I used the depth end of my caliper set at .300" to set the parting tool blade which worked ok but the 2 spacers were a little off. One was .301 and the other was .304. How do I or can I get a better result.

Dan

[dallen]

your saying they have to be absolute .300"

not being smart or anything but you could superglue them in a pocket and the turn the extra off. or lock the carriage on the lathe and adjust the tool with the compound.

now where did I put that 1/8" E-clip at

[PixMan]

What material are the spacer made from, and exactly what kind of cutoff tool are you using? It's not uncommon for a parting operation to have variation in thickness because each cutting tool may deflect is different ways because of the variables of cutting speed, feed rate, material and tool geometry.

Back when I was running CNC screw machines, it often took several tries to get the thickness consistent. If you've only got a couple of pieces to make, consider cutting them off .005" long and machining them to final size. With a carbon steel material you could just throw them down on the mag chuck of a surface grinder and finish them all at once to the exact same size.

Or, screw them all up at the same time....not that I've ever done that. ;)

[DanH]

The material is 6061 T6 and I was using a HHS parting tool. These spacers are being used to space out a mounting plate for a DRO scale so the actual number is less important than having two the same. Maybe I am asking too much as they are only .003" different. I really was wondering if my method was correct or should I have done it differently. I asked my boss and he said he would have left it long and then milled it to length. Maybe I'll try that next time if I have to be really picky.

Dan

[dallen]

cut no thicker then that superglue should hold it with a light cut in aluminum, won't hurt to try it sometime see if it works or make a collet by splitting a piece of tubing then counter bore it enough to hold the part would work.

[TomG]

Dan,

You can part off multiple parts accurately, but it requires some care. The parting tool must be set dead square to the work. Don't guess, use an indicator and get it right. Reduce tool overhang to an absolute minimum and use lots of oil or flood coolant. Take a small cut off the end of the stock with the parting tool, set the carriage stop to zero, then move over the length of your part plus the thickness of the parting tool for each part. That said, if you only ave a couple parts to do, it would be better to part them long and face them to length.

Tom

[PixMan]

Tom's suggestion is excellent, just what I would do. Measure the width of your parting off tool (exact), add it to the .300" thickness you need. Turn and bore the workpiece long enough to make several of the spacers. No mount a long-tavel indicator (assuming you don't have a DRO on the machine), and move over by that amount for each successive part.

If you can't do that, make them long and either follow dallen's suggestion or (better) bore out a soft emergency collet with a counterbore/stop surface and bring them to length as a secondary facing operation.

[DanH]

Thanks for the suggestions