Need Help!- Turning small iron pins

[DALEK]

Hello,
I need to turn 1/8" OD bar down to 3/32" for about 3/4" in Iron . These pins are for electrical connectors so they have to be perfect size and parallel.
I have tried machining on our cnc lathe but cannot hold size as the bar bends. I can feed the bar by parting nearly all the way through, opening the collet, pulling the bar out by moving the parting off tool in Z+ direction, closing the collet and finishing the cut.
Is there such a thing as an external reamer? Is there some sort of steady I can use with a bar this small?
Any help or Ideas would be appreciated.

Thanking you in advance.

[beege]

Box Tool!!!!

http://65.108.9.49/model_rtc.htm

[Geof]

Do you have a CNC mill available? I have done things similar to this by interpolating around the rod and going to the final size in one cut. I can take 1/4" Delrin round bar down to less than 1/8" for a 3/4" length and it is parallel; there is no way this could be done by turning.

An alternative if you have to use a lathe is start with larger material; turn the 3/32" diameter in one cut, then the 1/8" diameter in one cut. This way you are using the larger diameter in the starting material to provide rigidity. Even so you may need to program a compensating taper to account for deflection and get a parallel finish.

[beege]

Originally Posted by Geof Do you have a CNC mill available? I have done things similar to this by interpolating around the rod and going to the final size in one cut. I can take 1/4" Delrin round bar down to less than 1/8" for a 3/4" length and it is parallel; there is no way this could be done by turning. An alternative if you have to use a lathe is start with larger material; turn the 3/32" diameter in one cut, then the 1/8" diameter in one cut. This way you are using the larger diameter in the starting material to provide rigidity. Even so you may need to program a compensating taper to account for deflection and get a parallel finish.

Geof,

Have you ever used a box tool on a lathe? I regularly cut Ø.375 down to Ø.180 in one pass, for a length of 4", and hold a tolerance of ±.0005" for the entire length, no tailstock.

Dalek, these people at Boyar Schultz are very helpful. Give them a call.

[Geof]

Box tool? Many times when I ran turret lathes. I used to get frustrated setting them up but once they are set they can as you say give very good results.

[beege]

They also work great on CNCs.

[Mcgyver]

iron, as in cast iron? and how many do you have to make, and what's perfect? i'll leave production to the box tool guys but for onesy twosy, here are some ideas that work

start with a slightly larger dia piece, capable of supporting its, and take it all off in one cut. easy way to make 3/4" lengths of 1/16 - 1/8 dia or whatever

the other way is to do it in steps, just keep poking more out of the collet.

finally you can make a version of box tool...basically a brass block with a hole in it of finished diameter with a tool bit clamped to it. fidgety to set up, but it works

[mc_n_g]

What is wrong with using a follow rest on the part as you cut it? Not a steady rest.

[Andre' B]

You can get hollow milling cutters (inside-out endmill) which can be plunged over a part for making trunnion type features.

You can also get cutting blades for doing such things with a thread chasing head.
http://www.landisthreadingsystems.co...ingProgram.pdf

Edit: Some better pics.
http://www.geneseemfg.com/gallery/index.php

[DALEK]

Thanks for all your replies guys.
I have tried a boxtool we have here but it is too big, I will have to beg or borrow a smaller one. I can not change up a size in bar as it is actually drawn iron wire, and I can not get any larger size. Yesterday I tried using an ordinary 3mm die and feeding it on slowly, the size is OK but I don't know how consistent it is. Has anyone tried this before?
Thanks for the pictures of hollow milling cutters, I did not know there was such a creature, they may be the answer to my problems.
Unfortunately I dont have a CNC mill.
I have to make about 4000 in Iron and another 4000 in a material called Constantan,
which seems similar but more brittle.

[beege]

Can you send it out to a centerless grinder in your area? I've seen $80 setup and .25 per unit for a price, and you can bet they can hold ±.0002, which should be fine for your needs.