Lathe Part

[cqualls]

I have a part that finish size is 3.272" O.D. x 3.114" I.D. x 1.600" long. The part is made from 52100 and is hardened 60 to 65Rc, with about .030" stock left on for finishing. Using a cnc lathe what is the best way to keep these parts round while turning them. The O.D. tolerance is +-.0002 and I.D. is .0015, the finish on the O.D. is .2 Ra max.

I'm using a 2 axis cnc Mori Seiki lathe.

 

Thanks

[Guest]

In my experience, if you don't start the CNC process with a round part at this point it is nearly impossible to get it round, as soon as you release if will go back to it's originall shape.

 

I would generally do a manual operation holding carefully and turning a section of the OD round, then grasp on that round section to being the finish machining.

[chris m]

how round are they now? This has a huge effect on how to hold them.

 

The thickness is an issue as well. How many do you need to make? If you need to make a sh!tload then I'd suggest buying some very specific tooling

 

We machine a lot of thin wall steel so drop me an email with some more particulars and I'll try to be more help

 

C

[cqualls]

I'll be making around a hundred to start and could be an ongoing project.

[cqualls]

I'm roughing the parts out on the cnc lathe also, they are round when they go out for heat treat. My process right now is when they come back from heat treat I put them on a very loose fitting round fixture and use a cap to bolt them on the fixture. indicate the outside and get them as true as possible, machine the O.D. with no pressure applied to the I.D.. The cap is holding them against a shoulder. The check round until I pull them off of the fixture then I see between .001" & .002" warpage.

[crazy^millman]

Yeah and unless you grind them going to be very hard to hold that close of a tolerance. You need the things as free and untouched as possible and grinding gives you that as long as really put no stress in the part.

 

HTH

[kenfromlodi]

Do these parts have prior mill work done?

How big is the throat on your mori?

Is there any reason you can't part these off?

I have had great success in turning and parting some very thin walls in hard materials.

 

 

Ken

[cqualls]

The throat isn't big enough to accomodate the hollow bar stock but I'm starting with a piece that is long enough to make 4 parts at and am parting them off but I'm doing this in the roughing stage of the operation, before heat treat.

[chris m]

Craig, do you have a tool that will part the thing off hard? Or would that leave a soft spot on the cutoff end that is unacceptable? If you can part it off after it is hard then I would suggest lightly chucking on one end and turn the other end round to fit a collet or some other form of 'full coverage' clamping device. Then I'd clamp on the turned end and whack them off one at a time. If that doesn't work, sometimes we use a '3-pin fixture' where we press 3 pins into a plate that form a diameter a couple of thou under the bore size to support the part and 3 more pins that act as a work stop, then we clamp against the face of the part with a cap that has 3 tangs on it to concentrate the force over the stop pins. This usually yields a fairly round OD. I'lll try to dig up a sketch and email to you.

 

C

[kenfromlodi]

Parting off after it is hardened sounds like it might be worth a try.

It might even save you a op as well as produce a better part.

Let me know if you need some insert grades that will work for hard materials.

I machine them all the time and can give you what I use.