Centerless grinding of carburized parts

[Larko]

Hi all,
I've been given the task of figuring out how to centerless grind some of our parts in-house. It's a sleeve roughly 4" in length, .7500/.75005 12Ra finished OD, with a .4995/.5005 finished ID. They are made from 9310, with a case depth of .035/.045 and hardness of 59/61Rc, core hardness of 32/44Rc. They also have to be nital etched afterward. I'm having a difficult time finding any information on the internet or in literature. I have a limited number of setup pieces, so any advice on speeds and feeds would be helpful.
Thanks in advance!

 

[ornerynorsk]

Do you currently have centerless grinding equipment in-house, and an experienced operator? You shouldn't need more than a handful of parts for your operator or machinist to get it figured out.

 

[Larko]

We have two Royal Master TG-12X4 centerless grinders. Calling our operators experienced would be a stretch.

 

[ornerynorsk]

How much material do you have to remove? Your best bet would be to start with the grinding wheel manufacturers for a baseline point to start. Half a tenth can be a pretty tall order for inexperienced operators. If the machines are in good shape, they'll hold it, but it definitely takes the right setup.

 

[mfgenggear]

uPnORT

Is your diameter a typo?
.75000-.75005
is .7500-.7505 which is grinding tolerance

because even seasoned machinist grinders are are going to have a tough time with this job.

this is grind & lap tolerance.

grind with a soft wheel j or k 80 grit
first part of the machine must temper etch inspect
to make sure it not over tempered or reharden.

 

[Larko]

Yep, typo, sorry. The tolerance is .7500/.7505. I've been told we that we have an I wheel for the machine, but I haven't been able to find it yet. There is .002/.003 grinding stock.

 

[saberblue]

Unless you have a lot of parts you might want to look at doing these parts between centers on a cylindrical grinder
== set up etc is less of an issue with cylindircal grinding and you should be able to sneek up on you size -- it should also solve the issue that you don;t mention which is relationship of to bore to the OD.

A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com

 

[Larko]

We have to maintain runout of .001 between the ID and OD.

 

[mfgenggear]

.002-.003 stock is light. the parts must be straight & round w/i .001 before grinding.

also the bore must be concentric prior to grind otherwise
it will be out of tolerance.

there should be .007 min stock total.

Saberblue has a point.
it will be easier to grind between centers, however
the parts must run true to centers before grind.
it is possible to true up the centers to the od & bore prior to grind,

it is also possible to grind centerless, but the operator must be seasoned. or a bunch of scrap is possible.

 

[tamechdev]

UpNort,
You may want to call a bearing manufacturer. I know that they use centerless grinders to grind carburized parts all the time to tolerances in the millionths of an inch. They may have some guidelines for you. Just a thought.