[chrisryn]

I am currently trying to machine some bearing races that have been case hardened to R60 .06 deep. I haven't found anything tooling wise that will machine the part after heat treat that will last longer than one part. I machine the part .02 over size with extra material on the back to help keep warp down. I then turn the .02 off to final size ( to remove warp). Then part off the final race. My inserts are usually shot after one part. I have used several different grades of inserts and even tried a pcd insert. I know that grinding is the best way to do this but the shapes of the race prevent this. Any suggestions?

[PinMan]

In my experience, CBN inserts work best for anything 60Rc+.
Here is a good article on Sandvik's new insert.

[HuFlungDung]

You don't mention how big the part is, or insert grades that you have tried.
Kennametal K090 ceramics (with T-hone) will machine that easily and they will stand up for quite a while under smooth, uninterrupted cut conditions. Much less pricey than CBN, and you can get far more cutting tips for the dollars you spend. I've never been comfortable with running $200 inserts unless the job really requires something special

You might opt for a semi and a final finish tool. This will make the finish tool last longer.

[chrisryn]

The OD is 6.745 the ID is 6.045 and it is .352 thick. It has a 46.55 degree angle on the surface were the rollers will sit. I have tried a Sandvik PCD insert ( I can't give more info because the rep brought 2 in for demo and when they broke he took them with him.) We currently are trying a Sandvik 3115. These .125 parting inserts. We haven't tried anything other than a standard insert on the turning. My boss wanted to find a grade that will part it off then use that grade for turning. I have suggested ceramics but at this point we haven't tried them.

[DareBee]

Turning is the easy part.
I wouldn't attempt the parting, but it likely can be done.

You could also rig up a toolpost grinder and part off with that.

[chrisryn]

Do they make tool post grinders for cnc? I have used them on a manual but haven't ever seen it on cnc.

[HuFlungDung]

Yes, I missed the part about the parting-off That is a tall order.

Parting off the piece might also cause some warpage due to stress relief. Is it not possible to hold these on a magnetic chuck for boring, or perhaps, in full pie jaws?

[chrisryn]

Yes, I missed the part about the parting-off That is a tall order.

Parting off the piece might also cause some warpage due to stress relief. Is it not possible to hold these on a magnetic chuck for boring, or perhaps, in full pie jaws?

The problem with that is that the part is so thin that the case hardening creates to much warp on the part.

[mactec54]

Hi chrisryn

Iscar is the only one for parting of your part any of there grades will do it for turning go with the ceramics or titanium

[DareBee]

Do they make tool post grinders for cnc? I have used them on a manual but haven't ever seen it on cnc.

You obviously work in a machine shop.

You make it work.

Part of my job entails thinking outside the box and to design or think up ways to do anything that is asked of us, so maybe I am envisioning this as being a lot easier than other people would.
(Interesting to see half a milling machine clamped to a hoe to slot a new piece that we welded on for repair or to see some of the wild 1-off satellite components going out the door.)

Anyway, I forget that you are only case hardened.
For parting you could, turn a start notch on the OD, bore a start notch on the ID and then you will only have to part through the core of the material.

[chrisryn]

The process you described is exactly how we are doing it. I am not sure how the heat treat company is doing the case hardining but my experince tells me its heat treated all the way through. Thats were are problems are I think.


I like to think outside the box also. It doesn't allways go my way though.

[DareBee]

4140s maximum hardness without case hardening is 50Rc.
That would be the extent of the hardness that you are dealing with.

As I said earlier - I would not consider trying to part that material, although my experience in hard machining is limited compared to others here.

[chrisryn]

I had an iscar rep out here yesterday. He is sending some inserts for us to try that another shop has had success with. The grade is a IC907 which is for hard part turning it should be here soon and I will report back on how it works.

[mactec54]

Hi chrisryn

I would not go to much on what the rep is trying to sell you as most don't no what will work best the crazy part is the standard uncoated insert works just as well as the high tec coated ones The high tec coated inserts may last longer in your case the secret is not to wide .08 to .100 wide max & getting the speed & feed just right with a rigid setup

[chrisryn]

I learned long ago that most of the time reps will try and sell you more than what you really need. I have had several different tool reps in here trying to tell me that the only insert that will work are ceramic or pcds that are $100.00+ per insert. I have worked with this paticular rep for several years now and he is the only on that has recommended a standard grade of insert. Plus the fact that the inserts are comming in as a demo so we don't have to pay for them unless they work. So its not hurting to try it out.

[Big Daddy]

Boy have I got this thread beat… I’m single point thread cutting hardened 4140. Hasn’t been much fun>:wee:

[Delw]

Sometimes its easier faster and cheaper to make the part from scratch than to modify one, you didnt say how many your doing but I am guessing a quite a few if your dicking around with inserts and reps.

old used inserts are best used for this type of job as there already used and you really dont care if you scrape them.
I have gotten through case harden parts with micro100 parting tools and machesters when nothing else worked,

there is a dog bone type parting tool I beleive for a manchester cut off holder., I used them many years ago, cant remember the manufacturer, they were .250 and .187 wide, they also worked for light od work and facing along with part off.
I am thinking they were kenmetal.

[Big Daddy]

Yes your absolutely right but in this case that’s not my call, I have to work with what was put on my desk although be it reluctantly.. lol And yes I started the job out with old top Notch 5degree positive rake uncoated inserts which are completely useless in this situation. I talked it over with the tool company and swapped out the harder insert with a rake for a softer grade insert with a flash coat TicN & zero rake (Their made by Horizon). So far so good! The inserts are taking the shock but in order to make the insert work for you, you got to run them much higher rpm and faster then simple logic dictates. Right now she’s cruising at 1,715 rpm but they can go as high as 2,546 rpm for my application. I’m not running water soluble, instead I’m using a tapping fluid applied with an acid brush and the inserts seem to like it and the parts are coming out pretty darn nice.
>the best thing coming out of this experience: the harder the work piece the softer you’ll want the insert or face
curtain catastrophic insert failure. I’m confident in saying this concept could be applied straight a crossed the board for any turning/part-off threading op’s in hardened 4140.

[PixMan]

Hi chrisryn

I would not go to much on what the rep is trying to sell you as most don't no what will work best the crazy part is the standard uncoated insert works just as well as the high tec coated ones The high tec coated inserts may last longer in your case the secret is not to wide .08 to .100 wide max & getting the speed & feed just right with a rigid setup

No offense, but your statement about coated inserts not working any better than uncoated carbide is flat out wrong. For you to say that indicates that you have not been properly educated about the benefits of coated carbide cutting tool technology. Perhaps you've been machining with uncoated carbide to your standards for years, but you clearly haven't had a worthwhile, knowledgeable salesperson show you what really works.

You certainly CAN machine that 60Rc steel with coated carbide. I just machined 62Rc hard weld on H-13 mold steel quite successfully with Valenite VP9605 grade inserts in a CNMG432M2 shape at 320sfm, .015" depth of cut, .006ipr feed rate. Try THAT with ANY uncoated insert and let me know how you make out. They now make that grade in a "Top Notch" style threading insert too.

[OldSchoolProgrammer]

Ceramic or cermet cutting tools may work for you but your machine, your tool holder and and your work setup must be very rigid. If you do use ceramic tools, do NOT use coolant. Note that while ceramic tools are extremely hard their compressive strength is not so great as you might guess and their cutting edge can be deformed on Rc 60 material. If you try a ceramic cutter and it gets through one part, examine the cutting edge with at least ten power magnification to see if it has compressed before trying to machine another part.