Thread: Turning case-hardened gear bore

Wondering if anyone has experience with turning case-hardened material.

Looking to bore out some gears that originally ran on needle rollers so they will take a tapered roller bearing. Its definitely been done with these particular gears (old Landrover 4-speed gearbox) and apparently the bloke used ceramic inserts to gradually get through the hard case and then turned normally.

I'm hoping with the right technique it might be possible to just get under the case with carbide tools.

Any tips would be appreciated.

Steve

I have had success just taking a very deep depth of cut in one hit to get under the case, I was on a 5 HP machine though. Doing it with a flimsy internal boring bar will be had though, what's the Id?

I don't have one close to measure, but from memory ID would be around 35mm.

I've got 3HP on the lathe, and the races are only about 12mm wide so should be able to use a short fat bar.

How deep a cut were you using, and what style/size inserts if you can remember.

Steve

I use a lot of this extremely obsolete sumitomo insert which is only suitable for od turning, the depth of cut would have been more than .125" maybe closer to 0.200" but the case wasnt anywhere near that deep. the insert had slight negative rake and was square to the face of the work, but trigon inserts or WNMG might work better as they would bulldoze the case off.

I kept the speed fairly low, the shafting was 2.75" and i was at maybe 300 rpm

Thanks for the info.
I've got some WNMG in 08 size and a 20mm boring bar to suit so will have a crack at it with those when I get a chance.

Steve

Yes I've done turning on through hardened steels, though don't think I've ever done a bore. Do a search here for hard turning as I know I put up some posts on it. I would probably use a Cermet insert for this, but you may be limited and just have to cop the insert wear. Inserts are cheap these days anyway. Few here are doing production work, and if it costs an insert corner to get a tricky job done it's likely no biggie in the grand scheme of things.

Taking a deep cut to get under the hardened layer is definitely the way to go if you have the HP and the rigidity. It's what I'll do if turning cast iron, as some castings the skin can be glass hard. My noodle has neither the rigidity nor the HP, yet hard turning was definitely doable. Most boring setups lack real rigidity, so it's likely a similar scenario. Expect the chips to be glowing as they come off, that's normal. I found the DOC was quite limited due top both the above, however the finish is spectacular. If it's only case hardened then just finish as per normal.

You should be able to do it with the wnmg inserts you have. Tool wear will be a issue, but normal inserts are cheap. I have done this many times before we kept CBN inserts at work. I would try 30-60M/min for cutting speed .1-.2mm/rev for the feed and don't use coolant.

Definitely cutting with dirt cheap eBay WNMG insert.







Steve

You can definitely see the depth of the case hardening. 1-2mm I'd say.

Only took 2 insert edges to do that much so I was surprised how easy it was.

Bore is 50mm, settings were 60m/min (380rpm), 0.15mm/rev feed and around 1mm DOC.
Insert is one of the cheap unbranded ebay specials they give you with a toolholder - WNMG080404

This one is just a test. It's a genuine gear but gives a ratio that I'll never use so happy to sacrifice it

Steve

Do you have a Datum to ensure that the new bore is concentric to the gear PCD when finished?
Anything more than about .001" runout could result in annoying gear noise.

I bored some motorcycle drive shafts that were case hardened without any issues here:
//metalworkforums.com/f65/t2014...torcycle-drive

Originally Posted by Techo1

Do you have a Datum to ensure that the new bore is concentric to the gear PCD when finished?
Anything more than about .001" runout could result in annoying gear noise.

I bored some motorcycle drive shafts that were case hardened without any issues here:
//metalworkforums.com/f65/t2014...torcycle-drive

Don't have anything to check the bore to gear PCD, but its mounted in a 4-jaw and set up to < .01mm runout on the original bore that the needle rollers ran on.
Knowing what Landrover's manufacturing tolerances are like I reckon that should be plenty good enough.
I'll take a lot more care with the setup of the real thing - making sure the face and both front and rear of the bore are all pretty much spot on.
Since both sides need to be bored for the new bearings I'm not sure how I'll make sure they are both true. Would be best to do the machining in one setup - possibly by ripping the case off the rear of the bore (while chucked rear facing out), then reverse it, rip the case off the front and then bore both front and back to finished size. I'd probably need to make a boring bar for the rear bore to do that.

Getting a bit ahead of myself though.

Steve

What box is it.... LT95?

Originally Posted by waxen

What box is it.... LT95?

You guessed it

Steve

I can save you the trouble if you want, I have the the whole box and dice sitting under the bench in boxes.

Originally Posted by Techo1

Do you have a Datum to ensure that the new bore is concentric to the gear PCD when finished?
Anything more than about .001" runout could result in annoying gear noise.

I bored some motorcycle drive shafts that were case hardened without any issues here:
//metalworkforums.com/f65/t2014...torcycle-drive

It’s an English gearbox. It’s designed around a annoying noise.