Any tips for Machining (turning down) a Hardened (60c) shaft on a Myford 7

Hi

I am looking for any tips or experience of turning down the ends of a hardened (60c) shaft on a Myford 7.

The shaft is for a 3D printer and I want to turn the ends down from 12mm to 8mm for a distance of 25mm on each end.

I have been trying a few cuts with mixed resullts using a CCMT insert tool.

The core of the rod is soft (ish) and the surface has been hardened and polished.

Thanks

Have you checked the insert manufacturer's recommended speeds & feeds?

If the core is soft(ish) as you say, you may be able to grind the hard skin off the ends, then get in with a deep cut underneath the hard outer layer on the OD and remove it in one fell swoop. Or you might even very carefully grind the outer layer off the OD on the bench grinder then finish the softer inner material in the lathe.

Otherwise, you might have to experiment with rpm. Sometimes going slower helps with harder materials, other times with insert tooling, if you spin the job fast enough and get the metal basically up toward melting temp at the cutting point it will work too. Might sacrifice a tip or two in the process though. In this scenario, sparks and red hot swarf coming off the job are good. On such a small diameter though, the ML7 probably won't spin fast enough for this.

Edited By Hopper on 12/07/2018 00:23:05

Edited By Hopper on 12/07/2018 00:23:51

For 60hRC, the happiest solution would be to find a CBN insert and use that at the fastest speed the lathe can cope with (whether the original 650-odd rpm or a faster VFD driven speed). Take shallow cuts, 1 to 8 thou with a 5-10 thou feed. If the swarf is coming off as a red cascade, then you've got it sorted.

Once you're through the case, the normal inserts will do.

Even with just carbide inserts, use the fastest speed you can get on an ML7 at that diameter

The last time i had to do that i cheated ! Chucked it up in the lathe and used an angle grinder with a new wheel to knock most of the hardened skin off then machined it with my normal carbide tooling . One reason for this is i found the tool tended to push off a lot rather than cut as the skin was thicker than i expected - close to a mm from memory .

You could try taking a deeper cut and try to get under the hardening .

ccMt means moulded .ccGt means ground and that is what counts for hard things

https://www.homemodelenginemachinist.com/threads/carbide-cutting-hard-things.16796/

Edited By Niels Abildgaard on 12/07/2018 05:27:15

It's perfectly possible to turn hardened steel with ordinary CCMT style inserts, but for best results I'd agree with Mark and go for CBN inserts. Just sit down before looking at prices.

The posts in this thread on turning hardened silver steel may be of interest:

**LINK**

Andrew

60c shaft, was it induction hardened? could it be annealed?
Sounds like you'll be removing the hard case anyway?

If turning the shaft is too difficult, an alternative might be to bore the shaft and insert smaller, softer ends?

Edited By not done it yet on 12/07/2018 10:12:38

.

They can be surprisingly reasonable if you don't buy from a 'name brand' supplier. Here's one I just spotted.

I got mine from a second hand tool dealer (findurstuff on EBay. No connection etc) and the CCMT 09XX tool holder I needed for them cost more than the five inserts.

I have found that the ccgt 09 and ccgt 06 inserts from kyocera on the myford are best. You want around 400 rpm for the hard skin and then around 600 for the rest. Get the small radius 0.2mm inserts and take no more than 0.2mm cuts (0.4mm diameter ) at about 0.05mm per rev,(2 thou per rev) feedrate. If it gets hot, use water or some coolant on it. I have a picture of the ccgt inserts that I turn bearing races with in my album.

In my experience , unless you can get a 0.2mm cbn and they are expensive, the regular coated carbide will be a far better choice on a Myford lathe.

Neil

For the odd job you can search for CBN inserts off ebay, youl'll find branded inserts which although used are still good. That said to run CBN effectively very high speeds are required and is mostly used on cnc machines.

I have recently purchased these : **LINK**

Slow speed, high torque with carbide or cobalt tooling

Finish at high speed with light cuts

Shapers munch through everything and their secret is slow speed with masses of torque

Edited By Ady1 on 13/07/2018 00:28:57

I have turned hardened ball screws but not on a Myford. I used carbide inserts, not a massive speed but certainly an aggressive feed rate. This got rid of the hardened outer layer and allowed a more typical turning process when the hard skin was gone. This was also with an interrupted cut due to the outer layer being a spiral groove. The stock was held in a collet.

I think I used absolute minimum overhang for the tool holder and ball screw to keep everything as stiff as possible. I may also have done a few millimetres at a time and pushed the stock out a bit more after each section of a few millimetres was done. I'm sorry I can't be more exact, it was a few years ago.

Martin C

The only way i could turn ultra hard Perkins valves down on an ML7 was to use Kenametal NR 48R K68 inserts running in excess of 1000rpm 1phase 1hp motor.
These are radiused tips so you would turn what you can leaving minimal to touch up at the end with another cutter.

You should have no problem using carbide inserts. I have cut lots of induction hardened and chromed piston rod material on my South Bend 10K. It is just a 9" lathe raised 1/2". I use a relatively high speed and light cut until I get through the hard layer. Expect the chips to come off red. The carbide I use for that is of unknown grade. It is just carbide I don't mind destroying.

Just a quick update.

I sucessfully completed the job using CCGT 09 carbide tool running at 300 RPM with a 30' (0.75mm) depth of cut working dry. The swarf came off cleanly and a dark blue colour. The surface was rough but I was then able to use another CCGT tool at 1800 RPM to clean up the shaft to finish size.

Thanks for all your responses, gave me confidence to get stuck in !