Mystery metal

T

ttabbal

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I've been posting in the HSS grinding thread about this, but I think it's getting off topic there. I have some random metal I was wondering if someone might help me identify and get machining properly.

To start with, I know that the answer might well be that my machine isn't up to it. But it's worth a try.

Machine is a PM-1127VF-LB.

Material is a magnetic bar about 2.75" diameter. There is some corrosion on the outside, so I don't think it's stainless. A normal file does mark it, but it is noticeably harder than other metals I've tried that file on.

Here's a picture of the material and a bit I turned with the carbide insert displayed, with one of the nicer chips. Speed is 350 RPM, max in the low range for the machine. Faster doesn't seem better. 850 RPM throws red sparks. Feed is 0.005/rev. I was mistaken in the other thread on the feed, read the wrong chart. DOC is 0.030 diameter. Much deeper stalls the lathe. That could be improved with slower feed, I haven't tried it yet.

HSS can cut it, M2, but above about 200 RPM it wears a flat on the tool nearly instantly. Even with a 0.002 diameter cut.

IMG_20181015_220034.jpg
 
Others with more experience may chime in here but I'd suggest a higher feed if your machine can take it and see if you can get that chip breaker working which should improve the surface finish. Make sure the cutting edge is fresh - a dulled insert will just generate more heat and give you a poor surface finish.

Also maybe a slightly bigger DOC may help to bury the radius of the tool into the work piece or alternatively a carbide insert with a smaller nose radius. It may also be worth considering alternate carbide grades. Cheap inserts from china are OK for most materials but for harder to work stuff like this good quality inserts are worth the extra. Look around at various suppliers - I can buy individual inserts here in the UK so if I'm tooling up for a job I'm not forced to buy an entire pack that I'll likely never use. You do often get a better price for larger quantities though so it's worth considering if you will use them again.

You may have to slow the machine down slightly to do either of the above but looking at the tool tip in your picture the cut is generating a lot of heat so this may not be such a bad thing. Do you have coolant set up on your lathe at all?

If all else fails it may be worth considering putting this back in your stock pile and saving it for a project that requires a harder material.
 
Hi Guys,

I've seen stainless steels go rusty, not to the extent in the picture ! Also "Magnetic", hard materials whilst attracted to a magnet don't retain much magnetism at all. Possibly one of the Pre-hardened steels.
 
400 series stainless will corrode and is magnetic . It can be heat treated . 15-5 , 17-4 etc .
 
It’s probably a alloy steel of some sort. My general turning is almost always using inserts. Like one other posters said even the low cost carbide from China will work.

Personally I try if I purchase inserts to get them off of EBay because most times the name brand ones are surplus. Even the value inserts sold by the vendor like MSC and Travers are surprisingly good. You have to remember we aren’t turning the SFM on our lathes to over stress most inserts


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Thanks for the info guys! I've read about spark testing, but have zero experience with it. I'll give it a go though. It might at least rule some things out. The wikipedia page makes me wonder if I might have been throwing carbide sparks with the higher speed test, bright red and not much forking.

The insert is a China import DCMT070204. The discoloration is mostly debris, but it did get hot on a previous run. I'll try flipping it, the other corner is unused. And a fresh insert. I'll also look into some of the better brand inserts, it would be interesting to see the differences. I do have coolmist available, I was using tap magic for this test, but the heat does make coolant attractive.

The material isn't needed for an immediate project, I was just trying it out as I have a bunch of it and wanted to see how it turns. Not so well at the moment. :) But as a beginner I think it's useful to try to learn how I could use it, if I can anyway.
 
mmcmdl said:
400 series stainless will corrode and is magnetic . It can be heat treated . 15-5 , 17-4 etc .
Click to expand...
There is one exception to this, 430 stainless is non-hardenable. I found out the hard way. I purchased a full sheet of .06 for some blades. Expensive mistake.
 
Try the correct tool...

Use a side cutting tool as it does better here.

Pictured tool is for thread cutting.

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I'm going to go with something like 4350 pre-hard. Machines really nice with carbide tools. Use an insert with a good chip breaker in it to prevent the long stringy chips, nasty buggers. Feed and speed whatever your lathe will take.
 
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