Adventures with carbide insert tooling

The vast majority of turning on my 1963 Chipmaster has been using home ground HSS, with the exception of a couple of boring bars with inserts. I spied an advert from Arc Euro with insert based turning tools at a very attractive price. So I invested in a 16mm shank turning tool with a CCMT09T304 insert and thought I would give it a go.

So said tool arrived and I mounted it up against an offcut 1.25in of (I think) MS bar from my friendly engineering shop. Cranked up the Chippie to scarily fast speeds (2000ish RPM) and off we went... "interesting" times.

1) Neat cutting oil is not ideal for this task clouds of smoke obscuring my view of the job and filling the workshop. Conventional suds would be much better. Also coolant splashing around everywhere.

2) Hell I need an insert witha chipbreaker. Streams of very hot curly blue swarf. A real tendency to come off the insert and route behind the toolpost screws and shoot out horizontally very close to to where I was standing. At the end of the job it wasa really good excuse for a major sweep-up of the workshop and I am still finding little blue black spirals in obscure places.

3) Boy did it make my Chippie grunt, don't think the Inverter has every run so hard and it did slow the spindle speed significantly.

4) Whoa the workpiece didn't half get hot...

5) On a positive note, really nice finish on the work and it certainly can shift material.

So an interesting experiment, I can certainly see why HSS is recommended over carbide for smaller lathes. I won't be completely swapping over to carbide, but will certainly be finding an insert with a chipbreaker before doing any serious work.

Most will break the chip if the feed rate is right (high enough). If you use a fine feed rate the swarf is thin and will bend rather than thick swarf which breaks. Try double the feed rate but half the depth of cut, this will remove the same amount of metal per rev but will hopefully break

Out of interest what sort of depth of cut and feed rates were you using? Turning or facing?

Edited By JasonB on 09/05/2016 18:44:00

Thanks for the feedback Jason. I was turning, about 50 thou DOC and tried 2 and 4 thou per rev feed

...and don't use coolant. You want the swarf to get as hot as possible. The tool already has a chipbreaker, you just have to use it correctly, as JasonB suggests.

Look for a feed and speed calculator to get you in the right ballpark. If you have an Apple or Android phone, most of the main manufacturers provide them free. Why spend good money on something like this and then guess how (not) to use it?

Need to keep the heat off the job and tool, would you do that with a hardenable steel or alloy, I think not.

Presume running 220v 3ph Stuart with equal power inverter, should do 3 - 4 times that at a presentable speed and feed rate.
Break the strings up by disconnected power feed momentarily but as above get speed and feed right will work much better.

I'd say the feedrates were too low for proper chip formation. I very rarely use less than 4 thou per rev for finishing and higher rates for roughing. Aluminium often seems to need on the order of 8-10 thou per rev to get proper chip breaking.

Personally I'd be running more like 1200 rpm for 1.25" steel, but that's partly because my lathe is **** noisy at top speed. To keep the metal removal rate up I increase DOC and feedrate. I never use coolant with insert tooling. You want the shear zone to be hot. In theory at least most of the heat generated ought to be in the chips rather than the work. The work can get too hot to touch, but steel chips come off straw or blue, and so are much hotter. If a chip goes down your shirt front it turns the air blue too!

Andrew

This is an interesting video about insert geometry and how they work together on lathe and mills

Its a good 25 mins worth

https://www.youtube.com/watch?v=bbMbFvsRTJo

I remember when I was at Tech Collage in Dunedin in 1963, the school got a new Chipmaster and our teacher gave us a demo, don't know what steel he used, but a 3" bar, and a 1/2" depth of cut, and blue swarf for miles, you could have made bandsaw blades from it. Us kids were most impressed, and then we went back to the old Harrisons with the line shaft drive, and clicking belts.

Ian S C

I'm puzzled why that would be the case.

Let me guess the answer to Martin 100's question:

If the metal being cut is heated enough, it becomes soft, and so (a) easier to cut) and (b) with less problems curling or chopping up the swarf.

I made a clutch disc (6.5" dia) from a circular saw blade on my Myford using a carbide insert, and the swarf came off red-hot. Slower speed produced juddering, etc.

Cheers, Tim

It's not so much the swarf as the shear zone where you want the heat. Hot metal takes less force, and hence energy, to shear. And since the sheared metal is hot it is more pliable and should flow more easily over the insert chip breakers and bend and break into short chips as the designer intended.

The theory behind turning of hardened steel relies on a sufficiently aggressive feedrate to ensure the shear zone is at red heat and therefore relatively soft. Even for normal turning and milling it is sometimes possible to see dull red chips coming off in subdued light. I've never had an insert red hot but I have had carbide milling cutters just reaching red heat.

Andrew

PS: Darn, beaten to it!

Edited By Andrew Johnston on 10/05/2016 14:30:01