Hi Mike,

I have used carbide insert tools for many years, especially when machining work with hard spots. Carbide tools can be run two times the speed of HSS tools or more, just make some tests with vaying speeds. My chips often come out blue. The inserts intended for Aluminium works well on other metals too, as you have already discovered. The special polished inserts may cost a bit more, so use them for the finishing cuts, and cheaper inserts for roughing.

Thor

Mike You should have no problems using the **GT inserts on steel Just be careful not to chip the edges as they are very sharp and can chip easier than **MT inserts which have a stronger edge. Go to the thread Jasons tips, and you will see a few pics of various ** GT and a **GX coated and uncoated.

Mike, http://www.shop-apt.co.uk/ Large range of inserts etc and good service. Lynne.

Carbide inserts can be run at considerably faster surface speeds than HSS tooling, but whether this is a nice to have or essential to get a good finish depends upon the material. For instance EN8 needs to run fast with inserts to get anything like a good finish. Likewise the depth of cut versus finish with inserts also depends upon the material. The low carbon steels seem particularly bad in this respect; possibly leading to the blanket statement that inserts don't work with small DOC. As a contrast it is possible to get a good finish on 303 stainless with a 2 thou DOC.

Generally feeds need to be higher than most MEs use to get the chip breakers on the inserts working properly. The aim in industry is to produce short, easily removable, chips. A long length of swarf or a birdsnest looks impressive, but in my case it usually gets in between the tool and work, fudging the finish along the way. I never use less than 4 thou per rev and particularly for roughing I'll be at 12+ thou per rev.

This thread may be of interest as to the behaviour of different materials when turning:

**LINK**

Andrew

+1

By hard experience I have found that carbide inserts don't seem to like cutting less than about 4 thou/rev. Below that they chatter and/or break. I usually run between 4 and 8 thou per rev, the softer the metal the higher the feedrate.

Andrew

I think Neil was talking about parting tool inserts? Not the polished inserts the OP was talking about. I've certainly found the polished inserts much more fragile than more common types. Like many of us on here with hobby lathes I'm not interested in what industry does.

Ajohnw, Hi John, Here is a CCGT tip that has seen a lot of use [only the first of the 2 proper corners ] It has been used mostly on En 1 and 8 and very little Aluminium. As you might be able to see it has lost it coating at the used corner [and did so a bit past] but the tip is still very sharp and still gives an excellent surface finish [please note, I always use flood coolant for steel] So I can't agree on your statement that once a coating wears off the finish goes down. Certainly not all tips are created equal, and that may have a bearing. This particular insert is Arno CCGT 090304 TiCN/ TiALN coated.

Cheers.