On Tue, 06 Mar 2012 17:48:20 -0500, Wes
wrote:

The other day, I needed to turn a shaft to 25mm diameter for a machine at work. Not a big
deal I thought. I only need a 7" shaft, I'm turning 12L14, this should be easy.

The first problem I ran into is that the normal CMNG tool holder I use would not clear the
live center (this is a big lathe). So I looked around, I found a tool holder of the
trigonal type. It had a ceramic insert in it but I knew where we had a machine running a
carbide trigonal insert and installed one of those.

Well, I never got a decent finish, it was so bad you could ridges across the item I
turned. I tried a different carbide insert and it wasn't any better.

By "ridges across," you mean chatter-type? Or was your tool-nose
radius too small for your feedrate?

If it's chatter, you know what things can cause that.

--
Ed Huntress


It got to the point that I used a bit of sand paper, pressing the shaft through a bearing
to burnish it to get a shaft I could use.

I tried playing with the feed, speed and tweeking the tool height. Nothing made a
difference.

I should have just turned a longer shaft using the CMNG tool holder that always worked and
parted off the excess.

Anyway, what was the likely issue? It did look like the trigon tool holder had a bit more
inclination but I didn't measure it.

Thanks,

Wes