Hard turning ?

[Dudemanrod]

I have an R-8 milling arbor that had a large unruly head that I don't want to use but I have one I want to use but has 800 thou hole the arbor is 1 inch. Using ccmt cheap carbide and slow feed and 500 rpm or so. I know that is slow but there not much to turn .anyway the chips are blue coils and stringy blue and hot as hell it sounds like a rock crusher turning it. Should I make one using 1 inch bar stock with a pin pressed in it? Or change feeds an speeds?

 

[Dudemanrod]

Pics

 

[JimDawson]

I guess I would try a slower speed and feed. On the other hand, blue chips off of carbide is not a bad thing. I would support the end with the tailstock.

 

[MrWhoopee]

You're getting curls, not dust, and the carbide is surviving? What's the problem?

 

[Dudemanrod]

It was groaning and the power feed was sticking I just turned it way up and it's much better no noise and it's nicer finish. I think I was pussyfooting around with and had to push it increases depth of cut helped but hot as hell. Thanks guys

 

[Mitch Alsup]

CBN inserts (cubic boron nitrate) in CCMT can deal with hardness's up into the 60 Rockwell C scale.

 

[Ianagos]

Yea I think cbn inserts with basically maxed out rpm would leave nice finishes.

 

[Tim9]

So...just to confirm ( since I purchased some CBN inserts and may try using them soon )
when hard turning with CBN .... HIGHER speeds are better than low rpm’s ?
I know this is a general question. I’m not asking specifics. Just curious About average general hard turning with CBN inserts

 

[Ianagos]

Yes you want fast. Most manual lathe can’t get fast enough on small diameters that’s why I say crank it up.

I’ll attach a chart with some recommended starting numbers for cbn

There is a typo in the chart. It should be inch per revolution not inch per minute(ipm)