Part off blades

[rhundl]

What are you guys using and how do they hold up?

I am using the carboloy hss blade witha 1/8 wide insert...

The problem I am having is that they work really well and then all of a sudden snap. could be your first part with the insert or twentyeth. setups are rigid and tool is square. Just wondering what you guys are using, and what kind of life are you getting out of it?

Thanks

[HuFlungDung]

Are you running this on a manual lathe? If so, tool life can be unpredictable because of the lack of consistency of the cutting conditions. Stainless requires a slightly sharper insert geometry. Seco makes a different grade and chipformer for stainless, if that is what you are cutting.

The tool will last longest with full flood, this is not often convenient on a manual lathe A steady feedrate of about .004/rev seems to work well for me, and maybe back off to .002"/rev for the last 1/2".

[rhundl]

We cut alot of different material but mostly 4140 h.t. which is about 30-36 Rc. I have had the best luck running about 500sfpm and .008 per rev. on the feedrate. We do part off in the manual lathes but dont have any problems there. Its in the cnc where we get the lack of consistancy in tool life.According to Seco's navigator I am right in the middle of optimum range. It says I can go all the way up to .01or.012 per rev on the feedrate but that seems a little excessive. I have found that if I go slower on the feedrate (like .004-.006) The blade starts to walk of and cut a dome shape. I was thinking about going to a thicker blade and insert to see if I got better tool life

[Geof]

Are you parting into a turned surface or are you going into the untouched bar OD?

If it is the untouched bar I suggest taking a small cut at the parting location so your parting tool starts in a clean surface. Unless it has been machined or ground the heat treated surface is going to have an oxide layer that can be quite hard; this can play havoc with a parting tool because you hit right across the full width of the tool. A turning tool gets most of its nose under this surface so doesn't suffer as much.

If the surface has been previously machined then I am not being helpful.

[HuFlungDung]

I think a dome shaped cut is due to insert damage, primarily burning the corner off, or chipping it. Part-off is heavy duty cutting, I'd probably run around 350 sfm in 4140 HTSR, and .004/rev using constant surface speed, of course. Running at even higher sfm causes more coolant throw off and turbulence that may not consistently and evenly cool the chip or the insert. A very accurately placed stream of coolant will also be necessary.

[star-turn]

I use Iscar self grip - depending on the m/c it is either 1 2 or 3mm wide.

In general i have no problem parting off ( even on unturned bar, altho' if poss. it is best to get under the skin )

3mm wide General pt.off is 0.06 to 0.1mm per rev on CSS. with max RPM @ 1400 - usually drop to G97 and around 600 RPM with 0.04 feedrate for the last mil of feed to stop the job bouncing around.
use GFN ( Neutral ) for parting into tube or items with a hole GFR/GFL ( right/left handed ) for solid bar.

2mm is just a little slower @ 0.05 to 0.09mm per rev and used for bar 15mm to 25mm in dia. of thin walled turbe.

1mm slowest of all @ 0.02mm to 0.04mm feed per rev but higher speed upto 2000 rpm and used for anything 15mm or less in diameter.

Doming is a sign of tip wear, usually too slow a feed combined with too high RPM

ST

[jhowelb]

Ever try cutting a tool from an old carbide tipped saw blade?

Regrind the carbide tip and you got a great ( and free ) cutoff tool!