[How do I?] Parting Blade Help

I hate those parting tool holders. My ALORIS, yes, Aloris parting tool holder was not machines square to the back dovetail surface, I had to regrind the slot on my surface grinder to make it remotely usable. I am still having problems with it, as when I clamp the blade in it twists! So all my parts have a tapered cut. Ugh. I'll be making a new parting tool holder very soon.
 
There are a lot of you tube videos on lathe work, might want to check out a few on parting off.

michael
 
I had luck on my 11" rockwell by turning the tool over cutting edge down and putting lathe in reverse BUT not so good if you have a screw on chuck
 
Would it be possible to make a tool holder for a QCTH that holds the blade upside down, for cutting with the part turning backwards?
 
Ed, believe me, your post hadn't appeared when I wrote mine.
 
that holder gives the blade alot of top (or back) rake, so if you get a little chatter or uneven feed suddenly BLAM it digs in, takes a huge bite and because the blade is so thin and the sides are unsupported due to the T shape, it twists and snaps. Even on my Atlas 618 I've parted steel successfully. Some things that help me -
  • sharp (honed) blade
  • 0 deg top/back rake
  • everything snugged down as tight as it can be (carriage and compound locked, cross slide jibs snugged up tight)
  • flood the slot with cutting oil
  • if it's a deep slot, back out, move the blade 1/2 it's width over (whichever direction works for the part you're making) and plunge back in. Swap back and forth - this creates side clearance for the blade
  • slowish speed in back gear and really stuff the blade in. It should always be producing a nice curl. If it starts breaking up or making an odd sound, back out clean the slot and flood it again.
Even then it doesn't always go to plan and the part will want to try and ride up onto the blade. At that point I stop and finish it off with a hacksaw. I've learned to leave a little on the part for cleaning up the face of the parting cut for just this reason.
 
I've used that exact same setup of parting blade and holder many, many times. It works fine and the design is solid. You're barking up the wrong tree worrying about this.

Parting isn't about finding the one thing that's wrong, it's about doing all the little things right. Mrpete222 on Youtube has several videos about parting you should watch if you haven't. In another vein, Frank Ford has an excellent write-up about modding the import parting blade holders, just so you understand what everyone is talking about:

http://www.frets.com/HomeShopTech/Tooling/CutoffHolder/cutoffholder.html

But this mod isn't necessary to use these holders, it's just eliminates the need to shim the blade and even then it isn't that big a deal, it's just one of the little things.

I looked at your gallery of pictures: Are you sure your tool is clamped as it doesn't look right? It's clock-wise to tighten. Also, in relation to your AXA QCTP toolpost, that lathe looks on the small side. It's quite possible that even with a perfect setup that the machine isn't rigid enough to perform this operation.

Also remember that as the tool enters the work ideally the lathe should turn faster. After turning, usually I drop down one belt speed on my SB to part. If everything is correct, the blade should pull a chip as it works.
 
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Hi zimm,

You’ve got some good guesses so far, but let me throw this out there as food for thought. Your tool holder looks very similar to the Tormach parting tool holder from LMS that I have, except mine holds the blade horizontal, with no rake, and has a “T” on the end of the model number, 250-007T. I’ve used it on 2 different bench lathes over a couple of years and haven’t had any problem with it or the blade. I use a 1/16” P type, HSS blade that is .041”+/- thick at the bottom edge. I line it up vertically in the tool holder and cinch it down. I’ve used it on aluminum, brass and steel rods, up to 3/4” diameter. I would have to guess that (1) you aren’t getting the blade aligned vertically in the holder and (2) it may be digging in due to the rake built into the tool holder and/or (3) the blade is just too thin at .012”. Did you double check that measurement?

Maybe reaching for straws a little with this question, but do you lock down the carriage when you part off?

Tom
 
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