Anyone else use cutoff tool for threading?

tigtorch

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I have been "machining" for a few years but only for odd jobs or artistic work. My lathe was free but was missing the parts for threading. I now have a fully operational lathe (Rockwell 10") and just successfully made my first threaded part.

Anyway I am very new at this but this article caught my eye. It makes a lot of sense to me, has anyone else here used a cuttoff blade for threading?

http://castboolits.gunloads.com/showthread.php?67723-Sharpening-Lathe-Thread-Cutting-Tool-Bits
 
My only concern would be side deflection and if the overhang is kept short and the blade has enough width it should work. The fellow that wrote the post has lots of experience and it works for him - so it should work for us. Nice idea - I'll give it a try.

Michael
 
I could see where that would be practical for small diameters. It would seem to me if you just wanted something that was faster to grind you could use a 1/4" bit. I grind my parting tools out hss blanks....so I don't feel compelled to turn them into threading tools.
 
Even though the person doing that has plenty of experience (which I do not) I've still got to think that it is not a good idea. If you are cutting threads in the "standard" way, with the compound at 29.5 degrees you end up cutting mostly with the leading edge of the "V". The cutting blade is not really designed for a force being applied perpendicular to the blade and the added flex will have a detrimental affect on the threads (IMHO). The alternative is to cut threads by plunging in perpendicular to the work piece, while this will work it's not considered an "optimal" technique.

The other concern I would have, especially with larger diameters, would be the lack of side clearance. If you were to cut the needed side clearance into that thin of blade you would also be making it less stiff.

Bottom line is, you could probably get away with it in a pinch but why bother? It's just as easy (and better) to grind out a threading tool from a standard hunk of HSS.

JMHO

-Ron
 
There's no reason why it wouldn't work for fine threads, but coarser threads would definitely be a problem. The coarser a thread is, the higher helix angle it has and you would end up grinding most of the tool away to get the proper side clearance. A 1/2-13 thread for instance has nearly 3º of helix angle, adding side clearance to that will eat away most of a 1/8" wide parting tool. I'm not sure what would be accomplished using a parting tool anyway, just grind a square lathe bit to suit the thread you want to cut and use it.

Tom
 
I use a cut off tool to thread, its usually fine pitched threads that i use it on. deflection can be a problem but if you watch and take it easy it works well. I like the fact that it works well up to a shoulder.
 
I thought most of the forces would be tangential (downward) and that the side forces would be somewhat countered by the backside of the V. I may be wrong on this but that is why I found the idea intriguing since a cutoff blade has lots of rigidity in the downward direction.

As far as being useful for only fine threads, the author of the post said this: "About three weeks ago I cut a 6 turns per inch pitch thread without any problem even though the parting tool is less than 1/6-inch wide, which is possible because the compound feed is used to deepen the cut. The tool bit only sees the depth of cut and not the entire width of the thread face since the thread is cut using several passes."
 
As far as being useful for only fine threads, the author of the post said this: "About three weeks ago I cut a 6 turns per inch pitch thread without any problem even though the parting tool is less than 1/6-inch wide, which is possible because the compound feed is used to deepen the cut. The tool bit only sees the depth of cut and not the entire width of the thread face since the thread is cut using several passes."

Whether the compound is used or the cross slide has nothing to do with side clearances on the tool, both sides need to clear on the leading and trailing edges if the tool is to cut.

The diameter of the thread has a direct effect on the helix angle. For instance, a 3" diameter 6 pitch thread has a helix angle of about 1º, but on a 1/2" diameter 6 pitch thread, the helix angle is 3º. Add 5º to that for clearance on the leading edge of the tool and there won't be much left of a 1/8" parting tool. If you had a way of slanting the parting tool to the angle of the helix, then it would work fine.

Tom
 
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