Threading Tools Keep Breaking

[armytbone]

I've been tinkering with my new G4000 for a month now. Some decent success turning W1 to a set taper and finishing it smoothly. I decided to try threading as my next learning project.

I'm trying to turn 1/2 inch rod to have an end with one inch of 8mm-1.5. This will fit the tool post turret bolt to hold my tool post secure.

I had a 1/2 inch carbide tipped bit and also a 5/16 Grizzly carbide, a McMaster-Carr indexable carbide insert bit, and a McM-C carbide bit. All had 60 degree points for threading.

First I tried on W1 tool steel. All of the bits chipped.

Then I tried on cheap hardware store steel rod which I knew was softer, thinking maybe I shouldn't turn tool steel.

My inserts broke and the point under the insert, on the tool, chipped.





I made sure the tips were on center, using a dead center as a reference. I only advanced the tool .005 per pass. Spindle speed was slow.

Seeing as I'm a newbie, what is happening? Why are my bits being eaten by even hardware store rod, considering I have turned tapers using bit from the same makers and they were fine?

Thanks for the advice.


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[coffmajt]

What kind of cutting oil did you use ? What degree did you have your cross compound set to? 29.5 is what you need. Also I have learned to back out after each pass with the compound feed with it set on a zero then advance it back to the zero before advancing the cross compound by .002 to .003. You may need a little faster spindle speed as well. Hope this helps. Jack

 

[Karl_T]

You are going to be WAY better off learning to thread with HSS...

Carbide chips easily, you already know that. it just doesn't work well with the very low speeds for manual lathe threading.

Carbide threading tools work GREAT on my Hardinge CHNC lathe at 1000 RPM.

Karl

 

[T Bredehoft]

Not that it will keep your tools from chipping ( yeah, go with HSS) you might find it easier with an inch sticking out of the chuck and forget the live center. Under no circumstances (until you find out you know better) take a depth of cut of more than .005 on one side. .002 or .003 is really enough until you're really comfortable with threading.

 

[Mork]

I'm fairly new to machining but i have successfully cut thread probably 10 times (not counting a couple of mishaps). First off, those are not threading tools you are using. Threading tools have a very sharp point. Threading requires quite a few passes and the amount you take off needs to be very slight on the final few passes. the compound has to be set to 29.5 degrees and the tool dead square and on center. Basically you only use the compound to move the tool in with each new pass so you are only cutting one side of the cutter.

Here's a very good two part video:

 

[Billh50]

As the others have stated, the tools you show are not for threading. Threading tools have a very very slight radius if any at all. I myself do not set my compound at 29.5 degrees. Some people, myself included, will just set the tool at 90 degrees to part and feed in with the cross slide. The cut depth should be very small and last couple only .001 - .002 deep.
High Speed tools do much better on the smaller lathes than carbide. Also if you are only threading 1 inch of the bar then move it closer to the chuck with no center. You will get much more rigidity that way.

 

[Mork]

Wow... I tried going straight in and it didn't work well at all. It cut rough and was difficult to control on the final passes. Maybe with a larger more solid lathe it would work better but my results were not good.

 

[Wreck™Wreck]

WAY to much nose radius on the tools shown, none appear to be threading tools.
Threading 1018 mild steel stock is dodgy at best, small wonder that you destroyed a few tools.

 

[Tozguy]

Same thing happened to me when starting. Chipped a bunch of carbide tools before switching to HSS.
Once my confidence was up and I tried carbide again at higher speeds it was better. But it is still too easy to chip a carbide for my liking.
Since brazed carbide tools need sharpening too there is really no way to avoid learning to grind tools yourself. As already said those are not threading tools. Spend the time to practice tool grinding and use sharp tools.
Threading next to a live centre is not rigid enough for what you are doing. A dead centre is better but cutting close to the chuck is best. Locking the cross slide and compound for the cut might help if the gibs are not broken in and set snug.
Hang in there, your eureka moment is coming!

 

[wawoodman]

You might want to pick up some 12L14. Very nice on a lathe.

And like everyone else has said, HSS, and take it easy!