Threading Tools Keep Breaking

As others have said, you haven't used any threading tools. the included angle on a threading tool is 60º, the left hand and triangle tools are included angle 120º, twice the angle you need.
 
Rough out single pointing then clean up with a die. When threading mild steel I get it close then finish it with a file to have some hope of a decent surface finish.
 
this is why I only use taps and dies unless I realllllllllly have to do threading
 
My first couple of tries with a carbide it broke like yours. I found that you have to back them off before reversing each time or it will chip. Light cuts, on mine. I have cut a few threads since getting mine, some look better than others. Plenty of cutting fluid, helps, and even with the tail supported it seemed to give, thus I put it as close to he chuck as possible to thread. HSS is also good. Keep trying and you can get it.
 
And this is why I joined the forum. Thank you!! Many good things to learn. I need a threading tool. I need a threading setup on the compound. I should go shallower per pass. At least it's an affordable mistake and a good investment in learning!


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T Bredehoft said:
As others have said, you haven't used any threading tools. the included angle on a threading tool is 60º, the left hand and triangle tools are included angle 120º, twice the angle you need.
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There you would be wrong, an equalateral trianglular insert has an included angle of of 60° by definition, however the relief angle on a tool may make a fine OD turning tool yet impossible to thread with depending on the lead.
 
If you haven't heard it yet, the inserts are not threading inserts. :) Looks like two of the three brazed on carbides might have been. Like Wreck said, the angle on the inserts is correct being a 60* included angle, but not relieved for threading. Most threading tools have about an .008 radius max. For that small of a diameter, my guess is you are going way to slow. Carbide does not like to cut slow. Best to start with a HSS blank and grind it for threading. Did you use any cutting oil?
 
I love single point threading and have only used carbide. Make sure your tool height is exactly centered. You can set your compound to 29.5* off perpendicular to the spindle if you like but I rarely do that anymore. I just use the cross slide for adjusting depth of cut most often. I don't see anything in your photo that wouldbe a good threading bit, turning yes but not threading. Here's a picture of what I use. Sorry it's not the best quality, the camera on my tablet is nothing to write home about.
20160224_205004.jpg
 
Looks to me that you have too much flex in your tool post/tool holder. Typically things start out fine but as you get towards the last pass, the tool will grab and go under center, causing a chipped cutter. I can tell you if you are using a QCTP, a wedge type has a big advantage over a piston type.
 
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