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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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.
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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