What Threading Tool?

[65BAJA]

I want to buy a threading tool holder and insert to do some 1/4"-20 or maybe 1/4"-28 single point threading. There are so many different inserts I don't know what to get. UN thread type or partial 60*? Is there an advantage to one vs the other? It looks like the UN inserts are thread pitch specific whereas the partial are more universal.

The lathe I will be using is a 12x36 Pratt&Whitney with a QC tool holder that looks like it will take a 3/4" sq shank. I was going to buy a 1/2" though as that is what is being used in the machine. I don't know if 3/4" puts the insert above centerline or what. The material will be 4130.

 

[RJSakowski]

UN Threads have a radius at the root of the thread which is related to the thread pitch. specifically, the radius is such that it is tangent with the flanks of the thread at a point 1/4 of the pitch from the bottom of the virtual 60 degree vee. As such a geometrically correct threading tool can only cut one pitch. Most of us "cheat" by using a tool with a smaller radius which will deepen the root of the cut thread slightly. The resulting threads are not to the UN standard. The chart below shows the geometry.

As long as the tool radius is smaller than the standard radius, it can be used to cut any pitch thread, hence "universal". Unless you have really critical needs, the universal threading tool will work just fine.

As to the height of cutting tool, you can measure the height above your compound slide with a 1/2" tool at the lowest setting in the QCTP and add 1/4". If that distance is less than or equal to the height of the spindle axis, you're good to go. You want your threading tool to be at the same height as the spindle axis for threading.

Bob

 

[65BAJA]

Wow. Thank you for that. I'm just getting started at this so I still have a bunch to learn.

 

[Chipper5783]

Threading tool for lathe work? You are right, there are quite a number of options - depends on the job, the equipment, the operator etc. Here is a picture of 7 configurations which I use from time to time for external threading. My recommendation is that you simply grind up a tool blank and start threading.
From the left: a triangular insert straight on, a "Diamond" tool holder, a HSS toolbit ground, a carbide brazed toolbit, a Mesa Tool, an Iscar full form, and a Top Notch holder. The Diamond and Mesa work well. The full form gives the prettiest result, but you need a different insert for each pitch. I know there are a number of other options (likely you'll get numerous additional responses and even more options).

 

[4GSR]

One note about UN threads, they do not necessarily have to have a root radius to them. You can have a flat instead. Unless the Unified National Standard has change in the past 20 years, it states a formula for a maximum flat you can have. It also states for "rolled" threads, you can have a radius root of "x" amount according to formula. And when a rolled thread has a raduis root, it's designation is "UNCR" or "UNFR" or if an UN thread "UNR". But I'm getting too technical for our needs here on H-M.
Ken

 

[kd4gij]

This is what I use. The price is right and it does most s.a.e threads

http://www.mesatool.com/products/threading-tools/

 

[savarin]

Interesting, thanks.
I'm just in the process of attempting to get an insert for internal metric threads.
My home ground one does a job as can be seen in my telescope project but I would like to get the correct thread form.
Any advice on tips to be had?

 

[kd4gij]

ISO metric threads are the standard 60 deg. that s.a.e are. So just grind the tool the same. Or the mesa tools will do a great job for you. I have the 1/2" that is external on one side and internal on the other side and use the same inserts. You can also get grooving inserts tor it to cut the under cut.