Thread mills

==================== If these are one off you may consider a single point tool or boring bar with formed cutter. Slow machining but cheap tooling. Should also be good for special profile threads like stub acme or buttress.

See

I have never done anything like this either, but I could see that a tool meant to cut right-hand internal threads would work better for left-hand external threads than right-hand external (think about the slope direction of an external thread versus and internal as you look at it from the cutter's point of view.)

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JTS Machinery has single point thread mills at a fair price last time I looked. Might be slower, but it will work.

There are single-row thread mills that can do a fair range of thread pitches with one tool. They generally are cheaper than true threadmills, too. I have a small Micro-100 single row threadmill, and it works great. I have only done internal threads, but I think that tool should be able to do either.

Jon

eBay is my friend. Taks time, but i buy threadmills for peanuts. I needed 1.5mm for an RPD receiver. Just scored four brand new ones for $99.

For external, get an insert threadmill holder and inserts. You can get the holders any day of the weed on the bay. You may have to buy the

Karl

I'm going to guess that it pertains to the smaller percentage of thread when cutting internal. If that is correct, then using a thread mill designed for internal cutting should produce a truncated root when used to mill external threads.

You would use the same tool to mill either left or right hand threads. The only thing that changes is the direction of the helix.

You would use the same tool to mill either left or right hand threads. The only thing that changes is the direction of the helix.

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I see you are right. As an amateur machinist I was under the mistaken impression that thread mills with multiple cutting rows had a helical pich to them like taps.

Looking into the reason for different internal and external cutters I see that the UTS spec has different profiles for internal and external threads. I guess you could cut both with the same cutter if you did not mind extra open space at the root of the external thread.