Threadmilling NPT
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  1. #1
    Join Date
    Feb 2010
    somewhere in Illinois
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    Default Threadmilling NPT

    OK, I have a thread mill for 14 NPT. Details of the mill are 4 fl diameter .490" loc 1". Material to be cut, brass or aluminum. Any advice on speeds/feed, offset (radius), depth, etc.
    I looked on-line but found no info where I looked. I understand some tool makers supply these details but have yet to find that data.
    Thanks in advance

  2. #2
    Join Date
    May 2007
    Central Texas, West and North of Austin
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    We thread mill bunches of 1/2x14 NPT and 3/4x14 NPT in class 30 cast iron. I run a thread mill very similar to what your describing, at 2000 rpm. That's a tad slow, as it's only about 262SFM, and should be a minimum of 300 on steel, probably more like 400 on cast, and a bunch faster on aluminum. I expect 600 SFM thread milling aluminum would be conservative. A lot of it depends on your machine and setup. These parts we run are fairly large castings,on a 4th axis, and the thread mills are pretty expensive compared to end mills and such, so I wrote the programs VERY conservative. Feeds generally fall in the 10 IPM range. Again, this is really conservative, but I like to stay easy on the tooling till I can tell how well everything is gonna hold up. We started running this job a couple of years ago on a linear way CAT 40 machine, we've now installed a CAT 50 box way machine in it's place, so I'll be stepping up the feeds, probably into the 20 IPM range.
    I also take two passes. Lots of folks don't, they just bog it to it and get it done in one pass. I like a lighter finish pass, but again, this was on a linear way CAT 40 machine. And not a premium machine at that.
    So, in answer to your question, start out kind tippy toeing, and work your way up till something breaks, then back off a step.)
    I also run a lot of 1.500x12 UN threads on a thread mill. But it's inserted( 1 insert), so the feeds are a lot slower. Speeds work out about the same SFM though.


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