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  1. #1
    Join Date
    Aug 2013
    Posts
    980

    Need thread milling insight

    With the help from Jacob at Tormach and some nice single point thread mills from Mari tool I have been thread milling quite a bit this last week.
    One problem I have been having is that even though I am using the major diameters as referenced in the machinerys handbook, the final I.d threads I have been making are typically too tight and I have been needing to oversize my major diameters to be able to achieve a reasonable fit.
    I have also use the drill sizes as specified for regular tapping.
    Have others had this experience? Does one need to add a minor slop factor to get better fits when thread milling?

    Thanks
    Nathan

  2. #2
    Join Date
    Jun 2014
    Posts
    1777

    Re: Need thread milling insight

    Probably a bit of tool flex depending on the overhang.
    mike sr

  3. #3
    Join Date
    Feb 2006
    Posts
    7063

    Re: Need thread milling insight

    My experience with thread-milling is that calculation alone will almost never give you exactly the right fit, other than by dumb luck. I nearly always find it necessary to do a test piece to dial in the exact right diameter for a perfect fit on each thread size. You can add a "fudge factor" (usually something on the order of 0.005") to ensure the parts will at least screw together, but to get a perfect, close fit requires a test cut.

    Regards,
    Ray L.

  4. #4
    Join Date
    Aug 2013
    Posts
    980

    Re: Need thread milling insight

    Thanks Mike,
    That is most likely one factor for the smaller thread milling I have done (#6 & #8). I have noticed that the larger sizes (9/16") have had a little less issues.

  5. #5
    Join Date
    Aug 2013
    Posts
    980

    Re: Need thread milling insight

    Thanks Ray. That is kind of what I have been doing to get my only successes. Just wanted to make sure there wasn't something I didn't know (or shall I say even more that I don't know)
    Happy Turkey Day
    Nathan



    Quote Originally Posted by SCzEngrgGroup View Post
    My experience with thread-milling is that calculation alone will almost never give you exactly the right fit, other than by dumb luck. I nearly always find it necessary to do a test piece to dial in the exact right diameter for a perfect fit on each thread size. You can add a "fudge factor" (usually something on the order of 0.005") to ensure the parts will at least screw together, but to get a perfect, close fit requires a test cut.

    Regards,
    Ray L.

  6. #6
    Join Date
    Nov 2014
    Posts
    2

    Re: Need thread milling insight

    the common procedure as with threading on a lathe is to take final "spring passes". these just repeat the final pass with no changes to depth of cut in the program as the name suggests to account for flex in the tool and/or workpiece.

  7. #7
    Join Date
    Sep 2012
    Posts
    1543

    Re: Need thread milling insight

    Good place to look for threadmilling.... .... ... . . . . http://www.cnczone.com/forums/tormac...ml#post1597008

  8. #8
    Join Date
    Aug 2013
    Posts
    980

    Re: Need thread milling insight

    I spoke with Frank Mari of Mari tools today. It is great when you can talk with the owner of the company and Frank has been very accessible when I have had tool questions.
    Basically Frank said what a number of you have relayed - that single points due to their sharp 60 degree ends don't cut the same way taps do and need to be experimented with to find the right major diameter.
    There apparently is no other formula than to just do some test cuts. If one needs tolerance then the use of GO/NO GO gauges will help guide.
    Also, new to me, these thread mills can be used for metric as long as the TPI is equivalent and one just uses the same drill-size as with a regular tapping procedure.
    I have dialed in the major diameters for the threads I am currently using and it is great to be able to teak them for tighter or looser fit.

  9. #9
    Join Date
    Jun 2010
    Posts
    26

    Re: Need thread milling insight

    You should never really expect anything to come out exactly to size - or to stay exactly the same size - so you should be adding cutter-comps to things like this. That's what they're there for.
    pearls ain't free

  10. #10
    Join Date
    Sep 2012
    Posts
    1543

    Re: Need thread milling insight

    I agree about Frank. We have talked through email a few times. I try and support them when I can!

  11. #11
    Join Date
    Nov 2007
    Posts
    2151

    Re: Need thread milling insight

    Did this a while back with couple Maritool spt. At the time it was hard to find small ones and maritool were only ones I could find.
    Like others said above it helped me get up to speed faster doing setup tests and samples.
    Lets you zero in on everything. P Smidt book on cnc programming provided all the math and diagrams required to understand threading and about any other cnc op!.
    Setup in cam takes a bit of messing around, still when have it done one time you can save these types of operations and use again.
    Attachment 258542


    Attachment 258544


    Attachment 258546

    Fun stuff!

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