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Thread: Correct drills for trapezoidal taps?

  1. #1

    Default Correct drills for trapezoidal taps?

    I recently purchased a 10x2 trapezoidal tap to make some new nuts for the leadscrews in my proxxon KT150 table, and have realised I've no idea what the correct drill size is to make the holes.

    A good bit of googling tells me lots about metric thread forms, and a reasonable amount about acme threads but nothing of use for trapezoidal threads. Could someone help me out here?

    • If I've missed an obvious web page, I'd be grateful if you could tell me where it is!
    • Is acme similar enough to trapezoidal that I could just use the rules for acme threads with appropriate measurements?
    • Would it have just been easier to drill a whole bunch of holes of decreasing size until I found one which fitted the leadscrews snugly when tapped?


    Thanks in advance!

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  2. #2

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    Quote Originally Posted by serriadh View Post
    I recently purchased a 10x2 trapezoidal tap to make some new nuts for the leadscrews in my proxxon KT150 table, and have realised I've no idea what the correct drill size is to make the holes.

    A good bit of googling tells me lots about metric thread forms, and a reasonable amount about acme threads but nothing of use for trapezoidal threads. Could someone help me out here?

    • If I've missed an obvious web page, I'd be grateful if you could tell me where it is!
    • Is acme similar enough to trapezoidal that I could just use the rules for acme threads with appropriate measurements?
    • Would it have just been easier to drill a whole bunch of holes of decreasing size until I found one which fitted the leadscrews snugly when tapped?


    Thanks in advance!
    According to DCSwiss its 8.2mm

    However Maryland say

    "Formula for tap drill (round to closest available drill size): D1+(0.05*p)
    D1 = minimum internal thread minor diameter, p = pitch"

    = 8 +.05*2 = 8.1mm

    both claim a 7H fit...


    BTW was that a LH or RH tap and where in UK are you?

    If you're in Europe why not come and visit the UK CNC Community at http://www.mycncuk.com


  3. #3

    Default

    According to the formulas found in ISO 2901, the minor diameter should be 8.000 - 8.236 for a 7H fit.

    Software For Metalworking
    http://closetolerancesoftware.com


  4. #4

    Default

    Excellent stuff. Cheers guys, you've been a great help.



  5. #5

    Default

    Quote Originally Posted by irving2008 View Post
    BTW was that a LH or RH tap and where in UK are you?
    Its a right-hand tap. It was about 20 quid from Marchant Dice. I'm not entirely sure why it costs a fraction of the price of trapezoidal taps from elsewhere; I expect I'll report back at some point when I find out

    I'm Cambridge based, as it happens.



  6. #6

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    Quote Originally Posted by serriadh View Post
    Its a right-hand tap. It was about 20 quid from Marchant Dice. I'm not entirely sure why it costs a fraction of the price of trapezoidal taps from elsewhere; I expect I'll report back at some point when I find out

    I'm Cambridge based, as it happens.
    Ah OK, yes I'd like to know how good the MD ones are - I want to replace the leadscrews in my lathe with metric LH 10x2... if it had been a LH one I might have negotiated a loan... I've made a RH one for delrin from a bit of scrap TR10x2 and might do the same for a LH one for brass with some TG10x2 and some case hardening power - MD want 31 for a LH one

    If you're in Europe why not come and visit the UK CNC Community at http://www.mycncuk.com


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