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Tapered Threads - (again)

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6件のコメント

  • Jacant

    Taper the hole to 1.8°.

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  • Tim Heeney

    Well, it's how i do it - not that i have...

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  • Hugh Keir

    Thanks Guys,

    Great suggestions.

    First thing I tried was to increase the thread pitch.

    Leaving the hole sides parallel, a pitch increase from 1.41( the height of the cutter) to 1.65mm (smallest I could go down to) allows a tapered hole to be created by the cutter.

    Any smaller a pitch and the build failed.

    I then set the hole to my desired1.8degree taper (NPT thread).


    With the hole tapered, I found that I could reduce the pitch to almost the same size as the cutter.

    The images show 1.43mm but found that 1.42mm cutter would work and 1.415mm cutter would fail.

    So to conclude setting a tapered hole helps greatly when drawing a tapered thread.

    Your cutter needs to be around 0.1mm less than the required pitch to be successful.

    Awesome job guys.

     

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  • Tim Heeney

    Hugh,

    I looked at this late last night.

    I found for parallel threads there isn't a need for a small land between the pitches, but for a tapered thead there was and as you also found, the tool width is best not to be the same as the pitch, this is perhaps because for a tapered thread, thread flanks ( forward / trailing ) are different lengths, so a larger cutting tool is needed. DSM ( and most modelers) don't like very small slithers of geometry - so make a cut or a boss a definite thing that can be measured in the practical world.

    Generally, aim for small slithers to be not less than 0.001mm and all will be fine. - i am not saying a size of 1.12345678 is a problem because of the decimel places, no, not all - it is the actual 'smallness' that a face can be, that i say aim for, not smaller than 0.001mm

    NOTE: the actual smallness limit is closer to 0.0001mm - but lets be sensible ; )

    Hope this helps if needed.

     

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  • Jacant

    It will cut with the 1.43. Just make sure the cutter is perpendicular to the taper.

    You can download a Step file from here to check your thread.

    https://www.mcmaster.com/npt-threads%2fpipe-and-pipe-fittings%2flow-pressure-stainless-steel-threaded-pipe-and-pipe-fittings-8%2fthread-type~npt 

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  • Hugh Keir

    Thanks Tim,

    I am 3D printing the thread profile, so small slivers are not too critical, like you this has not previously been an issue, I previously always drew the cutter height using the pitch dimension.

    There are limits to the accuracy on what can be achieved and also the print shrinks once it cools down, hence the test piece with 4 holes, they are all different diameters to see which one provides the best fit. 

    I re-drew the cutter 0.02mm undersize and used the correct pitch for the thread, so has been a great success and is printing out as we speak.

    Jacant,

    Thanks for the tip on the cutter alignment, I will use that on the final prints when I am pressure testing the components for strength.

    Also the step files, will have a look at the McMaster files to see how they compare with my drawing.

    Thank you both.





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