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Variable Pitch Helix

romeograhamromeograham Member, csevp Posts: 657 PRO
in Using Onshape
I need to make a feed screw with accelerating pitch (variable pitch) along its length.

SolidWorks has a variable pitch helix, of course.

I've been trying to mess around with @MBartlett21's Variable Section Sweep (but can't quite understand how it works, and can't quite get it to do what I'm after. Might just not understand well enough...it sure seems like it should be able to do it).

Anyone have any luck with a FeatureScript that would allow altering the pitch of a helix along its length?

(I have done something with 3 varying-length sections of helix, each with 10 turns...then use the resulting 3 helices to sweep my thread along...but the transition between sections is not continuous):


Thanks!
Romeo

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    MBartlett21MBartlett21 Member, OS Professional, Developers Posts: 2,034 EDU
    edited May 2019
    @romeograham
    By the way, it is actually @konstantin_shiriazdanov 's FeatureScript. Maybe he could help?
    mb - draftsman - also FS author: View FeatureScripts
    IR for AS/NZS 1100
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    mahirmahir Member, Developers Posts: 1,291 ✭✭✭✭✭
    edited May 2019
    You can use my Parametric Curve FS if you can describe the variable helix as R/Theta/Z(t). R and Theta would just trace a repeating circle while Z needs go from one constant slope curve to another with a smooth transition between. Problem is it won't be exact if you use a polynomial or trig function to approximate the constant sections of Z(t).

    https://cad.onshape.com/documents/57acdfaae4b005c413ed9b6f/w/3fd585a46d3af1b3ba413c53/e/9f334d884b522c64159c0322
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    romeograhamromeograham Member, csevp Posts: 657 PRO
    Thanks @mahir . I had forgotten about that one. I don't understand the math, but I do seem to be able to get it to make a simple variable helix.

    It would be really great if my inputs could be "pitch" (rather than the functions that are required). Is there a way to know what pitch would be produced from the functions in Theta & Z?



    Thanks again!

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    konstantin_shiriazdanovkonstantin_shiriazdanov Member Posts: 1,221 ✭✭✭✭✭
    Variable helix by the given pitch law involves some math with intagrals, but if pitch conditions are not so strict or you can find them iteratively it's surely possible with Variable section sweep or Sketch wrapper.
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    romeograhamromeograham Member, csevp Posts: 657 PRO
    edited May 2019
    Good point @konstantin_shiriazdanov - I saw the Sketch Wrapper example in the Variable Section Sweep doc - so I'll give that a try too.

    I am not the only person on the forum that has asked about variable helices....I bet a FS that uses Variable Sweep / Parametric Curve (in the back end) with the Interface / inputs more like the Helix tool (at the front end) would be well received by more folks than just me!

    I would be enthusiastically interested in helping with testing / feedback (sorry - won't be any help on FS or the underlying math).

    Thanks @mahir @MBartlett21 & @konstantin_shiriazdanov !

    Romeo
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    ilya_baranilya_baran Onshape Employees, Developers, HDM Posts: 1,175
    Someone has done this before: https://cad.onshape.com/documents/63c77e740cd8b149ab1fa50d/v/3d6e696f60d96f919a4c39fa/e/df162b42ecb1048d0818c450
    Ilya Baran \ VP, Architecture and FeatureScript \ Onshape Inc
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    romeograhamromeograham Member, csevp Posts: 657 PRO
    Thanks @ilya_baran.

    Between @brad_phelan's work and Sketch Wrapper, clearly there are tools that will allow me a great level of control on my feed screw.

    With Sketch Wrapper, I am able to create the variable helix that I'm after. The inputs and results are clear and easy to understand & control:


    I like the layout work showing in the Thread FS from Brad - good ideas for establishing what the screw flight should be doing at each turn.
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