Custom Thread won't model

[u.spaeth]

//Edit:

Guess I found the problem... PitchDia != Pitch. Gotta calculate that separatly. Haven't found out yet how...

Hello,

this is my first try on designing a custom thread. I copied, renamed and edited the DIN-Pipes file and my custom thread shows up fine in Fusion 360 and can be used - but not modelled. It gives an error.

I wan't to create a VG8 (both, bolt and nut) as can be found here:

https://www.gewinde-normen.de/en/valve-thread.html

This is my implementation:

<ThreadType>
  <Name>DIN Ventilgewinde</Name>
  <CustomName>DIN Ventilgewinde</CustomName>
  <Unit>mm</Unit>
  <Angle>60</Angle>
  <SortOrder>18</SortOrder>
  <ThreadSize>
    <Size>8</Size>
    <Designation>
      <ThreadDesignation>VG8</ThreadDesignation>
      <CTD>G 1/16 </CTD>
      <TPI>32</TPI>
      <Thread>
        <Gender>external</Gender>
        <Class>A</Class>
        <MajorDia>7.747</MajorDia>
        <PitchDia>0.794</PitchDia>
        <MinorDia>6.631</MinorDia>
      </Thread>
      <Thread>
        <Gender>internal</Gender>
        <Class>A</Class>
        <MajorDia>8.061</MajorDia>
        <PitchDia>0.794</PitchDia>
        <MinorDia>6.945</MinorDia>
        <TapDrill>0</TapDrill>
      </Thread>
      <Thread>
        <Gender>external</Gender>
        <Class>B</Class>
        <MajorDia>7.616</MajorDia>
        <PitchDia>7.035</PitchDia>
        <MinorDia>6.561</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
  <ThreadSize>

Of course I found https://knowledge.autodesk.com/support/fusion-360/troubleshooting/caas/sfdcarticles/sfdcarticles/Cus... and double checked my values.. what did I miss? (Class A, ignore B (unchanged))

[Ketherton21]

pitch diameter is the difference between your threads major and minor diameters total.

[TheCADWhisperer]

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@Ketherton21 wrote:

pitch diameter is the difference between your threads major and minor diameters total.

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What standard are you using?

Do you have a reference (something like this)?

Edit: I see now DIN - Pipe.  I withdraw my comments as I have no experience with that standard.

[Anonymous]

I'm trying to model the same thread. So in this case the PitchDia would be 7.747 - 6.631 (Major - minor)? 

@u.spaeth Have you successfully modelled that VG8 thread?

[HughesTooling]

In the post above the pitch diameters for the Class A threads are definitely wrong. Does the external class B thread work? The page from link in the first post doesn't show pitch diameters and also doesn't show how to calculate it in the diagram so you'll need to find better info.

[Anonymous]

I think the right calculation seems to be: PitchDia = (Major - Minor) / 2 + Minor

So this should be the correct file for a VG8 thread, as it works in Fusion, but I haven't tested it in real life

<?xml version="1.0" encoding="UTF-8"?>
<ThreadType>
  <Name>DIN Ventilgewinde</Name>
  <CustomName>DIN Ventilgewinde</CustomName>
  <Unit>mm</Unit>
  <Angle>60</Angle>
  <SortOrder>18</SortOrder>
  <ThreadSize>
    <Size>8</Size>
    <Designation>
      <ThreadDesignation>VG8</ThreadDesignation>
      <CTD>VG8</CTD>
      <TPI>32</TPI>
      <Thread>
        <Gender>external</Gender>
        <Class>A</Class>
        <MajorDia>7.6835</MajorDia>
        <PitchDia>7.1255</PitchDia>
        <MinorDia>6.5675</MinorDia>
      </Thread>
      <Thread>
        <Gender>internal</Gender>
        <Class>A</Class>
        <MajorDia>7.9975</MajorDia>
        <PitchDia>7.4395</PitchDia>
        <MinorDia>6.8815</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
</ThreadType>

[HughesTooling]

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@Anonymous wrote:

I think the right calculation seems to be: PitchDia = (Major - Minor) / 2 + Minor

So this should be the correct file for a VG8 thread, as it works in Fusion, but I haven't tested it in real life

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No it doesn't work like that. Internal threads have a more pointed peak and more truncation in the hole so the pitch diameter is closer to the minor diameter and external threads are the other way around.

You have about 0.3mm difference in pitch diameter for external\internal. That's way too much, if you look at a similar size like M8x0.8 it's about half that.

Something like this for standard metric threads.

[Anonymous]

I looked at some British Standard Pipe Parallel Thread tables and that was exactly how the pitch diameter was calculated. I'm not a thread expert, so I don't what to do otherwise.