Help creating a custom thread for Schrader [tire] valve cap

[teamriab]

Hi everyone, I'm new to F360 and am trying to create my first model, specifically a cap for a Schrader (tire) valve.

The part I'm stuck on is creating the threads for the cap.

My research has found that the Schrader valve has some rather strange threads. Here are the most precise measurements I could find for the valve [external]:

7.7 mm OD
32 tpi, or 0.794 mm pitch
Minor diameter is 6.9mm
Thread designation is .305-32 or 7.7-32

http://www.engineersedge.com/wwwboard/posts/2386.html

As far as I am aware, I need to create a custom thread XML file, which I've tried to do, but as the dimensions I've found are for the external thread, I am not sure how to create the internal threads for the cap piece I am trying to model up.

Here's my custom thread file:

<?xml version="1.0" encoding="UTF-8"?>
<ThreadType>
  <Name>Inch Tapping Threads-Schrader</Name>
  <CustomName>Inch Tapping Threads - Schrader</CustomName>
  <Unit>mm</Unit>
  <Angle>60</Angle>
  <SortOrder>5</SortOrder>
  <ExternalOnly>no</ExternalOnly>
  <ThreadSize>
    <Size>7.798</Size>
    <Designation>
      <ThreadDesignation>0-48</ThreadDesignation>
      <CTD>0-48</CTD>
      <TPI>32.0</TPI>
      <Thread>
        <Gender>internal</Gender>
        <Class>2B</Class>
        <MajorDia>7.798</MajorDia>
        <PitchDia>7.468</PitchDia>
        <MinorDia>7.239</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
</ThreadType>

I've basically entered the values from my best interpretation of the measurements I have, and my limited understanding of the thread's XML file structure as well as how threads are measured.

Can anyone provide me with some insight on how to create a custom thread profile for (I assume "internal") threads for a Schrader valve cap?

 Currently, my approach is to be able to model the external threads, then use it to extract (subtract) from my model, in order to get an internal thread, likely having to adjust tolerances a bit (admittedly something I am not sure how to approach yet either).

For a thread that is seemingly so common, I have found it very difficult to find much information on how to model it/create it.

Thanks in advance for your help!

[shekar_sub]

Hi @teamriab,

>Currently, my approach is to be able to model the external threads, then use it to extract (subtract) from my model

>I've basically entered the values from my best interpretation of the measurements I have

1. It would be best to get to the internal thread values for this type of thread and enter it into the file as shown in the link below:

 https://knowledge.autodesk.com/support/fusion-360/troubleshooting/caas/sfdcarticles/sfdcarticles/Cus...

To get the internal thread values I'm unsure how helpful we can be. I cross-checked Inventor thread specifications and I was not able to find an equivalent thread for this.

2. Then in Fusion when you try Model Workspace, Create, Thread command

3. You should be able to see the specification that you added  in Step #1 in the Thread dialog box.

4.  I'm assuming that you are able to create the shape of the valve cap using fusion's commands like Revolve, Hole, Fillet etc..

5. Then you can select geometry to apply the thread specification.  Please ensure "Modelled" is checked in the dialog box.

Another related discussion that you might find helpful: https://forums.autodesk.com/t5/fusion-360-ideastation-request-a/non-standard-threads/idi-p/5717744

What I'm suggesting above might not exactly solve the issue. Just trying to see if the above approach is feasible.

Regards

shekar

[teamriab]

Thanks, Shekar.

Yes, it's very difficult to find the internal thread measurements for a Schrader valve cap!

Since my post, I made a new custom thread XML file using the measurements I posted previously:

<?xml version="1.0" encoding="UTF-8"?>
<ThreadType>
  <Name>Schrader - Metric</Name>
  <CustomName>Schrader Metric Profile</CustomName>
  <Unit>mm</Unit>
  <Angle>60</Angle>
  <SortOrder>3</SortOrder>
  <ThreadForm>1</ThreadForm> <!-- triangular -->
  <ThreadSize>
    <Size>6.9</Size>
    <Designation>
      <ThreadDesignation>M7.7x0.794</ThreadDesignation>
      <CTD>M7.7x0.794</CTD>
      <Pitch>0.794</Pitch>
      <Thread>
        <Gender>external</Gender>
        <Class>6g</Class>
        <MajorDia>7.7</MajorDia>
        <PitchDia>7.3</PitchDia>
        <MinorDia>6.9</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
</ThreadType>

I did not have a measurement fore the pitch diameter, so I simply averaged the Minor and Major measurements.

Using this thread file, I created a cylinder and applied the thread, then Combined it with my cap model to create the internal threads. I then adjusted the tolerance (not sure how much to give here) to give the external threads some room so they do not interfere. I was able to animate the joint and do not see any issues with interference, but of course I am still not certain of the thread dimensions in the first place!

I plan to have my cap printed for personal testing, but perhaps I am getting ahead of myself as whichever manufacturer I end up using for final production may be likely tap the threads, so modeling them may not even be necessary?

Again, thanks for your help!

[shekar_sub]

Hi,

I found this link http://www.practicalmachinist.com/vb/general/tap-die-schrader-valve-who-stocks-them-320269/  which ultimately points to the Tire and Rim Association's website where you might be able to buy a copy of the standards?

http://www.us-tra.org/publications.html

http://www.e-taps.com/ofertapage-20140.html

Again you might not find your exact sizes for the internal threads.

>so modeling them may not even be necessary?

Agreed. Normally if you specify the thread specification (not modeled) and add a thread callout in the drawing that might be sufficient as manufacturers use standard tap sizes.

I'm glad that the internal thread can be modeled from the external thread (interesting approach).

Thanks and Regards

shekar

[HughesTooling]

Found the attached PDF with a bit of a search, think 8V1 is the one you're looking for.

Mark

[teamriab]

Awesome sauce! 8V1 does look like it matches up to what I've found so far.

Thanks! I'll give it a shot and let you know how it works out!

[Anonymous]

did work out?

[ash.palmer]

Adapted from Indian Standard -- Dimensions for tyre valve threads document here 

<?xml version="1.0" encoding="UTF-8"?>
<!-- 
Source: https://archive.org/details/gov.in.is.9449.1.1980/page/n3/mode/2up
Adapted By: Ash Palmer <ash.palmer@cryptmin.net
Threads 5V1, 5V2, 6V1, 8V1
-->
<ThreadType>
  <Name>Valve Screw Thread DIN 7756</Name>
  <CustomName>Valve Screw Thread DIN 7756</CustomName>
  <Unit>mm</Unit>
  <Angle>60</Angle>
  <SortOrder>18</SortOrder>
  <ThreadSize>
    <Size>5.200</Size>
    <Designation>
      <ThreadDesignation>5V1 5.2x0.705</ThreadDesignation>
      <CTD></CTD>
      <TPI>36</TPI>
      <Thread>
        <Gender>external</Gender>
        <Class>A</Class>
        <MajorDia>5.232</MajorDia>
        <PitchDia>4.775</PitchDia>
        <MinorDia>4.496</MinorDia>
      </Thread>
      <Thread>
        <Gender>internal</Gender>
        <Class>B</Class>
        <MajorDia>5.334</MajorDia>
        <PitchDia>5.004</PitchDia>
        <MinorDia>4.801</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
  <ThreadSize>
    <Size>5.200</Size>
    <Designation>
      <ThreadDesignation>5V1 5.2x1.058</ThreadDesignation>
      <CTD></CTD>
      <TPI>36</TPI>
      <Thread>
        <Gender>external</Gender>
        <Class>A</Class>
        <MajorDia>5.220</MajorDia>
        <PitchDia>4.705</PitchDia>
        <MinorDia>4.2</MinorDia>
      </Thread>
      <Thread>
        <Gender>internal</Gender>
        <Class>B</Class>
        <MajorDia>5.370</MajorDia>
        <PitchDia>4.885</PitchDia>
        <MinorDia>4.600</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
  <ThreadSize>
    <Size>6</Size>
    <Designation>
      <ThreadDesignation>6V1 6x0.8</ThreadDesignation>
      <CTD></CTD>
      <TPI>36</TPI>
      <Thread>
        <Gender>external</Gender>
        <Class>A</Class>
        <MajorDia>6.030</MajorDia>
        <PitchDia>5.670</PitchDia>
        <MinorDia>5.385</MinorDia>
      </Thread>
      <Thread>
        <Gender>internal</Gender>
        <Class>B</Class>
        <MajorDia>6.160</MajorDia>
        <PitchDia>5.830</PitchDia>
        <MinorDia>5.540</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
  <ThreadSize>
    <Size>7.7</Size>
    <Designation>
      <ThreadDesignation>8V1 7.7x0.764</ThreadDesignation>
      <CTD></CTD>
      <TPI>36</TPI>
      <Thread>
        <Gender>external</Gender>
        <Class>A</Class>
        <MajorDia>7.747</MajorDia>
        <PitchDia>7.239</PitchDia>
        <MinorDia>6.909</MinorDia>
      </Thread>
      <Thread>
        <Gender>internal</Gender>
        <Class>B</Class>
        <MajorDia>7.798</MajorDia>
        <PitchDia>7.468</PitchDia>
        <MinorDia>7.239</MinorDia>
      </Thread>
    </Designation>
  </ThreadSize>
</ThreadType>

[kendelm67]

I know this post is old but did you figure it out?

[MRWakefield]

Prompted by your question, I've created a custom thread file for ISO 04570 Tyre Valve Threads. You'll find it in a collection of custom thread files I've posted about here.