topic Re: Does the thread tool generate correct threads (pitch diameter)? in Fusion Design, Validate & Document Forum

Does the thread tool generate correct threads (pitch diameter)?

HansenDK — Sat, 03 Mar 2018 20:22:58 GMT

Hi all,

After doing some experiments with defining my own custom threads for use with the built-in thread tool, I've run into an issue with the pitch diameter always coming out wrong. I can not get the thread tool to actively use the <PitchDia> tag in my custom thread XML file. It seems like it really doesn't matter what diameter I define - it will always turn out as the same (incorrect) diameter anyway. I checked the built-in thread XML files, and it seems they behave the same way - i.e. the pitch diameter is not correct, when the thread is modeled by the thread tool.

The following is a snippet of the XML file defining the standard metric threads in Fusion 360 (2.0.3803). The snippet defines the external M10x1.5 thread:

      <ThreadDesignation>M10x1.5</ThreadDesignation>
      <CTD>M10x1.5</CTD>
      <Pitch>1.5</Pitch>
      <Thread>
        <Gender>external</Gender>
        <Class>6g</Class>
        <MajorDia>9.85</MajorDia>
        <PitchDia>8.928</PitchDia>
        <MinorDia>8.141</MinorDia>
      </Thread>

When I use the thread tool to model this thread and afterwards use a sketch to check the dimensions of the thread, I get this:

Hopefully, you'll be able to read what the dimensions in the sketch says, but if not the minor and major pitches are matching the values in the XML file, whereas the pitch diameter do not. It reads 8.876 instead of 8.928.

Has anyone been working with custom threads and using the tool to model the thread (and not just visualize it)?

Best regards

Jesper

Greetings from Denmark! 🙂

Re: Does the thread tool generate correct threads (pitch diameter)?

etfrench — Mon, 05 Mar 2018 02:08:55 GMT

If you model the thread using the ANSI/ASME B1.13M-1995 standard, what do you get for the pitch diameter?

Re: Does the thread tool generate correct threads (pitch diameter)?

HansenDK — Mon, 05 Mar 2018 17:02:29 GMT

The closest thing to your request is to select "ANSI Metric M Profile" in Fusion, and the answer to your question is 8.876 mm.

I do not know, if the thread data corresponds to that particular standard, but I'm not sure it is important. The issue is that I think Fusion is doing threads differently from what it is being told to do.

I start by drawing a simple cylinder with center at the origin. Height about 5 mm. Diameter is not important, because the thread tool will change that anyway. Then I create a thread on the external surface of that cylinder, and select the options as seen in the screenshot.

Then I do a sketch on the XZ plane and project the intersections with the thread. That leaves me with this:

So... I get a major diameter of 9.850 mm, and minor diameter of 8.141 mm, and a pitch diameter (which is hard to see) of 8.876 mm (assuming I understand the definition of "picth diameter" correctly).

This is from the ANSIMetricMProfile.xml file installed with Fusion, where the thread tool gets it's data:

    <Designation>
      <ThreadDesignation>M10x1.5</ThreadDesignation>
      <CTD>M10x1.5</CTD>
      <Pitch>1.5</Pitch>
      <Thread>
        <Gender>external</Gender>
        <Class>6g</Class>
        <MajorDia>9.85</MajorDia>
        <PitchDia>8.928</PitchDia>
        <MinorDia>8.141</MinorDia>
      </Thread>
    </Designation>

I read this as: if you select this particular thread, the tread tool will model a thread with a major diameter of 9.850 mm (which it did), a minor diameter of 8.141 mm (which it also did) and a pitch diameter of 8.928 (which it DIDN'T do). That is what I do not understand.

Do I misunderstand the term "pitch diameter" by measuring it that way in the sketch?

Jesper