topic Re: Custom square/trapezoidal thread. in Fusion Design, Validate & Document Forum

Custom square/trapezoidal thread.

philberndt — Mon, 20 Jan 2025 12:26:01 GMT

Is it possible to create a thread file where the root and the crest have different widths?

I have:

<ThreadType> <ThreadForm>0</ThreadForm> <Name>CS17-47 Diamond Core Drill</Name> <CustomName>CS17-47 Diamond Core Drill</CustomName> <Unit>mm</Unit> <Angle>5</Angle> <SortOrder>1</SortOrder> <ThreadSize> <Size>25.0</Size> <Designation> <ThreadDesignation>M25x8.20</ThreadDesignation> <CTD>M25x8.20</CTD> <Pitch>8.20</Pitch> <Thread> <Gender>external</Gender> <Class>7f</Class> <MajorDia>25.30</MajorDia> <PitchDia>23.65</PitchDia> <MinorDia>22.00</MinorDia> </Thread> </Designation> </ThreadSize> </ThreadType>

This of course creates a symmetric thread

This is used for geotechnical stuff and it is bases on the DIAMOND CORE DRILL FITTINGS - COMMERCIAL STANDARD Diamond core drill fittings (PDF)

Re: Custom square/trapezoidal thread.

MRWakefield — Mon, 20 Jan 2025 21:41:18 GMT

Yes you can. By adjusting the pitch diameter it will alter the root/crest ratio.

EDIT:

In your XML file the <Angle> value should be 10 (included angle in degrees) rather than 5.

If you add the mid tolerance crest and root dimensions it comes out to 8.2mm, which matches the specified pitch. This would be correct for a square thread but as the flanks are not square then this doesn't work out. You'll need to adjust your crest and root widths to allow for the flank angle.

Here's an example showing how adjusting the pitch diameter alters the respective widths of the crest and root:

If you have any more information on the thread that might help us provide a satisfactory solution. Is it exactly the same as detailed on page 3 of the linked PDF or are they meant to be different? Your figures don't match the figures on that page. Should I be looking at a different page?

Re: Custom square/trapezoidal thread.

philberndt — Tue, 21 Jan 2025 07:23:15 GMT

Thank you for the prompt reply! I have tried using your software before, great stuff! Thanks for sharing. I could not figure out how to do it though.

I "think" the threads are based on the Diamond Core Drill Fittings Commercial Standard CS17-47 and converted to metric.

On the picture below, the part on top was drawn before I was born, the one on the bottom I modeled myself, but it was very time consuming with a spiral, that is why I want to create the thread data and share it with the rest.

Bottom one I have created

And below is the roughly translated original drawing:

Thanks for the help!! ❤️

Re: Custom square/trapezoidal thread.

philberndt — Mon, 03 Feb 2025 11:58:46 GMT

Hei,

I am still stuck on this, you said

@MRWakefield wrote:
....
You'll need to adjust your crest and root widths to allow for the flank angle.

Here's an example showing how adjusting the pitch diameter alters the respective widths of the crest and root:

If you have any more information on the thread that might help us provide a satisfactory solution. Is it exactly the same as detailed on page 3 of the linked PDF or are they meant to be different? Your figures don't match the figures on that page. Should I be looking at a different page?

I am not sure how to adjust it on the file.

Re: Custom square/trapezoidal thread.

MRWakefield — Mon, 03 Feb 2025 15:12:45 GMT

Ok, having played around with this a bit more it looks as if you won't be able to achieve exactly what you want with the thread tool. Here's a sketch conforming to the dimensions in the drawing snippet you provided:

Note the pitch should be 8.467mm (3 TPI) rather than the 8.20mm in the thread file you posted so I've corrected this. Also note that to achieve the crest and root widths that are within the limits specified, the pitch diameter has to be smaller than the minor dia. Unfortunately Fusion doesn't seem to like this situation and alters the minor diameter from the specified value in the thread file, which as a consequence alters the root width as well:

The closest I can get is if I set the pitch diameter to the same value as the root diameter:

Here's the thread file I used to achieve the above.

<ThreadType> <ThreadForm>0</ThreadForm> <Name>CS17-47 Diamond Core Drill (Metric)</Name> <CustomName>CS17-47 Diamond Core Drill (Metric)</CustomName> <Unit>mm</Unit> <Angle>10</Angle> <SortOrder>1</SortOrder> <ThreadSize> <Size>25</Size> <Designation> <ThreadDesignation>M25x8.467</ThreadDesignation> <CTD>M25x8.467</CTD> <Pitch>8.467</Pitch> <Thread> <Gender>external</Gender> <Class>7f</Class> <MajorDia>25.3</MajorDia> <PitchDia>22.0</PitchDia> <MinorDia>22.0</MinorDia> </Thread> </Designation> </ThreadSize> </ThreadType>

I hope this helps.

Re: Custom square/trapezoidal thread.

philberndt — Wed, 05 Feb 2025 11:00:39 GMT

Thanks for the help!

I was able to print a quick test and both worked actually, so the tolerance is quite forgiving.

Re: Custom square/trapezoidal thread.

MRWakefield — Wed, 05 Feb 2025 11:06:50 GMT

👍