ACME threads

[BeeAmaker]

Trying to make 3/8-10 TPI AMCE threads, but 12 TPI seems to be the only one available. Other than the coil feature, is there a way to add a thread size? I tried this method

https://forums.autodesk.com/t5/fusion-360-ideastation/non-standard-threads/idc-p/5426293/highlight/t...

To no avail. It seems I do not have a file of that name.

Thanks.

[BeeAmaker]

Think I just found the file. Thanks

[BeeAmaker]

OK I found the .xml file to edit, I can change the TPI but I can not change the pitch.

This is all I am allowed to change,

TPI, Angle, Major and minor Diameters, and the Pitch Diameter. Changing the Pitch Diameter doesn't seem to effect it at all.

What am I missing?

[MRWakefield · Accepted solution]

I've been playing about with this for a few hours now and I seem to have something that works (after much head scratching!! - anyway, more of that later).

Ok, a few things first (I apologise in advance if any of this is obvious or you know any of this already):

1. The TPI determines the pitch (1/TPI=Pitch). Metric threads use Pitch and Inch threads use TPI. Fusion looks at the <Unit> value in the thread's XML file and looks for a <TPI> value if <Unit> is "in" or <Pitch> if it's "mm".
2. If you increase or decrease the Pitch Dia you need to increase or decrease the Major and Minor dia's by the same amount to keep the thread profile correct.
3. The difference between Minor dia, Pitch dia and Major dia will be the same for all threads of the same form and pitch (TPI) irrespective of the basic diameter (ignoring fit allowances). ie. a 10 TPI ACME will have the same height and the "pitch line" will retain it's position relative to the Minor and Major dia's whatever diameter shaft it's on and similarly for holes.

I had a go at creating a custom XML which incorporated the custom 3/8" x 10 TPI size as well as the standard sizes and gave it a <Name> and a <CustomName> of "My ACME Screw Threads". However, I got some really strange results! I tried umpteen times but kept on getting a really 'thin' thread (this was a male thread, I didn't try female). This even happened with an exact copy of the "ACMEScrewThreads.xml" file with just the <Name> and <CustomName> tags changed to "My ACME Screw Threads". I even compared the original to my copy using WinMerge (a program for comparing text files) and confirmed the only difference was in those two tags. Once I changed the tags back again I had a good thread! I've since found that merely changing the <Name> tag makes the thread go thin. Anyway, that may be something for someone at AutoDesk to take a look at as that can't be right!?

So, I've ended up inserting a 3/8" x 10 TPI ACME into the original thread file and it all seems to be working just fine. Hopefully the dimensions are correct. You'll find the new file attached. Copy it to the same folder as the original (after making a backup copy of your original of course! ). Let us know how you get on with it.

[BeeAmaker]

Wow that's great!

Thanks a million! I spent hours trying different combinations of the 3 parameters. I think we had the same numbers at one point! I was even using this calculator and tried all of those numbers

https://www.engineersedge.com/hardware/acme-threads-calculator.htm

I had the same issue, skinny threads. Thanks again!

[MRWakefield]

You're welcome, glad to be of help. That skinny thread thing is really strange.