Wrong external thread diameter

[miechh]

Today I was designing a lock-nut, with M20x1 metric external thread. I modelled a ring with an OD of 20 (the nominal major diameter of the external thread) and a thickness of 5 mm. Then I clicked "Create" followed by "Thread", selected the OD-face, after which the thread-dialog appeared with the M20 thread already preselected (See picture and attachment). Immediately it comes to my attention in the preview that the OD is reduced to 19mm, there's also a dimension 9.5mm visible under the part, which suggests the OD of 19 mm. After clicking OK and using an inspection dimension on the OD it is clear that the major diameter of M20x1 thread is incorrect, according to the DIN standard this should be between 19.97 and 19.79 for class 6g thread, and not 19 mm. Looking into the XML-file of the metric threads from which Fusion gets its dimensions shows no error though; it should be 19.884mm. I'm aware that 3D printing thread is subjected to the accuracy of the 3D printer, but still I'd like to 3D print this part. It shouldn't deviate this much though.

[Anonymous]

Hm... If I open to edit the thread feature (from your file), the thread immediately readjusts itself to correct values.

[HughesTooling]

On a quick test I don't see that error, have you tried a new design.

Mark

[HughesTooling · Accepted solution]

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@Anonymous wrote:

Hm... If I open to edit the thread feature (from your file), the thread immediately readjusts itself to correct values.

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Might be worth restarting Fusion or even a reboot. Could try a save and reopen first.

Mark

[TheCADWhisperer]

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@miechh wrote:

l I'd like to 3D print this part. It shouldn't deviate this much though.

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and set to Modeled rather than cosmetic if you intend to 3D print.

[miechh]

Rebooting the system and restarting Fusion did the trick, I'm actually not sure if I should mark that as a (permanent) solution. Really strange though. Thanks anyone for posting your comments.

[miechh]

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@TheCADWhisperer wrote:

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@miechh wrote:

l I'd like to 3D print this part. It shouldn't deviate this much though.

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and set to Modeled rather than cosmetic if you intend to 3D print.

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Thanks, I already knew. But even with modeled thread the dimensions were incorrect. Problem was solved now; rebooting my system and restarting Fusion did it...

[Remy18]

Re-doing the thread feature seems to do the trick at my design indeed.

This is something to be aware of. Especially if designs external diameters are used in CAM. I prefer to skip the thread feature where the diameter used for threading will be depending of the cutting tool anyway(for example we're using diameter 20 for threading M20). If it's desired to have visible thread in a design the major diameter will be modified for threading at CAM.

[Mike.Grau]

Hi @Remy18,

Thank you for raising our attention for this and thanks to

@miechh and @TheCADWhisperer for your help.

I have logged this with the development team to find out what´s the root cause of the confusing dimension.

Thanks again, we´ll keep you updated

[Anonymous]

@Mike.Grau, any update on this issue since 2017?

[TheCADWhisperer]

What is the problem in the year 2021?

Can you Attach an example?

What happens if you edit the feature (without making any changes)?

Ctrl B (CMD B)

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

(A new file, not the original file posted here years ago.)

[Anonymous]

The exact same problem.  My part (which I can not share as it is proprietary) has a 10mm cylindrical extrusion.  I add external threads and choose M10x1.25 as the "designation."  After threading, the major diameter is 9.85mm. I can close and reopen as suggested in this old post and the behavior is the same.

[HughesTooling]

That is the correct mid limit size for the major diameter of a 10mm bolt, you can check here.

[TheCADWhisperer]

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@Anonymous wrote:

My part (which I can not share as it is proprietary)

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Can't you reproduce the issue in a simple dummy file?

[Anonymous]

Good enough for me.  Thanks for that helpful online resource.

[TheManWithBlorns]

It may be the mid limit size for a given thread, but is there no way to have the major diameter exactly as it should be? It's incredibly frustrating. Reboot / restart hasn't solved it for me.

[TheCADWhisperer]

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@TheManWithBlorns wrote:

…is there no way to have the major diameter exactly as it should be.

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Exactly what size should it be? (Provide link to standard reference.)

What class of fit are you using?

@TheManWithBlorns 

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?