Creating threads (M3) seems to not be the same size as M3 screw when printed?

[chad711]

I just printed what I thought was a M3 sized threaded hole but the M3 screw does not fit. What ended up printing looks to be one size smaller in thread size. I am not 100% it's exactly 1 size smaller (M2) but I have a smaller screw that fits into what printed and just guessing I think it's a M2 size. I do know for certain the M3 screws are M3 as I ordered a large assortment of them.

Am I doing something wrong here or can someone explain what is happening? I am new to modeling and have been doing everything from tutorials but this thread tool seems to be straight forward, or so I thought! 

[TheCADWhisperer]

Did you add lead-in (Chamfer) for the thread?

Can you File>Export and then Attach your *.f3d file here?

3D printing is not a very precise manufacturing process.

An M3 would be a very small thread to 3D print - you must have a very expensive printer to print such fine detail (I have a $60k USD printer for fine threads).

I model additional clearance for 3D printed threads.

Do you have any taps that you can use to "chase" the printed thread?

[davebYYPCU]

More likely a printer error, more than a Fusion error.

Most 3d printers are not so size accurate, at your 3mm.

Tap the hole, and see if the threads are actually wrong, or over extruded.

Might help...

[lichtzeichenanlage]

Printing in this size your printer must be pretty good calibrated. Have you done a test print without a thread? Can you File -> Export and share your design?

[chad711]

Maybe I need to use hole instead of thread to create this? I am trying now. Will update shortly as the prints don't take too long. 

I will do a test print with out the thread too just to make sure the hole is correct...which I think it would be as I haven't had issues with these smaller holes printing right until I started adding thread to it.

Will reply soon, thanks.

[davebYYPCU]

Two more things to look for, 

Slicer adding support , needs to be cleaned out, 

no support, threads can droop.

Might help....

[JDMather]

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@chad711 wrote:

I will do a test print with out the thread too just to make sure the hole is correct...

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What size is the correct hole?  (This might be a trick question.)

[lichtzeichenanlage]

In some situations you can get away with a lower layer height. 

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@davebYYPCU wrote:

Two more things to look for, 

Slicer adding support , needs to be cleaned out, 

no support, threads can droop.

Might help....

---

[chad711]

Hmm my reply was marked as spam and removed. I posted a link where I got the screws from just to reference them but I guess links are not allowed? No big deal.

I printed out a 3mm hole, 3mm hole with M3 threads and then a hole with M3.50 hole. The 3.50 seemed to be a little better but a little tight getting the bolt in there. The 3mm hole with out threads is perfect. The 3mm hole with M3 thread pattern is way to small, no way the bolt will go in. 

Can someone explain why this is? I would think a M3 thread would be the same size a 3mm hole but it's not. Look at the attachment. The middle hole with the M3 threads is smaller than the 3mm hole on the left.

[lichtzeichenanlage · Accepted solution]

It might be a dumb questions, but I've learned that at some point somebody should start to ask obvious questions: Are you switching from cosmetic to modeled threads before you're creating the stl file?

[chad711]

I was not, I just tried that and it looks like this was my problem. What is the difference between cosmetic and modeled? I'm new to all this (3 weeks into Fusion 360 and 3D printing). 

Thank you!

[lichtzeichenanlage]

Cosmetic is just an image... wallpaper... it has no geometry. Model is real geometry. 

Edit: If you have many threads cosmetic threads are way faster to work with. Type removed

[chad711]

Thanks for the help. Curious, why when I was using cosmetic it was making the cut smaller? It looked like my 3mm cutout would go down to around 2mm when I applied cosmetic thread. Is that because the "image" of cosmetic is taking up space therefore making it smaller?

[lichtzeichenanlage]

I'm a hobbyist and just guessing, but isn't the core hole diameter diameter for a M3 thread 2.5mm? And if I measure your 3mm cosmetic thread it's 2.529mm. It would make kind of sense to me. 

[etfrench]

When I use M3 threads in a 3d print, I always tap them.  I'm quite sure my printer won't make good enough threads.  I create the holes using the recommended drill diameter (2.5mm).  If strength is an issue, then I do through bolts with nuts, optionally embedding the nuts in the print.

Here is the thread and tap guide I use for metric.  Their imperial guide is better as it shows drill sizes for different materials and fit class.

Here's a little screencast showing what Fusion 360 does when modeling threads using the minor and major diameters.

[lichtzeichenanlage]

I totally agree with @etfrench. I never print such small threads. I wouldn't trust my Prusa MK3 that much 😉

[etfrench]

Here's a holder for a 30mm fan I'm getting ready to print:

It uses 2.5mm bolts and I don't have a tap that size.