Threads using the Coil command vs the Thread command

[michael_ray_neal]

I am creating a water bottle (see attached .f3d file as well as .step file). The water bottle is very rude in shape and it's very short as I wanted to get the screw threads correct before printing a 190.5mm tall bottle.  Now for the questions and issues.

I did some research and have worked with threads in the past but found a video online that show using the Coil command for creating threads for the neck of the bottle and cap.  I followed the instructions and printed it out but the threads (using the Coil command) and way to tight and my cap only crews on a turn or so.  My question is do you need to offset threads when using the coil command if you plan on using the coil for threads like I have done for my project here and if not, what could be the trouble. I did do a Section Analysis (see attached) and I see both sets of threads really snuggly against each other which could explain the issue.  Now how to fix???

My other question is should I have just used the Thread command and did an offset in the first place?  Is the Thread command better that the Coil command when creating a water tight seal between the bottle and cap?

Thanks for any help.

[wersy]

Have you taken into account that internal threads shrink during printing?
If a gap is not provided from the beginning, you have no chance of screwing anything together.

[MRWakefield]

It is very rare to rely on the thread to form a seal. More often there will either be a soft sealing washer, 'O' ring or conical feature on the cap that seals on the inner edge of the bottle mouth. As @wersy mentioned you need some clearance between the external and internal threads to allow you to screw it together. As you know you can use the coil command for threads but it's not my favourite. I'd say it is better to use the thread command if you can. I'd either go for a square thread or a trapezoidal with a fairly narrow flank angle (such as metric trapezoidal, Acme or something bespoke).

I quickly made a demo thread file with a flank angle of 20 degrees and a pitch of 4mm with a 0.2mm clearance and modelled it up:

I've attached the demo thread file if you want to give it a try.

[michael_ray_neal]

The file you attached is a .xml.  Shouldn't it be a .f3d file?

[MRWakefield · Accepted solution]

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@michael_ray_neal wrote:

The file you attached is a .xml.  Shouldn't it be a .f3d file?

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No, it's not a Fusion model, it's a custom thread file that I used to create the demo model in the screenshot. I thought you might want to try it out to see whether it satisfies your requirements. To use it you just need to copy it to the folder where Fusion stores its own thread files. Unfortunately the location of this folder changes with every update of the software! To make things even more awkward, any custom thread files you've placed in the folder don't get moved to the new thread folder when Fusion gets updated. Consequently your custom thread files get 'orphaned' and no longer appear in the list to choose from. To get around this there's an add-in called ThreadKeeper that automatically copies your custom thread files to the new thread folder for you. I've also written a Windows application for creating custom thread files which will also enable you to copy your thread files to the correct folder. You'll find a link in my signature to a thread about it.

Hope this helps.