How to virtually test and verify your nut and bolt assembly without incurring the expense of 3D printing

Tutorials Requests & Discussion
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Continuing the discussion from Need help making nut and bolt:

Nut and bolt.skp (221.0 KB)
Hello justcheckinm8, I have followed the instructions in your video and made my screw. Thank you. I then used the TRIM tool to make the corresponding nut. First I insert just the flat head of the screw, at its widest point, in the top of the solid that I am using to make the nut. I then use the TRIM tool to make that first impression. Then I insert just enough of the screw so the flat head of screw emerges out the other end, up to its widest point. I again use the TRIM tool to complete the threaded nut. I went through this process to ensure that entry point of the nut would be wide enough for the screw. (see attachment). My question now is, how do I ensure that the screw will actually work with the nut before doing an actual 3D printout? I am using SU2018
Thanks to you all on this support channel, for the work that you do.

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Keep in mind that if you made the threads in the nut identical to the threads on the bolt, they are unlikely to fit together. Assuming the printing is precise, which it probably won’t be, there’ll be no clearance in the nut for the bolt. Also, since the shapes aren’t really round, there will be binding as the vertices on one part come up against the flats on the other part. If you try to assembly them, you’ll probably twist the head off the bolt.

Look at specifications for external and internal threads to get an idea of how much larger the internal threads need to be than the external ones. As not round as bolt is, you’ll need more than the standard clearance to get them to fit together.

I didn’t check your threads to see if they are a standard size. If they are, I would plan to chase the threads after 3D printing to make sure they are right. If they aren’t standard size, you should probably make them so they are.

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There appear to be larger issues beside fit.

The head is not perpendicular to the shaft.
The leading thread is not a thread, but an annular ring.

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In addition to the above very good points, my experience of 3D printing is that about half the width of the nozzle prints outside the drawn edges of the screw, and inside the edges of the nut. With a nozzle (as I have) of 0.5mm diameter, that adds about 0.5mm to the screw diameter, and takes about 0.5mm off the opening in the nut.

If you allow for that when drawing the screw, then another small amount for clearance (perhaps 0.1 to 0.3 off the radius), and use a standard size tap to cut the thread in a plain hole in the nut, you can get a pretty good fit.

I printed a 14mm diameter (ISO M14) screw with that kind of offset, and it fitted first time in a factory moulded 14mm plastic ‘nut’, and have done the same with smaller screws into a home-tapped 3D printed nut.

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In addition to what @john_mcclenahan indicated about the +/- issues related to outside/inside prints, there is also shrinkage to deal with. If your parts are both printed from the same material, then it doesn’t really matter if both are slightly smaller than what you wanted (~2-8% depending on the material). If you’re trying to mate with an existing part dimension, then it might be important.

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These reasons are also why I suggester chasing the threads after printing. Get the appropriately sized tap and die to run over them after printing.

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Once again, you guys offer very good advice. I had no idea that making a nut and bolt would be so technical. Now I am thinking that using an extension may be the way to go.:slight_smile: Do you guys know of any extensions that you would recommend for SU2018?
@DaveR, It sounds like even if I were to use an extension, I would still have to do some refinement to the 3D printout.
@Geo, I will fix the fact that the head is not perpendicular to the shaft. I saw it but I thought that the angle of the threads were creating that illusion. Is there a technique that you would recommend I use to check and correct objects that are not perpendicular to each other? I tend to use guide lines and axes but it ends up being more about observation which, as you can see, is not a very accurate method to use. :slight_smile:
@john_mcclenahan, I will apply your specs to my design to minimize the level of modification that may be needed in the field.
@jimhami42, The parts will be made from the same materials
Thanks all.

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Possibly. You probably really need to draw the internal threads separate from the external ones instead of using the same threads. I would use more sides for the initial circle so you get closer to round. And I still would expect to clean up the threads with tap and die.

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If these are standard thread sizes you could always chase the threads of the nut and the bolt with a tap and die kit from your local hardware store.

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There’s an echo in here. :wink:

1 Like
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Sorry didn’t see the earlier post.

The Machinery Handbook goes into the details with threads if you are really interested.

There is also a calculator here:

https://www.amesweb.info/Screws/AsmeUnifiedInchScrewThread.aspx

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Here’s an example of using 400 segments. Note that you can just keep the threads in one group and the head in another group. The slicer will figure it out.

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So how do I go about creating different threads for the nut versus the bolt?

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Yes they are

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Did you draw the bolts threads to match some standard? Or did you just make them with random dimensions?

One thing you could do is use the calculator in the link provided by @medeek to figure out the parameters for the internal and external threads.

Yes they are what?

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The link is quite in depth but informative. Thanks

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Yes the threads were drawn to match a standard size with fine pitch

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Ok, thanks

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So you should be able to figure out the dimensions for both sets of threads and model them.

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Ok, I will use the calculator. Thanks