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How to print matching threads?

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I'm attempting to print a 30mm diameter bolt and a corresponding nut.

I'm using Fusion360 and have created a 30mm cylinder onto which I create a M30x1.5 thread. The nut has a 30mm hole and I create a M30x1.5 thread on that too.

Both just fit together but because there is no slack they're extremely tight and sometimes too tight to put together.

How should I build in a bit of tolerance? Just make the hole in the nut slightly bigger before applying the thread or is there a more elegant way of doing it?

I print both on an Ultimaker 2+ using a 0.4 nozzle and fast print with PLA.

Edited by Guest

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I usually leave a 0.1mm or slightly less, depending on how tightly the nut and bolt have to fit. It also depends on how accurately your machine extrudes the width of each line, which of course will affect the tolerances as well. So, experiment away, until you change rolls and discover that every colour even from the same manufacturer behaves differently, and there go your measurements :-)

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I've run a couple more tests using Fusion360.

I have a pipe with a M30x1.5 thread on the outside. I then create a ring which has an internal diameter of 30mm and on the inside of that I create a M30x1.5 thread.

After printing, the ring is too tight on the pipe.

The next test was to give the ring an internal diameter of 30.2mm and the apply a M30x1.5 thread. After printing, the ring is again too tight on the pipe.

After playing around with Fusion it appears that no matter what size I make the internal diameter of the ring, as soon as I apply a M30x1.5 thread, that's what I get. Applying the thread changes the internal diameter of the ring back again and makes it 30mm. All that's happening is I'm getting a thicker wall on the ring and the internal diameter stays the same at 30mm.

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That makes sense, because it wouldn't be an M30x1.5 thread, but M30.2x1.5 instead.

Would be nice to have some feature implemented into CAD programs that would account for that. Such as "offset standard holes / threads by xx to account for material shrinking".

Note that circles usually shrink when printing because the printhead drags the plastic inwards a little while circling. It seems to be less of a problem with cylinders, which makes fitting a printed cylinder into a printed hole a very interesting thing...

/edit:

It "can" be a solution to scale your model in Cura (note you can scale X, Y or Z independently of each other). However, with anything more complex than a threaded cylinder, this will quickly become impractical because you'll ruin all the other dimensions...

I usually make threads myself. In SpaceClaim, there is a "rotate helix" function which lets me make threads (inner or outer) very easily, with any specified parameters. Maybe Fusion has something similar?

It takes a bit of genius / experience to make 3D printed threads which will work well even when someone else prints them with different printer / settings / filament / talent...

I usually work around that by using standard metal hardware :p

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I encountered the same problem in Fusion 360 and created a work-around which I haven't tested until now:

- create nut and bolt like you described (for example M12x1,5)

- the inner diameter of the nut for M12x1,5 is ~10,5mm ( I know it's actually 10,5xy :p )

- go to sketch a circle on the center of your nut with a diameter of 10,8 (or may be larger)

- extrude this circle "through" your nut, so that the cylinder cuts away the inner 0,3mm of the thread.

- now you should have a nut that fits "your bolt" ;):p

And yes, this is not very elegant nor high quality design, but it will work for sure.

hth,

Joerg

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I encountered the same problem in Fusion 360 and created a work-around which I haven't tested until now:

- create nut and bolt like you described (for example M12x1,5)

- the inner diameter of the nut for M12x1,5 is ~10,5mm ( I know it's actually 10,5xy :p)

- go to sketch a circle on the center of your nut with a diameter of 10,8 (or may be larger)

- extrude this circle "through" your nut, so that the cylinder cuts away the inner 0,3mm of the thread.

- now you should have a nut that fits "your bolt" ;):p

And yes, this is not very elegant nor high quality design, but it will work for sure.

hth,

Joerg

 

I don't think this will work, because the it makes no difference how much of the "tip" of the thread you remove, you still need clearance above and below the mating thread profile. I "hand-make" my threads because of this, by making a spiral extrusion. In Blender this is a doddle, there a screw modifier that does all the hard work in a matter of a few clicks. In FreeCAD this is a bit more painful, but still eminently doable using a helical extrusion path.

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I've played around with threads a bit more and I can now make good fitting threads without any adjustment. If I'm printing a thread then I make sure I set Cura to print in Normal or High. when the print is complete I brush round the thread with a fine wire brush (brass) and they fit very well. I'm using an Ultimaker 2+ with the 0.4mm nozzle.

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Wont making the external thread M30x1.5 and the Nut M30.2x1.5 solve you problem. you need to add some clearance so just make the Dia of the internal treads bigger. The pitch remains the same so its going to screw together.

Its how i print my threads and it works every time.

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It depends on your CAD system, and how you (or, the CAD) interpret what an "M..." thread is.

M thread sizes are specified in some ISO standard (or something alike) and given exact manufacturing parameters. There is no such thing as an M30.2x1.5mm nut. The standard already defines these threads to be matching (IF they are made from metal, which is what the standard was intended for).

I don't know many different CAD systems, but I suppose most will not let you define "odd" "M" threads. They will only let you make "standard holes" (SpaceClaim term) according to the underlying standard.

I would try to solve that problem by making the screw, then subtracting it from the part where I want the nut to be. Then adding an offset to all faces in the nut - how much of an offset I'd have to determine by trying out a few different values...

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This is just to share my final results with Fusion 360:

1. create threads (for example M12x1,75)

2. push the tip of the flank for a certain amount (depends on the thread size). For the given thread 0,2mm worked fine

3. round the edges of the flank tips (again 0,2mm was fine)

4. do the same for the bolt and nut

short video here: https://www.youtube.com/watch?v=IneE1eyvuuc

I made two test prints and both worked directly from the printbed.

hth

Joerg

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Thanks onkelgeorg, I'll give that a try. I was doing OK with threads using the Ultimaker filament but I've just tried the same thing using Verbatim filament (much harder to get to stick to the glass by the way), the threads now no longer work as they are far too tight. Different characteristics of the Verbatim obviously - not sure I'll bother with Verbatim again.

It'll be a good test to try your technique described in the video on Verbatim.

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This is just to share my final results with Fusion 360:

1. create threads (for example M12x1,75)

2. push the tip of the flank for a certain amount (depends on the thread size). For the given thread 0,2mm worked fine

3. round the edges of the flank tips (again 0,2mm was fine)

4. do the same for the bolt and nut

short video here: https://www.youtube.com/watch?v=IneE1eyvuuc

I made two test prints and both worked directly from the printbed.

hth

Joerg

 

Tried this a few times now and it works very well. Thanks

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I'll take a look at Kisslicer, thanks.

Just tried the same thread pair using ColorFabb and the results using onkelgeorg's method are more successful and fit even better straight off the printbed. Verbatim PLA wasn't doing me any favours - ColorFabb seems far more accurate.

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Just read through this thread, great info! Question, the standard thread profiles you guys are using have 30 degree inclines, which I would think would need supports to print. Are you guys print with supports? I have a project I'm working on that needs threads.

Thanks!

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I think it works well without support because curling due to overhangs usually needs some layers to build up and they build up at corners first. in a thread you only have circles and after only a few layers the overhang stops so there is little danger of curling.

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Success! I printed mating M75x1.5 (from Fusion360) first using the 2mm offset and fillet (for both threads) as suggested - which was too tight, then changed both to 2.5mm and it fits nicely. I had to clean the threads a bit by rotating the parts together back and forth (a metal brush as someone suggested probably would have worked). No supports. Nice fit - no wobble, and very strong connection.

Thanks!

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Hi gang,

I don't know Fusion360, but I did do some metric threading stuff last year that you might be interested in. I used openSCAD.

The results are at:

https://www.youmagine.com/designs/openscad-metric-nut-bolt-threads-library

And the tread about it is at:

https://ultimaker.com/en/community/5548-experiment-with-threads

(the bottom of page 2 is where things are working and there are images).

I have not touched it since, but I hope it helps or is of interest. :)

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