P2S threads not fitting together

[user_1886195338]

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I am totally new at this so I need a lot of help. I’m trying to print threads with the P2S I’m using the tinkercad thread tool. The problem I’m having is with the female end of the threads. I was trying to print a m10 by 1.5 pitch threaded hole and it keeps printing the holes too small. I couldn’t even get a tap started in it. I tried printing it as large as 10.8 of which allowed the bolt to start but it still seized up after a few turns. I lowered the print height to .08 and widen the hole 8% so I feel like I must be doing something wrong. I’m using bambu Labs PETG and the only thing I really changed in the slicer was the .08 profile. There must be more to it!

I would greatly appreciate any help at all.

[MZip]

I use Fusion for design but similar problem - threads by default are a bit tight when 3D printed.

What I do is clearance the threads/holes a little by knocking the peak of the threads off. The threads pitch/count is unchanged. The threads in the walls just don’t stick as far into the threads on the screws/bolts and vice versa. It really makes a difference for me.

Instead of the thread coming to a point deep in the mating thread, the points get knocked off and the threading works much better. How much to knock off depends on the thread size. You want to leave meat to mate but you don’t want the mating super tight either.

[beegee-rakwireless]

You can try one of the (many) screw generators, like this Screw Generator - Parametric Screws, Nuts & Washer

[Lindo]

Suggest you use an engineering data book before you use any CAD programme.

The Machinist handbook is good.

All commercial threads are truncated, the major dia of a male for example a 10 mm x 1.5 pitch is 9.75 mm.

The minor dia of a mating nut is 10.25 mm, ensuring the peaks of male to female do not touch.

This also ensures an easy path for lubrication.

[Eponymous]

if the printer is told to make a circle 20mm in diameter, it will put the center of the nozzle on that circle, but plastic comes out 0.4mm wide from the 0.4 nozzle, and the hole is threfore 19.6mm. The plastic then shrinks on cooling (usually by about 0.5% to 1% for common filaments), making the problem worse.

Generally allow 0.1mm to 0.3mm clearance when designing such parts, (i.e make the hole bigger)

[lkraus]

I’ve found it very difficult to print accurate model dimensions AND accurate hole diameters at the same time. Calibrating shrinkage for the filament profile usually produces the correct model size, but holes are still slightly undersized.

In addition, depending on thread size and layer height, the oval shape of extruded filament may be a poor match for the sharp sawtooth profile of a machine thread. Portions of the thread in every layer will be omitted where the slicer cannot fit a full line width and layer height.
Notice the “ghosted” edges of this M10x1.5 thread at .08 layer height, 0.42 line width:

If I’m using screws in plastic, I model a pilot hole, add modifiers in the slicer to thicken the hole walls, then drill and tap, or use self-threading screws. Use thread inserts for frequently removed screws.

[dann2707]

I’ve printed loads of male and female threads now and I typically make the hole 0.3mm oversize to account for the typical 0.2mm undersize it comes out. And then the male 0.2mm undersized too.

If that doesn’t work and the thread is too sharp depending on the profile and size, doing an extruded cut of the outer edges of the male and inside edges of the female can also help, especially with the printing side of it. Massively exaggerated for illustration purposes, so it looks like the green rather than the red

[user_1886195338]

Well the threads do look very long and pointed. I was working with a 10 mm bolt pattern. I increased it all the way up to 10.8 and the bolt still would not go in the hole. It would start but that was all. I finally clipped a little off The thread peaks and that did help quite a bit. I’m surprised that it seems to be so far off. The machines are brand new P2s and I’ve calibrated it twice now. I printed test blocks and they work just fine. It just doesn’t want to make threads correctly. I’m starting to think it’s tinkercad.

[user_1886195338]

@MZip

unchanged

I’m looking into the screw generators now thank you

[MZip]

@user_1886195338

It just doesn’t want to make threads correctly. I’m starting to think it’s tinkercad.

It might be but it has a big following and I’d bet an issue like that would be reported fast. Not saying it isn’t a bug but probably unlikely.

3D printing does great on lots of surfaces but screw threads are especially interesting because they have tons of overhang on the bottom surfaces of threads depending on orientation in printing. Threads I print here have a bit of irregularity to them which makes holes a tiny bit too small and male threads slightly too big.

[simon14]

You can use custom thread for 3D printing like this one

GitHub - dans98/Fusion-360-FDM-threads

There are many custom thread options out there for you to choose. Afterall they are just some XML tags that define thread parameters. Which XML file you can make it yourself if you have the specs of the thread.

Use ThreadKeeper pluggin to automatically reinstall the custom threads. As for everytime fusion updates, it wipes clean custom thread data.

For me, I’d use class 0.200e and 0.200i for external and internal thread, as to make it up to 0.4mm tolerance (as for matching 0.4mm nozzle).

Sometime for tigher fit, I’d use 0.100e and 0.100i, or maybe 0.200e and 0.00i depend on situation.

[RetroSharky]

@user_1886195338

There must be more to it!

I’ll give you some advice that’s different from what’s already been offered here… If you’re too lazy to do the math or just want to keep it simple: Get a set of screws in all possible sizes. Just make sure they have allen heads so you can apply some force.

Instead of modeling a thread, just create a slightly smaller hole and then screw it in. Slowly, but with force. Done.

You can also buy a Thread Milling Cutter for a few dollars. It’s a more elegant solution, and it’s worth having one at home, but it’s not really necessary.

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Keep in mind: What I’m describing isn’t meant to be a substitute, but simply one possible option. It’s always good to know how to calculate threads.

If you just want to tinker around, there are quicker solutions: Hole => Screw = Done.

This is actually a useful skill, since some designers create their models so that there is no thread inside the object. Instead, the person printing it just has to screw the screw in. This is useful because you never know how someone has set the printer’s tolerances. Just because a thread works for you doesn’t mean it’ll work for someone else. Regular screws solve the problem.

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But as I said, first learn how to calculate and use threads, but eventually, when you’re printing a lot, you’ll often just rely on a hole, a screw, and a little force.

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As an added bonus, here’s another tip: you can melt these into the object by heating it. Nut Inserts - Brass Hot Melt Threaded Insert Nuts

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Essential tools for 3D printing, Tuba Nut，brass threaded inserts #3dprinting #Utilitytools #tools

[user_3454396445]

Wow there is an awful lot of information here that I’ve never done. I’ll have to look into all of this at some point.

All I ever print is functional parts and the only thing I’ve ever done is calibrate my filament for holes.

Bambu Labs XY hole wiki

[simon14]

I personally think those “calibration” or “fine tuning” is unnecessary and sometime could works against you.

When you fine tune the compensation XY coordinate for a particular model, say hole 10mm, part 100x100 mm, and that is for a particular PLA you are using: for very specific shrinkage, very specific width of print line, very specific flow rate of that plastic. This compensation could be down to a very specific roll you have. For example, you increase the 10mm hole by a fraction (say, +0.15mm) to make it true 10mm. That would be correct and fine for your model.

But if you download model from the internet, print it out then you’ll probably find out some screw holes are too loose or too tight.

I tend to design a M3 screw hole exactly 2.8mm for 3D printed part, no thread, just clean hole. If you happened to compensate a hole with +0.15, this would make the screw hole 2.95mm. And then now all M3 screws just become loose.

M3 screws from Aliexpress could go down to 2.85mm, brand new one, not worn out one.

All that is just about 1 type of filament. And if you get into different filaments with different shrinkages like PLA → ABS → Nylon, then you now fall into a deeper rabbit hole.

My suggestion: leave it as default, as there is greater chance it would work for model you download from the internet, just because people would use default setting as well. Those default settings probably have gone through trials and errors thousands of times before you go.

This is where you should design your part with larger tolerance or with compliant mechanism to accommodate (or go around) the limitation of FDM printing.

Like this for a screw hole

Search youtube for Slant 3D. I don’t fully agree of what he said, but he has useful tips and tricks for designing 3D print part.

[user_1005844886]

Up to a certain point and depending on purpose, you can also use brass heat sets for the female side. Each heat-set has a certain diameter hole you make then use a soldering iron to push the heat set into the hole.