For FDM printing, how fine a thread is practical?

[WobblyHand]

I want to print a relatively fine thread on the inside of a tube (and on a mating plug). What's the practical limit of thread pitch (or TPI)?
The tube is only 2mm thick wall, so can't go with a coarse thread. I have printed 20 TPI, but have followed it with a tap, or pseudo-tap. How fine a thread can one print without being a superhero? I'd guess variable layers would be helpful.

Just looking for some guidelines so I don't waste a lot of time on this idea. It would be better if it was imperial, so I could make the pseudo-tap easier, but I'm just looking for how small a pitch is reasonable. Is 40 TPI possible? 32? Otherwise I have to glue this, and I really don't want this to be a permanent joint - I need to be able to take the assembly apart.

 

[MikeWi]

That's a great question, but I don't really know the answer! Just spit balling...

You would need to go to a finer tip for certain. The standard .4mm will make it hard to have the precise control for features that small. You also would have to have the axis of the thread oriented vertically I'm thinking.

There must be a way to do the math and determine how jagged the profile would be for a given pitch, layer height, and nozzle.

If you can't fit a complete set of layers inside a thread's triangular profile, then that would tell you something as well. If the thread is smaller than your layer height, it ain't happening.

Too many vertices in the model can ruin it as well, forcing too many pauses at each one where the filament can ooze (blobs, zits, whatever you want to call them)

 

[Lo-Fi]

You'll get nowhere near printing 32tpi. Print plain undersize and tap is the best bet.

 

[WobblyHand]

Not a standard size for a tap. The ID of the tube is 28mm. I can't change that. Would have to be single pointed on a lathe, which hopefully I can avoid. Yeah, I could do it, but it would be a lot less work not to.

32 TPI is 25.4/32 mm = 0.79375 mm. Features on a thread are on the order of P/8 where P is the pitch. So variable layers might be around 0.1mm to have a chance. I can make a pseudo tap for the female threads of the tube with some effort. (Single point the stock and machine out grooves. Works fine for plastic thread chasing.) I hope not to have to make the equivalent for a die.

Here are two pseudo-taps I made already, hoping not to significantly add to my collection! The hardest part is getting rid of the burs by the threads afterwards. 3/4-20 and 3/4-13 threads. These were made of 12L14, they have worked fine for chasing threads. They don't cut very much.

For that matter, a 1/2-20 GH3 tap only takes off a slight fuzz when I print 1/2-20 threads with 0.2mm layer height. 20 TPI is 1.27mm pitch. That's roughly 6 layers per thread. I may try around 8 layers per thread for 32 TPI, unless you all think it won't work at all. Am I crazy to try?

 

[MikeWi]

Am I crazy to try?

What possible harm can it cause? You can only learn from it!

 

[jwmelvin]

I printed a barbed nipple with m10x1 threads and it worked perfectly. I imagine you could go a little finer.

 

[WobblyHand]

What possible harm can it cause? You can only learn from it!

Fair enough... Jumping in. Need to check some stuff. I do have clearance between the threads - I checked that. Just added a little more.

 

[pdentrem]

I know some makers are successfully achieving 1.0 metric but I have not seen anyone going finer than that. Yet.
Pierre

 

[toprecyler]

Let us know how it works out. I’ve been playing with my 3-d printer again. Trying to relearn what I forgot over the summer.

I’ve yet to figure out how to make threads, at least from scratch in my cad program.

What program do you use to design your parts?


Sent from my iPhone using Tapatalk

 

[WobblyHand]

Let us know how it works out. I’ve been playing with my 3-d printer again. Trying to relearn what I forgot over the summer.

I’ve yet to figure out how to make threads, at least from scratch in my cad program.

What program do you use to design your parts?


Sent from my iPhone using Tapatalk

I use FreeCAD. Price is right, if you ask me. There's several ways to make threads. Add them, subtract then, or use threaded rods, or specific tap forms. As noted above, I made some internal 32 TPI threads on a part with and ID of 28mm.

All these 3d CAD programs are tough to learn, but are quite useful when you understand the basics. So far the limit on doing anything complicated has been me...