Thread Creation For SLA 3D Prints in SolidWorks

[Helepolis]

Hello all,

I'm trying to model a thread on a fitting with a lock cap for 3D print prototyping.
Previously i have modeled threads using the Thread Feature in SokidWorks and printed the parts successfully on an FDM printer, the MakerBot Replicator Z18.
This time I'm working with the FormLabs SLA Form 2 printer, and the threads from this machine just doesn't work, after the first 2-3 threads the cap just seize up.
I'm pretty sure that the reason for that is the much higher print resolution that requires a tolerance between the threads of the cap and fitting, with the FDM printer my guess is that the shrinkage of the extruded wire after it cools down add the tolerance "automatically" so to speak.

So my question is, can i somehow add tolerance during the creation of the threads using the Thread Feature or there is no avoiding doing the threads the "old fashion" way with Sweep Cut/Boss?

 

[JohnRBaker]

Since you've mentioned SolidWorks, perhaps you should post this inquiry in the SolidWorks forum as well.

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[Helepolis]

Excellent idea!

 

[Sparweb]

Are you sure you want to be altering the model design to suit the process?
Usually, it's the job of production to make the part within tolerances, not the designer's job to jimmy the model to suit one producer's shrinkage problem.

Shrinkage is a property of the material used and the temperature range held post-curing (on FDM, at least; don't know for sure on SLA).
The Stratasys FDM's allow for shrinkage compensation so I would look into what factor was used on the first part, and compare to the second part's process, if a correction was used there.

STF

 

[Gary_321]

I'm not sure if this helps, but...

I have done it using two prints. I print the knob at 0.35mm resolution and the nut at 0.10mm resolution. They are an interference fit.

Knob

M10 Nut

On my printer, you can only print using the same resolution for the whole print. I've not heard of any printers that can change resolution mid-print.

 

[Helepolis]

Are you sure you want to be altering the model design to suit the process?
Usually, it's the job of production to make the part within tolerances, not the designer's job to jimmy the model to suit one producer's shrinkage problem.

From my experience (product planing & design engineer) It's is much more sensible to design the product to suit existing manufacturing processes (saves money).
The thing I'm working on is a prototype (will be changed more than once and not only the thread).
All I'm trying to do is change the tolerance of the thread, which is common depending on your needs from the thread, and besides it's not like this change is irreversible and a major change to the part's functionality.
So I don't see the point of the question and remark.

Shrinkage is a property of the material used and the temperature range held post-curing (on FDM, at least; don't know for sure on SLA).
The Stratasys FDM's allow for shrinkage compensation so I would look into what factor was used on the first part, and compare to the second part's process, if a correction was used there.

I'm aware to the properties of shrinkage, and with the first part there were zero modifications/compensations to the thread, the model was sent to be printed as is.
This was the first time i was working with FDM printers for prototyping (woked with the Stratasys Eden500 before that), so i guess i got lucky on the first try.
And besides, MakerBot printers are total crap and unreliable, at least at the time when i worked with them (2-3 years ago) and it didn't seem that they had any compensation for shrinkage. I'm guessing that they updated the firmware since then.

 

[Helepolis]

I'm not sure if this helps, but...

I have done it using two prints. I print the knob at 0.35mm resolution and the nut at 0.10mm resolution. They are an interference fit.

I'm not sure i follow you.
You'r initial intent was to create an interference fit and by "playing" with the prints resolution you managed to get it or the fit is the result of the print parameters?
Asking out of curiosity, as the Form 2 has 3 resolution settings of 0.1, 0.05 and 0.025mm and I'm using the 0.05 resolution as i want to shorten the print times but still maintain some of the "delicate" features on the parts.
And the method of changing the print resolution sound like hit and miss solution, changing the tolerance of the feature in SolidWorks is a much more straight forward solution.

 

[Sparweb]

True enough, beginner's luck plays a role in a lot of prototyping. But reproducibility is crucial to production and I was assuming your prototypes would lead to production models. If so, then the interaction between design model tolerances and the final achieved surfaces can't remain a mystery to you, or this problem could come back. I can think of a lot of possible causes of the part interferences, so rather than try to tease out more detailed descriptions of your observations, here are a few tools for the toolbox, related to fixing mating surfaces:
[ul]
[li]sanding[/li]
[li]brushing[/li]
[li]bead blasting[/li]
[li]sand tumbling[/li]
[li]heat treatment[/li]
[li]surface fillers[/li]
[li]dry lubricants[/li]
[/ul]

Some won't be applicable to your parts, but hopefully one or two stimulate some ideas.

STF

 

[Gary_321]

I'm not sure i follow you.
You'r initial intent was to create an interference fit and by "playing" with the prints resolution you managed to get it or the fit is the result of the print parameters?
Asking out of curiosity, as the Form 2 has 3 resolution settings of 0.1, 0.05 and 0.025mm and I'm using the 0.05 resolution as i want to shorten the print times but still maintain some of the "delicate" features on the parts.
And the method of changing the print resolution sound like hit and miss solution, changing the tolerance of the feature in SolidWorks is a much more straight forward solution.

I press the cube into the knob - that is the interference fit I was referring to. The cube is 12.00mm square and the hole in the knob is 12.10mm square. If I recall, I created the fit by playing with the size of the hole (0.05mm was too tight to force the cube into the hole).

I found through experience that the thread needs to be as small a resolution as possible, or it won't work. I also run a tap up the cube to make sure it is clean.

You have better resolution and I suspect that your printer is much faster than mine. My printer takes 30 minutes to print two knobs at 0.35mm resolution, and another hour to print the two threaded cubes. If I had a faster printer, I would have made a threaded knob at 0.05mm or smaller.