3D Printing UNC Threads.

[cgbenner 0]

Hi,

 

We have been trying to get a decent print of UNC threads off of our Printer.  Ultimaker 5 using Cura slicer.  Variety of materials.  We have gotten one good part that can print repeatedly in ABS, Polypro and even Kynar.  But every part since, modeled in either Inventor or Fusion, has had the threads coming out on an angle leaning upward in the direction of the print (bottom up).  The threads are also kind of squished, and have a seam running down one side.  Needless to say we cannot get a nut on any of these. 

 

What questions should I be asking, or information should I be giving.... and what, if any, suggestions do you all have?  I have tried with nominal thread data for 1/2-13 UNC Class 1A... with and without an offset "fudge factor".  The attached image (look at the shadows) is of a standard 1/2-13 hex bolt, the middle orange piece is the one that works though you can see the angle there as well, the third piece is from this morning and the leaning angle of the threads is pretty visible in the shadows.  

[Oliveros 11]

I've printed a variety of threads, I use Cura as well but I find it's mainly in the design process you determine what your thread will look like.

 

I use Sketchup for my drawings, including to draw threads using various tools but I've matched 1/2"-13 thread perfectly as well as any other thread I've had a need to, including pump threads. I printed parts with this and it works every time.

 

A couple of things I've figured out strictly in Cura is that you have to print without support or at least support block your threads to minimize the imperfections in the thread.

 

It's also common to "cut" the tip of the thread on the male side to that it doesen't go in all the way, I've done it both ways and either worked.

 

The angle I don't think is coming from your printer or Cura, I think your model is doing that as it's simply too perfect to be a problem with the printer or slicer. 

 

I don't know how Fusion 360 or Solid Works makes their threads but I know in sketchup I draw the profile of the thread myself and then "follow me" around a helix curve with a set radius, amount of segments, turns, and any tapering. That gives me total control of the thread and how it looks when it's done. 

 

I just recently printed a larger 1/2" X 13 bolt for a customer out of nylon 6 without supports, which was put in a drilled out and tapped hole to 1/2"-13

 

Without blabbering on, I think your problem is in the model, not the slicer and not the printer.

[cgbenner 0]

@Oliveros

 

Thank you for responding.  I appreciate your input.  I can assure you that the model is correct,  Inventor and Fusion both model threads based on ASME and ANSI thread standards.  The geometry was based entirely on NOMINAL threads specs taken from those standards and the Machinery Handbook.  I've been doing mechanical design and drafting for over 25 years, and I am an Autodesk Expert Elite member.  Not to brag, just trying to assure the readers of this thread that I have modeled threads before.  This ain't my first rodeo.

 

If you re-read my original post, you'll see that one of these threads was actually usable, though still leaning in one direction.  Here is a screen shot of my modeled threads, compare this to the image in my original post.  The orange part at the bottom of the image, was printed from THIS model.

 

 

[tinkergnome 927]

Standard threads are designed for traditional shape cutting and are quite a challenge for 3D printing in general (because of very steep overhangs that like to curl upwards).

 

I think a small "fudge" factor is a good idea. Plastic threads usually need a bit higher tolerances than metal ones.

There's a reason why trapezoidal and buttress threads are preferred for plastic parts.

Your prints are looking a bit weird though. Like they are either printed with very thick layers or with activated experimental settings (like "Make overhangs printable").
All assuming that the bolts are printed in upright standing position...?
What material is used?

Take sure that you print those things with max. 0.1mm layer height (better 0.08), not too fast, with as much cooling (fan) as possible and without any tricks or supports.
It's well doable this way - at least for thread diameters of 8mm or more.

[Oliveros 11]

Okay, got it.

 

Based on my experience, I print threads with a layer height of 0.1 and 0.2 and 0.3, I just finished a print with rather large threads but they are exactly how they should be, per the model.

 

The only thing I can imagine is some sort of wipe or other type of setting that's messing it up in Cura, you could try running a blank setting parameter for whatever plastic or the "default" without any special settings. 

 

In a smaller pitch like what you are doing, print it vertical with the head down and print like mentioned above with small layer height, run 100% cooling if possible, at least for when the thread begins, no support, it'll do it and keep the temp in the higher band of the material as to offset bad layer adhesion caused by rapid cooling.

 

I've successfully done this in Nylon 6, Nylon 12, ABS, PLA and PETG, depending on the material and size, cooling may be necessary or might not be needed.

[geert_2 557]

Steep overhangs tend to curl up. Maybe that might cause this deformation? Watch closely while it is printing, then you can see if this is the cause indeed.

 

If you can't get it to print well, another thing you could do is make an undeep thread, so the overhangs are not so steep. And then using a standard thread cutter, cut the final thread.

 

When cutting threads in PLA, go very slow, and with lots of cooling. Otherwise everything will just melt. Don't ask how I know...   :-)

 

[Oliveros 11]

I've yet to have the need to revert to tap and die for making threads, looking closer at your picture, it seems the thread started out fine at the base and slowly worsened as it went up further. 

 

I've seen some materials act odd when printed vertically, as the head moves around it moves the piece with it and so you get very uneven layers, perhaps something like that is happening here? Causing it to be an uneven thread.