Fasteners Workbench thread and head scaling

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MostlyHarmless
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Fasteners Workbench thread and head scaling

Postby MostlyHarmless » Wed Jan 03, 2018 9:13 pm

As this is my first post on the FreeCAD forums, first a big "Thank You" to everyone involved.

That out of the way I am curious about opinions regarding two additional parameters to the screws and nuts in the Fasteners Workbench. These parameters would control scaling of the thread and head dimensions in the X-Y plane before placement. The purpose of this scaling is to turn these parts into actually working, 3D-printed fasteners. As things are right now, fasteners produced by the workbench using ideal dimensions don't work when 3D-printed due to material shrinking and surface imperfections. In other words, 3D-printing needs some tolerances to print working parts.

For this to happen I am proposing two new Parameters in the Fasteners Workbench.
  • tScale - A float for scaling the X-Y plane of the generated screw/nut/rod thread
  • hScale - A float for scaling the X-Y plane of the generated screw/nut head
I have locally cloned the Git repo for the Fasteners Workbench and hacked the code a bit. I was able to implement the tScale feature for Iso4017, Iso4032 and Tap with a reasonable amount of changes. The resulting PLA prints are perfectly functional bolts, nuts and taps down to M4. I will make this available as a github branch later tonight and follow up with a link.

In the meantime comments and suggestions welcome.


Best Regards, Jan
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MostlyHarmless
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Re: Fasteners Workbench thread and head scaling

Postby MostlyHarmless » Thu Jan 04, 2018 4:18 am

Here is the work in progress:

https://github.com/wieck/FreeCAD_Fasten ... ee/scaling

https://github.com/wieck/FreeCAD_Fasten ... bb5b52989b


As said, so far only tScale is added and it is only working in ISO4017 (hex-bolt), ISO4032 (hex-nut) and the tap rod. In the end all the make*() functions in screw_maker.py would need to handle the two new parameters when calculating points and diameters. This branch is far from there but it demonstrates that the original goal of 3D-printing working fasteners using the workbench is possible.

Since the scaling to use depends on the material as well as the print quality, I cannot give anyone a sure fire set of parameters. What worked for me on a (slightly modified) Anet A8 with PLA at 0.1mm layer height printing M6 or M8 is a tScale of 0.98 for external threads (bolts) and 1.05 for internal threads (nuts and taps).


Regards, Jan
chrisb
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Re: Fasteners Workbench thread and head scaling

Postby chrisb » Thu Jan 04, 2018 8:37 am

MostlyHarmless wrote:
Thu Jan 04, 2018 4:18 am
What worked for me on a (slightly modified) Anet A8 with PLA at 0.1mm layer height printing M6 or M8 is a tScale of 0.98 for external threads (bolts) and 1.05 for internal threads (nuts and taps).
What nozzle diameter does your printer have?
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MostlyHarmless
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Re: Fasteners Workbench thread and head scaling

Postby MostlyHarmless » Thu Jan 04, 2018 2:12 pm

chrisb wrote:
Thu Jan 04, 2018 8:37 am
What nozzle diameter does your printer have?
Still the original 0.4 mm. I was surprised that it is possible to print a working M4 thread with that. I am sure it won't work if the thread isn't aligned with the Z axis. But that case can only occur when printing tapped holes, never when printing individual fasteners.


Regards, Jan
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MostlyHarmless
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Re: Fasteners Workbench thread and head scaling

Postby MostlyHarmless » Fri Jan 05, 2018 3:17 am

MostlyHarmless wrote:
Thu Jan 04, 2018 2:12 pm
I am sure it won't work if the thread isn't aligned with the Z axis.
Wrong! Just printed a M4 tap along the X axis. tScale=1.08 and it worked like a charm. So much for that.

Anyhow, I'm going to continue and try implementing the hScale part for ISO4017 and ISO4032 so that they properly fit into wrenches.
chrisb
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Re: Fasteners Workbench thread and head scaling

Postby chrisb » Fri Jan 05, 2018 6:13 am

do they work out the box or do you rework them with taps and dies?
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MostlyHarmless
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Re: Fasteners Workbench thread and head scaling

Postby MostlyHarmless » Fri Jan 05, 2018 2:13 pm

chrisb wrote:
Fri Jan 05, 2018 6:13 am
do they work out the box or do you rework them with taps and dies?
No taps and dies involved. I scale them so they are tight at first. Turning them against each other a few dozen times focusing on the rough spots makes them work just fine.
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Re: Fasteners Workbench thread and head scaling

Postby chrisb » Fri Jan 05, 2018 4:32 pm

MostlyHarmless wrote:
Fri Jan 05, 2018 2:13 pm
No taps and dies involved
Amazing. Could you upload an image of an M4 or M5 screw please?
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MostlyHarmless
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Re: Fasteners Workbench thread and head scaling

Postby MostlyHarmless » Fri Jan 05, 2018 9:44 pm

chrisb wrote:
Fri Jan 05, 2018 4:32 pm
MostlyHarmless wrote:
Fri Jan 05, 2018 2:13 pm
No taps and dies involved
Amazing. Could you upload an image of an M4 or M5 screw please?
DSCF5192_2.JPG
3D printed M4 fasteners
DSCF5192_2.JPG (550.78 KiB) Viewed 1275 times
Everything in red are 3D printed M4 fasteners. I didn't have a metal hex-bolt in M4 at hand, but the little black setscrew does the job of demonstrating that these printed parts mingle quite well with actual metal hardware. And yes, the do really work and don't slip.

The bolts are printed upside down so that the hex head is printed first. Apparently my bed is a little too high causing the first layer (top of bolt head) to be a bit squeezed. But I rather have that and fix it with a nail file or Dremel tool than having a stringy first layer.
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NormandC
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Re: Fasteners Workbench thread and head scaling

Postby NormandC » Fri Jan 05, 2018 10:40 pm

M4! No way my 3D printer could do that! It probably could with tinkering, but I'm not much of a tinkerer.