Learned something today - Fastener Workbench only has UNC, no UNF for taps

[WobblyHand]

Sort of learned something the hard way today. The Fastener Workbench has a tap object, which one can use to cut female threads in an object. I chose a 1/2" tap and a custom thread of 1.27mm (20 TPI). What I got in the model, but I didn't recognize, was 1/2"-13 threads. I exported my model to stl to make a 3D print. I couldn't understand why I couldn't run a 1/2"-20 tap through the hole.

Going back to the model and TechDraw, I dimensioned the thread pitch and discovered that the thread was 1/2-13. So FreeCAD was ignoring my custom pitch, with a tap diameter selection of 1/2", and substituting in the UNC pitch, rather than my desired UNF pitch.

Back to Fastener Workbench, one can select a custom diameter and pitch. I tried that and got what I expected. Kind of irritating to have wasted the time, but I did learn that UNF is not native to FreeCAD. So printing again, and hoping to have better results!

What have I made? A protective cap for 1/2-20 UNF threads.

 

[WobblyHand]

It goes on this piece. Just finished the barrel adapter recently.

 

[Flyinfool]

I have never had good luck printing usable machine threads. I just print the proper hole size and then tap it after printing. I always have to tap them anyhow after printing.

 

[WobblyHand]

I have never had good luck printing usable machine threads. I just print the proper hole size and then tap it after printing. I always have to tap them anyhow after printing.

Well, the tap just shaves off a little bit this way, basically the work is all done by the printed threads. Very little is removed by the tap. Can hand tap with little effort.

I chucked the part in a collet and used a tap holder in my tail stock, just to keep it straight, but really didn't need to. I rotated the chuck by hand and the tap went right in (after making sure it was properly synced with the thread). Would have been easier if I had a tapered tap, but all I had was a tap whose taper was ground off, which made the start more difficult.

I have directly tapped small holes like M3 in printed stuff, that's ok. But for something like this, I'd rather print the threads. They are pretty close, at least with a 0.2mm layer height.