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Bolt and Nut in FreeCAD

Posted by pwn4 
Bolt and Nut in FreeCAD
April 16, 2012 03:48AM
Hi Guys, so I've taken to freeCad as I'm getting the hang of it, and wanted to make a bolt and nut (this one is round... it's just a test) while I wait for my reprap parts to arrive. Attached is a picture - I used parametric helix objects, offset them, and then used "Create a ruled surface between two curves" to flesh out the threads. I think it works pretty well as a technique, and I can then use cubes and stuff (with some effort) to then cut the threads to length.

The bolt works pretty well, and with some repairing (this technique does seem to create holes and stuff... weird) using netfabb it seems fine. I checked the layers with pronterface, and it all seems good (neat to see the threads being printed. It's just a spinning oval.)

However, when I try and slice up the nut, I have some real problems I guess due to the "hole"-ness of the helix curves. Basically to make the nut I do the same thing as the threads, but I increase the radius of the threads by some small amount to make sure that the bolt will slide in. I then took a cylinder, created a second one the same size as the outer helix of the threads, and then cut the larger one with the smaller one so that the helix threads fit perfectly in the big cylinder (and there's a hole for them in there).

If I then use netfabb to repair the model (it needs it, apparently), it treats the threads on the inside of the nut like the threads of the bolt, and fills them inwards instead of joining them with the outer shell - thereby filling the nut's ends. I can't seem to figure out a better way to make threads with freeCAD or fix this. Anyone have any ideas? Attached is the freecad file for you to play with also
open | download - screwtest.stl (168 KB)
open | download - screws.png (113.3 KB)
Re: Bolt and Nut in FreeCAD
April 16, 2012 08:35AM
Modeling bolts and nuts with a thread is nice for learning the application, in the "real" world, however, you wouldn't do that. Think of how many millions of triangles you'd have to render if you have just 100 bolts and 100 nuts.

Most mechanical CAD applications have a special function for "this cylinder is a thread", FreeCAD might be too young for that.

Generation 7 Electronics Teacup Firmware RepRap DIY
Re: Bolt and Nut in FreeCAD
April 20, 2012 12:46AM
For anyone that wants to know, I found a way to fix the problem. Use the method I outlined above, but then you have to extrude the faces that you create (even just by a tiny amount like .01 along the z axis) I guess to flesh them out. At some point when I have my machine and can test the prints I'll make a tutorial on YouTube for other freeCAD users
Re: Bolt and Nut in FreeCAD
April 20, 2012 07:08AM
Re: Bolt and Nut in FreeCAD
May 13, 2012 02:19PM
Traumflug Wrote:
> Modeling bolts and nuts with a thread is nice for
> learning the application, in the "real" world,
> however, you wouldn't do that.

You would if you were going to make them by an additive process, rather than machine them.
I agree that normally there would be a thread spec callout on the drawing, but that's no good for a RepRap or similar.
Re: Bolt and Nut in FreeCAD
October 21, 2012 03:05PM
I am very new to all this but if you had a good commercial model of a machine screw that passed all tests could you not use that via
a boolean subtract operation to get internal threads - might have to scale the model diameter to make it look like the clearance distance
has been added.

Again, this would be only for visual appeal, I assume you would be just specifying the threading.

I just started playing with all this type of thing 2 days ago so here goes a real newbie question - can you change the color of the crosshair in freeCAD, the default white is driving me crazy.
Re: Bolt and Nut in FreeCAD
October 22, 2012 04:13AM
You can use any count of Bolt and Nut in FreeCad there is no limit.
Re: Bolt and Nut in FreeCAD
July 07, 2014 06:07PM
man that would be so awesome if you did make a youtube video tutorial....I need some help with this for sure! grinning smiley

Edited 1 time(s). Last edit at 07/07/2014 06:08PM by semitonesonata.
Re: Bolt and Nut in FreeCAD
July 08, 2014 04:46PM
ben11c, it's not about any kind of hard limit on number of polygons in the application, it's about weather or not the file will bog your computer down with each change... Or you know, possibly take days to put through a slicer, if it will even slice at all.
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