realthor wrote:I need a piece of advice regarding a type of gear that I think I've seen somewhere but can't remember anything more than that.
This is a screw-type threaded rod that also has a gear profile on its threads so that another gear can engage it to rotate and advance through the nut, something like this:
I am sure this does exist. Does it have a name? I am thinking about this as a way to spool without having to rely on sliding/extending couplers.
1)Would this be a printable design?
2) Would an extended coupler of the type i've previously shown be easier to print/create than this?
Thank you.
Cozmicray wrote:I suppose it would be good to know what this
mechanism has to do?
Cozmicray wrote:Even a outlandish complicated mechanism that you like?
Cozmicray wrote:Now that I look at your drawing
Cozmicray wrote:You could take a splined shaft and thread it
it is a screw with gear teeth cut axially around the circumference.
or
take a threaded rod and cut splines (gear teeth) in it.
Nicholas Seward wrote:@realthor: No you could easily print the bolt and the nuts. I would use a nominal diameter of 16mm or bigger. This could be an easy 3 part assembly.
1) Two integrated nuts and stepper mount
2) Worm gear
3) Spur gear/ screw thing
You just size the components so that they are strong enough.
Cozmicray wrote:Why is it so critical to provide precise spooling.
If it were a good design every winch and fishing reel would using it.
Cozmicray wrote:I accept you are anti KISS
Cozmicray wrote:You could have built six Wally's in the time?
Nicholas Seward wrote:This could all be 3D printed easily. The design side is a little tricky but not too bad. I would like to prototype this if I can find the time but let me make a few notes for discussion purposes.
1)The nuts would be printed in the same part that holds the stepper.
2) The nuts can be designed to not get close to the root of the screw so that the string can actually wrap around the screw and go through the nut at the same time.
3)I would have the string leave the screw between the nuts.
4)The screw will have a large enough diameter (20ish mm) so the screw doesn't need travel very far axially. For most desktop printers you can get by with 3-4 rotations.
Now for a little math... I think the worm/spur ratio could easily be 16+:1. With a 20mm root diameter on the spool and a 45oz-in stepper you will 100+lbs of force and you will get a resolutions of about 20um per full step.
Nicholas Seward wrote:This setup is prone to backlash but gravity should take care of that. You can also make this a two sided design with the stepper turning a worm that interfaces with two screws. Tensioning the string in the system will remove the backlash.
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