3 starts lead screw
by aubenc, published
Description
It has been hard to find back most of the parts I was printing and using to do those tests and it has been really hard to find the OpenSCAD file that I upload here. I have hundreds of them.
I've choose this OpenSCAD because is the most complete one and the one that is less hardcoded (but still quite a shame). I've put some effort to clean it here and there but still there's no warranty at all that it will work fine.
No warranty neither that the stl provided will fit properly, I think that they should but... who knows????
This time I don't have extra pictures to show (my pleasure), instead I have this video... youtube.com/watch?v=a-4naMl-TOQ
I just hooked up the motors to bot1334 and ask it to build one stl via RepG.
The lead screw provided has a travel per turn of 36mm and I was not modifying the machines.xml to adjust to real sizes.
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I "almost" agree :-D
This is one of those things that one cannot stop playing with when you have it in your hands and it's nice to see how good it looks to work after some goings and comings.
I started to think about something like TheRuttmeister is suggesting when I realized that the nut makes the screw turn BUT th
e screw don't makes the nut move.
I mean, by hand, I'm not able to distinguish if I the nut has already move, say 0.1 or 0.2mm when the screw starts to turn BUT I do realize that I can turn the screw few degrees before I feel pressure in the nut.
Anyway, my design differs than yours so there are c
hances that my lead screws are prone to fail quicker ;) tests will say
Thanks!
the 1st time I did a lead screw I was not wanting to do it :-P I was just trying polygons in OpenSCAD and when I twisted one I saw the lead screw!
Plastic is flexible so, they will bend accordingly to their dimensions, the load and the way this load is applied. That is also true for breakage.
In
a setup where the load is taken by rods/rails/whatever the dimensions I used could seemed to me sturdy enough but I have not tested them (I don't want to break them yet :-P). Anyway, OpenSCAD is there and the script is full of parameters to make them stronger, faster...
Seriously amazing work, i frankly would not have thought it possible to make something like this printable in any form or way !
Given that my original repstrap is still fully leadscrew driven i might give this a try as replacements (multiple start leadscrews are way too expensive, and hard to find, so even more bonus points to your design)
A big question though: how sturdy is the leadscrew ? any risk of bend /breakage ?
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Instructions
-Yeah, ok print one, print the nut.
-Then use the scad to print a small lead screw, set RL parameter to... 20mm (?)
-Take in account that this thing adds a motor mount to the lead screw, unfortunately this is hardcoded. you may want to comment this part of the code and then use "put in platform" in RepG.
-Check if it's worth to keep on printing.
There are hundreds of horribly named and unproved parameters that should allow you to use other motors, brass (or not) rods...
Have fun!
I FORGOT TO MENTION something important!!
I was printing those when bot1334 was even less fine tuned than it is now, cleaning the lead screw was a pain in the... there.
Maybe, with stepper extruders and the advice of PacManFan (modify the code to add slices=length/layer height) it will work better.
Good luck!
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One thing I did to make the nut a good fit tight enough in the Z direction to eliminate backlash, but loose enough to slide, was to subtract the threaded rod from the nut, then scale it in the x/y direction but not the Z. This loosens it up enough to rotate but gives no play in the Z.
I did take a look to your code before uploading this thing and I saw the "scale" trick :-P I also tried this but I was not satisfied with the results. The reasons are... well I'm not using squares but a very too much hyper mega overcomplicated polygon :-[ that is not scaled nicely.
Also, most probably because I was not using your master's trick of the slices, I had to scale it too much to be able to see good results for the friction but then backslash got too noticeable.
Excellent work! I spent most of the past 2 days designing and printing some test jigs and screws. I'll have to try your out too.
Nice. Although the video features some truly horrible noises :P
Makes me think of digging my attempt at lead screws/ball screws back out.
How was the friction (I'm assuming you were using ABS)? and how quickly did things start to wear?
You're talking about the noise those birds in the background do? :-D
Yeah, the set using aluminum is quite a big disaster, also, those things are just let on the table: vibrations are amplified by moving parts.
Yes, that's ABS. The "nut" and the "screw" have no friction at all... in most of the travel but they do have a little bit here and there. Be sure that the belts are tensioned correctly to get perfect circles too :-P
Z artifacts (jigsaw, raise blob...) are big enemies of this thing, specially because lead screw and nut are laid down following the same axis. Friction will "attack" first those and I also used friction to smooth them.
First I did a cleaning with a small hobby file, then I used a nut printed with the gap parameter set to something like 0.3, and give it some end to end travels (by hand) forcing/pushing the nut. This procedure makes shine the Z artifacts, file touch and repeat with another nut this time printed with a gap of 0.15.
Backslash do exists and normally, the more this thing is used the more it will be noticeable. Ways to minimize backslash are also there :-P Setting the travel per turn parameter to something like 50mm or more (why not?) may be one of the ways to minimize friction/backslash.
The brass based set it's the winner of the three shown. It's not good enough but quite acceptable as a starting point (just my opinion). The "tool head" should benefit of longer bushings or even better, I think that 4 small bushings making a square would work very nice.
Seriously amazing work, i frankly would not have thought it possible to make something like this printable in any form or way !
Given that my original repstrap is still fully leadscrew driven i might give this a try as replacements (multiple start leadscrews are way too expensive, and hard to find, so even more bonus points to your design)
A big question though: how sturdy is the leadscrew ? any risk of bend /breakage ?
Thanks!
the 1st time I did a lead screw I was not wanting to do it :-P I was just trying polygons in OpenSCAD and when I twisted one I saw the lead screw!
Plastic is flexible so, they will bend accordingly to their dimensions, the load and the way this load is applied. That is also true for breakage.
In
a setup where the load is taken by rods/rails/whatever the dimensions I used could seemed to me sturdy enough but I have not tested them (I don't want to break them yet :-P). Anyway, OpenSCAD is there and the script is full of parameters to make them stronger, faster...