RepRap Extruder V2.0
I have been building a RepRap in my spare time from instructions you will find if you follow the link. The instructions detail an extrusion mechanism which uses a direct drive from a stepper motor. It turns out that no matter what I do I cannot get enough torque to operate the RepRap in that configuration. I made a quick fix out of erector set gears, but it was bulky and didn’t perform very well.
With an insane amount of work and school leading up to Christmas, and having invested about 20 extra hours just trying to get it to work I had to put the RepRap project on hold. Fortunately I had some free time this past week so I designed and machined a new extruder which utilized some old brass worm gears I had lying around (actually they were extremely old – off some 50+ year old model trains I have, I choose not to think about their potential value). The bad news is that I had to take the heater off to make the upgrades and to reinstall the heater I will be needing some kapton tape – which I seemed to have misplaced. I’m looking hard though! I will give an update once I get it working. I’ll also post the plans – I don’t know how useful they will be though, as I used what is most likely non standard gears. The design borrows its geometry liberally from a design I saw once here.
*Update* I have since tested the extruder – it works very nicely when I’m not actually printing. There seems to be a problem with the host preventing the extruder from extruding during a print. I’m out of time for now but I will try to sort it out ASAP.
Howdy,
I’ve got to say, I sure am impressed. I’ve been obsessing over the Mendel RepRap project over the last week and I just found your drawings for a purely machined frame. Great work! The drawings are exactly what I was looking for! I do have questions about your extrusion mechanism. Was the worm gear really necessary? Was the problem not having enough force (between the motor and bearing) to push the filament into the heater module? I’m just a little lost at the redesign of the module. Any words of wisdom would be amazing.
Thanks,
Alex S.
Hey alex – I apologize for my extremely late reply. I haven’t been doing anything leisurely ever since Jan 5th when school started (I’m a mechanical and electrical engineering double major, as well as a 20hr/wk research assistant – its all I do) in fact this is the first time I’ve checked my website since.
I’m glad that you are finding my drawings useful, it is for people like you that I made them. The purpose of the worm gear was to increase the torque that the motor could supply to the pinchwheel. When I had the motor configured in a direct drive setup it didn’t have enough torque
E.g. not enough force – the torque required from the motor is the force required to push the filament through the nozzle multiplied by the radius of the pinchwheel – the torque is usually in inch pounds or newton meters, depending if you use SI or english units. An example is if a pound force was required to push the filament through the nozzle and you had a 1 inch radius pinchwheel then the torque the motor would need to supply is
1 in * 1 lb = 1in*lb of torque
So in order to increase the force on the filament you can either decrease the radius of the pinchwheel, get a bigger motor that supplys more torque, or gear the motor down to get more torque. I believe with the wormgear I am getting something like 100 to 1 gear reduction so it (theoretically) gives me 100 times the torque.
The motor not supplying enough torque was more of a electrical/software problem that they have probably fixed at this point. I started building the mendel the DAY that they published it on the reprap wiki – and it still had a bunch of bugs and wasn’t even fully documented. The worm drive was a fix that I machined in a pinch because I wanted to get my mendel printing. I would try building it whatever way they have it documented on the site because they have probably fixed it by now.
Also if you get the nema 23 stepper for the extruder instead of the nema 17 you are guaranteed to have enough torque – this is what I would do if I did it again. I can’t guarantee that my extruder design is compatible with the nema 23s.
Spring break is coming up soon – hopefully I will find some time to work on my reprap. If so I will post everything on here!
If you make a mendel I would love to see it!