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Sprung Extruder Gear

by chylld, published

Sprung Extruder Gear by chylld Feb 21, 2011

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Summary

This is an experimental replacement for the larger of my two silent Rapman extruder gears.

After extensive printing with the silent gears, some 'click-clack' noises started to reappear, probably due to friction wear.

This gear attempts to solve this problem once and for all by incorporating a spring into the gear which itself is about 1.5mm larger in diameter. The spring provides constant pressure between the extruder gears, removing the tolerance and therefore the noise.

The big unknown of course is whether it will be durable and effective in the long term!

Update 22/2: The test gear survived a 5-hour torture test that contained a lot of reversals. The noises are gone, but this is most likely due to the gear simply being bigger - the teeth ring isn't flexing around the hub like I wanted. Basically, it's too strong. I think a new design with 6 (rather than 8) spring units is next on the todo list!

Instructions

This design is currently being tested with Orbi-PLA as its supreme elasticity lends itself well to the design. Theoretically however, any plastic should be suitable since the spring components do not move more than a millimetre.

To print this gear successfully you will need an extrusion width of no more than 0.5mm, as that is the width of the spring elements.

Obviously, you will also need the smaller extruder gear from the Silent Extruder thing :)

Good luck!

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This is probably my favourite piece to print. I print it every now and then with different colors and materials and every single time it comes out perfect :)

nice tried it  a bit too big but one can file it down I think should be a bit more flexible  would use ABS  great stuff

You are pretty much a fricken genius! Can't wait to try this out!

i don't know why but the idea of putting in less supports and filling it in with some sort of urethane epoxy seemed to come to mind.

but good idea, i am eager to see if you get some of your other troubles worked out.

This is an incredibly smart part. I'm interesting in seeing how well it holds up to wear and tear.

Have you thought of designing that part as a scissor gear? I can even picture it being made of two identical parts fit together with space and holders for a torsion spring inside.

unless i'm mistaken, designing it as a scissor gear would give rotational allowance but no lateral allowance (i'm making these terms up btw) i.e. it would allow the hub rotation to vary from the teeth rotation, but keep the centres the same.

the role that this gear must play is the exact opposite - allow as much movement of the hub centre as possible (relative to the teeth centre) whilst minimising rotation variation.

wow, very clever!

I'm not sure it will be strong enough to transfer the forces but it looks very interesting.

let us know how it works ... I fear the backlash will be too high for precision anti stringing operation..

no backlash problems - probably due to the gear being such a tight fit on the extruder shaft! print came out perfect, no stringing.

it is very good that there are no backlash problems with it .. I might try the concept with my 0.25mm head (that requires bit more precise extrusion control but as you say, rapman uses heavy gearing from motor to filament) ... only, I don't see where you get the problem with "clicking" - I don't hear anything from extruder even at very fast rates and I still use original acrylic gears?!

yeah I remember your video showing you had no extruder gear noise - i think my extruder motor plate may be warped slightly. easy fix would be to squeeze some foam between the motor and extruder main section... but that wouldn't be fun now, would it? :)

M227 performance doesn't seem to be affected - halfway through printing my 15cm Penrose Cube and there are no boogers to be found :)

Unfortunately I seem to have once again been too optimistic in my use of orbi-PLA. What makes it elastic in the spring section also seems to have allowed the centre hub to be 'crushed' partially by the washer - the split-ring washer behind it has pushed the washer about 0.5mm into the gear :( I go
t some grease onto the tightening bolt too so that is also coming unstuck.

Fingers crossed it makes it to the end of this print!

Very interesting design... I've never been able to get an extruder gear 100% perfectly centered... this might be just the thing. How do you decide how many uh... spring-parts to put around a given size gear, and how big to make them, and such? Is there a science to it I can duplicate in my custom extruder gears script? ( http://www.thingiverse.com/thing:6544http://www.thingiverse.com/thi... )

Parametric Herringbone Gear Set for Stepper Extruders

It was trial-and-error. I knew I wanted as many spring units as possible to distribute the force around the gear, and I started with a spring arm thickness of 1mm. I printed it and it came out solid as a non-sprung gear, so I reduced it to 0.5mm and while still a bit tough, does show some flex with orbi-PLA.

I have a feeling it will be heavily dependent on the material used, and in the case of PLA, the temperature at which it operates! (i.e. the behaviour would be unpredictable if the gear was mounted to a hot motor shaft)

I think 6-7 spring units would be the sweet spot :)

Thanks for the information... Do you think this introduces any torque buffering -- you know, like introduces a little delay between motor and gear?

For the design above, the torque buffering would be absolutely minimal, easily less than 1mm at the gear's circumference. In the Rapman, this gear is mounted onto a shaft with a thread on it, and it is this thread that feeds the filament - i.e. the reduction ratio makes any torque buffering absolutely negligible.

However it might be an issue without such a drastic reduction ratio and if you reduce the number of spring units to below 8 (since that would make the little spring arms longer)

Chylld, very inventive, FYI PLA creeps and will slowly compress from the clamping forces exerted on the hub by the nut. I suggest you change the spring design and use a pattern of 6 short spirals. I was quicker to draw what I mean see below. Sorry can't be bothered to do the math so you will have to use trial and error :-) and do as you said playing with the thickness and number but I think 0.5 mm thickness and 6 should do the trick. I can
’t wait to try it J

Using spirals was actually my first idea, but I thought it wouldn't work as each spring inhibits compression movement along itself. Looking at your picture though, it may work if there is enough curvature there...

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