Issues with a Greg's extruder

I printed myself a Greg's hinged extruder to upgrade my perfectly functional Wade's extruder (first mistake, ain't broke, don't fix it), and I'm having trouble with the gears getting stuck seemingly randomly. It'll work fine until all of a sudden the stepper will start shuddering, the way it does when there's too much torque for it to handle. The lightest touch on the big gear gets it moving again, but it means I have to watch every print to help it along. I can't see what the issue is. There's a tiny tiny variance in how closely the teeth mesh (I'm not sure if its due to the gears not being perfectly round or being off center on their axles), but its small enough that it should be within tolerances, and how closely they're meshed doesn't seem to affect them getting stuck. I watch them get stuck when the teeth are tightly meshed, and then again half a revolution later when they're loosely meshed.

I thought this extruder was a really good print and I can't see any visible issues like blobs getting in the way. Anyone have any ideas of what could be wrong?

try disengaging the motor and spinning the pinion gear by hand. see if you feel any tight spots. get out the soldering iron and carve it like a turkey.

did ya grease it? is it catching against the base of the small gear (behind the gear part)? Is it catching on a screw or bolt anywhere? Is it meshing too tightly? Maybe just move the motor back a bit to loosen the gears up a bit. And do disconnect it and turn it by hand, it's amazing how such a simple step gets overlooked so often. (I've done it myself many times. ) Your fingers are far better mechanical diagnosticians than your eyes in many cases. The fact that it doesn't correspond to a particular spot on the large gear points to the small gear or motor. Maybe the set screw is dragging on something.

You might be stalling the motor. Make sure the gears turn freely, and that you haven't overtightened the nuts onto the hobbed bolt. As the hot end warms up, small expansions can have these kind of results.

It turned out to be a combination of things. First, the big gear was definitely not round. I babysat it long enough to make it print a new big gear and that one worked better. Second, a touch of silicone lube on the small gear helped. I never needed it before but that may have been just luck. Third, when I put this new extruder together I used stronger springs on the idler. Those appear to have been too strong. They put so much pressure on the filament that its makes it hard for the bolt to turn. And here I thought "hey I have stronger springs now, stronger is better right?". All those things fixed and it's working great. Thanks for the advice.

You should always keep the gears lubricated. Their lifetime is about an order of magnitude longer than it is when run dry.

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[www.hydraraptor.blogspot.com]

sounds fixed but if it comes back maybe the nut of the hobbed bolt is slowly doing itself up as you extrude, eventually getting too tight for the motor. it doesn't have to be super tight. i use two nuts, i tighten one to the bearing by hand, the second to it, then i undo the second a bit and using wrenches tighten the first nut back into it, leaving some give. or a nylock would probably have the same effect. or just leaving it not tight.

i think .. if you have 1 nut tightened on a wades it will eventually just come loose and not really effect anything but on a gregs because the screw is mirrored, in the wades config it does itself up. i think maybe greg puts the nut in the gear itself and the bolt head on the other side from memory.

One more question. I print my extruder block out of ABS to prevent heat damage, but as for the gears, would PLA work better? My old ones and new ones are both ABS, but would the stiffer nature of PLA cause the teeth to last longer? Or would the tendency to creep do it in quicker?

I would use ABS. ABS may not be as stiff as PLA, but it's tougher. This makes it less likely to fracture. A more extreme example would be the stiffness of a ceramic vs the toughness of a metal. I'd say metal gears are more common than ceramic gears.

PLA also creeps until it's beta phase transistion temperature¹ (-45 C, the negative isn't a typo), so it's not really a good material to put under constant stress.

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Chris Sketch
Ann Arbor, MI
blog.chrissketch.com

We’re here to put a dent in the universe. Otherwise why else even be here?
—Steve Jobs

My extruder motor gets too hot for PLA.

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[www.hydraraptor.blogspot.com]

I've never had the issues other people do with motors being too hot for PLA. Every part in my mendel aside from the X carriage and extruder are PLA, and none of the motor mount points show any warp. My X carriage *used* to be PLA, but once I started printing ABS, the carriage warped to become unusable.