QUBD extruder mod

by mickb, published

QUBD extruder mod by mickb Jan 20, 2013
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QUBD extruder mod by mickb is licensed under the Creative Commons - Attribution license.

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11674Views 1443Downloads Found in 3D Printer Extruders


You will need 608 bearing and a spring.

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I still can't understand why there's a fan pointed to the inner of the extruder and nobody wants to answer me.
Shouldn't it point to the piece under construction?
Is it to prevent the plastic of the extruder to melt?

it's to prevent the drive mechanism and feed area from getting warm. if the drive rollers are warm they will soften the plastic and just smear through it instead of gripping it and pushing it downward, or bend it to the side before it enters the hot end.

Ahhhh thank you dude! :)

There appears to be a small problem with this design, the inside edge of the lever, just underneath the bearing, is fouling against the ridge on the center of the stepper, which means there is a tiny gap that you cant close between the drive wheel and the bearing. Its probably not an issue in most cases, but i have some particularly thin filament (1.63 mm) and its slipping. I was able to fix it by shaving off a small amount along that edge with a craft knife, but it might be a good idea to put a small inset about 1.5mm high along that bottom edge, if you make the top a curve, you wont need support material to print it. alternatively, shift the pole for the bearing forward by a small amount, so the bearing is closer in.

I'm curious which drive gear you were using. I changed over to Bart's design some months ago and recently had exactly the problem you describe. So I created a new one of these and completely solved it, just the opposite of what you experienced. I'm using an MK7 gear and the 608ZZ0 bearing. The first thing I noticed was that the bearing turns when I run the motor WITHOUT any filament in it, meaning that the bearing is running up against the MK7 body face (you can't get closer than that!). Also, I had to recalibrate the flowrate - turning the Slic3r Extrusion multiplier down from 1.18 to .94 (that's how bad the bdring was slipping due to the arm running into the ridge on the stepper). I've got 18 hours on this new setup and no buildup on the gear teeth yet running ABS at 100mm/sec @ 225 degrees.

The fan/heatsink are pointless and unnecessary.

the fan/heat-sink cools the cold end of the extruder, and prevents heat creeping up the hot-end from softening the filament before it goes into the hot-end barrel, which causes jams. this design actually could do with more cooling, I'm experimenting with drilling holes in the heat-sink, to allow some direct cold air draft from the fan to circulate around the filament driver gear and the motor shaft, which is another source of heat. I'm also looking at substituting a 65 cfm fan which would significantly improve cooling.

I tried milling the heat-sink's 5mm hole out to 9mm. That helped just a little, so I abandoned it. The real change was using heat-sink compound between the heat-sink and the mounting bracket and the barrel threads into the mounting bracket to increase heat transfer to the heat sink. Then, for PLA I adjusted the retraction down to 0.5mm at 22mm speed. With those two modification, plus this mod or the one by dbring, and an MK7 gear, I have printed over 1,000 hours of PLA with the QU-BD MBE extruder with not a single gear strip or plugged extruder. I print PLA at 70mm perimeters and 100mm infill @ 200C. The only time I use ABS anymore is for a piece subject to heat, like this mod.

Thanks, i'll give that a go, i'm just running up two mbe9's on a zen tool works cnc rig.

I struggled making the QU-BD extruder work until I found this MOD. I also hobbed the brass gear and was able to get the original to work long enough to make this. I used the same spring for a Wade's hinged without cutting it. It was tough getting it compressed but there is no doubt that there is grip. I have printed for over 6 hours without a jam.

After using this mod for a couple weeks, this mod works great!

What kind of spring is needed? One from a standard wade extruder would work?

I am using a spring with 10mm diameter. I think I got the pack at ACE hardware. I had to split it in 2 because it was too long.

Did you need to change out the drive wheel / hobbed bolt as well, or were you able to use the QU-BD one?

I hobbed the original drive wheel with a 3mm tap. It may work without hobbing, but I haven't tested it. I tried modifying the drive wheel first, and after that did not help I created this.

Looks a lot like Bart Drings mod - have you used this very much?

Yes, it is based on Bart's and few other designs floating around here on Thingiverse. I used it for about 4-5 hours of printing so far and it works great.