QU-BU Extruder Improvements

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QU-BU Extruder Improvements

Postby bdring » Tue Dec 04, 2012 12:47 am

Let's move the QU-BD Extruder discussion here. That other thread got way off track.

I am out tonight. I hope to print my parts tomorrow or Wednesday.

I have two extruders. I might setup a tug-of-war between the various methods. I know the gear and idler is not the only issue, but good pull strength helps.

Edit: A wiki page has resulted from discussions on this page. http://www.buildlog.net/wiki/doku.php?i ... provements
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Re: QU-BU Extruder Improvements

Postby robotdad » Tue Dec 04, 2012 5:32 am

I just got two qu-bd's in the mail today. I'm happy to keep one stock and follow along with suggestions made here. I've settled on using PLA with both as the machine is in our living room. Got a batch of new filament on the way from ultimachne and use it or lose it vacation. :D
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Drive Gear

Postby bdring » Tue Dec 04, 2012 1:07 pm

The drive gear was purchased from the RepRapMe store on eBay.

http://www.ebay.com/itm/MK7-Drive-Gear- ... 1012284234

drive_gear.JPG
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Still working on idler.

Postby bdring » Thu Dec 06, 2012 5:56 pm

I printed a few versions of the idler wheel mechanism last night and non of them were worth keeping yet. The last was was pretty close, but the idler was not exactly centered and the filament might jump off.

Here are my thoughts on idler bearings

I have tried a number of bearings. The best one I found is a 13mm dia x 4mm shaft x 5mm thick. You want it as thick as possible so the filament stay on. A larger diameter helps because everything is easier and stronger if the axle is further away from the drive gear. A small diameter axle so the hardware is not too huge. (I don't like trying to print the axle)

I also don't want the bearing so large that it protrudes past the edge in release mode. My extruders are right next to each other.
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Idler

Postby bdring » Fri Dec 07, 2012 4:22 am

I am pretty happy with this version.

The idler pulley mounts to one side of the level. My other designs used a pocket like the thingiverse version, but I was having a few tolerance issues with my bigger bearing. The put the big knob at the top because the end of long skinny tapers tend to start to peel up on some of my prints. The bearing mounts with a button head M4. It self taps into the hole. The head is just below the heatsink so I don't think it will back out. There is a thin washer under the bearing so only the inner race touches. I should probably print that little offset.

The spring support block does not cross the to the other motor hole like the thingiverse version because I needed the lever to be full width for strength. It just has a little nub to prevent rotation. The spring is centered so the is no real torque on it.

I somehow screwed up the alignment of the spring pockets, so it is at a slight angle.

2012-12-06_22-09-15_59.jpg


2012-12-06_22-10-01_511.jpg
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Re: QU-BU Extruder Improvements

Postby kbob » Fri Dec 07, 2012 5:40 am

I have never understood what the fan and heat sink are for. What are they actually cooling? Is something bonded to the back side of the heat sink?

Maybe if I saw and disassembled one in person it would make more sense...
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Re: QU-BU Extruder Improvements

Postby brnrd » Fri Dec 07, 2012 7:17 am

The heat sink is connected to an aluminum block that is attached to the stainless steel filament barrel of the hot end in the bottom and the motor on the opposite side. The fan and heatsink are meant to prevent the heat from the hot end from traveling up the barrel into the motor and pinch gear. If they get hot, then the filament would soften and retract would fail resulting in ooze and the pinch gear would slip. The motor might also get too hot.
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Re: QU-BU Extruder Improvements

Postby bdring » Fri Dec 07, 2012 12:46 pm

never understood what the fan and heat sink


Like @brnrd said, the primary reason is to keep the heat of the nozzle from climbing up.

Motors can also get hot. On these direct drive styles, that heat can transfer to the drive gear from the shaft and soften the filament right where you want it strongest. It is something to watch for. If you motor is too hot, try dialing down the current.
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Re: QU-BU Extruder Improvements

Postby orcinus » Fri Dec 07, 2012 3:37 pm

Looking good! How's it behaving in actual use?
And will you put it on Thingiverse?
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Re: QU-BU Extruder Improvements

Postby bdring » Fri Dec 07, 2012 3:52 pm

I did not test it in use yet. I locked the motor with a bench supply and gave it a tug. The stock QU-BD slips right away and this holds really tight.

It might be a few days before I test it. I am helping the Boy Scouts build a dog sled tonight and working as a Judge for the midwest First Robotics Competition all day tomorrow.

I'll publish the files if it works out.
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