QU-BD MBE SINGLE 1.75mm Extruder – Part 1

Introduction

Quite some time ago I received my QU-BD extruder.

At first I had problems deciding if I wanted to try it or not, the reason for hesitating was because it was both good looking, and at the same time stupid looking, here is what…

Pros:

  • Compact
  • Good looking
  • Insulation for keeping the heat shielded from various fans blowing air over the print
  • Seemed easy to fit onto multiple carriages

Cons:

  • Filament drive wheel having flat teeth
  • Short metal barrel between extruder and hotend
  • Needing active cooling
  • Idler pressing filament against drive wheel being just a bolt with a smooth end, which causes extra unneeded friction

But I ended up getting one anyways, because $49 (including stepper motor) isn’t that bad, even if it would totally fail.

The package

First up, let’s have a look at that is in the package.

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These are all the parts needed, which is not overwhelming and also looks pretty straight forward to put together. But let’s also have a closer look at the individual parts.

The parts

Filament drive wheel

This is the item in the package I was most worried about and as you can see on the pictures, the teeth where the filament is pressing against is also completely flat, I suspect it might have been better to just do nothing to the gear instead of making that groove into it.

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After testing it a bit on some filament in free air it actually seems to grip it, but requires a lot of pressure to to so.

Idler bolt

Instead of a ball bearing which many extruders use, this one just uses a bolt with a flat end instead.

This bolt concern me with two things, both the extra friction between the filament and bolt surface, and also that the end of this bolt actually isn’t flat, but instead a bit round. This round end will try to push the filament away from the groove, while the groove is trying to keep the filament at the right place. It might work, but my philosophy is always to design things to they help each other, instead of fighting each other.

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Power resistor

Next thing on my table was the power resistor, which immediately made me shake my head.

The function of the resistor is to get hot so the hot part of the hotend gets heated up. To heat this up the heat from the resistor needs to be transferred to the hotend, and to do this you need surface contact, as much as possible. And as you can see on the picture, this resistor could not have a worse shape.

This shape as an american football would mean it only got surface contact on two small points, it might work fine if you fill the hole around it with exhaust putty, but why use a resistor with this shape when there are more suited available?

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Stepper motor

Last part of the items I am going to look at is the stepper motor.

To be able to compare it properly I decided to get the stepper motor from QU-BD too, and it seems to be a good one they decided to provide.

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The specs is not that different from most nema17 stepper motors, but what worried me was the extra friction from the idler pressing the filament against the drive wheel, and also direct drive with the drive wheel mounted directly on the motor. These forces might mean some steppers would not be strong enough, but this motor should do the trick.

Assembly

The assembly went pretty easy without any drama, but here is another look at the things that concerned me.

Filament drive wheel and idler

After putting the first things together we can now have a look at the two parts I don’t like the most.

The round ended idler ready to press the filament into the flat teeth on the drive wheel mounted on the motor.

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Putting the drive wheel on the motor was not easy either, all bolts seems to be metric, except the bolt on the drive wheel. From the part list on QU-BD’s website they should all be metric, but no key in my umbraco set fit into it, either it was too big or too small.

Hotend

Next assembly was the hotend, and as you can see, I decided to not even try to use the power resistor QU-BD provided with the kit.

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Here one of my concerns also was the short metal barrel between the cold and hot part of the extruder. At the same time it is also connected directly to the plate using to mount the extruder to the carriage, so if this is made of plastic you really don’t want any heat to slip out there.

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One of the things I really like about this extruder is how nice it looks with the insulation put on.

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This instantly gives it a more professional look.

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Overall assembly

After putting it all together, this really looks like a nice piece of hardware. The wires seems easy to route, the entire thing is compact and does not feel like it is about to break in any way.

But does it only have the look, or can it actually do some work?

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Getting it to work

Loading filament

When I tried testing it, I ran into problems right away, my problem was I could not get the filament to go into the barrel leading down to the nozzle.

As you see here, the filament must be straightened out before putting it into the extruder, just slightly bending makes it miss the hole.

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Filament grip

The thing that worried me the most was the grip on the filament, and while it seems to work it also seems to require more force than I normally use.

This filament is only 1.75mm in diameter, and to be able to grip it I had to tighten the bolt enough so it would be pressed into the drive wheel.

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These are the marks from the drive wheel and it looks like it got a good grip on the filament, but at the same time I also had to turn the driver for the stepper motor up to overcome the extra friction.

The extrusion from it looked fairly smooth and consistent, but when feeling over the extruded plastic it felt like it was full of small waves. Before deciding on if it is the extruder, hotend, filament, or me being the issue I need to do some more testing.

Stay tuned for part 2

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