ToM APB Belt Tensioner

by gaerisl, published

ToM APB Belt Tensioner by gaerisl Nov 23, 2011

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The goal of this creation is to place the ToM APB (Automated Build Platform) belt under high tension, so it acts much like a solid plate surface (emulating the HBP (Heated Build Platform) surface) while retaining the ejection capabilities of the APB.

This is a lever arm that stretches out your APB belt. Under high tension, the belt resists flexing up at sides due to warping stresses during cooling and sits flat on the heating board before printing. The arm attaches to the sides of the roller bar, and friction is kept to a minimum by bearings at the point of contact.

The lever arm tension is set by manipulating a screw.
This bolts onto the stock APB, requiring only two bearings and two short m3 screws to be purchased. Misc M3 screws will allow this to be bolted onto the ABP. However, proper-length countersunk head 10mm to 15mm M3 screws should be used for the tension-setting screws in order to avoid their sticking out and running into the z-stage bars during homing and printing.

I recommend using a sturdy belt to handle high tension (such as Tunell's Steel Conveyor Belt for ABP. http://www.thingiverse.com/thing:9127).

Using this tensioner and a kapton-covered steel APB belt, I have been able to achieve quality near that of the Kapton-covered Aluminum HBP while preserving the ability to queue up multiple parts and remotely print. It's not perfect, but I'd say it's pretty darn good.


1) Print & Clean up parts
-I suggest more than zero shells, higher infill levels, as this must be sturdy.

2) Assemble:
-Place bearings into lever arm,
-Place m3 nut into lever arm,
-Partially screw in the 10-15mm, countersunk M3 tensioner screw

3) Put it on the ABP
-Remove the ABP from printer
-Remove existing side screws, bolt on the backing bars, making note of where the X axis endstop should fit.
-Remove APB screw on the lower back (and do not bolt on the lever arm yet!)
-Place lever arm onto the roller bar (roller bar into the bearing), THEN -Bolt in the lever arm pivot point.
-Repeat for other side.
-Put ABP back onto ToM

(I suggest sir MakeaLot's http://www.thingiverse.com/thing:9420 for easy build platform snap-on-snap-off's)

4) Tensioning the belt
-Finger tighten each tension screw until it can no longer further tightened.
-Screw each side in equally... keep tensioning until it is difficult to -Put a fingernail between the belt and the heating board.
-Run the ABP motor to see that you haven't put on too much tension (should still turn belt)
-Wait and see that the belt doesn't drift to one side. (further tighten the side that it drifts towards, if there is drift)

5) Check freedom of movement
-check that the end axis fits and triggers normally.
-check that the screw right before the end axis passes under the backing bar properly.
-check that the tensioner screws don't run into the Z-Stage bars.

6) Be Happy, Queue, Print Remotely, and try to convince people that ABP doesn't suck... it just needs a few modifications.

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Currently designing a shortened lever-arm for this one as the lower bolt is a bit higher due to my removable ABP mod ( http://www.thingiverse.com/thing:8878http://www.thingiverse.com/thi... ).
Have to start from scratch as there ar eno original design files posted.

(moved) Thing-O-Matic: Removable ABP mod

Two things:

1) The endstop connector hits the front part of the brace for me :(

2) Where's a good place to buy the bearings? (in the US)


1) Hmm... i'm not completely clear what you're referring to... Is it something an Xacto knife can fix?

2) I went with mcmaster-carr. (http://mcmaster.commcmaster.com) for the bearings. Shipping is fast (for me, because they're in the DC area), they have a good selection, and shipping costs usually come out to about 5 dollars. However, if you're looking for a cheaper alternative (and you can wait), I believe there's a
lot of online bearing stores.

Hope that helps!

By the way, this is great for repairing a broken ABP side acrylic piece. I was planning on doing the mod anyway, but I accidentally snapped the little bracket off, so I'm doing it now.

I must be confused ... I don't see the bearings on the pictures and I don't understand how they interface with the lever arms. Are they really there or are the original bushings the only contact with the lever arms?

Apologies, I made it before I decided on putting it on thingiverse.

The bearing is located in the concave, curved, cup-like tip of the lever arm.
The center rod for the belt-roller comes in contaact with only the bearing, and not the entire level arm, thus reducing friction in high-tension states.

If you look closely at the primary picture (full sized), you can a
ctually see the edge of a bearing, located on the other side, concentric to the metal rod.

Hope this helps!

So, it looks like the beaaring is inside the lever arm and the original bushing rides on tthe lever arm. Is that right?

Seems like someone should create a mod to put bearings in both ends. Then we could pull the tension even tighter.

Okay, so now I see it. I think I can get it now. Pictures when I have it all together.

This is great, I broke the little acrylic tabs on the abp trying to get the tension tight enough, I'm currently working on replacement brackets, and I think I might include this design as part of the rear ends...

Of course! Feel free to use the design!

Please let me know if I can send you the Solidworks Files.

Finally a workaround for this design flaw!

Thanks a lot!!!!

Thanks! Hopefully someone can improve further on this!

Will this work for the cupcake?

the APB mounts and holes should be the same, but I'm not sure if the endstops are in the same location. If so, then it'll probably work! It's not much plastic, so you could try printing it out and seeing if it will likely fit