ToM APB Belt Tensioner
by gaerisl, published
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.
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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.