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BunnyScience

Bunny and Bear Universal Carriage for Bear or Prusa X-axis

by BunnyScience May 6, 2019
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A few further comments.
The Prusa belt path should be around 1mm deeper. At its current depth it is not aligned with the idler pulley.
If we want sexy parallel belt paths, then the Prusa idler side belt clamp should sit around 1.5mm higher. Not sure if the Bear has asymmetric belt heights on each side but if it does that could work out nicely.
It would be nice to include versions with and without the self aligning ridges. Some bearing systems prefer not to be squished in the centre.

Cheers

We'll have to put together a Prusa x-axis to check that again. No more Prusa x-axes here. Once switched to tension adjust pulley mount, the stock Prusa design feels so primitive.

It sure is. I've modified mine heavily enough that I've got rid of most of the disadvantages. You should be able to check it against the CAD though, rather than putting it together in the real world.

Looks like there isn't a full height channel for the filament sensor wire down to the cable bundle. At full height the sensor cable will "interact" with the MMU.

Martin, could you attach a pict of the interference please?

Difficult to photograph. I hope this is ok. :D

I think you are showing the lower leg of the MMU2 mount hits the filament cable where the cable passes behind the top x-carriage cover. Bunnies removed the channel to stiffen that cover due to the access hole and bolt arrangement.

If that is the interference that you are having, we can see about adding channel.

I'm adding one now. I'll send through my version in a short while.

Channels added. STL could do with a cleanup though.

Added your covers to the files.

First thanks for your work. Second is it normal the belt isn't parrallel ? Can it cause geometry problem with my print ? I use the standard prusa 16toorh pulley in the motor and an e3d 20t idler. The belt on the motor side isn't parrallel even when using the lower belt path.

A small amount of belt up/down tilt won't make much of a difference. If the top belt segment (the active one) tilts greatly, printing linearity at extreme leftward travel may suffer. The Prusa scheme for adjusting belt tension normally shifts the belt slightly downward as you increase tension. Short ears x-ends change tension without shifting up/down.

Can you post a pict showing how much the top belt is pulling up/down?

I measured a 1.5mm difference . Will post pics when my print is over .
12mm from rupper rod to top of the belt on the left side (motor)
13.5 from upper rod to top of the belt on the right side(x Carriage)

Hmmn. Not sure if we should do anything. Rechecked the Universal x-carriage and Prusa x-carriage CADs. There is a 0.54 mm difference in how far they space the belt from top rod. However, the Universal x-carriage is 0.54 mm CLOSER to the top rod. The Prusa carriage would have the belt even farther down.

Your picts and measurements show the belt is LOWER (farther from rod) than needed for perfectly parallel with top rod. Matching with Prusa x-carriage dimensions would worsen things. We already pulled the path upward as far as possible without excessively thinning the holder for the Bear (upper) belt path.

I don't think the 1.5 mm will make much of a difference in your prints, but if you really want it super aligned, I'd swap out the x-ends to the short ears and use the top belt path. That combination is the most accurately aligned belt path.

1.5 between belt and top rod or legs of belt? The distance that matters is top rod to belt being different at left end of travel vs mid travel. If that is 1.5 mm, then the effect on print linearity will be minimal.

Top rod to top belt .

On the drive side I get around 0.7 - 0.8mm difference, with the Prusa being lower than the BNB Universal. On the idler side BNB is around 1.3mm lower (which is the side that looks really wrong). The Prusa belt path is asymmetric, with the belt clamps at different heights on each side of the carriage to account for the different pulley diameters. I don't think it will affect the print or print dimensions at all. The belt from the carriage to the motor controls dimensions and it looks fine.

I've printed all of the parts for the Short Ears extruder and your x-carriage, thanks for the work that went into this! I have one question on the x-carriage - what's the reason/purpose for the ridges at the center of each of the bearing cavities?

Thanks!

The ridges allow bearings to find their own self-alignment as the carriage backs are tightened. This was particularly needed if the carriage is printed in a stiff material like polycarbonate. Without the ridges, final bearing alignment is determined entirely by the printed carriage which typically would put the bearings out of natural alignment. Bearings were thus likely to bind as cover screws tensioned. The ridge allows bearings to self-align until they lock into position at increased screw tension.

Please do remove any rough, high points on the ridges for best effect.

Would you considering shortening the bottom cover somewhat to expose the belt? This would allow belt maintenance/replacement without having to remove the cover. vekoj did it in https://www.thingiverse.com/thing:3560116

Thanks!

X-Carriage for Bondtech Prusa Extruder MK3(+MK3S Add-on) (Revised X-Axis)
by vekoj

As requested, look in the files for

BNB Universal Bear or Prusa x-carriage short bottom cover (BNB9S)

These bunnies are incredibly swift and hard-working. Thanks!

Hi;

A question has come up asking if this has passed calibration?

Thanks

I've only tested with Bear and BNB extruders - yes. Will pass calibration. The Bear and Prusa axes differ only in their belt placement. The rod to extruder and PINDA position doesn't shift. So you can pass calibration on either axis. Where you WILL run into calibration problem is moving back and forth between short body (MK3S) and std body (MK3/Bear) style extruders. If the firmware isn't expecting the change in Z travel, calibration will fail regardless of the carriage.