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Bed_Hoist_for_a_3D_Printer_ (D-Bot, Core_XY)_-_Version_2

by printingSome Feb 14, 2019
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I had a similar problem with a cheap set of worm gears. See https://drmrehorst.blogspot.com/2018/04/designing-low-cost-printable-worm-gear.html

I used an industrial surplus Rino 30:1 in my printer and it works perfectly. It cost about $108 via ebay, but you get industrial quality motor, gears, and bearings all mounted in perfect alignment in a sealed, solid metal package. You can't buy the parts cheaper.

I see a couple other problems with the construction of the belt lift, too. The motor mount looks very flimsy. The gears are going to be pushing on the motor shaft and will flex the mount the way you have designed it. The idler pulley mounted at the bottom of the frame appears to be printed with horizontal layers. The force from the belt is working to pull those layers apart, yet the pieces that hold the bearings have very small connections to the base of the part. All that needs to be made more solid. I'd probably put the screws that hold it onto the frame member on the outside of the belt tensioning screws so you can adjust the position of the pulley after the belt is installed.

The belt clamp design isn't good. I used a similar design in my printer and it failed. The belt will stretch over the cords in its core. The belt needs to be folded/bent to prevent that. See: https://drmrehorst.blogspot.com/2018/12/another-interesting-3d-printer-failure.html

Thanks a lot, Mark, for your extensive comments and the links to your ditto webpages.
Coincidentally I saw both of them a couple of days ago, the same day of my last edit, I think.
When I saw your ribbing, bulges, whatever, the same as my waves, it confirmed what I had found. I only doubted whether it was inherently a thing of the worm or more a fabrication error, as I wrote. The fact that your Rino performs perfectly and does not have those artifacts means I can forget the inherent cause.
I found similar graphs in https://www.witpress.com/Secure/elibrary/papers/LAMDAMAP97/LAMDAMAP97025FU.pdf, but there is talk of micrometers, a different kettle of fish, I suppose.
A quick look at ebay revealed one which was a lot dearer, alas.

Your belt damage is not a pretty sight at all.
I seems to be a matter of steel cores slipping out of their environment and your solution of curving the end makes that a bit less easy. I saw similar solutions for the X-belt in my hesine printer and its likes.

The 6mm belt coupler I used in the first Bed Hoist, which had 2 parts, performed well. It had room for 9 teeth for each of the belt ends, which is a bit better, and it didn't have the full load of the bed.
The belt clamp I use here does have the full load at one side, so it is something to keep an eye on (when I keep using this hoist, which I don' t know yet), though certainly with a 10mm belt I still have confidence in it. If I would doubt it I would lengthen the grip at the upper end, not use a curly end, because I need to be able to manually adjust the belt. I used a 6mm belt for a while in this construction, which did not show any aberrations, after I replaced it with the 10mm belt, but that was too short a time to make real conclusions from it.
I don' t use steel belt cores, but I feel that it would be a good advice to have the belt stick out a good bit, so there is more length/resistance for the fiberglass cores to overcome when they feel the need to leave. The straight clamps I used in the hesine (reprap-like) had longer gripping lengths too.
Did you happen to see similar damage with clamps used in the original D-Bot (or in mine at one end) for the X-Y-belts anywhere? There they have to deal with those acceleration forces etc. and I never saw complains about those (not that I looked for them).

I feel that the motor mount itself is rather robust, but I indeed had some doubts whether the flangemount mounts would be strong enough. I felt that they were for the downward force but was not absolutely sure about the sideways force from the worm drive, which is why I made the side where the slot for the axis is 3mm thick. Decisions, decisions...

Great tip about layers versus the forces, which indeed would like to pull them apart. Certainly something to reckon with.
Luckily the forces here are so small (have to be less than the force on the belt between bed and upper pulley) that I really have no fear at all. 5mm thick, well, that is as much as the parts that hold the printer together. In the Notes I emphasize that, it just serves to keep the belt tight against the pulleys, to prevent slipping.
Unless, of course, things would happen in the very long run, but I wouldn't know how much more solid I would have to make things for that.

Of course you have a point with the screws but until now I never felt the need to adjust that position, given also the mark I made on it, and I have often adjusted the other parts with my trying out things. It was a conscious decision, but still...

Obviously you are much more professional than I am and it is good to be forced to think things over again, so I am grateful for your comments and I am happy to give you my reasons for what I did.
Edit: slight, not substantial text-changes.
Edit: some doubtful text removed.