Y Belt Rubbing Solutions

Hello MarkerFarmers!

1stage and I were discussing a common issue we were having where, despite our best aligning efforts during the build, we can't seem to get the Y belt to stop rubbing against the wall of the captive bearing mount in the front of the printer.

One thing I was thinking of trying is to add wedge shaped washers that I would print out and press fit over the bearings to force the belt away from the wall.

Have any of you guys been able to solve this problem?

Enjoy as I attempt to draw my idea in ASCII for great justice! :P

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So you've tried adjusting the tightness of the bolts holding the pulley clamps to the front plate? Adjusting the angle of the bolt with respect to the belt should affect where the belt rides. My pulley clamps were glued in place prior to assembly, so all I could do was use a round needle file to ream out the bearing bolt hole in the side opposite from where the belt tended to creep to. It's still not perfect, but it helped.

The way the belt can rub against wood is kind of rinky dink. At least on the X idler you can adjust the angle of the bearing bolt pretty easy and adjust where the belt rides. I still hope to eventually retrofit something like what you're talking about to both the X and Y idler.

I slotted the bearing mount hole and added some eye bolts to adjust tension and alignment.

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Originally Posted by gmay3

Hello MarkerFarmers!

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One thing I was thinking of trying is to add wedge shaped washers that I would print out and press fit over the bearings to force the belt away from the wall.

Have any of you guys been able to solve this problem?

Enjoy as I attempt to draw my idea in ASCII for great justice! :P

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|==|/++\|==|

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Originally Posted by beerdart

I slotted the bearing mount hole and added some eye bolts to adjust tension and alignment.

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Originally Posted by printbus

So you've tried adjusting the tightness of the bolts holding the pulley clamps to the front plate? Adjusting the angle of the bolt with respect to the belt should affect where the belt rides. My pulley clamps were glued in place prior to assembly, so all I could do was use
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So I don't have a MakeFarm printer.... But it is RepRap. Can't you just print yourself an updated part and make the problem go away?

You might try this http://www.thingiverse.com/thing:45955 I'm assuming that you have washers on either side of idler bearing and they don't move. I don't have my prusa i2 anymore but I never could get the thing tensioned and adjusted to stop the belt from rubbing against the washer which remained stationary.

Thanks for all your replies! Sadly, I'm not able to get it aligned with the parts supplied.

I think I'm going to try the pressfit print you are suggesting KDog. If that works I will update this post with my a solution process.

If a printed part press fit over the bearing doesn't work I may redesign the bearing mounting parts in place of the wood ones so they are more adjustable like you suggested beerdart.

Can you post the .STL files of the parts where the problem manifests itself? And a good picture would be helpful too. Almost for sure a small change in the source code would address the problem. And if so, you just print a new part and put it on your printer.

Good topic gmay3, and good question, Roxy. I have a few things to print tonight, so I'll take some pictures and maybe video of the problem.

So far, there's been no fraying or damage to the Y belt, but there is a noticeable U-shaped scuff on the left wooden laser cut arm of the Y idler. I print at least four 60-90 minute jobs a week, and I built the i3v in early April 2014, so that should give you a gauge of my usage.

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Originally Posted by Roxy

Can you post the .STL files of the parts where the problem manifests itself? And a good picture would be helpful too. Almost for sure a small change in the source code would address the problem. And if so, you just print a new part and put it on your printer.

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Here's a pic that shows the Y idler and how there's nothing to keep the belt from rubbing against the i3v's wooden brackets. I measure about 10.5mm spacing between brackets.. I'd like to find something like this idler pulley, but it'd have to be sized for the smaller MR125 5x12x4mm bearings used in the i3v. We don't have the vertical height needed for the larger 625 5x16x5mm bearings used by that pulley without notching the main frame panel a bit.

EDIT: Frankly, I think another flaw in the design of the i3v is the way the i3v idler is mounted to the flat side of the veneered MDF material. The slightest amount of flex in the forward plate will have a significant effect on the belt tension. I encourage those with an i3v to observe how the Y-belt sags when you press even slightly on the front of the idler plate. Whatever idler system I retrofit will likely also add a brace across the forward plate to keep it from flexing. There's a similar concern with the Y motor mount at the rear, but there the motor at least has an added brace that will provide some partial support.

Hmm. The thing I'm worried about with adding a GT style (smooth or toothed) adapter to the idler is that it changes the diameter of the bearing which will cause some inaccuracy. I wouldn't have to want to tweak the firmware steps more unless necessary.

I think I'm going to design two rings and will be press fit over the bearings which will hold the belt on the left and the right side. This way the belt still rides on the bearings in the center and it will just be held in place.

Quote:

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Originally Posted by printbus

Here's a pic that shows the Y idler and how there's nothing to keep the belt from rubbing against the i3v's wooden brackets. I measure about 10.5mm spacing between brackets.. I'd like to find something like this idler pulley, but it'd have to be sized for the smaller MR125 5x12x4mm bearings used in the i3v. We don't have the vertical height needed for the larger 625 5x16x5mm bearings used by that pulley without notching the main frame panel a bit.

EDIT: Frankly, I think another flaw in the design of the i3v is the way the i3v idler is mounted to the flat side of a piece of plywood. The slightest amount of flex in the forward plate will have a significant effect on the belt tension. I encourage those with an i3v to observe how the belt sags when you press even slightly on the front of the plywood plate. Whatever idler system I retrofit will likely also add a brace across the forward plate to keep it from flexing. There's a similar concern with the Y motor mount at the rear, but there the motor at least has an added brace that will provide some partial support.

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So I think what you are saying is you want to print up a pair of these pulley bushings that are the right size and put your bearing inside it???

Check out the attachment in Open_SCAD. This is what is used on my i3 printer to keep the belts aligned.

gmay3, adding a GT2 adapter (like you linked to) shouldn't affect the accuracy, so long as you re-tension the drive belt.

But I'm wondering, isn't there a real, machined GT2 bushing/pulley/bearing that exists? If it's one with guard walls, it may be easier to alleviate the problem at hand.

As to the core design problem with the Y-idler belt rubbing, I think the mounting brackets on the bottom of the Y-bed are what's out of alignment (shifted to the LEFT of the i3v), as I've had to move the GT2 driver further to the end of the shaft on the stepper motor to compensate. This makes the problem on the Y-idler even more pronounced, as now both the bed and stepper are 2-3 mm further to the left.

I wonder if adding some thin O-rings to the edges of the bearings would be enough to keep the belt in check.

Ok so here is my solution.

Looking from the top, my belt was rubbing on the left side of the bearing bracket.

Step 1: Loosen the right bolt about 3 full turns.
Step 2: Insert as much of a Medium Fender Guitar pick behind the now loose wooden part.
Step 3: Tighten the bolt.

Attachment 1644Attachment 1643

My belt is running smooth now!

And? How's it working now, gmay3?

1stage, I haven't ran the printer since the fix, BUT to confirm the belt was staying in the same place I disabled the steppers and moved the heat bed back and forth fully several times. So, I'm relatively sure it is all fixed now.

Thought I'd add this i3v Y-idler belt guide I ran into on Thingiverse - http://www.thingiverse.com/thing:359773

Very cool, I have added that to my things to make on thingiverse. That's exactly what I was looking for. Thanks printbus!

I recently printed a pair of the Y-idler belt guides and installed them today. In addition to putting one on the Y-idler, I also put one on the X-idler. I think these are perfect for the job. I used a total of three M5 washers, one as a spacer between the two bearings and then one outside each bearing. The washers on the outside of the bearings provide just enough clearance for the pulley sidewalls. On the X-idler, I swapped out the MakerFarm wood "washer" for the same three washer approach and an M5 Nyloc nut.

Two cautionary notes - you'd want to make sure the teeth of the pulley print clean to minimize "noise" in your prints, and you may have to extend the length of the belts some to accommodate the increase in diameter of the pulleys.

These are definitely something every i3v should have, if nothing else just to improve the design quality of the machine.

Adjusting the screws on the Y idler to adjust the angle works fine, but leaving one screw slightly loose isn't very satisfying. If you're using Slic3r and have it set to print loops around the part, you can peel up these thin bits of plastic and use them to shim one side of the Y idler. I just put one sliver in behind the right-hand piece of wood and snugged down the screw. You can tighten the screw to crush the plastic to get it to the angle you need without leaving the screw loose.

For bonus points, you can fix the belt rubbing on the wood part at the front of the X idler as well by using longer screws and an extra nut where the belt anchors to the X carriage. The stock bolts just aren't long enough to get the belt deep enough between the extrusions to not rub on the wood. You'll need to adjust the position of the X motor pulley slightly, too. If you can sight down across the front surfaces of the X extrusion from above and you can see the belt, it's too far forward.

All of that said, the rubbing doesn't really cause any problem, as far as I can tell.