Use pulley as idler

Please leave your thoughts on using a second pulley as an idler in a pulley belt assembly. Obviously it would need to rotate so perhaps attached to a shaft and two bearings. It seems every idler I've seen simply uses a few side by side bearings constrained by washers. Disadvantages to this? Belt teeth wear? Wouldn't think it'd be much worse than the constant flattening a bearing imposes.

Don't think this is a repost per se, as I've searched, but my apologies if it is.

Edited 1 time(s). Last edit at 08/21/2013 06:59PM by DennyCrane.

My simple solution is just to put a half twist in the belt so it has the flat side against the bearings.

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[www.hydraraptor.blogspot.com]

...and mine.

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Waitaki 3D Printer

DennyCrane Wrote:
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> Please leave your thoughts on using a second
> pulley as an idler in a pulley belt assembly.
> Obviously it would need to rotate so perhaps
> attached to a shaft and two bearings. It seems
> every idler I've seen simply uses a few side by
> side bearings constrained by washers.
> Disadvantages to this? Belt teeth wear? Wouldn't
> think it'd be much worse than the constant
> flattening a bearing imposes.
>
> Don't think this is a repost per se, as I've
> searched, but my apologies if it is.




Can't you use shaft Collars?:


[www.ruland.com]

Since your talking idler i am assuming your talking about a full loop of belt on a Y or X axis,. if so, then the length of belt that travels over the bearing idler actually never reaches the toothed pulley. So weather or not the bearing idler flattens the teeth of the belt area that touches it, it has no effect on the belt that touches the toothed pulley. (unless your prone to flip/flopping your belt)

move your axis carriage to one end and put a small piece of tape on the belt near the idler, then move it to the other extreme and do the same,. you'll see what i mean.

The half twist is still a good idea on some printers, but really just to smooth the flow of the belt over the idler.

Edited 1 time(s). Last edit at 12/22/2013 12:12AM by AlexCphoto.

I've had good results using the toothed side of the belt against the idler. If the idler has flanges to keep the belt from running off, the teeth will rub on the flanges and cause noise and maybe wear and artifacts. I printed a crowned pulley to keep the belt on it without the problems caused by flanges.

Crowned pulley: Thingiverse 14117

in industry it is common practice that the belt is run over idlers without teeth. It IS important that the minimal radius of the belt isn't underrun, this would make it wear much faster, but the idlers without teeth are totally ok.

Quote
stahlsau
in industry it is common practice that the belt is run over idlers without teeth. It IS important that the minimal radius of the belt isn't underrun, this would make it wear much faster, but the idlers without teeth are totally ok.

Yes, there were a few times I'd chuck them up in a lathe, and turn down the teeth quickly.

I am sure a bearing is perfectly fine but I opted to use a pulley with two bearings as an idler. I do not think it really makes any difference.

While building my own printer, I started out using a toothed pulley as an idler. I didn't think it would be an issue because thats how the Solidoodle is designed and it works fine.

Eventually I ended up swapping that toothed pulley out for flanged bearings on my machine and it seemed to work better. I think the main reason that worked better had more to do with the way I had idler pulley mounted as opposed to the way I had the idler bearings mounted. I had the idler pulley mounted on a wooden dowel rod that could spin as the belt did. I had the idler bearings mounted on a stainless steel socket head cap screw with nuts on either side of the bearings to keep them from sliding around on the shaft.

At the end of the day you are most likely right about it not making a difference if you use a toothed pulley for a idler or flanged bearings. However, the flanged bearings can be less expensive.

I have been using bearings as X and Y axis idlers in my printer for about a year. I recently put half twists in the belts and found it does make a small difference in print quality, at least with the type of belt I am using. I am using a 5mm pitch urethane belt with embedded steel cables. Before I twisted the belts, when I printed an object with straight sides running parallel to the X or Y axes, there was a ripple in the surface of the object. I believe this is due to a slight variation of the speed of the print bed/extruder as the teeth on the belts struck the pulleys. The slight variation in speed would cause the slight modulation in the width of the line of filament being laid down, ultimately resulting in the pattern seen in the final object. The ripple pattern has all but disappeared since I twisted the belts.

Flanges on the idler are not necessary if your printer frame is mechanically sturdy and the pulley axes are parallel to the motor axes. The belt may wander a little over the pulleys without flanges but will remain on the pulley.

Edited 1 time(s). Last edit at 02/28/2014 12:03AM by the_digital_dentist.