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Idler pulleys with spacers between their bearings..???

Posted by incognico 
Idler pulleys with spacers between their bearings..???
August 22, 2016 03:41AM
Hi folks,

Just wondering if anyone has come across a source of GT2 idler pulleys, with -

- decent bearings that aren't notchy, noisy, or grind straight out of the box
- a spacer between the inner races so you can actually tighten a bolt against them

The ones that seem to be all over eBay (sample image below) don't meet either of these criteria confused smiley (Well, to be fair, about half of the ones I got had bearings that ran smoothly).



I've tried a forum search with very limited success - apologies if I've missed this info somewhere else.

--Nick
Re: Idler pulleys with spacers between their bearings..???
August 22, 2016 09:06AM
I haven't seen any that come with a spacer between the bearings. That's one reason I just use flanged bearings instead of those pulleys.

For 9 mm wide belt, a pair of F608zz bearings stacked back to back makes a very good, 22 mm dia x 11 mm high pulley. A pair of F6903zz bearings makes a good 30 mm dia x 11 mm high pulley. If you want to use 6 mm belt, or prefer to use a larger or smaller axle (usually a shoulder bolt or similar), there are plenty of other standard sized bearings that will do the job, You still have to be careful not to use oversized washers with them.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Idler pulleys with spacers between their bearings..???
August 22, 2016 10:10AM
I have the same problem, order several of these pulleys from ebay and the quality is pretty poor.

In my case i will go with 12 flagged F695zz bearings for 6mm belt and 2 of this crappy pulley with 20 teeth. The two belt will be on the same plane and i you use the twist solution, so the belt teeth will touch the pulley only on two of them.
For the cheap pulley i found a solution that solve most of is problems, i can post a image later of the solution if you want. But this solution is still not 100% and bearing are better secured. I still have in consideration a second solution to remove the pulley and use bigger flagged bearings in case the pulley do not work like i want.
Re: Idler pulleys with spacers between their bearings..???
August 22, 2016 02:50PM
Can't help with toothed idlers but for smooth idlers, I use these which fit the bill for twin bearings with a spacer. [openbuildspartstore.com]. I throw the bolt away as I prefer to have the idlers supported top and bottom so I use a longer bolt. They are very light weight so a good choice on the ends of axes which need to move.
Re: Idler pulleys with spacers between their bearings..???
August 22, 2016 06:27PM
Re: Idler pulleys with spacers between their bearings..???
August 22, 2016 06:50PM
Re: Idler pulleys with spacers between their bearings..???
August 23, 2016 03:15AM
Here's what I got recently and they work:

[sg.misumi-ec.com]?

I agree about the quality of the bearings in these pulleys, but I really want to use them as I want to run toothed pulley on toothed belt and vice versa.

And damn those delrin idlers look better.....plus I could use a (quality) 6mm bore bearing with makes it much easier to use a standard shoulder bolt.

Is there any real downside to running a smooth idler on the toothed side of the belt in a corexy gantry?

Edited 1 time(s). Last edit at 08/23/2016 03:56AM by hobbymods.
Re: Idler pulleys with spacers between their bearings..???
August 23, 2016 12:06PM
I run the tooth side of GT2 belt on a smooth pulley made from stacked bearings (F625zz IRIC, 16 mm dia) in the X axis of my printer. I see no difference between the X parallel surface of prints and the Y parallel surface that is driven by a precision ground ball screw.

SDP/SI says smooth pulleys in contact with belt teeth should have equivalent 40 tooth pulley diameter which is about 25 mm for 2mm pitch belt.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Idler pulleys with spacers between their bearings..???
August 23, 2016 01:07PM
Quote
the_digital_dentist
I run the tooth side of GT2 belt on a smooth pulley made from stacked bearings (F625zz IRIC, 16 mm dia) in the X axis of my printer. I see no difference between the X parallel surface of prints and the Y parallel surface that is driven by a precision ground ball screw.

SDP/SI says smooth pulleys in contact with belt teeth should have equivalent 40 tooth pulley diameter which is about 25 mm for 2mm pitch belt.
Well, a 40-tooth pulley is still quite a bit bigger than a 20-tooth one, so a toothed idler is still a preferred option if space is of concern.

Are those Chinese ones just coldpressed together?

Edited 1 time(s). Last edit at 08/23/2016 01:07PM by Mikk36.
Re: Idler pulleys with spacers between their bearings..???
August 23, 2016 05:59PM
Information overload....

I based my whole design on 20T timing and idler pulleys.

I made sure I had toothed on the toothed side and vice versa, but now am reading that the idlers should be at least 1.5 times the dive pulleys diameter.

For me it makes sense at a glance, but I'm buggered if I can find anyone with 30T smooth and toothed idlers.

I'd probably be prepared to go with 20T drive/30T idlers, or even 16T drive/32T idlers.

Anyone with links/suppliers?
Re: Idler pulleys with spacers between their bearings..???
August 23, 2016 11:05PM
Quote
hobbymods
Information overload....

I based my whole design on 20T timing and idler pulleys.

I made sure I had toothed on the toothed side and vice versa, but now am reading that the idlers should be at least 1.5 times the dive pulleys diameter.

For me it makes sense at a glance, but I'm buggered if I can find anyone with 30T smooth and toothed idlers.

I'd probably be prepared to go with 20T drive/30T idlers, or even 16T drive/32T idlers.

Anyone with links/suppliers?

20 tooth idlers are are fine on the toothed side of the belt and 20 tooth size smooth idlers are fine on the smooth side of the belt. Only if you want a smooth idler on the toothed side of the belt does it need to be 40 tooth size.
Re: Idler pulleys with spacers between their bearings..???
August 24, 2016 12:51AM
Nice - lots of thoughts and info coming out here.

To those of you who have tried affixing an idler pulley with no top support (ie, the top of the idler is held in place only by the mounting bolt, not by a top bracket)...

...would an idler pulley with an internal spacer between the bearings so you could crank down the mounting bolt "tightly" improve the solidity of this approach? Or is the flex that I have read about on this forum coming from the (let's say M5) bolt itself?

My design would have this bolt going into one of the linear carriage mounting holes, which is several mm of threaded steel - not a T-nut or similar.

An opinions? Is it worth me pulling out a bearing and inserting a spacer inside the idler so I can torque it down properly, or should I just bite the bullet and design in a top support for the idlers?

--Nick
Re: Idler pulleys with spacers between their bearings..???
August 24, 2016 04:23AM
check the youtube video i have posted. it use a crappy 20T pulley, M5 bolt with a small head and a reversed M5 screw with nylon lock. With this solution you can secure the M5 screw very well on the mounting hole, the force is directly apply to the M5 nuts and not the pulley. the only downside is the need to have 5mm gap between the pulley and the mounting hole.

Edited 1 time(s). Last edit at 08/24/2016 04:23AM by filipeCampos.
Re: Idler pulleys with spacers between their bearings..???
August 24, 2016 08:42AM
Public service announcement from the "doh!" department:

I've been struggling to sort out a problem with a Solidoodle printer at the makerspace and finally realized its cause yesterday. The problem was that solid infill such as that done in the first few layers of a print was coming out with gaps between the lines. Careful observation found that the printer would lay down a line, then back-track over the same line instead of shifting to lay down a new line. Video here: [vimeo.com]

It turns out the X axis motor mount is tilted slightly- it looks like the belt tension caused the 3D printed, ABS motor mount to warp. I believe the angular contact between the belt and the pulley caused the pulley teeth to grind the belt teeth. The result is that the X axis is unresponsive to small movements- such as the offset that occurs when doing solid infill. A friend at the makerspace wrote a couple snippets of gcode to wiggle the extruder back and forth by 0.2 mm and we found that the X axis motor was responding normally but the belt, and so the extruder carriage, wasn't moving at all. Stepping the wiggle up to 0.5mm got the extruder carriage moving again. Inspection of the belt found the teeth flattened, like the tips were ground off. The temporary solution is to replace the belt and shim the motor mount to upright the motor. I'll be designing and printing new components for the Y axis and extruder carriage, and eventually may replace all of that stuff with aluminum parts (new CNC Tormach mill at the makerspace to try out!).

There are several lessons here:
1) 3D printed parts in 3D printers often suck, especially if they are exposed to belt tension and heat.
2) you must keep the pulley/drive gear axles perpendicular to the belt path.
3) if you have 3D printed parts in your printer, you have to inspect things carefully on a regular basis
4) with all the pulleys in a CoreXY machine, it might be best to use smooth pulleys instead of toothed pulleys, especially if you can't guarantee that the axles are all going to remain vertical.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Idler pulleys with spacers between their bearings..???
October 26, 2018 12:15AM
Sorry to necro-post but I was looking for an answer to this for some time before I found one so I thought I'd share.

These worked well for me: [www.amazon.com]
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