Double-thick Idler Wheel?

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Marty McGuire

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Aug 18, 2009, 8:54:01 PM8/18/09
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Hello,

I'm going through the extruder part of the build for MakerBot #131,
and I noticed a couple of things.

The instructions show that an idler pulley should be made by gluing
together a bearing and a single Idler Wheel laser cut piece.

However, my kit came with 2 Idler Wheel pieces, and according to the
"Filament Slipping Off Idler Wheel" section of the "When Things Go
Wrong" page (http://wiki.makerbot.com/when-things-go-wrong), a double-
thickness Idler Wheel "was easier to position and worked perfectly the
first time".

Does this mean that the double-thickness is now preferred when
constructing the idler wheel? If so, how does that change the
instructions for that step? I am trying to be careful here because
super glue is tough to undo. :)

Thanks,
Marty

Nick Ames

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Aug 18, 2009, 11:24:24 PM8/18/09
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Not having any superglue, I used hot glue to affix my idler wheel to the
bearing. There doesn't seem to be any functional difference, but I don't
know how well it will work in the long run.

Zach 'Hoeken' Smith

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Aug 19, 2009, 11:51:20 AM8/19/09
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I can't personally vouch for that technique, as it was a customer contribution, but its worth a shot.  If you follow the instructions exactly and use 2 M8 washers as spacers, the idler wheel is exactly the right spacing on the 608 bearing to be in the middle of the pinch wheel.  Also, the metal pulley needs to be as far down on the shaft as possible.

The downside with using both is that if it doesn't work for you, you're out of pulleys and have to bug us for another one or find someone with a lasercutter and 3/16" acrylic.

Jonathan Mayer

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Aug 19, 2009, 12:04:18 PM8/19/09
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Ahoy,

I was the contributor of the double-wide idler wheel suggestion.

My experience was that the single-wide idler wheel was touchy.  I spent a fair amount of time fine-tuning the spacing, and still got occasional ruined builds.  The double-wide idler wheel was my "cut the gordian knot" solution, and allowed me to ratchet up the tension in the extruder to a point where the filament feed rate was constant, and the filament never slid off the wheel.

So I think the answer you're looking for is:
  1. it worked great for me.
  2. I can't see how it could hurt.
  3. if you are patient, feel free to try the single-wide wheel first, and if it gives you grief you can always switch to double-wide.

Best wishes,

 - Jonathan.

Robert McGuire

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Aug 19, 2009, 12:23:43 PM8/19/09
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Robert McGuire

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Aug 19, 2009, 12:25:15 PM8/19/09
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Argh, I fail at GMail! Sorry for the empty post.

Thanks for all of the feedback! I'm going to give it a shot with the
single wheel and see how that goes. I need to get over my fear of
superglue being impossible to undo. :)

Thanks,
Marty

Bo Lorentzen

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Aug 19, 2009, 12:30:23 PM8/19/09
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Marty,

Superglue is hard on the acrylic and metal, simply lay the assembly on
a flat hard surface and find a bit of pipe which will fit over the
bearing.. a firm tap will separate them.

in case of catastrophic failure I have both acrylic and laser, just
shoot me a email.

Bo

Bo

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Aug 27, 2009, 2:01:06 AM8/27/09
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Possible Double wide idler wheel issue.

Following the fearless leaders, when my idler wheel failed today I
figured "double wide is good" made the sandwich and popped it back
in the system... only to discover that the tooth-wheel in my kit is
TOO narrow for two... and the disc have to push in between the flanges
of the toothwheel in order to create enough traction.

Soo, in the morning Im tossing my new double wide idler on the laser
and engraving a ring on each side for a perfect fit, the final
thickness will be roughly 1.5 single idler - or about 5mm I guess,
the engraved area will be from the edge and roughly 5mm in, I want to
keep full thickness on the rest for better stability. I will upload
a picture once its done.

If the double wide is a future design stable, the engraved edges
could be done in cutting before the kits are shipped at the same time
the text is engraved on the boards. using a double-wide would
prevent as much flexing on the bearing so it could be a good solution.


Bo

Gav

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Aug 27, 2009, 7:27:43 PM8/27/09
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My solution to the slipping issue was to lathe up a not-quite-double-
wide one out of Delrin. (After reading comments suggesting double-wide
versions I made it twice the thickness, then realised that didn't
fit). It's not 100% perfect, but it behaves better than the old one.

Some details here, if anyone's interested:
http://sites.google.com/site/mechatronicsguy/makerbot-troubleshooting
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