gears not working with belts

So I thought I'd be able to start putting all the parts I've printed/purchased for a Mendel, but I noticed that most of the gears aren't meshing properly with the belts. The build file spreadsheet specifies 5mm or .2" belts and I know the belts I got are .2" pitch because they have exactly the right number of teeth for a given distance.

The gear that seems to work is the drive-pulley_3off and the z-drive-pulley_2off doesn't work; they're here [reprap.svn.sourceforge.net]

Neither of these alternative gears mesh properly either
set-screw-drive-pulley_4_6-5_9_7_3off
set-screw-drive-pulley_7_9-5_13_7-3off
[reprap.svn.sourceforge.net]

From wrapping a piece of paper around the gears the alternate drive pulley seems to be 6 teeth per inch and the Z pulley seems to be 5.5 teeth per inch. Is it possible the 3d files are being improperly scaled? And, if so, what are the dimensions supposed to be?

It is difficult to measure the pitch of the pulleys as the teeth of the belt get closer together when they bend round a small radius. To get the accurate dimensions you would need to look at the drawings for metal pulleys.

I use these [www.thingiverse.com] and these [www.thingiverse.com], which have the same pitch as the originals that I based them on. They mesh with 5mm pitch belt, so they wont be correct for 0.2".

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> They mesh with 5mm pitch belt, so
> they wont be correct for 0.2".

Okay, so, in the Mendel build file where it says "RepRap attempts to print its own parts wherever possible. This includes toothed drive pulleys. 5 mm pitch (or imperial equivalent XL pitch, 0.2")" it doesn't actually mean you can use .2" pitch belts?

I rescaled the offending pulleys until they reached the correct number of teeth per inch. Can I use the slightly off-sized gears by adusting the constants in the software? I figure I'm gonna have to do that anway since I'm using 5/16-24 threaded rod instead of metric.

Any help I can get here won't go to waste. I'm trying to put together a complementary build file for those of us in the States who don't feel like paying 10 times as much for metric parts. So far some stuff is pretty straight forward. 5/16 is a nice equivalent to 8mm, and 6-32 seems to be a reasonable replacement for m3/m4, but those are structural parts. The positioning parts, like threaded rod and belts/gears are being more difficult.

5/16-18 would be a better pick for the Z. You really don't need the extra resolution, and the extra speed may come in handy.

5mm is .236", so .2" is almost certainly close enough. The toothed pulleys should seem to be less than that though, as the belt's length is measured (sorta) from the steel reinforcing wire that runs down its back. That wire is going to be held off of the pulley's surface some, and all the teeth are going to squeeze together as it wraps around the pulley. So the "nominal" circumference (#of teeth times teeth-per-inch) is going to be somewhat larger than the actual gear should be.

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I'm building it with Baling Wire

I think 5mm is 0.197", which is even closer, which is why I thought maybe the files were slightly off scale or something. It doesn't seem like it should be a significant enough difference for a properly sized 5mm pitch pulley to not work with a .2" belt. But after scaling them up until the belt meshes the teeth are still thin enough that they can leave some play.

So, maybe the standard Mendel timing belt pully files are optimized for a different belt geometry than I got.

Based on the assumption that the belts I got have a different geometry, I ran a few iterations of Erik's parametric timing pully script and ended up with a pair that fit the belts perfectly. For what it's worth, the belts I have say "Gates Powergrip" on the side.
[www.thingiverse.com]
[www.thingiverse.com]

I have had trouble with the pulleys too on my Prusa build. Unfortunately, there is such variation in print size with skein settings, that it is very hard to say whether a particular file is "good". I can get a particular stl to do almost anything in real life depending on what my skein settings are. Also there is a lot of tweaking of stl's to account for hole shrinkage, etc. so the stl's may not even have the nominal size that is needed in real life. I have yet to print a pulley I am satisfied with. I can get some that fit the belt, but they are not solid, the solid ones don't fit. I'll probably end up scaling the stl for use my printer, but I doubt my scaling will work for anyone else. It would be nice if there were some part specific guidelines for the tight tolerance parts like the pulley. Anyone get it to work well? Wanna share? What skein settings work for the prusa pulley?