Tilted Y axis motor gear

I'm building a Prusa 2 and just finished putting together the Y axis. The gear that mounts to the motor shaft is tilted unfortunately. The gear seems fine, but the hole for the shaft seems to be tilted. This causes the belt to get tighter and looser for every rotation of the gear. I would contact the maker of the kit but I bought it second hand and the maker doesn't seem to be in business any more.

So do you think this will have a huge impact on the prints? It seems that the motor will work and move the Y axis, but it may cause some variation in movement. If it is not too bad I could live with it until I could print a new gear.

Do you think I could straighten out the hole somehow? I could run a drill through it at the correct angle, but then it would be too wide at each end. Maybe the set screw will be enough to hold it well, but I'm afraid it will make it worse. Any other ideas?

Thanks for the help!

Are you talking about the Y-axis pulley? What size belt are you using?

I wouldn't recommend using a pulley that isn't concentric. It would almost certainly show up in a print.

If it's a T5 belt and pulley you're using, I can send you a good pulley in the CONUS. I'm not using the T5 belts anymore so the pulleys are yours if you want them.

Edited 1 time(s). Last edit at 03/30/2013 05:13PM by Knimrod.

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ΜΟΛΩΝ ΛΑΒΕ

Well, I don't know that I'd call it a pulley. The Y axis belt goes from an anchor point on the bed plate around a bearing on one end then all the way up to a gear that is directly on the motor shaft. Then up from there around the near bearing and back to the other anchor point on the print bed. I'm talking about the gear the is on the Y motor shaft. The hole in that gear is not perpendicular to the gear so when it is on the shaft it wobbles a bit as it rotates.

I'm not sure which belts I have (just what came with the kit). They are white with teeth on one side. Probably about 4 or 5 mm wide. I haven't measured them or the tooth spacing. What is the difference in the different belts anyway?

Thanks for the offer, I'm just not sure if it is the right part.

Sounds like the normal toothed pulley. I have a MendelMax and not really sure about the differences but it sounds like the exact same arrangement. The pulleys I have are 10 tooth for a 5mm pitch (T5) timing belt. Like I said, I'll send them and the belts to you if you want them. Let me know.

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ΜΟΛΩΝ ΛΑΒΕ

I'm home now and was able to count and take measurements. It's definitely T5 (5mm pitch tooth to tooth) belt and gear, but the gear only has 8 teeth not 10. It looks exactly like this one: [m-pulley.jpg" target="_blank" rel="nofollow">www.reprap.org]

I can see now that it's officially named a pulley as you say. I normally think of a pulley as a turning point for a belt/rope allowing free movement but not adding drive as in this case. But that's what it says in the official Prusa mendel instructions (where I copied that link). I suppose the 10 tooth would work but I would need to factor that into the settings somehow. Does your pulley look like this one? Thanks for the offer.

It also sounds like people prefer smaller tooth pitch on the belts to get more accuracy? Is that what I'm gathering from some other belt discussions I've seen?. I couldn't ever quite figure it out because I really didn't know the Tx naming. So a T2 would have a 2mm tooth pitch and I could see how that would translate to better accuracy between stepper motor rotation and belt movement.

Any ideas on how to rescue this one? Maybe drill it correctly and then if it doesn't sit solidly insert a drill bit shaft to keep the hole round and put some epoxy in the gaps? Thanks.

Generally, fewer teeth gives you more resolution and more torque. Since you have a fixed number of steps in a revolution, a smaller pulley yields a shorter linear distance per step. However, this extra torque and resolution comes at the expense of backlash and accuracy since the T5 belt is a timing belt and not really intended for accuracy and repeatability in a bidirectional pulley. The rule of thumb here is to have at least 6 teeth in contact with the pulley at any given moment. You can't do this with an 8 tooth pulley. It's probably splitting hairs though as the goal is to get started printing. At that point, you can print whatever gear you prefer. The 10 tooth pulleys worked fine for me. You would need to recalibrate your steps/mm in your firmware (a relatively simple matter) if you change the number of teeth.

Personally, I wouldn't recommend trying to correct your existing pulley as it's likely there will be other issues with it if the hole is not concentric or it's crooked since it was printed as one unit at one time.

Shoot me a PM with an address if you want my pulleys.

Good luck!

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ΜΟΛΩΝ ΛΑΒΕ

Thanks Knimrod. I'd love to take you up on your offer for 10 tooth pulleys (BTW, I discovered that the X pulley is off center in a similar way). I'll send you a PM. With those I should be able to get up and running and print my own 8 tooth ones if I want. Eventually I may move up to T2 setup, but this should get me printing :-). Thanks a bunch for helping me out.