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Changing from MXL to GT2 belts? And other XY goodness

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I searched the forum and couldn't find anything related to using GT2 belts so I thought I would ask. I'm considering doing some upgrades to my XY gantry and was wondering if this was a worth-while upgrade. GT2 belts are supposed to have significantly less backlash than MXL and should also yield greater positional accuracy. I will be printing these replacement XY blocks with built-in tensioners


Probably converting to direct drive and also replacing the 8mm brass bushings for proper bearings. I've found a source of 20 tooth GT2 pulleys with both 8mm and 5mm bores and two set screws rather than just one. (Obviously the 5mm bore pulleys won't be needed if I go to direct drive).


Any thoughts, recommendations, warnings? :)



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I did some quick back of the napkin calculations with both the MXL and the GT2 pulleys. The only thing that should need to change in the firmware is DEFAULT_AXIS_STEPS_PER_UNIT. My calculations for the stock MXL pulley arrived at the correct default value of 78.7402. The GT2 pulleys have a metric pitch of 2.0mm (vs 0.08" or 2.032mm for MXL). When you compute the steps per unit for that pulley pitch you get a nice round number of 80 :) I think I might go ahead with this upgrade. The other parameters of the belts are close enough to not matter (6mm width vs .25" or 6.35mm) I can also source belts in a variety of lengths so I can get a tighter belt to avoid taking up too much slack with the tensioner.

I'll report back how things go.



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Not sure you can upgrade the 8mm bushings.

Most bearings are designed to be linear or radial but in this

application they would need to be both as they slide back and forth

on the rod as well as the rod rotates radially.

I think you'd only see an improvement in belts if you upgraded to a wider

belt. A wider belt would vibrate less and be less prone to stretching.


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I've found a few bearing manufacturers who sell linear bearings with ceramic or other materials for the friction surface rather than ball bearings. I'm going to contact one of them today via email to request additional info. From this page:


"Simultaneous linear, oscillating and rotary motion in 1 bearing"


"Linear & Rotary Motion Together are Required"

So.. sounds promising. The page is a bit confusing (they use the product name for a different bearing at one point) so I will be requesting additional information.

With regard to the belts, my thinking was that GT2 belts and pulleys are designed to have less backlash and to work in both directions. MXL timing belts are really designed to just run in one direction and are not optimized for the rapid back and forth movements we subject them to in our printers. Of course, it's also possible that the accuracy difference between the two belt systems is small compared to other accuracy limitations in the mechanics of the printer so no net improvement would be observed...



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I made this upgrade about a month ago, and am appreciating it more and more as I use the machine next to others which haven't been upgraded.

XY motion by hand is much, much smoother - and much easier - at the same belt tension as well-functioning (ie concentric) Ultimaker MXL pulleys. The prints that come off of this machine are definitely much better prints than the ones that come off our other two Ultimakers with MXL pulleys. The printhead is different though, so it isn't a direct comparison, but the XY system is helping, no question.

Another major advantage is sound - the machine is much quieter using GT2 vs. MXL.

As I've said in other posts, the biggest reason to upgrade is simply the fact that Ultimaker's stock pulleys have some pretty sloppy tolerances and can be extremely eccentric, but I think the other touted benefits of GT2 (lower backlash and smooth, silent motion) are probably worthwhile.


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I found this spreadsheet from this forum: https://docs.google.com/spreadsheet/ccc?key=0Asw52Abkg8IIdEF6d0lBZ2poOC0xU3VPTXM4TlVGRkE&usp=sharing#gid=0

That great part list encouraged me to do my own ultimaker 3d printer. I have now ordered nearly every parts for that project.

Few days ago I notified that original belts are xml and I have ordered gt2 pulleys. It's not bad thing at all because you can see: http://reprap.org/wiki/Choosing_Belts_and_Pulleys

So...Gt2 pulleys and belts should work fine but I have no idea how long those belts should be. Only Gt2 belt which I now have is "Closed-loop GT2 Belt, 101 Teeth 202mm Long". What are those other gt2 belts which I will need in my project?

Any ideas?


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