X-bar clamps snapping, and X belt tension - A proposed solution.

I have 2 "official" Mendel90s from nophead, and have built another 6 machines.

The bar clamps consistently snap when tightened enough to hold the bars firmly enough to tension the X belt appropriately. Even when "quite tight" the clamps can't resist the tension applied by the belt, this pulls the X-Idler out of square, so the belt runs forward onto the idler fender washer where it rubs. This is with degreased rods. You can shim the rear fender washer to push it back into square, this does help but it's a bit hacky.

In the past I have used a lathe to add a knurl to the ends of the rods that help the clamps grip, so you don't have to tighten them up so much. This works, but in terms of a solution it's not for everyone, and certainly wouldn't suit nophead for a mass-production solution as it would add a huge machining cost.

I propose replacing the clampy-screw-arrangement with a simple box around the end of the rod, which traps a nut, and allows you to clamp the rods with a grub screw (or indeed two grub screws per rod end). Just like how printed pulleys are attached. This would mean all the clamping force is planar with the layers, so you wouldn't have to worry about delamination - which is the failure mode of the current clamps.

Another idea is to add a trapped nut and screw that pushes the threaded end of the idler bearing bolt, thus changing it's angle to make the belt run tram.

I'm using my machines for production at the moment so can't have any downtime to test these ideas out, but I thought I would just throw it out there and see what people think.

Edited 1 time(s). Last edit at 08/02/2013 08:42AM by SanjayM.

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I Design/Sell all-metal hotends. My company is called e3d-online - you can buy at [www.e3d-online.com]

This seems to be a recent problem. I still have an early kit which has run 24/7 and the belt is tight and the clips are intact.

Either the belt has got less flexible or, more likely the clips have got weaker. Since they are printed with the same gcode I think perhaps the plastic bonds less well than it used to do. My supplier changed from GEHR to Orbitech ABS. It looks the same but is definitely a different plastic because it has less die swell.

I will have to experiment to make them stronger again.

I don't understand how grub screws would not push the layers apart? They would have to be vertical to have room for the nut. They would then be like the original Prusa Mk1 x-ends which did not work well. They did use ordinary screws rather than sharp pointed grub screws though.

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[www.hydraraptor.blogspot.com]

My intention was that the screws would be horizontal and could be accessed though the belt. Looking at the machine next to me and holding a nut up to the clip there seems to be enough room, but it is marginal. I expect you could have a small boss that the nut sits in.

Edit, just to give you some data, on the two machines you supplied as kits, only one of the 8 clips has not snapped. The belt runs forward and rubs the fender washer on both machines. One I have shimmed with the polyprop so it only just barely runs forward, I should shim it more, and shim the other machine too, but both are running fine and I can't have any downtime.

Edited 1 time(s). Last edit at 08/02/2013 12:26PM by SanjayM.