Belt snapped, and you want to keep printing? No problem.

[626Pilot]

The bad news is that new belts cost money and take time to arrive. The good news is that you can get by on a spliced belt in the meantime, even if "the meantime" is measured in months. One of my belts snapped in July or early August, and I immediately ordered a replacement, second day air, because I didn't want the downtime. I needn't have bothered! The spliced belt is still operational and I haven't even opened the box with the new one yet.

All you need aside from your broken belt is a sharp pair of scissors (or some nice edge cutters) and some Superglue. There is enough extra belt to afford material for the splice, which will hold up for months. It will also withstand being bent around the top idler many times per day. On my setup I noticed that I lost something like half a thou of repeatability, but that half a thou doesn't "wander" - it averages out, so you can still get good quality prints. Other than that, it will perform just like a stock belt.

You don't want the splice to have to ride over the stepper drive pulley. That won't work - at all. Ideally you don't want it to have to go around any bends, but due to the place where these belts tend to fray and fail (right where the stepper pulley is) your best bet is to set it up so that the splice is on the outside of the tower near the top with the machine homed. As the carriage descends, the splice (being on the opposite side of the tower) will move up, travel around the idler, and then descend to follow the carriage. Do a test fit of the belt before you glue anything to make sure it isn't going to be made to travel around the stepper pulley. In my case, the belt had to be "flipped" - the end that was clamped to the bottom of the carriage wound up being clamped to the top, and vice versa. If your belt has broken in a place that allows it to be spliced such that the splice never has to go around any bends, that's even better.

Once you've got all that straightened out, cut off the frayed ends of the belt, taking care to cut directly across one of the "valleys." You want the cuts to be as flat as possible, and as centered in the middle of the valley as possible. Then, cut another segment nine teeth wide, again taking care to cut flat and as perfectly centered in the valley as possible. This will be the "bridge" part of the splice.

Put the two surviving halves of the belt together, then turn the bridge upside down and fit it over the ends of the two belt halves. It should be centered, with one tooth fitting into the half-valleys you left on the belt halves. It should mesh perfectly with them, and there should be four teeth engaged into four valleys on either side of the rift. Verify that the belt halves have been cut properly and that they are not pushing against each other. (They can sit up against each other, but you don't want one of them to tweak the other into a funny angle - the fit has to be good and straight.) Once you're satisfied with this, Superglue the bridge in place and pinch everything together with your fingers for at least two or three minutes. If any Superglue flows out, get rid of it with something plastic or metal. Let the mended belt sit to cure for ten minutes or so.

Then, reinstall the belt and do a four-point calibration. (Or a 12 or 25 point calibration, you know, whatever it takes to get the printer accurate enough for you.) Over time you may notice the first tooth of each belt half coming unglued and standing up a little from the splice. That's OK. Mine has been that way for a long time and it still prints fine.

N.b.: I also tried gluing some belt to the OTHER side to make the splice stronger, but that made the stepper grind the belt for a second and finally ripped the piece off as it went around the idler, so don't bother. It will work fine spliced on only one side.

[Eaglezsoar]

Great tip! Thanks for sharing that with us, I would have never thought of that on my own.