Belt sander -- belt runs off

Way back in the 1970s, when Craftsman tools were still USA-made and sort of respectable, I bought a new floor-model belt-disk sander. (Yes, I should have taken it back but didn't.) Despite the tiniest of incremental adjustments, the belt keeps running off-track after a minute or so of use, so I tucked it into a back corner, piled junk on it and sort of forgot it. Now I'm thinking of trying to revive it and need ideas. I've never pinpointed the cause of the problem -- doubt I could see it with the naked eye anyway. Does it make sense that maybe the aluminum "drum" (don't know what to technically call it) on which the belt rides was slightly mismachined? I'm thinking that somehow truing up the drum might fix the problem, but that might mean machine-shop work (i.e., more dollars than the unit is worth). I'm really at a loss about fixing vs. scrapping. All ideas are welcome.
 

On old belt driven machinery the pulley surfaces were always domed slightly to avoid the belt doing just that . Try wrapping a few turns of gaffer or duct tape around the centre of the drums . This might solve the problem or at the very least pinpoint the cause .
 
The first thing that I would try would be a better, different brand of belt. I've had some that wouldn't track no matter what I tried. I cut them up and used the pieces on my hand sanding blocks. I had the best luck with no-brand belts that I ordered online

I've also had some that just the smallest turn on the adjustment would send the belt off to the other side. I doubt that there is anything wrong with the drive roller, but check to make sure that there isn't some play in the adjustment parts somewhere. I anything can move, that could throw the belt one way or the other.
 
This is probably useless information to you, but back about that same time I had a 4x24 Craftsman belt sander which stopped working because it needed a bearing that Sears no longer stocked---in other words, they had stopped supporting that model. Today, that would probably be enough to make me stop doing business with a company, but I must have been more easy-going back then. Anyway, I let the person in the Sears repair facility talk me into buying a 3x21 Craftsman belt sander. To this day, it stays in my memory as one of the worst engineered hand tools I've ever owned. The belt kept slipping off after a short amount of use. A bit of inspection convinced me that it was engineered in such a way that it would never be possible to adjust it in such a way that that would not happen. I have absolutely no memory of the specifics of the problem, but I still trust the quality of my technical reasoning at that age (although other decisions my 30 year old self made appall me now). If I remember correctly, I was able to get my money back for the bad sander, and I do remember that I got the bearing I needed to fix the 4x24 sander from a different source, and that sander still runs on the rare occasions that I need one.

Stan
 
Hello rossow (mn),

It sounds like an alignment issue. Which ever end of the sander the belt is coming off first that would be were I'd look real close. If the belt runs out, then the drum is less the 90 degrees towards the other drum. using a square would prove that, Do it on both sides. Bet you find one of then out of line. Shoulders built in the outer part of the drum usually help this problem. Let us know if you find the problem. But if all is well those shoulders are not needed. Trashing machines come to mind.....



Guido.
 
You might try and see if you can replaces those bearings, if you have access to a bearing specialty house or a good NAPA dealer. A check with MSC or Master-Carr might help. If those bearing have numbers that number would be a big help.
It is possible to get replacement bearing by measuring the width, ID and OD.
 
There are several things that could cause the belt not to track well. Sometimes it's the belts. I've had entire boxes of belts that were unusable. The shoe plate or cork pad could be worn out. There could also be excessive dust built up in the mechanism. Currently I'm using a Harbor Freight belt sander and if I don't keep the dust blown out the belt won't track right especially if I put too much pressure on the sander.
 
belt is too loose. Tighten up both ends of th adjustable roller (right side) until the belt won/'t turn when you start it. Very gently move it in until it starts to turn. Now adjust for in and out travel.
 
The tilt on the idler roller (top) is adjusted to put the belt where it belongs. It is usually a knob on the side of the housing. We have 3 of them from the 60s and the belt runs to the high side of the pulley not the slack side. Jim
 
Rossow:

Remove both drums. Find the center of each drum and with a felt tip marker, mark a center line completely around the circumference of each drum. Now, file or sand a 3 degree taper from that center line to EACH END OF EACH SIDE on BOTH drums. The drums should be high in the center and taper to each side. Reinstall the drums, reinstall the belt and adjust your belt tension. Now the belt should run straight on the drums and not wander.

Doc :>)
 

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