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jime
09-16-2014, 11:44 AM
I have a Delta 6"X48" belt sander that I'm having a problem with. I've been using 3M 963G belts for years. The last two lots of belts have displayed the same problem, that being they're cupping out on both edges. This happens immediately, not something that appears with use. The cupping is about 1/4" and has cut into the table on both sides. I've checked both the upper and lower rollers, and both appear to be normal. No signs of wear or loss of crown. I called the 3M technical rep, and he thought I might have gotten a bad lot, but I think this is unlikely as I've experienced this on two lots of belts purchased about a year apart. The only thing he could recommend was to change belts to a 777f style. I probably will try that, but would still like to know if there might be something I'm missing.

JRouche
09-16-2014, 01:33 PM
Mine will cup upward if I tension the belt too tight. Never had it cup downward though. Bummer for the table, thats a nice sander... JR

DR
09-16-2014, 01:43 PM
I don't know exactly what the different belt designations mean. What I do know is the heavier the belt's cloth backing the more cupping I see on my 6x48 sanders. The coarser grit belts cup much more than those in the 100 grit and finer grit ranges.

Recently, I ran out of my usual 120 grit belts and put on a 60 grit belt since it was all I had at the time. It cut into the table on both sides. This is a very old sander, maybe 40 years old, it surprised me that it had never happened previously in all those years with various users. Could it be belts have changed?

On edit: Something else....years ago I had a woodworking business with a wide belt sander. I wasted a couple thousand dollars on 3M belts. I went to an independent abrasive supply house with my problem. They switched me away from 3M and my belt problems went away. This was after talking numerous times with 3M tech support and following their advice. You might try another brand.

Black Forest
09-16-2014, 01:57 PM
maybe 40 years old, it surprised me that it had never happened previously in all those years with various users.

Wow DR. That took balls to admit you are a Clumsy Bastard.

JoeLee
09-16-2014, 06:27 PM
Storing them in a damp environment will cause that to happen. I think there is two different expansion and contraction rates between the two surfaces.

JL.............

jime
09-16-2014, 07:29 PM
DR,

I think what you're saying is what I'm seeing. It's a 60 grit belt and the rep told me that particular belt has a thick backing as it's designed for very heavy pressure. He also said the heaver backing will cup more than the lighter ones. That's the primary reason he recommended the 777 series, it's a lighter back. It would be easier to accept his explanation if I hadn't been using this same belt for the last 15 years with absolutely no cupping until the last two orders. I think I'll follow your advise and check into some other brands. It still chaps me that I now have two gouges in my table.

Jim

jlevie
09-16-2014, 08:54 PM
That sounds to me like insufficient belt tension.

Paul Alciatore
09-16-2014, 11:06 PM
You say they are "they're cupping out on both edges". I am not familiar with that terminology. What exactly does it mean. And someone else talked about belts cupping "down". In would be the opposite of out and up the opposite of down. Could someone describe what all this cupping means? Are the edges bending? Are the separating? Or what?

Boostinjdm
09-16-2014, 11:47 PM
I believe he is saying that the edges are lifting off the platen.

atomarc
09-17-2014, 12:39 AM
I thought he was indicating the belt was cupping or folding downward at the edges, into the platen. That's what has damaged it, the cupped edges grinding snail trails in the pristine bed plate.

Stuart

DR
09-17-2014, 06:40 AM
You say they are "they're cupping out on both edges". I am not familiar with that terminology. What exactly does it mean. And someone else talked about belts cupping "down". In would be the opposite of out and up the opposite of down. Could someone describe what all this cupping means? Are the edges bending? Are the separating? Or what?

My sander in question is the old classic 6x48 Delta in the vertical position. Work rests on the table. The edge of the table is approximately 1/8" or less from the moving sanding belt.

The coarse grit belts have a tendency to lift away from the platen at both edges. The lifted edges then grind into the table widening the original gap.

I've seen two repair methods for tables with this type damage. One is to mill away the table edge and inlay a piece of steel. The other method is to build up a new edge with braze.

jime
09-17-2014, 09:01 AM
DR,

You're correct, the belt is lifting toward the work table on both edges. I think I'll plan on inserting a wear strip on the table next to the belt as a repair. Obviously won't do it until I find a belt that will lay flat.

Jim

darryl
09-17-2014, 02:09 PM
The most reasonable conclusion that can be drawn from this is that the belts are not as good anymore. If nothing changed mechanically (overnight?) then the consumable part, the belt, is now crap. Brand names have no meaning anymore- anybody can outsource their parts from --- and still put their name on it. Doesn't mean the quality is up to par, and in fact in many cases I've seen personally, it isn't.

J Tiers
09-17-2014, 08:31 PM
I have found that 3M products are rarely very good for general use, aside from a few consumer products. They are really two companies, one that makes consumer stuff, and the other is a "B2B" company doing custom products.

The industrial products are good in a particular environment, doing exactly what they were made for. Any change from that, and they may cease to work at all, or at least cease to work very well.

Family members worked for 3M and had the ear of higher ups, but 3M never seems to have changed their ways, and I am NOT the only one who noticed the problems.