Sanding belts curling, won't track

Gentlemen,

I use an old Hammond 5 hp belt grinder for surface finishing (graining) parts from our CNC dept. The machine takes 6" x 60" belts, and I'm using grit sizes between 80 and 240. We use Qualichem 251C coolant in this machine; a synthetic of about 90% water.

This machine or maybe, more likely, the belts we use, is/are giving me some problems I hope someone here can help me with. First, the belts won't track very well. I have to constantly readjust while I'm running it to keep the belt near the center of the platen. The machine has no automatic tracking mechanism. I've noticed that this condition varies a lot depending which belts I'm using.

Worse yet, the belt edges curl, sometimes as much as 3/4" or so from the edges, and that severely limits the amount of belt width we can use. Tensioning of the belt is done by means of an air cylinder, with an air regulator being the mode of pressure adjustment.

I'm of the opinion that there are quality belts out there, which can run with coolant, run flat, and that will track straight. Purchasing here gets me generic looking aluminum oxide and silicon carbide belts, likely based on the best price. They would get me whatever I ask for, if I just knew what to request. Can someone here advise me what abrasive belts would probably work best in this situation? I'm hoping to avoid a process of trial and error if I can. Local suppliers seem to be of little help.

Sincerest thanks,
Tom

I would call Norton or 3M. They have app support folks. As you alluded to, I doubt your current belts are meant for coolant, which is making them curl. Most likely your belt tracks by means of a crowned roller. If the machine is very old or heavily used, it is possible that the crown on the roller has been reduced too much to be effective. I would start with a good belt though as that is the easiest thing to try.

Norton Wet or Dry Belts: Norton BlueFire
3M Wet or Dry Belts: 3M Architecture & Construction : 3M? Cloth Belt 461F

Also 3M 464W, 577F and 777F can be run wet.

Good Luck
Matt

Quote:

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Originally Posted by tr4252

Gentlemen,

I use an old Hammond 5 hp belt grinder for surface finishing (graining) parts from our CNC dept. The machine takes 6" x 60" belts, and I'm using grit sizes between 80 and 240. We use Qualichem 251C coolant in this machine; a synthetic of about 90% water.

This machine or maybe, more likely, the belts we use, is/are giving me some problems I hope someone here can help me with. First, the belts won't track very well. I have to constantly readjust while I'm running it to keep the belt near the center of the platen. The machine has no automatic tracking mechanism. I've noticed that this condition varies a lot depending which belts I'm using.

Worse yet, the belt edges curl, sometimes as much as 3/4" or so from the edges, and that severely limits the amount of belt width we can use. Tensioning of the belt is done by means of an air cylinder, with an air regulator being the mode of pressure adjustment.

I'm of the opinion that there are quality belts out there, which can run with coolant, run flat, and that will track straight. Purchasing here gets me generic looking aluminum oxide and silicon carbide belts, likely based on the best price. They would get me whatever I ask for, if I just knew what to request. Can someone here advise me what abrasive belts would probably work best in this situation? I'm hoping to avoid a process of trial and error if I can. Local suppliers seem to be of little help.

Sincerest thanks,
Tom

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Does this model belt grinder have a hard rubber wheel on the end of the air cylinders piston? If so try to barrell shape this wheel slightly. these belts have a cloth backing and tend to be easily deformed. That said if you can induce a slight deformation in the center it will help self track the belt and avoid sever deformation at the belts edges from tracking off center and rolling the corner of the wheel. The high point of the barrel should be formed to about .050 larger than the ends. Attachment 187982

Thank you keebler303 and ATWdwilliams.

Both upper and lower wheels are flat across and are just plain castings, no rubber surfaces. Also, they're different diameters; the upper about 4" dia. and the lower closer to 6" dia. I'd expected them to be crowned, and was surprised when I saw they weren't.

I think you are right about approaching the manufacturers, and I will do that.

Thanks again,
Tom

They don't "look" crowned or they are not? Did you check with a straight edge?

Quote:

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Originally Posted by keebler303

They don't "look" crowned or they are not? Did you check with a straight edge?

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Sir,

I should have checked with a straight edge, but I did not. After your post, I checked both wheels against an edge, and found that they were both flat, but with a slightly uneven pattern of wear; The top wheel has a depressed area of about .015" x approx. 1.0" on the right side, the bottom has a similar dip on the left. Curious. Also, the wheels (drums actually) are grooved in shallow spirals which run in both left/right and right/left, sort of like a right handed and left handed thread cut into the same bar. It looks intentional, though I can't guess what the OEM might have had in mind.

Thank you for your advise; I was looking mainly at the belts, now I think I should consider what may be wrong with the machine also.

Tom

The depressed area may be intentional, they would act like a crowned roller and help to keep the belt straight. The groove pattern is probably to improve the grip on the belt. We had an edge sander that had a rubber drive wheel with chevron shaped grooves in it.

A good quality belt would be the easiest thing to check and see if that improves the tracking. A worn bearing could cause one drum to tilt a bit which may make it difficult to adjust and so it won't track.

Matt

The 'spirals' cut in the drums are supposed to be there, all Hammond's that I've seen have them. Was told a long time ago that they are to let the air between the belt and drum escape. To keep the belt flat to the drum. Hammond's at one time were THE belt sander, best on the market.

Did you look at the arrows on teh inside of teh belt? If they are not in teh direction the belt runs, it curls and never tracks straight.