Dressing a Wide-Belt Sander Drum
The problem is, when I adjusted the table level, it is tight in the middle. This seemed odd since I expected more wear in the center from use. I put a straightedge on the drum and it rocked back and forth on the center all the way around. I checked the diameter and sure enough, it is .5 to .6mm larger in the center. I thought maybe this was from the way the tracking worked or something. How do I true this up? The drum looks to be in good shape otherwise.
I'm guessing you have an enclosed machine with a rubber drum and no platen. You need to glue a sheet of sandpaper to a panel and feed it through the machine to re-dress the drum.
Disconnect the power from the machine. Confirm that the inboard of the sanding drum and the outboard are close to the same diameter. Outboard is the side you remove the belt from. I use the sizing tools the lathe turners use to confirm diameters. Remove the belt from the machine, lock the outboard side of the head and using a reference block of some kind, confirm the bed is close to being level in relation to the drum. The drum will be dressed to this relationship, and if the drum is turned to a cone, you may never be able to track a belt.
Now, take a piece of particleboard or MDF (preferably) and cut a rectangle that is longer than your drum is wide, and 2" narrower than your drum. Route a 1/2" radius down the length of this panel on both of the long sides. Taking a new sheet of paper - 50, 60, 80 grit - tear it at the seam and glue it to the panel with contact adhesive (glue to the side with the radius), making special note to wrap the paper over the radius edges. Trim off all the excess, so you have a board wrapped on three sides over two radius edges that is longer than your drum is wide.
Now turn the power back on to the machine. Start the machine with no sandpaper, and the conveyor at high speed (if able). Feed the panel through the machine with the radius edges first (the radius keeps the edge of the paper from peeling back). Lightly, very lightly, raise the table as the panel is being processed.
As the table is raised, the drum will contact the paper and be dressed to match the panel. Do not get too aggressive with this. When the rubber heats, it grips. When it grips, it vibrates. When it vibrates, it can sand your drum to an oval, or throw the panel back out to the machine.
Be very cautious of kickback. Light touch, light passes, and if you hear the machine change its tone, be ready to back off the height adjustment. Very simple - just make sure no one is in front of the machine, just in case. And no dust collection. Heated rubber in a dust collector is not a good thing.
From the original questioner:
Thank you very much - that is the information I was looking for. The sander is an old 25" Jet. It is closed with a platen. I figured I would be addressing the platen adjustment after truing up the drum. Just pulled it out for now. It needs new graphite anyway. I figured we would have to sand the drum, so already glued paper to board.
Your statement about making the panel 2" narrower than the drum is throwing me off. We made the board a little wider than the drum so it would make sure to sand the whole drum. It will still feed through the machine fine and I did not think the length really matters as long as it is not too short to feed properly, of course.
From the original questioner:
I get it now. If we use the same size belt as the machine uses and glue it on in the width so it covers the whole drum, we will only have 25" of paper in length to use.
From contributor J:
Correct, the width of the board is wider than the drum, therefore rotate the paper 90 degrees to accommodate the entire drum. This will cause the paper to not cover completely from front to back. Hence, narrow the panel front to back to allow the full coverage. Also, rounding the corners is very important. It allows the smooth transition from the edge of the panel to the face without lifting the paper. One last thing, rotate the panel 180 degrees every pass to help eliminate inconsistencies in the panel.
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