So I have read through some of the sander tune up threads and did not find what I was looking for. I purchased a used Jet 25" wide belt and just hooked it up today. Actually it did not sand too bad, considering only one belt of the three belt drive from the motor was working. I noticed right away that it was sanding thinner on the left side and checked the bed to rubber drum was off 1.5mm from side to side.
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.
(Solid Wood Machining Forum)
From contributor J:
Is this an open ended machine or is the conveyor and sanding head completely enclosed at both ends? What kind of drum is it - rubber or something else? Does it use a platen for sanding or is the drum used as the reference surface? (If you answer with "what's a platen?" then you most likely don't have one.)
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.
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.