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WideBelt Sander problem....3/21
I just discovered that I have a problem with my wide belt sander. I think I know what the problem is as well as the solution, but it wouldn't be the first time I've been wrong so thought I'd get a second opinion.
So I run a 77' 43" Timesaver with an 11-1/2" rubber covered drum, no platen. I was sanding a 40" wide 1-1/2" thick oak top yesterday and seemed like the machine was working too hard. Several passes at the same height would still tax the machine. After a full hour of sanding this beast I finally got it flat....or so I thought. Looking at it standing on edge I thought I saw a slight bow in the middle. Grabbed the straight edge and sure enough the middle was a bit high. Worse yet it's high on the bottom as well! Maybe a 16th on each side. So I figure either my drum is flexing, (unlikely), or my machine is showing signs of close to 40 years of use....I think my table is dished!!!
Now it's a great machine and a real workhorse, but it's up there in age. Pulling the table, (assuming it is dished for now), having it machined flat and re-installing is going to cost some cash. At that point I'd have to buy a new feed belt as well. Not sure if it's like an old truck where at a certain point your throwing good money after bad? Or if it's worth it since an affordable entry level sander won't come close to the quality? I guess I'm just looking for advice from the group on how to choose a direction.
Perhaps I am misunderstanding your post but it sounds like the rubber drum has some wear. You should be able to true it with a sandpaper covered flat panel. Call timesavers, I am sure they can advise.
Hi Rob, thanks for the idea but it's not the drum. Drum is fairly flat across most of the width….PO trued it up.
Jeff, is this something that suddenly showed up, or you just noticed it? Has the sander been producing consistently sized parts across the bed width?
It would seem that the problem must be due to a worn contact roller, a worn conveyor belt or a dished table. Can you loosen the conveyor enough to get a straightedge under it to check the table?
I guess you are in the best position to evaluate the costs and benefits of tearing down and rebuilding vs. new. I will say that when we were in the same position we went with a remanufactured Sandingmaster from Woodshop Specialties in Rutland, VT. It cost us about as much as a new SCMI at the time, but we felt we were getting a very solid and simple machine. It might be worth a call to the owner, Mike Shahan. He is a very good tech and a straight shooter and probably has worked on old Timesavers like yours. I think he might give you some good perspective on the repair vs. new decision
The drum and conveyor are both wear prone . No matter how good your operator the parts always overlap in the middle so the conveyor wears more there. The drum can too over time.
I absolutely hate dressing drums inside machines. You put sandpaper/wood on your worn conveyor and grind that wear pattern into your drum. No one ever levels the drum first. They end up cone shaped. Once you remove rubber the spin balance is lost and it starts to chatter.
If you see multiple passes at the same height unloading more pressure onto the product then you are most likely taxing too fine a belt. Many passes with a fine belt are very bad for color consistency and quality. It is much better to grind a surface with 80 or 60 grit than to do 10 more passes with a 150 grit. Much less pressure accumulation.
I suggest checking the flatness under the conveyor, but I bet simply dressing the conveyor will fix you right up.
Hi Adam, I was using an 80 grit belt to flatten the panels. Except it just wasn't flattening them as I expected.
If I were to try and tune up the sander do you have any advice where to start? You say you don't like truing the drum in the machine, so do you send it out to be trued? There's no way to inspect the table without removing it and the belt. At which point I'd want/need to install a new one, existing belt is pretty thin. Then if the table is out of flat I'd have to deal with finding a place that could grind it back to flat. After which I'd have to re-address the drum which is mostly flat across it's width, but does flare out roughly .004 at the very ends.
Trying to come up with a game plan as it seems as though it's an all or nothing type of situation.
Has there ever been anything done to your rubber drum, dressed, changed out, ect? If not then you have a few options. 1. you can remove the drum and send it out to be ground and dynamically balanced (balancing is critical). I would recommend replacing the bearings at the same time. OR 2. you can attach 2-1" thick pieces of MDF together along with a 80 or 60 grit sandpaper glued to it and dress your contact drum while in the machine. Why so thick of a dressing board? Because if you are unsure of any wear that may be in your bed plates, the thickness of the two pieces of MDF together will be rigid enough to minimize the wear in your bed plates by not allowing the dressing board to bend/conform to the wear pattern in the plates, provided you are using light sanding pressure to dress the drums with. Our website has a section on how to dress a contact drum that may help as well.