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Need some help trouble shooting some uneven sanding on my friend's drum sander:

I have sent some tops through his Grizzly 1066, and I am finding the middle of the board to be left roughly .008" thicker than the sides. I have tried running each piece through multiple times before reducing the thickness more, but it still is high in the middle. Anybody have any experience with how to remedy this or something like this?

P.S. for those not familiar with this particular model, it is not open ended. It has two drums (coarse then finer).

Thanks for your help.

Peter

Guess it's better than being low in the middle. I find with any sanding equipment, with tension controls, too much or not enough tension...especially with a new belt, can sometimes create this annoying result. Another problem may be that there is something stuck to the inside of your sanding belt or stuck to the drum. Sometimes (rarely) cloth belts can have a glob or a piece of something stuck on the backside. That WILL create thickness inconsistency for sure. It is also possible that if you remove the belt and inspect, the intruder to the belt may stay attached to the roller/rollers.....so look in both areas. Stick a straight edge against your drum (without paper) in several places along the circumference. This will tell you if the drum is out of round (YES THAT HAPPENS in manufacturing). It is also possible the roller itself is not centered with the bearings....another manufacturing issue.
Kent

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Thanks, Kent for the insights.

Simplest thing to do is make a sled. Run a piece of particle board or MDF through the sander, glue a lip on the back edge, then run your wood through on top of the sled. The sled will now be parallel to the drum and the work will conform to it and be uniform thickness.

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I like this idea!!! So the sled will remain still on the conveyer belt? I am having trouble picturing how the sled's lip would work. Thanks!

The sled's lip is made slightly lower than what you plan to sand your tops' final thickness to. As you face the sander, you'de place your top on the sled and the lip will be on the edge toward you, against which the edge of the top is placed so it can't be thrown back by the sanding drum.

Make the sled thick enough so it is ridged - 3/4" or more, and larger than your top all the way around by an inch or so.)

Wonderful, thanks, Jim. Is it a problem to make the sled even a few inches bigger (so that it will do bigger sets of wood)?

Bigger is fine. Only thing to watch out for is sometimes a piece will want to ride up over the lip of the sled. Make sure you hold the wood down on the sled until the lip gets within a few inches of the drum.

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http://www.chassonguitars.com

Thanks everyone for all the help.

Peter

Some people rig their sander to purposely get this type of result.

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In Markham,Virginia

I have this sander and use a sled of mdf for the thin pieces I run through. The lip will work, but I have found that the board will sometimes ride up over it and cause some significant problems (such as sanding through the last several inches of the board until it is paper thin). I find that using contact cement to attach 100 or 120 grit sandpaper sheets to the top of the sled gives plenty of grip and much less chance for problems. Also it is fine to have the sled larger than your pieces, just make sure it fits on the belt if you skew the sled.

Kent

Does the contact cement and sandpaper affect the correct compensation of the sled?

I use a 3/4" sled with my machine without a lip and very seldom have any problems, just hold the piece in place until the rollers grab it and off it goes(most of the time).....I have an old Woodmaster 36/37"? drum sander.

Cheers

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Gwaltney Guitars

Just put the sandpaper on the sled first. Flip it over (end for end so the left side of the sled stays on the left side of the machine) and sand the back of the sled until it is evenly covered with sanding marks (then mark it so you always send it through the same way)

Will the sled also work on small sanders like the Jet 10-20 where you have to run a top or back through twice to get the full width sanded?

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Dan

Great! Awesome technique. Thanks for the trick.

peter

I would think both drums may be out of parallel with each other. I have a jet and it took a lot of tweeking to get to sand evenly. It only has one drum and it was sanding high on the inside. You also so need to take very minute passes with thickness sanders or it can cause unevenness...Mike

forgive me, i dont mean to step on anyone's toes here, but it seems like the problem peter is having will not be solved with a sled. at least, if i am understanding the problem correctly. the kind of sled that has been described here will correct for an out of parallel drum, but if something else is going on it seems like you would end up with the same result.

kent bailey's advice to check the drum with a straight edge is a good one IMHO. have you done that?

a few questions:

are you getting a high center when running the board dead center through the sander? how about when you offset the board to one side or the other? 24" is a lot of real estate to move the board around to get things nice and even.

also, is this a brand new sander? grizzly has a pretty good customer service department and they might have something to say. a brand new sander set up properly should not have this problem. a sled is just a band aid and unacceptable IMO.

edit: i just read what mike said and that makes perfect sense. if both drums are out of parallel in opposite directions, that would give you a high center. nice call mike.

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sweat the small stuff.

Thanks so much for all the input!

Some notes . . . it did not seem to be cutting much with the second drum, can't say that for sure though. The sander overall seemed to audibly cut the heaviest on the back end of each piece.

I have the same sander, the second drum is wrapped in felt, and it is my feeling that the "soft" drum causes exactly what you are experiencing, my solution was to raise the second drum making the sander a one drum, using only the first solid drum.

Thanks, Chris!

Have you seen this. It's not an answer to your question but my come as some use for your dust collection.
http://www.doolinguitars.com/articles/blower/