Drum sander problems creating cupping

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Forum topic by Adrian A posted 12-29-2010 07:31 AM 1620 views 0 times favorited 9 replies Add to Favorites Watch
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Adrian A

169 posts in 2902 days

12-29-2010 07:31 AM

Dear Woodworking Experts,

I glued up some 2” wide strips to make a 16” wide 36” long Glued up Panel. (making an end grain cutting board).

I then put it in the drum sander to level out the panel and it made it all smooth and level…. So I thought. Upon further inspection the middle was thinner than the edges creating a dished effect across the 16” width.

This doesn’t make sense to me because the drum is flat and if anything you would think one side would be higher than the other side because the drum might be angled, but a dish doesn’t make sense.

Anyone know what could be causing this?

This problem is okay if making a face panel, side grain panel… But when making end grain it causes horrendous problems in the next glueup step.


9 replies so far

View childress's profile


841 posts in 3541 days

#1 posted 12-29-2010 08:17 AM

I have a performax and the manual says to raise the end of the drum (like a couple thou) if sanding boards wider than the actual drum to prevent this very thing from happening.

I also don’t recommend sanding the edge grain before cutting and re-gluing. I personally don’t believe it leaves a good enough glue joint surface. I’m sure others think it’s ok but I don’t. The board really needs to go through the planer before crosscutting and gluing.

-- Childress Woodworks

View Adrian A's profile

Adrian A

169 posts in 2902 days

#2 posted 12-29-2010 08:55 AM

I’m not having problems like the manual shows. I’m only feeding a 16” wide piece but, that 16” piece is coming out cupped instead of flat.

I’d use a planer but my planer is 12.5” wide, not big enough for my 16” wide board.

View Loren's profile (online now)


10401 posts in 3647 days

#3 posted 12-29-2010 09:54 AM

Check the platten for distortion. You may be taking off too much
material in a pass. Drum sanding to accurate thickness takes several
passes in my experience with a cantilever drum.

Loose paper in the center of the drum could possibly cause some problems.

You might want to correct the problem with a handplane for now
and try sanding to thickness again working from a flatter panel.

View rhett's profile


742 posts in 3667 days

#4 posted 12-29-2010 03:31 PM

It sounds to me like you are either trying to remove too much material in a single pass, or your pressure rollers need adjustment.

On my drum sander, the two drums and the feed belt are a softer composite material. With enough pressure, I could imagine they would deflect just enough to produce cup or non flat surface.

-- Doubt kills more dreams than failure.

View dbray45's profile


3320 posts in 2776 days

#5 posted 12-29-2010 07:00 PM

You may want to check both sides for flat. If the whole panel has a bow in it, the rollers will flatten the panel through the equipment and the bow returns on the other side. If this happens, put the panel on another board, put spacers under to bow so the panel cannot flatten and then run it assembly through the sander. I have a board with a whole bunch of machine screws that I adjust to “mold” to one side, run the board a couple of times to make it flat, turn the board over and run that without the “leveling” board.

If you don’t want to go through this trouble, I have run a board about 4 times without changing the hieght, this puts less pressure on the board and tends to flatten things out.

-- David in Damascus, MD

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Adrian A

169 posts in 2902 days

#6 posted 12-29-2010 11:22 PM

Thanks for the replys. Let me clarify a little. When the board comes out it comes out cupped but thats not really the problem. The problem the thickness isn’t even acrossthe panel. The middle is not only cupped but thinner in thickness than the the outsides.

View John Ormsby's profile

John Ormsby

1285 posts in 3736 days

#7 posted 12-29-2010 11:53 PM

What grit sandpaper are you using. You can start with 60 to 80 grit. Then proceed to finer grit up to about 150. Any more and it will start burning. Finish with a ROS .

-- Oldworld, Fair Oaks, Ca

View dbray45's profile


3320 posts in 2776 days

#8 posted 12-30-2010 02:04 PM

I would call the manufacturer.

-- David in Damascus, MD

View patron's profile


13604 posts in 3341 days

#9 posted 12-30-2010 02:23 PM

i do my wide panels and boards
in multi-passes
just a little at a time
flipping over and over
and end for end
and cleaning the table of sawdust in between
takes longer
but helps with this problem

-- david - only thru kindness can this world be whole . If we don't succeed we run the risk of failure. Dan Quayle

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