# Cupped board on a planer



## GISer3546 (Jan 30, 2013)

I'm trying to fix some old cupped fence boards on my planer. I ran it through a few times and managed to plane the full width of the board but when I checked with a straight edge the planed surface was still slightly convex. I'm not sure if this means I'm trying to take off more than I should or if the spring tension on my rollers is too high. Anyone have experience fixing this?


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## 27207 (Jan 25, 2012)

You'll need to take very light passes so the rollers don't compress the board flat. It's difficult to completely get rid of a cup this way, but the lighter of a pass you can take, the better it will turn out.


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## Steve Neul (Sep 2, 2011)

Yea I'm assuming the wood is cedar and easily flattened with the feed rollers. You would have better luck flattening them with a jointer first. I think I would try Dwillems26 method first and try very light cuts in the planer. It's a lot safer.


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## GISer3546 (Jan 30, 2013)

Yea I don't have a jointer at the moment. I will have to try the light passes. I was hesitant to lower the tension on my feet rollers since they say high tension is best for less than straight wood... and this is definitely not straight.


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## walnutavenue (Nov 9, 2011)

What you need is to prevent the pressure from the rollers flattening the board. The rollers flatten the board, the cutter head cuts a flat surface on the artificially flattened board, then when the rollers aren't applying pressure the board goes back to being cupped... But thinner than last time. 

Lay a straightedge across the cupped side of the board to measure the depth of the cupping. Then attach a strip of scrap of that thickness along the length of the board, in the bottom of the cup. Use double sided tape, or glue if the surface is too rough for tape. This piece will serve as a shim so that the feed rollers cannot flatten the board. Flip the board shim side down and plane the top flat. Flip it again, remove the shim, and plane the other side flat. If you glued the shim on you can run it through the planer to remove it with the rest of the cupped material. 

A jointer would be easier, but the planer and a shim can get the job done.


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## GISer3546 (Jan 30, 2013)

Sounds like a good solution walnutavenue, much appreciated.


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## MT Stringer (Jul 21, 2009)

Search You tube. I have seen videos...using a sled, and some shims. Might take a while but if the board is important to your project, give it a shot.
Good luck.


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## Maylar (Sep 3, 2013)

Honestly, this is the perfect example of where hand tools are the ideal solution to a problem. I would take a #5 or #6 hand plane to the cupped edges and bring the board close enough to flat so that the planer could take a final skim cut. You have much more control this way and lose the minimum of wood.


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## Pirate (Jul 23, 2009)

Maylar said:


> Honestly, this is the perfect example of where hand tools are the ideal solution to a problem. I would take a #5 or #6 hand plane to the cupped edges and bring the board close enough to flat so that the planer could take a final skim cut. You have much more control this way and lose the minimum of wood.


I've done this with good luck.
Also have put the board on a sled, with the cup up, and put wedges under the raised edges, hot glued in place.


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## Larry42 (Jan 10, 2014)

Use a carrier board, trap the cupped board on it and put shims under it to support it so it doesn't compress or twist. The carrier has to have a sturdy back stop glued on.


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## TimPa (Jan 27, 2010)

realize that after you make a board perfectly flat, by whatever method, that you have exposed a new surface to the air. depending on how stable that board is, it may or may not stay flat immediately after the process. just don't lay them on a floor/bench/flat surface where the air can only get to one face, is likely to warp again.

a jointer (machine or hand) is much better at flattening boards than a planer


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## Larry42 (Jan 10, 2014)

If you want to flatten a board use a scrub plane, much faster than a #5 or 6.


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## wericha (Apr 29, 2012)

Simply put, a planer is NOT the tool to use to flatten boards. Its intended purpose is to thickness a board. Trying to do so will only make the situation worse. If you don't have a jointer, a hand plane should be used to flatten one side as best as possible before running through the planer.


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## Pirate (Jul 23, 2009)

Try to plane the same amount off each side to minimize warping.


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