A cupped board....

[Ken Fitzgerald]

Hardwoods are terribly expensive in our locale probably due to transportation costs so I try not to waste my hardwoods. I am currently building an endtable that requires a 15" top. I have an 8" jointer and a 13" planer. One of the red oak boards I have is 8 1/2" wide and cupped ever so slightly the entire length of the board. Could I flatten the board by running the "high" side of the board up through my planer until it's flat. Then flip the board over so the now flat side is down and run it through my planer until it's flat too?

Or.....

Should I trim it to 8" wide, run the "high" side of the cup up through my jointer until the bottom is flat and then run it though my planer, flat side down?

[Brian Tymchak]

Hardwoods are terribly expensive in our locale probably due to transportation costs so I try not to waste my hardwoods. I am currently building an endtable that requires a 15" top. I have an 8" jointer and a 13" planer. One of the red oak boards I have is 8 1/2" wide and cupped ever so slightly the entire length of the board. Could I flatten the board by running the "high" side of the board up through my planer until it's flat. Then flip the board over so the now flat side is down and run it through my planer until it's flat too?

Or.....

Should I trim it to 8" wide, run the "high" side of the cup up through my jointer until the bottom is flat and then run it though my planer, flat side down?

Hi Ken. Assuming you are using 4/4 or 5/4 stock, many do option 1 with a planer sled because you have to support the cup in the board from below as the planers rollers will try to flatten the board against the bed. With 8/4, it's not as big a concern as it is difficult to bend 8/4.

[johnny means]

Sometimes the planer will flatten the cup out some as it planes. When it comes out of the planer the cup springs back. This can be negated with several light passes, so as to avoid downward pressure on the stock. It may not be an issue with thicker boards. In general, planers don't flatten very well

[johnny means]

Also, keep in mind, that cupped boards got that way for a reason. removing material from the faces will often just introduce a cup. Personally, I'd rip the board in half and glue them up with opposite faces adjacent.

[Ken Fitzgerald]

Brian, thanks for the information! I just watched a video at FWW and Andy Rae IIRC said the same thing about the board springing back.

I think I will use my 2nd option, ripping it to width, jointing it and then planing it. I'll sticker it overnight, check it tomorrow and adjust if necessary.

Johnny, thanks for the information! I always work all 4 edges and then allow the wood to set overnight.

[Jerry Wright]

I have successfully planed many cupped boards, convex side up with great success - DW-735. In fact, I seldom find an 4/4 or 8/4 hardwood board that doesn't have cupping. Just take light skim passes until cleaned up, then flip and proceed side to side.

[John C Bush]

Hi Ken,
Having a planer sled on hand is a good thing to have. Torsion box with MDF "skins" and solid stock frame and internals--glued and screwed. My big one is 8' x 18" (20" planer) and is a bit heavy when milling thick slabs. I used 1/2" MDF leftovers and 4/4 x 2" maple for the frame etc. I would consider using 1/4" hardboard if I were making another one--guessing it would be as stable as the MDF,
Opinions/advise from the experts here would be helpful. I use cedar shims and a hot glue gun to level and secure the stock to the sled. Good luck!

[roger wiegand]

Yes, that can work. The other approach, which will save more wood (especially on badly cupped boards) is to rip the cupped board into two strips, joint each of them separately, then glue them back together carefully matching the grain. Done carefully it is often extremely difficult to even see the joint.

The other thing I used to do a lot when I only had a 6" jointer was to take the fence off and run the center of the convex side of the board across the cutter, creating a flat in the center of the board. On the first pass it is hard to maintain the board perfectly level; once you have a flat it is much easier. A jointer plane is sometimes easier to do this with than the machine jointer. Once the flat is wide enough you can run the board through the planer, taking very light cuts to start with.

[Justin Rapp]

Brian, thanks for the information! I just watched a video at FWW and Andy Rae IIRC said the same thing about the board springing back.

I think I will use my 2nd option, ripping it to width, jointing it and then planing it. I'll sticker it overnight, check it tomorrow and adjust if necessary.

Johnny, thanks for the information! I always work all 4 edges and then allow the wood to set overnight.

This is somewhat of the ideal situation. The rip can help take some of the tension out of he board and you know you will get a flat surface on the jointer. If you did try to use the planer to fix the cup and the board ends up to thin, you've just put that wood in the 'for another project' pile.

Ripping it right down the middle of the cup will help reduce the need to thin out the board to much. Just be careful if you rip it on a table saw and it binds.

[Ron Citerone]

When I only had access to jointers smaller than the wood I was working with, I used a Jack Plane and knocked off tke high spots before planing. Nothing of finished quality, but enough so one side rested flat on a table saw table or a known flat work bench. Did it many times successfully.

[Doug Dawson]

Hardwoods are terribly expensive in our locale probably due to transportation costs so I try not to waste my hardwoods. I am currently building an endtable that requires a 15" top. I have an 8" jointer and a 13" planer. One of the red oak boards I have is 8 1/2" wide and cupped ever so slightly the entire length of the board. Could I flatten the board by running the "high" side of the board up through my planer until it's flat. Then flip the board over so the now flat side is down and run it through my planer until it's flat too?

Or.....

Should I trim it to 8" wide, run the "high" side of the cup up through my jointer until the bottom is flat and then run it though my planer, flat side down?

Method 1, running the crown of the board over the jointer, is a common technique in hand planing, and can reduce a mild cup. Then less has to be removed to get parallel faces. There’s something about the manual labor of doing this that focuses the mind wonderfully. :^)

But it’s an advanced technique on the ‘lectric jointer.

[Mel Fulks]

If you have time ,you can always try the method used by Wintertur. Keep the ' high side' moist. That makes the wood
expand ,compressing the fibers. That's makes them narrower when dry, so they pull in the needed direction. More info
easily found.

[Ron Selzer]

Ken
have done both of your options and way too many times ended up with a board that was thinner than I wanted. most of the time went ahead and used it. Sometimes just too thin and start over.
A lot of the time wished I had ripped the board in two cleaned it up and glued it back together. Someday I will quit trying the same thing expecting the results to be different. The very few times I have ripped the board in half I have been very satisfied with the results.
Ron

[John TenEyck]

Brian, thanks for the information! I just watched a video at FWW and Andy Rae IIRC said the same thing about the board springing back.

I think I will use my 2nd option, ripping it to width, jointing it and then planing it. I'll sticker it overnight, check it tomorrow and adjust if necessary.

Johnny, thanks for the information! I always work all 4 edges and then allow the wood to set overnight.

Not picking on you, Ken. I see this comment so often but it's only valid for lumber that's not in harmony with the EMC of your shop. If your piece of wood has been in your shop for months and the RH of your shop changes pretty slowly then there's no benefit to letting the wood sit. Worse, if the RH does move then there's a real chance what was flat today won't be tomorrow. Commercial shops could never afford to let wood rest yet somehow many of them turn out a good product.

John

[lowell holmes]

You could belt sand the hollow side until it is flat, then run it through a thickness planer with the bow side up. Then thickness plane the other side up.

[Warren Lake]

skip the belt sander, embedded sanding grit dulls knives.

[Jim Becker]

You could belt sand the hollow side until it is flat, then run it through a thickness planer with the bow side up. Then thickness plane the other side up.
This is better accomplishing on a jointer...it would be extremely difficult to get a board actually flat with a hand held belt sander...ie, without twists, etc.

[Mel Fulks]

just gone thru whole thread. Don't see any comment on my Wintertur info. The method is not a instant fix,but for a project where grain matches are important it might be the best fix. Based on much more science than wearing masks.
Not asking anyone to believe it ,but I do suggest that when one asks a how question ....proven research from a place with
lots of dedication and the funds to try stuff is worth a try.

[Alan R McDaniel Jr]

I have read and been told that when a board is cupped and planed, it is going to cup again. The cupping has to do with the location in the log that the particular board was cut from. You can't change that. But, Mr. Johnny Means has given you a solution that will work. It is not a quick fix either but It will salvage a board that would otherwise be a disappointment if you were to use it on some visible part of your work.

Another alternative is to use the board in smaller or thinner pieces and in areas that are not readily visible. That would actually be my suggestion.

Alan

[lowell holmes]

I have both toys er.... tools.

[Tom Bender]

Method 2 is straight forward and since you are going for a 15" wide top it seems like the way to go.