Options for bowed stock

protectedvoid · August 21, 2010

So, I'm new to starting with rough stock and Marc has already given me some great advice on hand planes for the workbench top I'm in the process of starting. The workbench top is going to be constructed from 6/4 Hard Maple (regular, not Tiger or curled ? curly) and skirted with 3/4 Sapele. The place I got the rough stock from milled it for me (was supposed to be S4S) very cheaply.

So, here's my issue. The maple has already been thickness planed to 6/4, and each board is 11.25" w x 47" long. I planned to join them using a few large floating tenons and some titebond II (although, I had thought about fox-wedging the tenon). Anyway, each piece of maple is "cupped" - basically bowed along both the width and length of the face, though the thickness is consistent at 6/4 the entire perimeter of each board. I don't own a power planer or a jointer, so I'm afraid if I have a cabinet shop flatten the boards, I'm going to lose close to 1/2", and I'd really like to keep the boards as thick as possible since it is going to be the surface of my workbench.

As funds are relatively tight, I really cannot drop another $100 or more on more maple stock to increase the thickness. Now, if I clamp the boards to each other (face to face), I can get them to near perfect flatness. So, my question is, is there a way for me to flatten these boards without thickness planing them, and do it relatively quickly?

I had thought about routing a channel on the convex side of each board, and using tempered straight steel stock from Lowe's to force the boards straight...but that just doesn't seem the "proper" way to go about it.

So, any suggestions you may have would be much appreciated.

Thanks.

PaulMarcel · August 21, 2010

A picture would be helpful to get a better idea of the degree of cup.

Normally the reason for the cup after planing is moisture imbalance, hence the common advice to take as much from both sides. Grain lines will try to flatten so the convex side is likely the one originally facing the center.

Sounds silly, but "fill the cup" with boiling water. Clamp two boards together with the cup facing each other like this ( ). You'll need cauls on both sides of the boards so your clamps reach the middle unless you are lucky enough to have 5" throated clamps. Keep it clamped up for several days so the water makes it in, swells the cells then dries in place. It won't take all the cup out, but I do this pretty often to remove cup and it can significantly decrease it. Never did Maple; did often on Poplar, Walnut, Oak. Granted, most of my boards were thinner than your 6/4 beasts. I'd have to admit that I use a large boiler for it so I dispense right from the boiler and keep filling the cup until the boiler is empty so that cup side gets pretty hot, too. I'd imagine some "steam-bending" effect might be taking place, too.

Worth a shot. Caveat: I live in Arizona and the outside of boards is always significantly drier than the insides so I'm always dealing with moisture imbalance.

If you don't like the water idea, safely ripping each board into narrower boards (and squaring up the edges) will take out a lot of cup, too. If you cherry-pick the rip locations, you might be able to reduce the number of cuts and loss.

protectedvoid · August 21, 2010

A picture would be helpful to get a better idea of the degree of cup.

Normally the reason for the cup after planing is moisture imbalance, hence the common advice to take as much from both sides. Grain lines will try to flatten so the convex side is likely the one originally facing the center.

Sounds silly, but "fill the cup" with boiling water. Clamp two boards together with the cup facing each other like this ( ). You'll need cauls on both sides of the boards so your clamps reach the middle unless you are lucky enough to have 5" throated clamps. Keep it clamped up for several days so the water makes it in, swells the cells then dries in place. It won't take all the cup out, but I do this pretty often to remove cup and it can significantly decrease it. Never did Maple; did often on Poplar, Walnut, Oak. Granted, most of my boards were thinner than your 6/4 beasts. I'd have to admit that I use a large boiler for it so I dispense right from the boiler and keep filling the cup until the boiler is empty so that cup side gets pretty hot, too. I'd imagine some "steam-bending" effect might be taking place, too.

Worth a shot. Caveat: I live in Arizona and the outside of boards is always significantly drier than the insides so I'm always dealing with moisture imbalance.

If you don't like the water idea, safely ripping each board into narrower boards (and squaring up the edges) will take out a lot of cup, too. If you cherry-pick the rip locations, you might be able to reduce the number of cuts and loss.

I'll post some pictures later this morning. The wife isn't feeling well, so she's still in bed. It was very late when I posted the original post, and I felt a bit like a dolt for posting w/o photos.

Anyway, I could give the water idea a try, though I'd probably only be able to boil a maximum of 16 quarts at one time. I had also thought about cutting kerfs into into the concaved side of each face, and using quarter-inch poplar to force the board flat (since I only care about the appearance of the top side). I also have some 1/4" red oak I could use.

I'll post some pics and see what you and others think.

protectedvoid · August 22, 2010

Okay, so, I've uploaded some photos for you all to evaluate. For the record, I did not bother to stage, light, or otherwise "set" the area to photograph these boards, nor did I bother to color correct the photos. With 80% humidity and climbing, it took my DSLR almost a full 5 minutes just to acclimate to the external temp / humidity.

Anyway, these images have been sized down, but are otherwise unedited. Hopefully, with this resolution, you'll be able to see clearly the degree of twist, cupping / bowing (primarily on 1 board) to help me figure out how to "fix" them without losing anymore thickness.

Here are the URL's (just in case the image insert fails)

Board 1 - worst of the two - Mild cupping, bowing, twist. Uniform thickness on all four sides.

Board 2 - reasonably flat - minor bowing, maybe a slight cupping...no discernible twisting