Kerfing to flatten a countertop?

Hi All -
I bought a wooden countertop at a high-end cabinet shop's yearly yard sale last summer. It's 90"L x 25"W x 1.5" thick. I brought it home on the top of my jeep, and it cupped. Good side up, the cup is center up along the length about 3/8 inch, over 1/3 of the length from the left edge. It did not settle over the past year.
The edges are doubled 3/4 inch boards, and the field is 3/4 inch also.
I'm condsidering kerfing the underside to flatten to the top. My start would be 3/4 or maybe 7/8 inch deep kerfs thru the doubled boards on the affected end, probably at 1/2 inch spacing.
It's destined for the workbench, and the investment was $40, so I can experiment.
I saw Norm do this with a burned board on an end-table in the NYW, but I swear he broke it by the sound of the crack.
How deep would you go, and how often would you do it? Or, what would you do otherwise?
Thanks in advance.
...best, Capt N.
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Captain snipped-for-privacy@example.com wrote:
> I bought a wooden countertop at a high-end cabinet shop's yearly yard > sale last summer. It's 90"L x 25"W x 1.5" thick. I brought it home on > the top of my jeep, and it cupped. Good side up, the cup is center up > along the length about 3/8 inch, over 1/3 of the length from the left > edge. It did not settle over the past year. > > The edges are doubled 3/4 inch boards, and the field is 3/4 inch also. > > I'm condsidering kerfing the underside to flatten to the top. My start > would be 3/4 or maybe 7/8 inch deep kerfs thru the doubled boards on the > affected end, probably at 1/2 inch spacing.
<snip>
Have you tried to clamp this top to flatten it?
If you have some pipe clamps, cut a 2x6x10ft construction timber into 4-30" lengths and clamp them equally spaced, to the top for a couple of weeks.
Build the frame of your bench, then mount top to it.
My guess is it will stay flat.
Kerfing would be my last choice.
Have fun.
Lew
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in addition to Lews idea, if it s bare wood you could also wet the cup side to expand the wood. ross www.highislandexport.com www.sandlakeoutpost.com
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Did it cup while on top of your car? If it did it was the sun drying the top side by shrinking the surface. Try dampening the back side and put it in the sun for a couple of hours with the other side facing the sun, watch it carefully it may uncup. Then clamp some heavy boards on it to keep it flat and get it out of the sun and store it for a few weeks while clamped. It should stabilize - we hope.

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