desktop cupping advise wanted

[Mark Johnson]

SWMBO has commissioned a desk for her new home office, and requested a "beefy" look from 2x construction grade stock. It's not ideal construction, but she wants a finished quality, construction grade look to suit her job as a residential additions architect.

I've selected the straightest grain I could find at the Borg (it took awhile), let everything acclimate to the shop and then squared everything up. A few days after glue up, the top cupped a bit (as expected). It's slight enough that I can still force it flat when I attach it to the base, but I am wondering if there is a way to relieve the stress a bit and prevent further problems.

I'm considering routing a groove on the underside of each 5" plank, about half way through the thickness of the top, stopping 6 or 8 inches short of the ends. Hopefully, this would reduce the tendancy for cupping, bit I'm afraid it would lead to cracking instead.

Worst case would be I spend another $20 on materials and glue it up in smaller strips, but that's not the look she's after. Any thoughts or advice?

-MJ

[Upscale]

If you've taken grain orientation into account, then the only other thing you can do is to make sure that you finish both sides of the desk in the same fashion. Equally opposing finishes will tend to have equally opposing forces that can cause cupping.

[Lew Hodgett]

Mark Johnson wrote: > SWMBO has commissioned a desk for her new home office, and requested a > "beefy" look from 2x construction grade stock.

I had a similar problem with a hard maple top.

Clamped it flat to the carcass and installed pan head S/S coarse thread self tapping sheet metal screws on approximately 10"-12" centers.

Drilled pilot holes in the top and clearance holes in the carcass and used small S/S fender washers under the pan head screw to allow for movement.

Since you are using a softer wood, probably would get as much thread engagement as possible.

If they strip out, NBD, epoxy putty to the rescue.

HTH

Lew

[tom]

What's up with this bitch? Tom

[tom]

How long did you let it acclimate? Tom

[Leuf]

Something I read about using 2x lumber for workbenches was rather than use say a 2x4 to use a 2x10 or 2x12. These are usually from the middle of the tree, so if you rip off two pieces from the outside edges and toss the middle you end up with quartersawn lumber that will be more stable.

Assuming the base is as beefy as the top I don't see why you'd have much of a problem once it's attached.

-Leuf

[J. Clarke]

Was this the overpriced kiln dried D-select white pine or was it the dripping wet green douglas fir? If it was the douglas fir that stuff in a 2x section needs to "acclimate" (actually air dry) for two years or so before it stops moving. The KD white pine should have at least a couple of weeks and preferably a month or so of acclimation before jointing and planing unless you have a moisture meter to determine that it's reached a stable level sooner.

See if you can find a mill that can provide you quarter sawn KD lumber in the dimensions you need. If it doesn't look "construction grade" you can add that yourself. Round the edges, a few randomly spaced whacks with a catspaw, spill some coffee on it, shoot a few staples into it and pull them out with a screwdriver, make up a stencil and spray on some grading marks--not sure how you simulate the mildew though.

[Stephen M]

Eggzactly.

If you attempt the redo, seach for the widest boards with the pith in the center. Cut out the middle and you will have quartersawn stock with will be much less prone to cupping than flatsawn material.

Also, if you redo, do not just wait the usual 2-week acclimation that you would for KD hardwood. Construction grade lumber is not dried to that same degree. Essentially, you want to continue air drying for as long as possible. How long is long enough? Idunno, a couple months at least.

I've had great luck using rejointed jointed 2-by stock which has been laying around the shop for a long time for general cainetery-type applications. IME, fresh stuff is always problematically unstable.

Since you already have a top made, screw it down to the base (properly mounted with allowances for movement) to pull out most of the cup (crown up if possible). See how it goes. If the result is not flat enough, tell the swmbo be patient waiting for top #2.

-Steve

[Swingman]

construction,

I doubt seriously that will work and will likely cause further problems ... brute force (battens/screwing down, etc.) is often the only thing that works after the fact.

Too late now, but when you go to make her next "constructions grade look" piece, choose "Vertical Grain Douglas Fir". You will get the same look, but with less tendency to warp and bow, although there may be some sticker shock.

If you know what's good for you, SWMBO's are usually worth the cost of better grade materials.

[Pat Barber]

Very unlikely you will "ever" get this to work.

Your wife should know that construction grade materials have a moisture content of 20% or more.

To make this work, find somebody who carries KD furniture grade material. This will be tough, but there are people who carry that sort of thing for commercial applications. You need stuff with "about" 8% moisture content.

Good luck....

Mark Johns> SWMBO has commissioned a desk for her new home office, and requested a

[fredfighter]

That is frequently done and it works fine so long as the grooves are spaced closely enough together so that no one groove has to bend too much. (It has been called "breaking the back of the panel/board.")

WHy stop 6 to 8 inches from the ends? I think you would get better results by going as close to the ends as possible.

[Mark Johnson]

I'll save this for when she wants something "antiqued". Thanks.

-MJ

[Mark Johnson]

Sounds like a good plan B. Thanks.

-MJ

[Mark Johnson]

WTF?

-MJ

[Mark Johnson]

Good to know it's worked before. What would you consider close enough spacing? If I run one groove down the middle of each plank, they'll be 5" apart, and I'd be thinning the flat sawn portion and removing any remains of the pith.

If I run the grooves close to the ends, it would be more likely to split at the ends, I would think. Leaving more material there should reduce the likelyhood of a split, even if it leaves the stress point.

-MJ

[fredfighter]

Close enough depends on how much cup there is to remove.

I must admit I haven't done it myself. I've read about it and saw Nahrm do it on something like a bedstand which only needed one groove.

A trick for reducing end-checking in a glue-up is to take one piece in the middle and edge joint it so that it is slightly hourglass shaped. This can be done with a handplane, maybe three passes at the center and tapered out to the ends. Then when the panel is clamped and glued the ends will be in compression.

[tom]

Please forgive my drunken, flippant rant. I'm sorry to have been so quick to speak like that, as I'm sure she's a fine person. This is no excuse, but I tend to get familiar with people, quickly, and forget my manners about as fast. Again, I'm sorry. Tom

[Prometheus]

Here's a thought, but it may not be exactly what you're looking for-

When I made my woodworking bench, my budget would only accomodate

2x4s. So to make a top that was beefy and stable, I cut 1/4" off each side of the 2x4s, to get rid of the rounded corners, leaving me with wood that was 1.5"x3" (Or, to be truthful- that's what I wish I had done- in reality, I did that with the frame and legs and foolishly skipped it on the top- which led to many hours with a hand plane). Then, I laminated the boards face-to-face to make a 3" thick top, placing them so that any bows faced one another to even out the stresses over the whole thing.

So far, there has been no warping or cracking in the past few years, and it definitely fits the definition of "beefy". I also ran two pieces of allthread through the top perpendicular to the laminations to give it extra support, but I sincerely doubt that was necessary.

If you want a little different look, I'd imagine it could be pretty nice if you staggered shorter pieces as described above to make a butcher-block style top, instead of one with full-length planks.