help saving a bench project

[Alex Liebert]

I haven't posted here in a long while, but I got some great help from you guys starting out! (Although I'm still a beginner by all accounts.)

My job's been taking a lot of my time and woodworking projects go extremely slowly.

I have a 2.5" x 30" x 60" benchtop, beech boards laminated face to face. I finally found some time to restore the vices and install them.

2 weeks ago, I flipped the benchtop upside down and put it on my assembly table, and started chopping out a mortise to recess the front vise. Very pleased with the results of my first time doing this, by hand, but ultimately the bench was sitting top-down for 2 weeks.

Incidentally the humidity has been dropping like crazy in that time. I attached the end vise yesterday and noticed things were out of square. I stepped back and grabbed some straightedges and the benchtop is cupped, with the crown on the top of the bench- a little more than 3/32". So the bottom of the benchtop, which is facing the ceiling, is drier than the 'top' of the benchtop currently facing the floor. The benchtop is still upside down but I put a bunch of 2x4s underneath it to get airflow going around it.

I would very much appreciate advice on what to do next. I'd prefer not to remove the front vise if I can avoid it. My current plan is to apply a finish to the underside of the bench, flip it right side up again and put it on its base, then leave it that way for a week. Then plane the topside back to flat and apply a finish on the topside.

Is this a good strategy?

[Scott Winners]

My bench top moved seasonally. I built in January 2019 from home store construction lumber. It was flat in February. In July 2019 it was crowned. I took part of the crown off in July, but I didn't want it to be cupped in November, so I only kinda sorta flattened it a little bit. My plan is to wait until May next year to get it perfect flat, and then see how much it cups and bows for 12 months before I fool with it again.

I am in Fairbanks, AK, my outdoor year round EMC is 11%. Indoors I routinely see +80dF at 70% humidity in my shop, wintertime 8-12% RH at +65dF. Mine is going to move, but I do hope it settles down a bit.

[Jim Matthews]

I'm not convinced a dead flat bench is achievable.
If things don't roll off, it might not be necessary.

Once mounted to a base, the top might "sag" a bit in the middle. Consider mounting the vise, flipping it over and putting it to use before expending more effort.

[Michael Bulatowicz]

My current plan is to apply a finish to the underside of the bench, flip it right side up again and put it on its base, then leave it that way for a week. Then plane the topside back to flat and apply a finish on the topside.

Is this a good strategy?

Whether you should put a finish on the bottom now or not will depend on what you expect the humidity and your shop temperature to do. If you expect the humidity and temperature to to go back up, I’d wait for the top to catch up to the bottom in dryness. You can speed that process up (with, possibly, some risk of drying too quickly) by aiming a fan at the bench, making sure the air flows over the bottom and over the top, at least through the gaps between the 2x4s. If you put a finish on the bottom now, the bottom should exchange moisture more slowly than the top, which can be a good or bad thing depending on the humidity and whether it’s climbing or dropping, and what your shop temperature is doing. Ideally, the top and bottom should be somewhere near equal moisture content when you do any final flattening you desire followed by applying finish. After finishing, you can expect the moisture content in the benchtop to pretty well even out over time, whatever that means for the shape of your bench.

I agree that it shouldn’t be necessary to remove your vise.

[ken hatch]

I'm not convinced a dead flat bench is achievable.
If things don't roll off, it might not be necessary.

Once mounted to a base, the top might "sag" a bit in the middle. Consider mounting the vise, flipping it over and putting it to use before expending more effort.

I'm with Jim.

Flip it over, attach it to the base and go to work. You will figure out where the flat areas are and can use them when needed. In a year or so check it for flatness and make small corrections if needed. BTW, Beech loves doing stupid wood tricks, I've seen perfectly straight boards turn into a banana after sawing an edge off. That said, I use Beech for most of my slabs because it is close to a perfect slab wood.

ken

[Michael Bulatowicz]

My bench top moved seasonally. I built in January 2019 from home store construction lumber. It was flat in February. In July 2019 it was crowned. I took part of the crown off in July, but I didn't want it to be cupped in November, so I only kinda sorta flattened it a little bit. My plan is to wait until May next year to get it perfect flat, and then see how much it cups and bows for 12 months before I fool with it again.

I am in Fairbanks, AK, my outdoor year round EMC is 11%. Indoors I routinely see +80dF at 70% humidity in my shop, wintertime 8-12% RH at +65dF. Mine is going to move, but I do hope it settles down a bit.

I have good (anecdotal) news for you. I live in Madison, Wisconsin: my shop, too, routinely sees +80dF or higher (occasionally above 90dF and high humidity) in the summer with 70% or higher humidity, and as low as 40dF with 30% relative humidity in the winter. I built my bench in sporadic opportunities from home store construction lumber over the course of a year or so, finishing the basic build a year and a half ago. The top is just laminated 2x4s. I flattened it a little bit early this spring, because it had slightly bowed near the vise (enough to cause trouble with planing thin boards). Other than that, it seems to have settled in just fine and hasn’t given me any trouble at all: no cupping, crowning, or twisting. I have left it unfinished, which may be part of why it doesn’t seem to seasonally warp, or maybe it just settled in. Either way, I have proof that construction lumber benches can do fine with wild swings in temperature and humidity. Hopefully yours does as well.

[William Fretwell]

Alex, I’m assuming the top was flat and had been stored for some time, given your work schedule. As the humidity dropped your bench dried on the bottom more than the top because it was sitting on an assembly table. Pretty classic really!
i would restore the moisture on the bottom with a wet cloth, several times a day and watch it flatten, this gets rid of the stress. Stand it on edge for a week with even air flow both sides. As long as the air flow is even it should stay flat. I have done this successfully several times.

One of woods rules; what you do to one side, you do to the other.

Don't apply a finish to the bottom you are not applying to the top. Benches last a long time, varnish is not a good choice as it ages, flakes and cracks. Oil is a far better choice, I use boiled linseed oil (BLO) applied smoking hot with wire wool and tongs, three coats over three days. Wipe off the excess each time with rags. For the rest of the benches life, and mine for that matter, I apply Tung oil on occasion. BLO gives you a grippy finish without being sticky.

On a safety note throw the rags in a bucket of water, then throw them away. Rags with BLO have been known to spontaneously combust.

In Ontario we have 90% humidity in the summer and 7% in my shop in the winter, a terrible place for wood!

[Robert Engel]

Alex,

I believe there is a very good chance the top can be re-acclimated back to "pretty" flat. I think you're plan will probably work.

Another alternative is to turn it over (convex side up) and place a couple lights and/or a fan over it, let it go overnight and see what happens.

Incidentally, I made a built in for our living room with a TV cabinet, standard cope and stick doors. The gap was a little tight, but I new when I moved it inside it would widen. But for some reason when I remounted the doors, the gap was even narrower, so much that the doors almost rubbed when closed.

A little voice told me to leave it alone, and 6 months later, the gap is a perfect 3/32". This taught me a valuable lesson.

So I'm convinced wood can "reform" itself, in spite of human error.

[Alex Liebert]

Alex, I’m assuming the top was flat and had been stored for some time, given your work schedule. As the humidity dropped your bench dried on the bottom more than the top because it was sitting on an assembly table. Pretty classic really!

Thank you William, this is exactly correct! The top was stored in my shop for 10 months, on the base it's going to be installed on. I have to admit I didn't precise measure for flatness before flipping it for the vises, but it has cupped significantly in 2 weeks it spent on its back on a table.

i would restore the moisture on the bottom with a wet cloth, several times a day and watch it flatten, this gets rid of the stress. Stand it on edge for a week with even air flow both sides. As long as the air flow is even it should stay flat. I have done this successfully several times.

Interesting - so wet a rag and then use it to wet the entire face of the dry side? I'm not sure I can get it on edge with the space and physical help available to me, but I could keep it 'stickered' on 2x4s and blow a fan on it.

One of woods rules; what you do to one side, you do to the other.

Don't apply a finish to the bottom you are not applying to the top.

Absolutely. Plan is oil and light wax. I was considering staggering the timing of finishing the cupped and crowned sides if this could help restore the shape of the wood a little bit faster. Also I have to time when I can get someone to help me flip this thing, so finishing the cupped side, then letting it sit until I can plane and finish the crowned side is easier. But this is probably not a good idea.

In Ontario we have 90% humidity in the summer and 7% in my shop in the winter, a terrible place for wood!

Pretty close here. I have a hygrometer in the garage ("shop") because I mostly do hobby restoration / refinishing and it helps decide when the best time to work with lacquer is. Most of the year it swings between 60% and 80% over the course of any day. But this last couple weeks it's reading as low as 30% and I've never seen it that low.