Untwisting a workbench top
February 10, 2012 5:40 AM   Subscribe

A friend gave me an old woodworker's workbench (looks a lot like this), and I'd like to put it to use. It has been stored improperly, and has a pretty severe twist in the third near the side vise. The whole top is something on the order of 10 cm (4") thick, and glued up from birch boards. Ideally I'd like to untwist it and flatten it and use it for woodworking. I'm unsure if it's feasible, though. I'm willing to spend a little money, as a new one of the same size is really expensive (USD 1000+).
posted by Harald74 to Home & Garden (16 answers total)
Twist like this is generally not fully reversible. To the extent that it can be undone, it will happen by itself as the wood acclimatizes to a proper (i.e. reasonably low-humidity indoor) environment.

Put the bench wherever you intend to use it. Let it stabilize in its new environment for a while -- a few weeks at least, preferably a couple of months. Adjust the vises as needed so they work smoothly and then machine the top flat, making sure the freshly cut surface is as near parallel as possible to the vise guides.
posted by jon1270 at 5:51 AM on February 10, 2012 [4 favorites]

Untwisting it is probably not going to happen, but you can plane it flat (depending on how severe the twist is, since you'll basically be shaving the entire top down to its lowest point). I've never used a handheld belt sander, but my first thought is to start with one of those to get it in the neighborhood of flat, and then use something like a #6 handplane to finish the job.

This would be easy to do approximately correctly, more difficult to do very well. It's not unreasonable to hire an experienced woodworker to help with this project.
posted by deadweightloss at 5:52 AM on February 10, 2012

How much is the twist, is the question. Seconding that it will not be possible to untwist it, but maybe you can (after letting it stabilize for several months as jon1270 says) plane it flat, using a power plane for wood floors (to be rented). As deadweightloss says, the last finish should be done with a (also true - and sharp) hand plane.
posted by Namlit at 6:21 AM on February 10, 2012

I concur with all the above.....and would like to add, that having a flat, square and sturdy bench in your shop is one of the best "gifts" you can give yourself. This is not the place to cut corners as this bench / tool can have either a positive or negative effect everything you do for years and years to come. A few hours spent getting it just right will pay off 20 fold when everything you make is straight and true.
posted by HappyHippo at 6:34 AM on February 10, 2012

If you have or can borrow a router, the best way I know of to flatten a large surface like this is with a router sled bridging a couple of long straightedges (the factory edges of a piece of plywood, for example) clamped to the long sides of the bench. Site across those straightedges, as you would with winding sticks, to make sure they're parallel. Use the biggest diameter cutter your router can reasonably swing, and as short and stubby as possible while still long enough to reach the benchtop through the slightly elevated sled. The resulting surface will be a little rough, but nothing that can't be quickly cleaned up with a plane or scraper.

Doing all the work with a plane is possible, but it can be A LOT of work, and coaxing flatness out of a twisted surface takes quite a bit of skill.
posted by jon1270 at 6:57 AM on February 10, 2012 [3 favorites]

I was planning on doing what you describe, jon1270. Unfortunately, the bench has been indoors now for two months, so it seems like the majority opinion here is that the twist is unsalvageble.

Given that the twist is located to one end of the bench, I'm considering just cutting it off, and using the resulting, shorter bench for smaller stuff, maybe as a sharpening station or something.
posted by Harald74 at 7:05 AM on February 10, 2012

Remember that the ballpark for drying wood is 8-12 months per inch of thickness. If it's been somewhere where it can absorb moisture for a few years, it may need a few years to dry out.
posted by straw at 7:22 AM on February 10, 2012

The suggestion to begin with a sander confuses me. My (sad) experience with sanding first and then using an edged tool is that sandpaper leaves grit embedded in the wood which promptly dulls cutting tools. I now always sand last, if ever. Plus sanding, in my experience, is a poor way to remove a lot of material.
posted by Hobgoblin at 7:37 AM on February 10, 2012 [2 favorites]

I have no new solution to add, but I want to say every answer here is excellent. I think jon1270's router sled idea is especially good. I'm curious why you think this won't work now, is the twist so severe that you'd be removing too much material? It would be heartbreaking, IMO, to just lop off a chunk. Also, I'd fear that would release tensions in the laminations that heretofore were held in check - making the twist grow down the length of the benchtop.
posted by werkzeuger at 7:41 AM on February 10, 2012

Also if I were to go the router sled route, I would carefully construct the sled out of aluminum channel or speed rail or something similar. If you're going to that kind of trouble it's worth it.
posted by werkzeuger at 7:44 AM on February 10, 2012

If the top is removable, you could try to find a shop that's got an industrial thickness planer. That'd make short work of it.
posted by aramaic at 8:11 AM on February 10, 2012

You have to tell us how *much* twist. All workbenches twist, cup, and warp with age. If the top is 4" thick an the twist is, say, less than 1.5", you can still recover it. On the high leg, you'll likely have to re-make a leg or mortise in an extension, but that's no big deal.

Start with a roughing or fore plane and rough the surface down to very nearly flat. A couple make-shift winding sticks will get you there. Then plane it down flat like you would any other surface.

Also second'ing the notion of not using a sander before a plane. Benches don't need to be sandpaper-smooth (it's actually annoying if they are) and even the best-made sandpapers will leave grit in the surface. And you'll need to lightly re-plane the top in a few years, anyway...
posted by introp at 8:46 AM on February 10, 2012

The traditional way to flatten a workbench only requires the use of hand planes and aids like winding sticks, as noted by introp -- if you don't already own the planes and have the skills this will probably not be the simplest solution.

Al less skilled, more mechanical way involves using a jig involving straight edges and a router as shown in this Wood Magazine article.
posted by Quinbus Flestrin at 2:58 PM on February 10, 2012

I'm curious why you think this won't work now, is the twist so severe that you'd be removing too much material?

Yeah, I'm eyeballing it to be around half the thickness of the top, maybe more.

And as to how long it has been stored improperly, it has been years in a damp cellar.
posted by Harald74 at 1:17 AM on February 11, 2012

Half the thickness well yeah.

Let me tell you what they do with twisted 200 years old grand pianos: they disassemble the entire rig, neatly undoing all the glue joints, de-twist the parts one by one and finally re-assemble them. This is often greatly helped by the original glue-up being made with hide glue which can be soaked, heated, etc. until it lets loose; also some of the stacked (not laminated yet) frames have had the tendency to partly get unglued over time, so...

The problem with your workbench is likely that the glue is modern and difficult to get to let loose. But that's what would be needed to be done: disassemble, and untwist board for board. Untwisting single bits of birch would still involve some work but would possibly be feasible, with heat, dampness and some heavy-duty reverse-twist clamping. No matter what, this isn't for the faint of heart.

So maybe your idea is the best one in this case - sadly.
posted by Namlit at 3:54 PM on February 11, 2012

How about using a router sled as described above to level the top, then laminating a new layer of wood on top to bring it back to the desired thickness? As others have pointed out, it might be a good idea to get help with this from an experienced woodworker. Woodworkers tend to be enthusiastic about things like old benches, so it might not be too hard to find someone to help out.
posted by primer_dimer at 5:13 AM on February 13, 2012 [1 favorite]

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