How flat does a workbench need to be?

[Dave Anthony]

A few years ago I built this contraption known as the "ultimate tool stand" ref: http://christophermerrill.net/ww/plans/UTS/Tool_Stand_3.html. Basically, it's a cabinet built on a torsion box with 3 boxes on top. It can be used as an outfeed table, router table, chop saw stand, downdraft sanding table, assembly table, etc. It's been very useful, & I've found I mostly use it as an outfeed, assembly and sanding table, as well as supplying power to the center of the garage, aka shop. I also added a vise, and use it as a workbench for occasional planing & hand work. The other day I placed a straight edge on it and noticed the top is no longer flat, there is ~ 1/64" sag over the length. How significant is this? All the books & articles on workbenches state that they need to be flat, but they don't really specify why. I understand that it's difficult to build a square carcass on a surface shaped liked a bannanna, and if I'm flattening a board on a curved surface (something I rarely do, that's the jointer's job) I can wind up with a curved board, but is there something else I'm missing? I tend to use the jointer as my reference surface, as that's the longest/flatest reference I've got.

[John Coloccia]

If your bench isn't flat, flat boards will wobble on the bench when you try to work with them. And yes, banana shaped benches are generally bad. Is the little bit of sag causing you problems? Generally, I don't use my bench as a reference, but I do need to be able to put flat pieces of wood on it and expect that they will be well supported (no significant sagging over a couple of feet) and won't wobble (no significant high spots over a couple of feet). It's also convenient to have it flat to make it easier to align things for glue ups.

Other than that, I don't really think it matters all that much. I'm sure many will disagree. I'd worry about it when it starts causing problems, i.e. if it's not bothering you now then it's flat enough.

How did you measure 1/64"? Do you have a long straight edge or did you use a ruler? I only ask because rulers are notoriously not even remotely straight. Shoot, that's still only about .015". Have you measured your jointer bed lately? I'll bet that it's out somewhere around .005" to maybe .010" over a shorter distance. That's just to put it in perspective.

[Tom Rick]

If your bench isn't flat, flat boards will wobble on the bench when you try to work with them.



John is just being fussy.

On my benches I use a technique fostered by Victor Hugo.

I simply allow a critical depth of debris to accumulate on the bench which cradles the work piece preventing any movement. This is much like the machinists practice of placing paper under fitted surfaces to make up for the micro grain structure of the iron..

Use caution though- I have lost small children in the debris layer on my benches..
;)

[Vince Shriver]

"On my benches I use a technique fostered by Victor Hugo."

I'm trying to remember if there's something in the "hunchback of Notre Dame" about flat benches. Hmmmmm, that does ring a bell.

[Prashun Patel]

I'm sure you can compensate for an uneven bench during use. But having it reliably true is useful when you have other things to worry about during a project.

[Dave Anthony]

Thanks Tom, A few pieces of paper flattened it nicely :). Since I constructed it so the top 3 boxes were removable I just selectively taped paper to the bottom of the boxes until it was flat. Well, actually I don't know that it's flat, I'm using a 5' aluminum straight edge that may or may not be straight. I'm assuming it is, since it doesn't seem to make a difference which edge I use to measure. If it's not, at least the assembly table, saw, and jointer all have the same curvature.

[Chris Friesen]

Something that nobody has mentioned is that if handplaning a board flat you don't want the board to be dipping down into hollows in the bench as you plane over it otherwise it will not result in even thickness of the board.

[Bill Whig]

Everything above being said, is it reasonable to be able to expect to *hand plane* a 6 or 7 foot bench flat enough? I have collected a few old planes, including a #7, and was hoping to try. I think I'll start on something smaller and less expensive.

Bill

[John Coloccia]

Everything above being said, is it reasonable to be able to expect to *hand plane* a 6 or 7 foot bench flat enough? I have collected a few old planes, including a #7, and was hoping to try. I think I'll start on something smaller and less expensive.

Bill

Well, there was a time, way back when we were tired of living in caves and sitting on rocks, but before we'd invented European sliders and wide belt sanders, that it's rumored people did just that. I hear they didn't even have MDF. I just can't imagine.

I'm guessing they probably had much the same philosophy that I do when it comes to workbenches: get it flat enough to where it's not getting in the way, and then make stuff because I'd rather have a chair that's off by .005" than a rock.

But if I really wanted it flat, I'd take it to my local mill and have them put it on their wide belt. When mine is finally beat up enough to warrant it, that's exactly what I'll do.

[johnny means]

I don't bother with checking the flatness of work benches. There are plenty of reliable reference surfaces around my shop. As long as my bench holds stuff up it's flat enough.

[Bill Whig]

But if I really wanted it flat, I'd take it to my local mill and have them put it on their wide belt. When mine is finally beat up enough to warrant it, that's exactly what I'll do.

Thank you, By "wide belt", do you mean a large drum sander or something else?

Bill

[ian maybury]

I guess the one fairly concise answer to the original question is 'it depends'. (on what you want to use it for)

If the plan is to clamp cabinet work down on it for assembly or machining it'd be nice if the top was flat, and the sides square to that - otherwise it's either do lots of checking and shimming, or expect some distortion. Ditto if you use it as a reference surface from which to mark stuff out with e.g. a height gauge. Flat is also useful as already said for hand planing, especially longer pieces.

If on the other hand most of what you do is with short pieces and involves a lot of e.g. cutting down with a chisel, or woodcarving or rustic stuff then maybe it's not so important. Or if you work to very coarse tolerances.

It's I guess basically a case of thinking through what you may want to use it for, and then deciding - but it's hard to think of a situation where a flat bench top is actually going to cause a problem.

It's never going to be the equivalent of a marble surface table anyway, chances are it'll move around a bit anyway...

ian

[Ed Morgano]

All the books & articles on workbenches state that they need to be flat, but they don't really specify why.

Dave,
One of the problems I've had with two benches that I built is twist and that can really be a problem with assembly. Doors end up with a twist, tables won't sit flat on the floor etc. I really think this is a bigger problem than a .015 sag.

[John Coloccia]

Thank you, By "wide belt", do you mean a large drum sander or something else?

Bill

Actually, a wide belt sander. Look it up and it will make sense. It looks like a big drum sander but it actually has a belt on top instead of a drum.

[michael osadchuk]

One reason for a flat workbench - you can use it as a very quick reference surface when dressing long pieces of wood.

I can toss the edge or face of a board on a flat benchtop and instantly see where my handplane needs to be applied.

Much, much quicker than dragging out the metal reference straightedge or winding sticks.

good luck

michael

[Mike Cutler]

It needs to be as flat as you can make it.

[Erik Stol]

I am in the middle of redoing my shop. I used to have a big workbench at the back of the shop, from which the surface was one peace of 40mm plywood (exterior quality) 4'x7' in dimension. It turned out that it became one big storage area. So I did cut it in half and now I have a workbench of 15' long, (placed along the long side of the shop) with place for the CMS I am intending to buy. Lots of cabinets underneath it and hopefully it stays clear of all kinds of debris. ;)
Flatness: Perfect. The plywood is so stiff, that you can use it to align the cabinets underneath it.

[Tim Boger]

A few years ago I built this contraption known as the "ultimate tool stand" ref: http://christophermerrill.net/ww/plans/UTS/Tool_Stand_3.html. Basically, it's a cabinet built on a torsion box with 3 boxes on top. It can be used as an outfeed table, router table, chop saw stand, downdraft sanding table, assembly table, etc. It's been very useful, & I've found I mostly use it as an outfeed, assembly and sanding table, as well as supplying power to the center of the garage, aka shop. I also added a vise, and use it as a workbench for occasional planing & hand work. The other day I placed a straight edge on it and noticed the top is no longer flat, there is ~ 1/64" sag over the length. How significant is this? All the books & articles on workbenches state that they need to be flat, but they don't really specify why. I understand that it's difficult to build a square carcass on a surface shaped liked a bannanna, and if I'm flattening a board on a curved surface (something I rarely do, that's the jointer's job) I can wind up with a curved board, but is there something else I'm missing? I tend to use the jointer as my reference surface, as that's the longest/flatest reference I've got.

I've never got within a 64th on anything I've built .... I can't even sharpen my pencil with a tip that fine. geez.

[Lynn Floyd]

I agree with Ed that twist would be more trouble than a slight sag. I have a 42" wide belt sander and I can say that it will not surface accurately closer than a 1/64", not even when it was new. Could you put a support post in the center, or put stiffener straightedges on the bottom?
Lynn

[Mike Cutler]

I've never got within a 64th on anything I've built .... I can't even sharpen my pencil with a tip that fine. geez.

You can do it easily, but the next morning the wood will have changed enough to negate the effort.
It's wood, not metal. As long as you cut to "your same pencil line" you're fine.

A person can get away with a not perfectly flat bench top just fine. Having it statistically flat is a big help though.
I have a 3'x3' piece of tempered glass that used to be a coffee table top. I throw and old towel on the bench, put the glass on top and now have as flat a reference as I need. My 6' Starrett says it's good enough at least.

[scott vroom]

I'm using a hollow core door (torsion box construction) on saw horses as an assembly table. It's not perfectly flat but for what I'm building (faceframed cabinets) it's fine. I'm using pocket screws on the faceframes which pull the frame square and flat enough. I'm using the Somerfeld method on the boxes...same thing, the joinery pulls the boxes square and flat enough. If I were building fine furniture maybe work bench flatness would be a bigger concern, however for the meat and potatoes stuff I'm doing it just isn't as important.

[Chris Friesen]

Everything above being said, is it reasonable to be able to expect to *hand plane* a 6 or 7 foot bench flat enough? I have collected a few old planes, including a #7, and was hoping to try. I think I'll start on something smaller and less expensive.

Absolutely. Chris Schwarz did an article on this in either Woodworking or Popular Woodworking magazine--might be some blog entries online if you don't have access to the magazines.

Anyways, he checked things out with winding sticks, traversed (went across the grain) with a fore plane to knock off the high bits, then used a jointer plane to go went diagonally both ways and finally lengthwise. As I recall, the end result was that it was flat within 0.006".

[Chris Padilla]

A few years ago I built this contraption known as the "ultimate tool stand" ref: http://christophermerrill.net/ww/plans/UTS/Tool_Stand_3.html.

I think you've gotten plenty of answers, Dave, so I'll move off topic a bit to say: I built the very same bench!

That was a good 8-9 years ago...maybe even 10.

The plastic laminate has since peeled up in a few spots.

The MDF sides have sagged. I had to put corner blocks everywhere to reinforce it and somewhat true it back up.

I want to rebuild from the torsion box back up...out of lighter plywood...and double up the plywood sides so they're 1.5" thick. The MDF is just too heavy IMO. I also built my bench 81" long by 32" deep. That is too deep, I think.

Overall, it has served me well but it needs a rebuild and slight redesign here and there. :)