How flat?

A straight edge tells you whether the piece is out of winding. Use a small engineers square or an accurate square you have in the shop to check the right angles of the piece. If you can place the square on all the edges and not see light under the arms of the square at any edge, you’re square and you can stop. This is what Ian Kirby does and there arent many master wood workers who are better.

Can’t add much but remember…..it’s a workbench :-). How far along are you? Have you flattened the top? How did you do it or how do you plan to do it?

I will finish my slab after work tonight, just need to glue the front laminate and tighten down the end block. If the vice works well, then it is on to finishing the base. The base is milled, I need to cut the mortises and tenons, install the leg vice, then draw bore it all together. It’s not a hard project other than wrestling big hulking chunks of wood, my back may never recover.

IMHO, feeler gauges should not be used for checking flatness of a piece your planning. Just check for light or high spots that lets the straight edge spin.

-- www.newageneanderthal.blogspot.com . @NANeanderthal on twitter

just a framing square, and a 4 foot level. Why the level? lay it along an edge, then in the middle, then the other edge. Any LARGE gaps? No? It is flat along it’s LENGTH. Take the framing square ( or a shorter 24” level) and set on the top. Check every 6-12” along the top. Any LARGE gaps under the straight edge? No? Then put the toys away, you are as close as you need to be. Mine has a very slight cup in the middle, MAYBE a 1/32”. Am I worried about it? Nope. I can set a piece of stock on the bench, anywhere, and there will be no”rocking” going on.

One could have a top “flat’ to .000001”, for a day or so. Tops are WOOD, and wood will move, accept it, live with it, and go make something. As long as all the ‘dippy doos” are gone, no big bumps, or dips, top will be fine. If one want that “Mythical” perfectly flat top, get one made from cast iron…..

-- A Planer? I'M the planer, this is what I use

I guess my question wasn’t clear. Disregarding the Roubo bench leg for now, is it possible to make the entire face of a board (not the edge) so flat that there will never be any light visible under a straight edge or that winding sticks will always appear to be perfectly parallel (at least as far as the eye can tell)? In other words, if there’s a sliver of light visible in a few places under the straight edge, and if the winding sticks are just a couple hundredths out of parallel, is that okay or should I be able to make the board even flatter (again, not a Roubo leg or top, any board that I want to make as flat as possible)? I’m not trying to nitpick, I’m just wondering when good enough is good enough.

-- More tools, fewer machines.

Bubba, I’m moving at a snails pace on the Roubo bench. I started buying lumber in December and have been rough cutting, drying, and thicknessing (with the help of a friend’s cabinet-shop thickness sander—lucky for me) the parts. Just last weekend I laminated the boards for the legs, and now I’m trying to flatten and square up the faces of the legs. The boards for the top are cut roughly to size, but they still need another pass through the sander. Also, almost all of the top boards developed a spring when I ripped the the 2×12s down the middle, so I need to straight one edge so I can cut the boards to width on my table saw.

-- More tools, fewer machines.

Brett,

Are you using SYP? It can do amazing tricks after milling :-). I went the other way, did the slab first, either works, mostly depends on your work space which is easier.

Yes, one COULD make it that flat, but it will never stay that way.

Beside the “wood being wood” issue, wear and tear on a benchtop will also affect the flatness issue. Ever see an old Butcher’s block?

Just get as close as you can, and continue with the rest of the build.

And then, put the bench to work.

-- A Planer? I'M the planer, this is what I use

Flatness is indexed by feel with a plane and by eye with
winding sticks if you need them. Train your eye enough
and you can see it without the sticks. Bow is variable
with gravitational pull on the board…. I use a 78”
level to reference board bow. Minor bow is seldom a
problem. Cup is annoying but can be corrected with
planes or by dovetailing, etc. Twist is the most insidious
and that’s what you need to see accurately.