[rgbfoundry]

I'm got a very heavy and large workbench/cabinet that was probably a retail store fixture. It's aluminum framed on all edges and the top is formica over two layers of particle board totaling almost 1.5" thick. My gut tells me it's "dead flat" (especially at the corners), but what do experienced woodworkers use to verify that? Do you just screed along the top with a machined level and a light behind it, looking for high or low spots? Is there some cheaper tool that would give me piece of mind? :blink:

 

[Brian T.]

A sheet of heavy glass, pressed against the surface and allowed to rebound, should show Newton's Rings to display the measure the surface with +/- wavelengths of light.
You phart, or move the bench, all bets are off.
Flat is for laboratories and lavatories. Please. Not for woodworinkg crafts.

 

[woodnthings]

flat is where it's at, but ....

How flat? When I made a torsion box for an outfeed/worktable I used the longest flat aluminum extrusion I had, 10 ft X 2" square.

You can take the longest straight edge , possibly a 6 ft long aluminum level and check the long edges and the diagonals and look for gaps with a bright light or a feeler gauge .... BUT what if you find some gaps ....what now? You will probably say, I can't fix 'em anyway. :no:

So, flat enough? Probably so. You can shim from underneath the top or the base it sits on. Woodworking is NOT watch building so for assembly and glue ups which may "move" anyway because of the natural tendency of wood to change dimensions a difference of 1/32" or less overall is probably OK. Even a 4 legged bench may not sit perfectly stable on a flat surface. Things twist and move in assembly regardless of the care and precision taken.

Continuous diagonal measurements and squaring as you assemble a piece will help insure a properly built piece. Drawers and frames must fit into the openings and some allowance for dimensional variations will be necessary. :yes:

 

[BernieL]

I would simply lay a straight edge as stated... even if you can't do anything about it. At least you will know where the lows and highs are if there are any. Many times we tend to overthink simple things, exaggerate minor problems and ruin things trying to make them perfect. If it ain't broke, don't fix it!

 

[rgbfoundry]

Thanks to all

So I'm hearing it's not THAT important. Thanks for the tips on diagonal measurements. I also hadn't thought about the dimensional instability. I think I'm approaching woodworking more like a machinist. It's probably a decent way to think about it, but there seems to be much more forgiveness with the wood/glue approach.

Thanks again.:thumbsup:

 

[Steve Neul]

If it is wood you can only do so much. If it is flat today, tomorrow it may not and be flat again the day after. It's going to move with the weather. To make a top like that more stable you could polyurethane the underside or what would have been better is to laminate the underside with laminate or cabinet liner so all surfaces would be covered.

 

[Al B Thayer]

So I'm hearing it's not THAT important. Thanks for the tips on diagonal measurements. I also hadn't thought about the dimensional instability. I think I'm approaching woodworking more like a machinist. It's probably a decent way to think about it, but there seems to be much more forgiveness with the wood/glue approach.

Thanks again.:thumbsup:

I like a flat work bench. Mine wasn't for years, and for me, it was annoying. I flattened it with a router set up in a rail system. If I was you I would get it close because there are countless times when you need it to be flat to avoid compensating for it. While you can't use a router. You could do something from the underside to put it back into "flat".

Al

Nails only hold themselves.

 

[Wendel17]

If it's not out that much, I wouldn't worry too much about it. If it's got no support in the middle, it may sag a bit. You could try adding support if it is sagged, but if it's only got laminate on one side, you may have a hard time pulling it back.

 

[GeorgeC]

I would simply lay a straight edge as stated... even if you can't do anything about it. At least you will know where the lows and highs are if there are any. Many times we tend to overthink simple things, exaggerate minor problems and ruin things trying to make them perfect. If it ain't broke, don't fix it!

!!!!!!!!!!

So true.

George

 

[Bill White 2]

How can anything be "dead flat" when the Earth is round?
Does anybody REALLY know what time it is?
Oh well........enough of that.:laughing:
Bill

 

[woodnthings]

it's time to get back into the shop...

Dead flat would require a layer of pouring epoxy which will seek it's own level. But for most woodworking and assembly "pretty dang flat" is close enough. JMO
I had to plane a plank built door "pretty dang flat" recently. I used a straight edge and marking pen to show the high spots and remove the marks and check again.

Since the OP's top is Formica covered, no planing or sanding solution will work. A warp or twist can be compensated by shimmed underneath and on top of the frame. Screws up from the bottom on glue blocks will pull a cupped top down if the amount is not considerable. A sag in the center can be compensated by shims on the frame. Otherwise, there are not many obvious solutions to me.

 

[Lola Ranch]

It's going to give your project a better chance of being nice and square if you assembly bench is flat and level. This is important if you are building cabinets that have to be assembled into a larger unit at some building site such as someone's kitchen, but might not be important for stand alone projects .

I use a laser to check my benches. My main assembly bench is 4 x 8 mdf over 9-1/2" TJI floor joists with a heavy leg at each corner. I set the laser off to one side and a little higher than the top of the bench and then use a small block of wood which I mark with a pencil once I find the highest corner. Then it's just a matter of shimming the other legs up to the line.

I'd say my tolerance at each corner is about 1/32" for level and about 1/16" for flatness across the bench. That's close enough.

Bret

 

[HowardAcheson]

My "flat and straight" reference is an almost 20 year old 48" Stanley level. A couple of times over the years I have compared it to an expensive Starrett or other high quality straightedge and found it to be perfectly straight. I only use it for checking straightness and store it in a protected spot along with my reference triangles

 

[rgbfoundry]

Thanks everyone

Thanks to all the responders. It's great to be on such an active forum:smile:!

 

[Knocky]

A sheet of heavy glass, pressed against the surface and allowed to rebound, should show Newton's Rings to display the measure the surface with +/- wavelengths of light.
You phart, or move the bench, all bets are off.
Flat is for laboratories and lavatories. Please. Not for woodworinkg crafts.

Difficult to keep a bench flat, if it's wood. That's why I'm making my new top with 4 x 2s glued together on the 4" faces. It should stay pretty flat, how I like it, as the flatter the bench the easier it is to plane truly flat surfaces.:thumbup1:

 

[Al B Thayer]

Difficult to keep a bench flat, if it's wood. That's why I'm making my new top with 4 x 2s glued together on the 4" faces. It should stay pretty flat, how I like it, as the flatter the bench the easier it is to plane truly flat surfaces.:thumbup1:

This one is flat and stays that way due to how its constructed.

Al

Nails only hold themselves.

 

[Chataigner]

As others have said - what is flat ? I'd be happy with anything better than say +/-1mm for general woodworking. The tough fact of life is that wood moves, it's part of the charm of our hobby : trying to make stable objects out of an unstable material.

 

[cabinetman]

The type of workbench may depend on what you will use it for. I never made a bench with a solid wood top made from a glue up. For casework construction, flat smooth tables work better than traditional woodworking benches.

For doing handwork, a replaceable plywood top works just fine. What's as important as flat is how stable and sturdy the bench/table is to start with. For standard tables, ¾" plywood can be used for legs. You can cut 4" or 6" strips and glue and fasten them at a 90° angle in 8' lengths. For cutting legs, set up a stop and cross cut all the legs the same length. Tops can be Melamine, or plywood. Make a gridwork of 4" or 6" strips from ¾" plywood and make a perimeter for an apron. The legs attach to the inside corners. The gridwork under the top can be a grid with 12" to 16" openings. Allow the top to overhang the apron enough to be able to clamp to the edge.

This type of table/bench will stay flat, and can be fitted with leg adjusters to adjust to the floor. My table saws have had this type of surround, usually at least about 8' x 8'.

.

 

[TooPicky]

OP, I like having a "flat" surface, also. For me it's generally the indeed table of my jointer. In a perfect world, I'd have a surface plate like at my old job. The thing must be 4' x 5'. It would also make an outstanding assembly table. I hear you, I also come from a precision sheet metal/machinist background. I also tend to intermingle this with woodworking, too.

PS, I would only trust your 1 1/2" formica-topped table only so far. Realistically, it's probably good enough for a lot of stuff. I have a similar one with no formica.

 

[Al B Thayer]

As others have said - what is flat ? I'd be happy with anything better than say +/-1mm for general woodworking. The tough fact of life is that wood moves, it's part of the charm of our hobby : trying to make stable objects out of an unstable material.

The bench I built has a main section glue up of maple. Its glued to the front side skirt/ bench dog section. The ends are in slots on both ends where it expands and contracts freely. The skirt is glued all together but in the tool tray there is room to take up the movement. It stays dead flat.

The top sets on the legs. The weight of the bench holds it in place. No fasteners are needed. The tool drawers are a carcass all to them selves and is just sandwiched between the legs.

I would encourage anyone to build this bench because it will meet the needs of almost all aspects of woodworking. If I'm doing plane old cabinet case work. I have an assembly bench that has a lower top and is made in the torsion box fashion. Also rock hard and dead flat.

Al B Thayer

Nails only hold themselves.