Workbench tops

[Herb Blair]

I've spent a considerable amount of time in the workshop during the Christmas and New Years holidays. In doing so, I found that the top on my workbench (4' x 6') is not flat, but rather sway-back by about an 1/8" in the middle.
When I originally built the bench, the foundation is made from 4x4 posts, with mortise and tenion joinery. The top is two layers of 1" MDF, glued and screwed together with a top of 1/4" tempered hardboard. The top makes contact with the legs and rails all the way 'round. This top is extremely heavy!
To correct the dip in the middle I drove wedges between the top and the front and back rails. This helped, but didn't completely flatten it out.

I think a better method of building a table top would be to use a torsion box with 1/2 plywood on the bottom, about 1 1/2 spacers (3/4" plywood), then a sheet of 3/4" MDF, with a 1/4 Plywood above.

What say guys, am I on the right track?

[Corvin Alstot]

Sounds like your ready to step up to a traditional solid wood workbench top. It could either be purchased or made. Probably may cost a little more, but you would not be in this situation again. JAT

[Bob Smalser]

For 30+ years, I've made all my working tops, jigs and panels out of hard maple, madrone or other heavy hardwood laid up on edge with creep-free urea resin (and now occasionally poly) glue and I don't recall ever having a flattening problem. Cheap, hard, heavy, stable, bulletproof, and an excellent way to use up rip waste.

Should I ever need to flatten, a straight batten or straight edge coated with string line chalk and the Stanley #8 or Porter Cable 24" belt sander will make short work of it.

http://pic3.picturetrail.com/VOL12/1104763/2594265/50414150.jpg

[Rich Person]

I don't get the impression that solid maple tops solve all problems. When you have to go back and replane every so often, that sounds like more work than I want to put into maintaining my bench top.

The main problem I see with a torsion box (for my use) is I want dog holes in my top, so a torsion box seems like it would catch a lot of dust and not provide the lateral strength needed to support the holes. My current design (in progress) uses central crossed beams that will be mortised into aprons kind of like an open bottom torsion box, but I will start with a layer of 3/4 ply on the bottom, and then use MDF above that. I'm hoping that will take care of any dish issues.

This may not work for your setup, but it is something to think about.

[Bob Smalser]

...that sounds like more work than I want to put into maintaining my bench top.


The only one around here I recall doing is my father's old 2X2" beech top made in 1954...that scantling size not being optimum for stability...look at my pics and I lay up 4/4 and 5/4 stock.

Had to flatten it once after 30 years of use...but mostly because of built up crud. Took 30-60 minutes with the belt sander and chalked batten as I recall....if I thought that was too much physical work, I'da took up library science instead. ;)

You'll do the same thing to plywood after 20 years of glue and goo drippings...only with a lot more difficulty than with solid.

[Tom LaRussa]

I think a better method of building a table top would be to use a torsion box with 1/2 plywood on the bottom, about 1 1/2 spacers (3/4" plywood), then a sheet of 3/4" MDF, with a 1/4 Plywood above.

What say guys, am I on the right track?
Herb,

It sounds like you're describing more of a work/assembly table than a cabinet-maker's bench. I think that's why everybody keeps telling you to laminate hard wood for the top.

If what you're looking to build is a big flat surface that you can paint on without really worrying about it, then I think a torsion box is a good idea.

But I would use exterior grade plywood for both the top and bottom permanent surfaces of the box, (to prevent delamination if you get it wet), and hardboard as the disposable top surface, because it's smooth and very cheap. If you want the hardboard to last longer you could put a layer or two of rub-on poly on it.