how important is a perfectly flat bench?

[tmbg]

My benches didn't come out perfectly flat... on one of them, I spent an inordinate amount of time trying to make sure the frame was square and true and flat, and it still bows down a bit in the center. Is this going to cause me problems? I was reading Spike's builder's log, and read about how his elevator ended up warped. I hope to avoid this sort of thing if possible!

[Spike]

Well, out of all the things that contributed to my warped eleveator, I would say what the table was a very minor contributor. My tables are generally within a 16th - 32th of an inch across their width. Get it as close as you can and then keep checking the parts while building.

Spike

[cjensen]

Hmmm...To tell you the truth, I've never even checked, or given it a thought if my table was level or not. The table could be sloped downhill for all I know. The important thing is to use the BEST top you can get. I forget what it's called that I used (MDF maybe ), but the table top is FLAT and finished from the store. It has a finished white surface on both sides, that's all I remember, other than it being $$$.

[tshort]

Get 3/4" MDF - it is about 25$ or so for a 4x8 sheet and is very flat.
I made all my tabletops out of that. It is not "finished" but is very smooth, I just sanded it with an orbital sander and put a few coats of polyurethane on it to keep dust down.

T.

[tmbg]

my tops are 3/4" MDF, there's just a slight bow to them so they sag a bit in the middle. It's very slight, maybe 0.050" in 8'

[Speed3Guy]

I periodically check my bench for flatness. It does make it easier to make straight parts, especially when working on trailing edges.

To adjust the flatness of my bench, I loosen the screws that attach the top to the frame and slide bits of folded paper or cereal box paper between the top and the frame at the low spots. This is a habit I picked up when I built furniture for a living.

It doesn't matter what you make the top out of--as long as the frame underneath is lumber it will move and change dimensions over time. If you want a truly flat and stable bench, you need to make the entire frame out of glued-up stacks of MDF. The top should be a box beam made up mdf too. More trouble than it's worth in my opinion.

[tmbg]

is there any easy way to check an 8' bench for flatness aside from buying an 8' level or straightedge?

I have a 4' level, 8' levels get expensive!

[Lorin Dueck]

How about a tight string across the whole length (assuming you have a sag in the middle)???

Lorin D
9A Wings

[tmbg]

ooh, good idea!