How Flat Does An Assembly Bench Need To Be?

Allen Bookout

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Punta Gorda, Florida
My plans are to build some furniture so I need a really flat assembly bench. I built one out of MDF and surfaced planed it to perfectly level so I decided to build a second one out of sandply since I had the other flat one to build it on. I decided on a second plywood one because I was afraid that the MDF might not hold up. I tried to laminate it but it did not come out exactly level so I ripped off the laminate and surface planned it again with a router sled.

Much to my supprise the new sandply one is not perfectly flat even though I had it clamped to the MDF one at all times.:bang: Across the three foot width it is very flat but lengthwise is where I have the problem. About one third of the way from one end it has a slight dip of .020 of an inch that runs about eighteen inches or so. The .020 of course is at the center of that span. I would plane it as I did the MDF one but the outer layer of the sandply is probably no more that .020 and then I would run into some rough wood.

My questions are: Is this flat enough? If not, what would you do about it?:dunno:
 
My plans are to build some furniture so I need a really flat assembly bench. ...Across the three foot width it is very flat but lengthwise is where I have the problem. About one third of the way from one end it has a slight dip of .020 of an inch that runs about eighteen inches or so. The .020 of course is at the center of that span. ...My questions are: Is this flat enough? If not, what would you do about it?:dunno:

Hmmm.. 1/50"... For me, that would be 'close enough.' That much variance would easily be compensated for by virtually any carpeting.

If you have hardwood floors, tile floors or linoleum floors, have you tried your straightedge across any of them? I'd bet that most - or all - of them are out of 'flat' at least that much somewhere across their span.

I wouldn't worry about it, Allen.
 
That's a tough one. 0.02 is a little more than 1/64th. You can see 1/64 on some joints, for instance table leg to apron.

I wonder if there would be a way to add a little to the area where it takes the dip, maybe a coat of shellac or two?:huh:

Having said all that, its awful darned close!:dunno:

What I would worry about is whether you will curse yourself in the future for not fixing it, every joint that isn't crisp may haunt you, I know it would me.:rolleyes:
 
Thanks guys! The good news is that the consensus is that it is flat enough. The bad news is that it still bothers me a bit. I just cannot figure out how to fix it without making more of a mess out of it. I though about flow coating a little epoxy in that area and then coating the whole thing with a couple of coats of epoxy and sanding smooth. That would make it pretty tough. Oh well, I will see how I feel about it in the morning.
 
Allen -

I guess it depends on how anal you are towards doing something to the absolute best of your ability. If your anything like me... I truely feel sorry for you. :)

I made my assembly table from 3/4" MDF as a tortion box - both upper and lower surfaces are faced with an internal honeycomb that's about 8" apart. Due to humidity in my shop, I noticed a slight depression in the MDF that almost clearly outlined the honeycomb core. The amount of sag was something like 1/64 at the very most. Just enough to be annoying, as it probably would have very little effect of projects.

Anyway, I knew it was there...and just wouldnt be content knowing I was working around this 'flaw'.

I used a floor leveling compond to level it out using a heavy staight-edge. I then then glued down a 1/8" piece of hardboard. (with lots of MDF and cauls!) Put a few coats of blo/turps then wax. Haven't detected a problem since. Or rather, It's because too chicken to check. :)


Like others have said, .02 isnt much to worry about. But understand, everything that you assemble on this table will also risk being .02 off. This is the part that would bug the heck out me. To me, "Good enough" often isn't.

It's almost like having a TS blade set to 89.9 degrees. I can live with this, or with just a little more effort I can get it set properly. It's my curse.
 
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Allen -

I guess it depends on how anal you are towards doing something to the absolute best of your ability. If your anything like me... I truely feel sorry for you. :)

Timothy,

I guess that I am a lot like you. I spent Friday night thinking about it. By Saturday morning I could not stand it anymore so I had my coffee, went out to my workplace, got down the trusty old router sled and went to work on that tabletop. It is now very close to perfect. I could have done better but I was getting throught the top layer of wood so I guess that I will accept it for the time being.

The floor leveling compount is a good idea.

By the way, welcome. I lived down near the intersection of 94 and 40 (Weldon Spring) from 1986 to 1991. That last winter, with all of the ice, got the best of me and I headed south.

Allen
 
I could have done better BUT...

:p Yup....same mold.

Thanks for the welcome. I actually moved to Missouri from Houston. There are about 5 months out of the year that I truely miss the south. I went north only to find work. I was one of those laid-off Enron guys that lost everything back in 12/01. Gotta go where the work is. But..I do miss playing a round of golf on December 26th.
 
How's this for a little contra thinking? I like my benches to have a 1/32" (or so) dip in the center - edge to edge. If I spill something, put something round down, like my marking gauge or pencil -- things tend to roll toward the dip, not off the edge. Plus, I have a theory that it is easier to make things imperfectly than it is to make them perfect. So if you plan for it, know it is there, you can work with it. Think about it. Can't say I have any trouble with making things square and level on my imperfect benches. I also don't like square fences, but I don't want to confuse anyone right now, so I'll post about that when you least expect it.:wave:
 
allen, personally i`ve never given any thought to how flat my benches are..where is this perfect world that the pieces you`re building are going? tod
 
tod,

I have built a lot of things in my lifetime but I have never tried my hand at building some "fine furniture" so I thought that I would give it a shot for my own satisfaction. Somewhere I had read that one requirement of the fine furniture builders (I see that you are one of them) was that they have a "really flat" place to assemble their pieces. Maybe I took the "really flat" statement too literally.
 
allen, it doesn`t hurt to get things flat.....but when the feeler gauges come out that might be going a bit far;)
 
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