Flattening a big table top


Hey folks, I will build a 4'x16' table whose top I would like to be as flat as I can get it. I don't know how best to accomplish this. The top will be two sheets of 3/4" Birch ply butted against each other along the short sides.
Thanks, CD
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
How do you plan on supporting the plywood, i.e., what kind of base are you building for it?
Or is that really your question?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I toyed around with the idea of building a torsion-box like structure out of ordinary studs to support the top. I was not successful in getting the tops of the cross members and of the aprons flush. Some sanding might do the trick but I don't know how to go about that either. By the way, the frame will be two 4'x8' frames put together as well.
Based on the answers I got from you guys, it seems that the flatness of the top is a function of the frame itself. What do you suggest for the frame in the way it is built? One suggestion that came through was 3" solid aprons with cross members every foot.
Say I got the frame right. How would I then insure that the plywood top is also flat? If the ply has any imperfections, I don't know how to get it flat across such a large surface area. Or is this simply not a consideration if the top of the frame is flat?
It will need to support about 600 lbs distributed roughly even across its length and I don't want the top to sag in time. I am planning to finish the top with some kind of plastic film like varnish.
Please forward any suggestions. I am not very experienced. Thanks for taking the time to answer.
Good day all, CD
Joe Tylicki wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Mon, 06 Mar 2006 15:40:11 -0700, CD wrote:

Its not likely you'd get a very flat top that way. Studs are seldom very straight to begin with, and if they are not already dry, they will probably bow and twist as they equilibriate to the humidity in your workspace.

I'd stick with a torsion box, but made of plywood. You'll need a way to rip the plywood into very straight runs about 3 inches wide (not trivial, but can be done with a table saw and some care, or a "shooting board" with a circular saw). And you 'll need a way to cross cut those strips at exactly 90 degrees.
If you can make those cuts, then run continuous pieces the long (8 ft.) direction about a foot apart. Cut shorter pieces to join them on about 1 ft. centers, forming a 1 ft. square grid. You can use biscuits or splines to join the parts. When joining the parts, use clamps and small blocks of plywood covered in clear packing tape to keep them in vertical alignment.

Use MDF, or melamine, instead of plywood.
--
Art


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ordinary studs are seldom straight. Consequently, they are a poor choice of material from which to create something which is flat and square.

How flat is flat? The fame should take a care of sagging issues, but not minor surface imperfections.
Crappy grades of plywood have more surface imperfections than good ones. Are we talking about CDX or cabinet grade ply?

Once again, we need more data. How is the table to be used? Does it need knee space? How many legs? How where will they me placed? If you want four legs under the corners, your going to need a hell of alot more apron than 3 inches to support a 16' span.
Start with the 30,000 ft view, like "I want to build a platform to support my model train set..."
-Steve
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
CD wrote:

More info, please. What's the function and what's your intended finish?
R
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A 3" solid apron with Xbearers every foot comes to mind.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Simple. Make it as flat as *you* can get it, or take it to someone with bigger equipment. The high school I attended had a huge blet-sander; that is, a suspended belt, and you ran a hand-held plate back and forth pressing the belt onto the work. It's called learned technique ...and having the right tools.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

manufactured, the real question is how to keep it so .A blet sander will not do that
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I guess I missed that. This has ot be a troll, because you have to be kidding about butting together 2 pieces of plywood and looking for serious comments on keeping it flat without an underlying support system.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
CD wrote:

What are going to use the table for, making airplane wings?
--

FF


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
CD (in lRNOf.10458$Sp2.757@fed1read02) said:
| Hey folks, | I will build a 4'x16' table whose top I would like to be as flat as | I can get it. I don't know how best to accomplish this. The top | will be two sheets of 3/4" Birch ply butted against each other | along the short sides.
A while back I built a 12' sign and had the same problem (there are a couple of photos at the link below). I routed a pair of matching (to +/- 0.0005") quarter-inch by three inch "steps" on the edges to be joined and used Titebond glue with a full-width clamp. When dry, I sanded lightly with 220 grit paper and it came out well.
Another option is to clamp the pieces together and to a good work support and inlay a piece of 3/8" ply across the back of the joint.
If you aren't concerned about the look or feel of the back, you could just glue a plywood strip of appropriate width across the back of the joint.
-- Morris Dovey DeSoto Solar DeSoto, Iowa USA http://www.iedu.com/DeSoto/PT_Sign.html
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.