Flat Table Top

[Ed Thomas]

Sight unseen, I agreed to pick up what was nominally a 4' x 8' sheet of 1/2" steel for a layout table from my brother. It is in fact 4' x 9' and either a very rusted 1/2" thick, or mildly rusted 7/16"... I can't tell. I was disappointed to find that it just isn't flat. It has too much warpage and crowning. I really need a larger layout table. Has anyone had any luck getting something like this truly flat? I'm considering cutting it into sections and building it back up, one foot at a time, but that seems extreme. Thanks.

[Glenn]

How flat? Perfectly flat, reasonable flat, or close enough - it's flat ?

[mike-hr]

I've tried but no luck. I had to cut a sheet to 4 x 6 with unsquare corners to fit a concrete hole for a well house in a driveway. It potato chipped (warped both ways) as soon as I cut it. I used a pile of oxy-acet, trying to heat warp it to flat, and quench in place with a wet gunny sack. I used chains and a bottle jack to try to warp it back. Then I used oxy-acet and the bottle jack. Then i went and got a 12-pack. I think I tried welding small stringer beads from the backside, but i don't remember how that worked, cause the 12-pack was getting the better of me. It got to the job still warped, and I tapped holes in the angle iron bed, and bolted the sonofagun down. I'm very interested in what other folks have done in this matter.

[HWooldridge]

Ed,

My first layout table was like that. I still have it and work around the depression in the middle but it's not right.

If I was going to make another, I'd build the legs and frame first and make sure that the thing was square, plumb and flat. Then, I'd put a piece of 1/4" on it, which is heavy enough to support a good sized piece of work but flimsy enough to lay flat on the framework. Tack it all around and you'd have a pretty flat table top.

If you want it FLAT then have it Blanchard ground. However, t'will be pricey - I'll wager...

I have a big mold plate that I scrounged years ago, which is 36"x36"x2" and has been surface ground so it is almost as flat as a granite surface plate but it's not big enough to do really large work.

[Ed Thomas]

Ideally, a layout table should be perfectly flat. So I need as close as reasonably possible. If you build an 8' rail section on your table and the table is not flat, then neither will be your rail section. It will introduce a rack or bow.

If I can't get this flat, I'll probably just buy a flat 4' x 8' sheet of thicker stuff new. I wouldn't want to go any less than 1/2" and probably will go heavier.

[one_rod]

If there are any engineering companies around your way, it may be worth enquiring if they have a Planer.

Some places still have one stashed away in a quiet corner somewhere.

A simple flattening job like yours is easy meat for these machines and should not cost much. (Probably a lot less than the cost of buying new steel, these days).

These machines are generally very accurate, and will take off all the rust, leaving a near perfect finish, ideal for your purpose.

If you have never seen a planer before, and a lot of people have not, then here is a picture of quite a big one!


http://www.techdirections.com/fpgplaner.html

It was the only pic I could find.


I have had heavy steel plate planed flat before, only to have it warp again a few months later as thermal stresses from the rolling process have relieved. This is why the really accurate marking off tables used in machine shops are normally made of cast iron.

So, if you do manage to get it flat then get it bolted or welded to some strong support frame as soon as possible.


one_rod.

[Ten Hammers]

My shop table is made from square legs ( I guess they're 1 1/2") with a band around the top (between the legs). Another band is around the bottom about 6" up from the floor. I stole (er bought) a piece of 1/4 sheet from an Amish feller that was goin outta business and was tired of lookin at the sheet. Pretty cheap but we were both happy. This top is plenty for my needs and I put some heavy stuff on it. I've been welding stuff to it (for clamp effect) and grinding it off for several years. The top is pretty flat but not perfect. If I really need it to be flat, I just put a couple of pieces of square tubing or pipe on top and lay the arch leg (or whatever) on top of this stuff and end up with what I want normally. If I wanted an absolutely flat square pure tabletop, I'd go to supplier and hand pick what I wanted. I'd then build the table first (as Hollis noted) and then weld overheads to tack the top to the frame. Actually you might also drill and tap the underside (extremes if needed) and bolt some heavy angle to it. Then you'd have supports to weld to the table undercarriage. I have no need for a layout like the Sterretts would use for plumbing but a nice flat table would be good. Mine fits my needs. ALSO, a 7" cup wheel on your big grinder will flatten a surface nicely (Norton cup wheel) to rid it of dingies or whatever. Just keep moving it like you would a belt sander. It'll make a man outta you in couple hours.

[irnsrgn]

ED, seems to me like you are going about this the hard way. No offense intended. Lets take the problem apart and assess some known facts and then figure out how to encounter any problems.

Facts -

1. Most plate steel will not be perfectly flat. It will either have a bow (warp) to it long ways or a bow cross ways. This comes about from the rack it was cooled on or the way the air circulated around it to cool it.

2. If the plate was sheared to length, the ends will have a pronounced bending at the ends from distortion of shearing. One of the main reasons for this is the clearance between the shear blades was not kept in tolerance and also from the plate being hot and in a semi plastic state when sheared. This will also occur along one edge if the sheet was sheared to width from a production sheet.

3. If it was flame cut to size there will be a prounounced warping due to the heat from the cut along the edges.

4. How the sheet was stacked at the supplier will also affect its flatness.

5. Its rusty so was it laying on the ground out in the open and maybe run over several times by something, was something heavy stored on top of it for any length of time causing it to bow from stress.

6. Heavy rust is going to leave pits and an uneven surface, sections with heavy mill scale will not rust as fast as clean areas.

Now to the solutions (engineering part).

1. Sandblasting would be my first option to follow to get rid of the heavy rust and reveal what I was actually working with and to prevent all the hazards of the airborne rust particles resulting from wire brushing or grinding the rust away. Also getting rid of the rust will have a benificial effect on the weld contamation when welding rusty material.

2. After sandblasting set the sheet up on some sawhorses or such and using a known straight edge, determine the amount of ward or bow to the sheet, carefully marking any deficiencys.

3. Remove any major distortion along the edges by flame cutting using a straiht edge as a guide. (NOTE) If the sheet has a bow to the center put the bow up when cutting as the flame cutting will have a tendency to bow the plate up.

4. Build a rectangular frame out of at least 4 inch heavy channel iron, flange out, using a good level to get it level both ways. Put the same size channel iron cross pieces inside the frame the short way at least every 2 feet. The frame should be approxiamely narrower than the sheet all the way around to facilitate clamping on the edges.

5. Position the plate with the convex side of the plate up on the system you used to fabricate the frame. Position the frame on top of this and centered. Take the frame in the center where it touches the plate and then proceed to pull the edges up to the frame with clamps starting at one end and working toward the other end. Use STITCH welds along the inside stiff edge of the channel one inch of weld then two to three inches of space between the next weld. Tack the outside flange to the plate 1 inch every 6 to 8 inches. REMEMBER LARGE LONG WELDS WILL DISTORT THE PLATE TOWARD THE WELDED SIDE.

6. Attach the legs to the frame now it would be best to have 6 legs to give the center support over the length. Now attach another light angle iron mid way between the frame and the bottom of the legs for added sideways support to the legs and for use as a storage shelf.

7. Now set in the desired place and level the table with a level.

8. Now check the top with a straight edge and grind or otherwise remove any high spots you don't want.


Hope this helps you and its the way I would go about doing the job.

[HWooldridge]

Like the announcer on Bullwinkle used to say, "Why the first table was not flat" - or - "how not to build a table..." (That may make sense to some of you old folks)

After first learning to stick weld some years ago, I decided I needed a table. I bought some 2 inch square tubing and a 4x8 piece of 1/4" smooth plate. I put the plate on sawhorses and clamped the square tubing to the underside so it would be easy to weld. However, I did not notice that the plate sagged around the outside edge so welding all the supports and legs to the table kept the bow in place. When I turned the table over, it had a 1/4" sag in the middle. I now use it to support my chop saw...

At a previous place of employment, we built a big table to support molds, the biggest of which went over 25,000 pounds. The table top was 4x8x1" and rested on 4" square tubing legs but they were cut short so the molds were at a comfortable work height. The legs and box frame were built first and the plate laid on top and tacked. It was quite flat and easy to scoot molds around on the surface. Due to the planned work load, we put eight legs in the box frame instead of four and had no trouble with sagging.

[Cory]

Ed I used to work at a place that did nothing but handrail and long dock sections.They had I beam tables, these were 6 or 8 inch I beams.They were 20 feet long to do dock sections but could easily be shortened to do rail only.This set up is nice because it is open in the middle and you have no welding spatter that collects on the table.We did straight pickets only not much good for scrollwork rail.The way they had it set up was on pipe pedestals with a 4 foot lenght of beam welded horizontal on the pipe pedestals and the long beams run across the 4 foot beams.One long beam was tacked down and the other was not so it could be moved and then clamped down for different applications.The end of the table would need to be squared for doing angled rail.Any handrail I ever worked on never was as straight as the table anyway, always a degree of warpage no matter how you jig or clamp it down.

[Ed Thomas]

one_rod: Thanks, but this sheet is too thin and too warped for a planer, even if there were any around here big enough.

Ten Hammers: Someone in the welding forum on Practical Machinist talked about a table made of 1' x 4' sections. Each section could be individually adjusted until the whole table was flat. Not too far from what you were suggesting.

Hollis: If I ever buy a tabletop, I'm seriously considering 1" also. I have a smaller section of 1" and it is SOOO nice.

Cory: I won't rule out a solution like that in the future because I have several pretty massive I-beams. But I really need a flat layout table more than a welding table. I don't expect to be doing enough welding on this one to be an issue. On a layout table, it is common to draw the project to scale and forge and fit the pieces right to the drawing. So I really want the whole surface.

irnsgrn: Once again, I am in your debt. I will try to follow your directions for this piece and keep you posted on my progress. It will be a bit yet, as I am doing other maintenance for winter. But I think this is exactly what I need. Thank you very much!

[ThomasPowers]

What about making a flat grid and then using counter sunk screws to suck the table down to the grid?

Thomas