Welding Table Flatness – Why, and When It Matters

What Exactly Is Flat?

One of the most misleading things in the welding table supply business is the way vendors intermix machine specifications while discussing welding table flatness, ignoring the difference between finished products and the machines they’re made on. So let’s clear things up. There are two primary types of welding tables being supplied in the industry:

  • Cast and surfaced welding tables.
  • Laser cut and fabricated welding tables.

Each offers distinct benefits.

  • Cast tables are machined flat to extremely tight tolerances. If it has to be perfectly flat, it has to be cast.
  • Fabricated tables typically cost 1/3 the price, are much lighter, and can be mobile.

The reason welders care about welding table flatness is because you can only build something as flat as the surface you have to work with. So the more precision required for the finished product, the more precision required for the tools used to build it.

The general rule is for each extra zero a customer requires in precision, the price of the product doubles. (i.e. – from .1″ to .01″) For this reason, it’s important to decide just how perfect any tool really needs to be.

The Laser Cut Kit Lie

We hear from people constantly with extreme anxiety about which welding table kit is “best” based on the specifications. A lot of vendors are very careful never to actually guarantee welding table flatness. But they imply it with language such as “Cut with +/- .003 Precision”.

But here’s the thing…

All providers cut parts for welding tables on industrial CNC lasers, which are built to very tight tolerances. For example, a Baileigh Fiber Laser quotes .0004″ per foot of repeatability, and ~.005″ minimum cutting width. And while these numbers are impressive, they have absolutely nothing to do with the quality of fabrication of a finished product coming off them! They are products on their own.

Consider the following:

  • When weld table kits are assembled, the parts intersect in up to 100 places.
  • Each tab and slot is cut with extra spacing in the slot so the tab can fit.
  • Plate steel that parts are cut from is always at least slightly warped.
  • ALL of the parts must be held perfectly in place simultaneously during assembly.
  • If parts are clamped too tightly, it can induce warping.
  • If parts are clamped too loosely, it can induce warping.
  • If parts are welded too long, it can induce warping.
  • If parts aren’t welded enough, welds can break.
  • Even the order of the welding can induce warping.

So if everyone is cutting parts that will generally fit together, assembly becomes the biggest concern by far. It requires a great deal of care, and experience counts.

An experienced welding table fabricator can build a table whose top is extremely flat as demonstrated with a level. The level will sit flat across the width, length and diagonal of the table with very little (if any) movement. The larger the table surface, the more difficult it is to achieve edge to edge perfection.

Cast and Machine Surfaced Welding Tables

If absolute perfection is required, only a cast iron table that has been machined will do, and it’ll cost you! For example, Baileigh offers a 78″ x 39″ table for $7,795 plus shipping. They describe the precision as…

All of Baileigh Industrial’s welding tables are made to exact tolerances and maintain flatness of +/- .0025″ and have a hardness rating of 140 to 160 Brinell.

While there aren’t any videos of surfacing an entire table, this video will generally demonstrate what has to be done. (Skip to about the 3:00 mark.)

How To Mill and Grind Cast Iron Angle Plates

Obviously, the bigger the table, the bigger the machine required to machine the entire surface flat, which drives up costs.

How Do You Choose

If you compare the $7,800 Baileigh table to our own 40″ x 80″ table which sells fully fabricated, on heavy duty casters, shipped for $2,749 some of the differences become obvious.

  • Price is the biggest factor. If perfection was free, it would always be preferred.
  • Mobility is another factor. Cast iron tables and platens are usually way to heavy to be mounted on wheels.
  • Availability is also an issue. Laser cut kits can be easily produced on demand. Cast tables require a lot more infrastructure.

At the end of the day, it really comes down to what you’re building. From end to end our fabricated tables generally have a variance of  1/16th” – 1/8″.  One of the most common issue is there could be a slight twist in a fabricated table. Again, generally in the 1/16″ – 1 /8″ range max.  Either way, that’s way flatter than a concrete floor, or a non-engineered welding surface. And would work perfectly for projects ranging from a motorcycle chassis to dining tables.

Let’s contrast this for a minute. BuildPro tables are rated at a table flatness of .004 inches per foot. Siegmund tables have a flatness rating of +/- .0025 inches per foot. So for example, an 8 foot table could have a variance of flatness of .032 (or about 1/32″) for the BuildPro or .02 inches (about 1/40″).

This demonstrates the difference between a robot milling a flat block of material, and a finished product built by a human from laser cut materials.

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