SO Much Marketing Hype!
Before I get started, let’s talk for a minute about how marketing departments of large companies mislead and misdirect – intentional or not – when it comes to welding tables. Flatness is a scientific term, but marketers with limited understanding and zero experience, try to sell everyone on how superior their products are both in terms of flatness and hardness. For now, we’ll stick to the topic of flatness.
Let’s Define Flatness
Flatness tolerance refers to the allowable deviation from a perfectly flat surface on a given workpiece, typically measured in units of distance (such as microns or inches). The flatness tolerance for a steel plate depends on various factors, including the manufacturing process used to create the plate and the specific requirements of the application.
When it comes to welding tables a lot of things can go wrong with a piece of metal to affect the product you’re building on it.
- The metal could be bowed. When this happens, the center of a plate pops up (or down) relative to the edges.
- The metal could be twisted. Sometimes this can be difficult to spot, because a level in the center appears flat, but when stretched corner to corner the deformation appears.
- The metal could be bent. In this case there is usually a visible bend line, even though both sides of the bend may still be flat.
- The metal could vary in thickness. Even if a plate was perfectly flat down the center plane, if it varies in thickness the surface would not be flat.
To be honest, we don’t really care exactly what’s wrong! We only care about how wrong it is. The main question we should be asking is, what is the maximum deviation from any one point on the table to any other point, based on a perfectly flat plane. If the metal is bowed, which almost all sheets are, it might not matter as long as no one point on the surface is very far off the plane from any other point.
In the illustration above, we would measure the distance from point A directly to the imaginary plane in the center, as well as the same for point B. Subtract one from the other and we have the amount of deviation between these two points.
Ways to Make Tables Flat
Various components and materials can affect flatness, but for this discussion we’re going to narrow down the number of ways to make a flat table to four categories.
- Build it yourself with a tubular frame infrastructure.
- Professionally engineered and fabricated.
- Assembled, welded and milled.
- Blanchard ground, combined with any other method.
Build it Yourself Tables
Virtually everyone who welds starts out with a “homemade” table. The range of quality here is extremely wide, and it’s not uncommon to find tables with deviations in the 1/8″ to 1/4″ range. For a good average let’s say 3/16″, 0r 0.1875″ might be a pretty decent table.
For this level of accuracy it’s necessary to support a flat top sheet with a tubular frame underneath. Let’s assume we’re using a 2″ square tube. Some of the things that can affect flatness include:
- Tubing curvature. Although tubing is generally flatter than sheet material due to the fact it’s supported by multiple walls, close inspection of any tube will still reveal a bit of curvature.
- Tubing squareness. Tubing is formed by taking a sheet and passing it through rollers to fold it, then welding the seam. The process is only so precise, and tubing routinely can be a little wider on one profile than the other, or bowed in the center between edges. In other words, a square tube is never really flat and square.
- Tubing strength. Tubing will flex wildly when unsupported unless it’s multi-layered and cross braced.
- Improper tooling. Without a perfectly flat surface, and tooling, to build a tubular frame it’s impossible to make it perfectly flat and square on a plane. The attachments at the corners could be off by a fraction of a degree, which imparts a twist down the line. Even the bowing in the center of a tube will ensure it doesn’t lay flat on a perfectly flat surface.
There is nothing wrong with a homemade table! In fact, for small projects, especially things that don’t require flatness, it’s a small, inexpensive and well matched tool for the job!
- Light weight
- Great for getting started
- Severely lacking in flatness
- Not much weight bearing capability
- Lacks tooling accommodations found in other types on this list
The next step up from a basic table is an Engineered table. These are tables which have been designed using some sort of CAD modeling tool. In the same way DIY tables can have a wide range of flatness, engineered tables can also vary due to the skill of the designer, the fabricator, the tools and the materials. A poorly designed or executed table could range from being 1/4″ or more off, where an excellent design with excellent execution can approach the level of flatness of a milled surface.
Although Texas Metal Works offers all variants of tables (other than homemade), we primarily sell the engineered variants of the tables, because the tolerances we achieve are consistent and can often exceed the tolerances of poorly milled table surfaces, making them broadly appropriate for probably 95% of all welding applications.
I previously wrote an article describing how we build extremely flat and consistent tables, so I won’t go into all that here. But suffice it to say several key factors contribute to a successfully fabricated table:
- Components should be engineered with cross-braced supporting ribs that are capable of sustaining far more weight than would be anticipated to be loaded on the table. This helps prevent sagging under load.
- All of the components should be precision cut by a CNC machine. Generally speaking Lasers and Waterjet machines offer the best precision, though Waterjets are extremely slow and expensive to operate.
- All parts must be thoroughly deburred and cleaned. Even a tiny spec of material between parts that are being assembled will affect flatness.
- Everything needs to be fixtured together perfectly and with identical pressure. For example, in our assembly method all bolts are torqued to 35 lb ft. If some parts are under more or less tension, when welding occurs there will be warpage.
- Having a reference flat surface to bolt the components to during assembly makes a vast improvement in the results.
- Proper and consistent welding technique, with a focus on minimizing heat input can make a huge difference.
- Although expensive compared to DIY tables, engineered tables represent the best “value” due to their attractive price point as compared to milled tables.
- Fabricated tables have an extreme weight advantage when compared to milled tables. It’s not uncommon for a milled table to weigh 2,000-3,000 pounds or more, whereas an engineered table is typically in the 400-1,000 pound range.
- Mobility is a big advantage. Due to the relative light weight, engineered tables can accommodate casters which allow them to be moved freely around a work area. Milled tables require use of a forklift to be relocated.
- Some engineered tables are built by individuals, some are built by companies in small quantities, and some are mass produced (like Texas Metal Works). As a result flatness is all over the board. An inexperienced fabricator purchasing a DIY kit to assemble could make a few mistakes, or lack the necessary tools to pull off the job and end up with a very expensive and unacceptable result. Companies without a repeatable process and experienced fabricators can have inconsistent results.
- Resale value varies wildly, and buyers are wisely skeptical of DIY engineered tables. Questions often arise as to WHY someone would want to get rid of a perfectly good table that should last multiple lifetimes. If a table is checked with a simple level and found to have problems it will only have value as a “table” not a serious tool.
Milled Surface Tables
Generally speaking, a step up on the flatness level involves the use of a stock material removal process. The most common of which is milling. When a steel plate is milled, a cutting tool is used to remove material from the surface of the plate, resulting in a relatively smooth and flat surface.
The CNC machine essentially uses a robotic arm mounted on a precision gantry to move back and forth continuously over every inch of the surface shaving off a little bit of material here and there to even out the high and low spots. The tool used for this process would typically be 2-3″ in diameter, so many passes are needed to cover the surface.
When tables are milled, the assembly process of any ribs or sidewalls is really pretty irrelevant. As long as they are generally in the right place and the welds are correct, that’s about it. These tables are not relying on a web of crisscrossing ribs to provide a flat surface to attach to. The flattening is the last step in the process… so kind of, who cares about the rest?
The flatness of a milled welding table may be on the order of a few thousandths of an inch, depending on the size of the plate and the level of precision available.
- Milling machines provide generally consistent and reliable results.
- Less skill or attention to detail is required in the production process, because it’ll all get fixed in the end.
- Milled tables are generally constructed from thicker materials, making them able to bear more weight.
- The milling process may introduce variability in the flatness of the table, depending on the quality of the cutting tool, the stability of the milling machine, and the operator’s skill.
- Milled table tops are often advertised with tolerances which they measurably do not attain, however buyers lack tools with enough precision to measure the results against the claims.
- Unskilled operators, or worn machinery can result in lower levels of flatness than a perfectly executed engineered table.
Blanchard Ground Tables
Blanchard grinding is a specialized surface grinding process that uses a rotating magnetic chuck to hold a steel plate in place while a grinding wheel removes material from the surface. Blanchard grinding is well-suited for large steel plates that require high precision and flatness, as the process can remove large amounts of material quickly and accurately.