Your "Precision" Aluminum Bed Can Have a Variance of 0.38mm and Still Be in Spec
Posted by Wade Wendorf on
If you've ever fought a first layer that's perfect in one corner and squished in another, bed flatness is probably part of the story. We get asked a lot about what makes our Ultraflat beds different, and why they cost more than a typical printer bed. This article explains what "flat" really means for aluminum tooling plate, what we found when we tested it ourselves, and what we do to get our beds flatter than they come from the mill.
"Flat" from the supplier isn't very flat"
Most quality printer beds are made from cast aluminum tooling plate (MIC-6, ATP-5, Alca 5, and similar). It's a great bed material because it's cast and stress-relieved, so it stays stable when heated. But tooling plate still ships with a flatness tolerance, and it's larger than most people expect. Most manufacturers follow roughly these guidelines:
| Plate thickness | Flatness tolerance | Total possible variance |
|---|---|---|
| 0.25"–0.75" (6.35–19.05mm) | ±0.0075" (±0.19mm) | 0.015" (0.38mm) |
| Over 0.75" (19.05mm) | ±0.005" (±0.127mm) | 0.010" (0.254mm) |
In other words, a plate in the thickness range most 3D printer beds use can be off by three-eights of a millimeter and still be "in spec" from the metal supllier. That's nearly two times a typical 0.2mm first layer.
What we found when we tested it
When we started making beds, we bought plates from 10 different brands of tooling plate and measured every blank. To get a good baseline, we bought 10 of each brand. The best we ever saw straight from a supplier in 1/4" or 3/8" plate was about 0.005" (0.127mm), and plates that good were rare. Most measured between 0.008" (0.2mm) and 0.020" (0.51mm) with some reaching as high as 0.025" (0.635mm).
That wasn't good enough for us. We set our own standard: a maximum variance of 0.1mm on beds up to 400mm, and 0.15mm on larger beds.
How we get there
To hit that target, we send our raw plates to an outside facility for our proprietary flattening process. The key benefit is that our process flattens the plate without undoing its stress relief, so the bed stays flat through the repeated heating and cooling of a 3D printer.
After we machine each bed from that flattened stock, we check it again on a granite surface plate with a dial indicator.
Why we don't use blind holes
Design choices matter too. We don't machine blind holes, meaning holes that go partway into the plate and stop, in our beds. A blind hole removes material from only one side, so that area is no longer the same top to bottom. When the bed heats up, that spot doesn't expand evenly. If it's near a stress point, it can taco the bed almost immediately. Through-holes keep the plate symmetrical, so it expands evenly as it heats.
Why our beds cost more
All of this adds time and cost. Every batch of material is shipped to the flattening facility, flattened, and shipped back to us, and we have to order a minimum of 50 pieces per size. From ordering material to starting to machine beds typically takes 6–8 weeks.
That's why our Ultraflat beds sit at a higher price point than most. You're paying for a plate that's been measured, flattened, machined, and measured again, so you're relying less on mesh compensation to cover up a warped bed and getting a more consistent first layer.
Thanks for reading! If you have questions about bed flatness or our beds, feel free to reach out.
Check out the beds we have available on our site by clicking here!
If we don't carry the bed you are interested in, we do custom beds as well!