I bought some metal yesterday for a project and the thickness is less than expected. I ordered sheets of 16Ga Cold Rolled steel from a metal supplier chain and when I picked it up, I thought they had made a mistake on the order as the stock looked thinner than I expected. I asked them about this and they used their gauge checker and it was loose in the 16Ga slot, but didn’t fit in the 18Ga slot. They said they don’t stock 17Ga so “it must be 16Ga”. I measured the pieces today and they measure 0.055", which, according to my sources would be 17Ga.
The 16Ga material I bought the last time from this supplier measures 0.065".
My questions are:
Is this common to have varying thickness for stock? What tolerance should I expect?
Fortunately for this project I can live with this, but I feel like I should question the supplier.
US Steel specs a +0.0025 or -.005" tolerance for CRS in 16ga. My primary metal supplier (onlinemetals.com) says 16ga is .0598" but they don’t offer 17ga either.
The ASTM standards (which are the ones manufacturers build to) says 16ga CRS is .0648 - .0548 with 17ga being from .0548 - .0498.
So it looks like the piece you got was at the minimum for 16ga and the last piece you had was the maximum for it (assuming a .002" measurement error which I would expect is reasonable unless you mic’ed it precisely).
It’s also interesting that the tolerance changes by gauge. It’s not a consistent .010" range min to max. Some have + .010 and -.005 and it’s all over the ballpark with different tolerances for thinner & thicker gauges but not always the same kind of range as you get thinner or thicker (which is what I assumed where as it got thinner it might have less of a range of min/max differences but sometimes yes, sometimes no). It’s also different by material (steel vs stainless vs aluminum) and treatment (cold vs hot rolled or oiled & pickled).
It doesn’t look like it’s easy to make very high precision parts just based on the chosen material. Or more likely there are grades of steel that are manufactured to tighter tolerances but I bet those cost a pile more money.