A. Woodpeckers manufactured the gage blocks from aluminum because they manufacture everything from aluminum whether it is the material of choice or not.
1. Aluminum has twice the thermal expansion rates as compared to steel.
2. Aluminum is soft. Adding hard anodizing will help, but steel that has not been heat treated has a surface hardness 8 times what aluminum does. So aluminum dents and scratches more easily. Hardening steel will increase that gap substantially.
Note: Decorative anodizing will add nothing to the surface hardness (no measurable difference), but “hard anodizing” will. Hard anodizing will bring the surface hardness to the equivalent of case hardened steel, but not to conventionally heat treated steel.
3. You can surface grind steel to +/- 0.0001”. (One tenth of a thousandth) with commercially available grinding machines. You cannot grind aluminum and milling cannot achieve that tolerance.
So, in my opinion, hardened steel gage blocks are a better choice for metal working, where tolerances are tighter and the risk of denting or scratching is greater. Aluminum is OK for wood working.
A. That's not necessarily a bad thing...and in this case aluminum is the material of choice. If it wasn't, they would have chosen another material. Woodpeckers produces products manufactured from aluminum, stainless, phenolic, Delrin, nylon, cold rolled and tool steel, If there was a better alternative I'm sure they would have chosen that alternative material.
1. Thermal expansion can be an issue, however if it's left in an environment to fully stabilize then it's no longer an issue. Besides, gage blocks are typically kept within the area that they will be used in. It's the raw materials that are sometimes kept in a colder/hotter holding area. So those materials then become the problem because you're waiting for those materials to heat stabilize...not the gage blocks.
2. Aluminum is soft but when working around sharp carbide tools it's a lot better than steel which can chip the carbide if adequate care is not taken.
3. You can surface grind aluminum to +/- 0.0002”. (Two tenth's of a thousandth) with commercially available grinding machines.
So, in my opinion, hardened steel gage blocks AND aluminum gage blocks are both good choices for metal & wood working, it just depends upon your needs at the time.
I also have a set of Starrett hardened steel gage blocks that I use for caliper & micrometer calibration. Incredibly nice stuff...incredibly expensive stuff. Nine very small gage blocks that cost $420 and they need to be carefully wiped down every 6 months to prevent rust from forming on the surface. They can be wrung together which aluminum blocks will never be able to do but then again Starrett claims the flatness accuracy of their Grade A1 steel gage blocks is in the neighborhood of .000004".
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I own both because I need both.
