I too have got a thick piece of glass. I have no way of accurately measuring it but set a DTI up in the scribing block and slid it around, not enough run out to worry me, I am not building atom bombs or interplanetary rockets.
Hey, lighten up. The only
interplanetary rocket I've (helped) build is the Atlas V -- if you count the Moon as being a planet and launch phase as counting as
interplanetary. The rest have been
orbital vehicles. However, I
did design and build the vector (steering) thruster
fuel pump for the
transfer vehicle (which counts as
interplanetary by any man's standard) carrying
Curiosity from Earth orbit to Mars orbit. That was pretty much a +.002/-.000 or +.000/-.002 assembly. Surface plates were only used for DTI measurement comparisons.
Atom bombs, on the other hand, are (generally) +/-.005 assemblies. It's the 8 microinch surface finish that's the killer. Hydrogen bombs require closer tolerances. ;-)
Ignoring gauge work done for the National Bureau of Standards (an entirely different world from anywhere else), firearms and high-precision tools are what require me to have the equipment I have. That's why I asked Ross what accuracy
he needed. The answer to that question sets the stage for a
real and
practical solution. Back in the dark ages when I was an apprentice, precision hole locations were made using tooling buttons and gauge blocks or adjustable parallels. There are numerous
solutions that improve accuracy without costing an arm and a leg -- if you need them.
My first
reference plate was a carefully reworked (20 X 40 inch) butcher block used to layout guitar and lute components. It was
visually flat by comparison to a 48 inch straight edge -- which probably meant flat within .015 FIM overall. It served me well and was wonderful!
