Hey guys,
Seamless mechanical tubing (or SMT) is used for all sorts of things like bike frames, hydraulics, and my personal favorite (sp?) race car chassis....anywhere weight, stiffness, and strength are required. Mechanical tubing (please note, NOT PIPE!) is also available with a welded seam in one side, from when the material was rolled to make a tube, this is also usable but it usually doesn't have the same dimensional tolerances that SMT does. SMT is mandrel drawn, and the tolerances are usually in the TENTH'S of thousands (.0001 to .0009"), where piping can be in the area of +/- .060" and seamed is usually +/- .020" and not completely round.
If you have a metal supplier or industrial hydraulic shop in your area, either they will have it or they can send you to where you can get it.
I'm using 1" o.d. .120" wall SMT for my long axis rails, as I am going longer on my bed than I can get ground rod at a reasonable price for. $7+ /ft for rod -vs- less than a buck/ft for tubing. BTW, regardless of who you get it from, ask them for NON certified tubing, the price difference will absolutely scare you!!
Also, at a rail length of 51", I have (visibly) much more sag in the rails using 1" ground, pre-chrome shafting than I have in the tubing, almost 3/16" with no load. Checked this one out at work using a pair of Vee blocks on the granite table.
If you stick to the plans for your first machine, it should go together nicely as is. I'm moding the design to suit my own preferences, as I have quite a few successful lower cost DIY builds done already, to give me some idea of what will work -vs- what is likely to give me ulcers.
BTW, maintaining and rebuilding CNC's is also a good part of my day job.:cheers:
HTH,
Iain
Maintenance Supervisor
Weldco Beales (Ontario) Mfg
When all else fails, it's time to think outside the box!