Designing a better bed

[D.C.]

Thank you everyone for your thoughts.

I'm currently clearing out a garage to convert into a workshop and literally sweeping the cobwebs off the ceiling. In a week or two the paint will be dry and I'll need to put an order in for some steel to start building work surfaces, tool storage etc.

MichaelW - I had thought about levelling a concrete platform, but any cost saving would be outweighed by me explaining to prospective future buyers that yes, this was once a garage but now it is an excellent place to park your lathe. Sorry about the giant lump of concrete, how are you with a hammer drill? The machine will need to be be theoretically moveable, even if that means hiring a forklift. Realistically it will probably never be moved and reused. If I really needed to dismantle it, the expensive bits electronics/rails/etc would be for reuse/ebay and a better shiner machine frame built.

Routercnc - I've been reading every paper I can get my hands on to do with CLD, (so many are pay-walled, grrr) as far as I can tell, a thin layer of steel is not required. What is required is a 'viscoelastic damping layer' sandwiched between two comparatively rigid layers and strongly bonded to them. As long as 'pond liner' can not move in relation to the rigid layers, it has no choice but to convert the vibration into heat, which is where the damping effect comes from.

Boyan - You are right about the channel section strength but in Britain steel costs a lot than in Spain. There is also the problem that when you hit a piece of steel with a hammer it rings like a bell. That sound is massive shockwaves travelling through the material and forcing air out of the way as it flexes. The 'perfect' cnc machine would be completely silent, there would be zero vibrations that you could introduce into it that would result in a measurable distortion.

DaveGrennan - I think 20mm seems to be the standard approach around here because of the z-axis. The vast majority of people have a similar requirement for z-axis movement and 20mm alu plate is recommended for multiple parts of the machine. It thus makes cost effective sense to order one sheet of 20mm plate and use it for everything, including the bed.

Because I need some steel anyway before I start my cnc build, and because I know that I will end up using epoxy levelling for my rail mountings I think some testing is in order.
I will buy a bit of 80mm square steel, some pond liner, adhesive, reinforcement etc, and do some comparative tests. Deflection is easy, vibration can be done on a smartphone with a seismometer app, weight, easy, cost easy.



This is a beam design I have being considering. In terms of machining and CLD, it was first done in the 1960's but still crops up in the 2000's as the optimal design.
Bare metal beam VS sand filled beam VS reinforced CLD/EG beam. I'll post the results and go from there.
Any other tests I can do with peasant level equipment and any advice in setting up a fair test?

Thanks,

D.C.