[AGireland]

Hi, I’m still in the design phase of building a small cnc mill.
I was thinking oh getting two 600X400X100 granite surface plates
And bolting them 90deg to each other as the bad of the mill.
Has anyone tried this method,
My worry about the plates is that the Z axis plate might break
Or shatter with the force of the spindle and also the overhang
Of the spindle. The plates will be the cheap version and are about
300euro each.

[kawazuki]

Sounds like a good way to waste 600 euros ! Your thought will rely on a bolted connection that can't be threaded so must use either expanding bolts (very risky) or a resin anchor system, which by its very nature (plastic) will introduce flexibility!
You could bolt the base of the mill to one plate and the column to the other with the two plates isolated using silicone to allow a degree of flexibility - this would dampen the vibration but not significantly improve rigidity - only a single L shaped
monoblock of stone would do that - even that would have a weakness at the internal angle.

[peteeng]

Hi AG - There are many machines that use a machine bed and a rear wall. The issue using granite is how to connect it together? If you want to be able to disassemble it then it needs to be bolted so long holes through the base need to be drilled. Then it needs to be squared and then epoxy set. Prior to bolting it together you wax the surfaces so it can be separated later. You also need to embed threaded inserts into the wall.

If its permanent then you can epoxy bond it. In terms of $$$ this is up to you to figure out. Its unlikely service loads will shatter granite. A quick search in the forum will show up many granite builds. Some of them are the best machines in the forum. But depending on what you want to do guides the design process. For instance if you only intend routing timber, a granite machine would be overkill. Thick plywood would do the job and be much easier to deal with. Peter