[muppy]

Hi All,
my name is Andrea, i'm from Italy.
I'm interested to build a rigid CNC machine. I'm interested to machine metals with high precision.
I've thought to realize that machine in epoxy granite, moreover I plan to use C3 grade ballscrews and high precision Hiwin linearguides.
X and Y ballscrews has diameter of 32 mm and Z axis ballscrew has diameter of 16 mm.

I attach to the post the layout of the machine. The base has sizes of 1000x1000 mm.

I'd like to receive suggestions from people on this forum on how to improve stiffness of such machine and improve machining precision.

Many thanks,
Andrea

[awerby]

That doesn't look like a metal mill and it doesn't look like a design that would benefit from epoxy-granite construction. It looks like a simple cheap gantry router.

To mill metals, you want to maximize rigidity, which usually means substituting a moving table for the moving gantry. That way the bridge, which holds the Y and Z axes (or just the Z axis, if you move the table in two directions) can be as heavy as it needs to be. If you're making something out of epoxy and granite, it will be quite heavy, but if you have to make it move, then the weight works against you. If you design it with a fixed bridge then the extra mass is a good thing.

Andrew Werby
www.computersculpture.com

[muppy]

Hi Andrew,
i mainly need to machine aluminium. Do you think that machine will be rigid enough for aluminium ?

Best regards,
Andrea

[jharvey407]

Hi Andrew,
i mainly need to machine aluminum. Do you think that machine will be rigid enough for aluminum ?

Best regards,
Andrea

The simple answer is, yes it will mill aluminum.

The question you should be asking yourself is whether or not this machine is going to be able to mill aluminum fast enough and well enough to make it worth building the machine. The answer is probably 'no'.

Metal work is typically done with a fixed gantry machine, as was pointed out in an early reply. There are better machine designs for metal work, and they lend themselves to EG construction as well.

I will be watching with interest. I am considering doing some work with EG in the near future.

James

[jharvey407]

Here are a couple of mill designs that lend themselves to EG construction.

What size of work envelope do you need?

[dwalsh62]

I was asked by I chose such a small size of stone and why basalt as the main aggregate.

My choice of material size was based on the best results given a max/min wall thickness without sacrificing strength.

By using small aggregate material (sand and stone) of varying size not to exceed 3mm I ensure minimum void in mixed aggregate material which improves strength and cohesion when mixed with a binding agent (epoxy).

My choice of material was based on the stability of the material, it's availability and hardness and, low surface deterioration level, there are other suitable aggregates that meet these criteria, my choice was based on availability from a local supplier.

I could have chosen Apatite, Augite, Amazonite, Dioptase, Hematite or Hornblende if my supplier had them as any of these would have met my needs and even Feldspar would have been an acceptable choice since it is a major component of Granite.

Also note, Sand, Lime and Shale stones are poor choices for aggregates in machine castings due to their high fracturing or high level of surface deterioration.

You can test a stones surface deterioration level by washing, drying and wetting then air dry, if it develops surface dust it has a high surface deterioration level which means that it will eventually separate (de-bond) once sufficient deterioration has occurred.

You can test it's fracturing properties by dropping it 6 to 10 feet onto a hard(er) surface (not asphalt), if it breaks don't use it.