Steel Frame 8' x 5' CNC - Advice Sought

[BrentonSpear]

Hi All,

I have been reading this forum with interest and busily designing my CNC machine.

It will comprise of a steel frame, steel gantry and aluminium Z axis.

I want it to be as accurate as possible and will be cutting acrylic, plastic, wood and hopefully light aluminium.

Over all the machine size will be 2600mm x 1500mm (8' x 5') with a cutting area of 2200mm x 1150mm (7.5' x 4').

I have already purchased 2500mm linear rails for the X axis and will mate them to dual HGH20 linear blocks on each side.

The Y axis will use linear rails with HGH20 blocks also.

I have read with interest the threads that use bolted top rails for the X axis and I am thinking of using epoxy to level the top of the rail between the linear rail and the top rail.

I will have a rack and pinion system on either side of the X axis mated to NEMA34 stepper motors. I am going to use the R&P drive systems from CNCRouterParts.com

Here is the frame design as it stands at the moment:





The Gantry will be made from a 250mm x 150mm RHS steel beam and I am going to add a flat plate inside the bean to strengthen it.

I am working out whether to use a ballscrew on the gantry or to use a R&P system here as well.

Here it is:





I would like to hear peoples opinions on the frame as this is what I will weld up first.