operation cnc

[Jonathan]

The design you've just posted with the tool operating below the X-rails is far stronger, especially with an adjustable height bed. See mine here (or come and see it in real life if you want), don't pay much attention to the Y-axis though as that's weak.

I have an abundance of wood available to me, so Im thinking the uprights and cross members that support the Y linears etc (the table as it where) is going to be made of wood. then the gantry out of ali... does anybody think this is a really bad idea?

I do...it is far easier to make a machine to cut aluminium efficiently if you only use metals in the design. You'll need to use coolant if you're cutting aluminium regularly and clearly the wood wont last long or stay put if it's getting wet. You'll be much better off with making a steel frame. I get steel box section from a place called Adey Steel in Loughborough, which is not too far from you. 60mm box section is a good size for the frame and if you stick to 3mm wall thickness it's much easier to weld with a cheap welder.

Not sure what thickness it is in the drawing, but the Z-axis plate looks a bit thin. 20mm thick is a good size.

Put a few supports for the long rails on the frame to help stop them bending towards the middle.

(Edit, forget this bit - written before previous post.

With the one piece of box section the gantry torsional stiffness is quite poor - imagine what happens when you apply a force to the cutter when the Z-axis is at it's lowest point, the gantry will twist. If you just put a second piece of box section below the top one, aligned to the bottom face of the aluminium plate then the torsional stiffness will be much improved.

If you're after 1m travel then a 1300mm wide gantry is a bit generous since 200mm is plenty for a Z-axis.

Instead of putting the rails for the Z-axis on the Y-axis carriage, put them on the plate which holds the spindle and moves up/down and have the bearings attached to the Y-axis. This is generally a stronger configuration, especially with an adjustable height bed, since it minimises the vertical distance between the cutter and the support bearings (the overhang). This also can save some aluminium, depending on where you put the stepper motor.)