[pippin88]

I'm building a moving gantry router.
1100mm long, 600 wide, ~500 tall
Working area: 900-950mm x 450mm x 150mm

I'd been planning on a mostly MDF build (and have in fact got a torsion box for the working table drying, but it was very difficult to build with limited tools and no flat surface, so I'm dubious as to the quality and flatness of the end product)

I initially thought aluminium extrusion would be much too expensive (it is much harder to get and more expensive in Australia than in the states), but AME System | Workstation systems for efficient workplaces have reasonably affordable gear.
I will be using aluminium plate (10mm) for the gantry uprights and a few other bits.
I have a chinese spindle which weighs 5-6kg.
Single X ballscrew in centre under table.

I have two things I need to work out:
1. I have SBR16 rails from Chai (Linearmotionbearings2008) which have a hole spacing of 30mm - I think this means I may have trouble connecting straight to series 30 (30mm wide) extrusion from AME. Thoughts?
2. How strong is this stuff? My longest span is 1150mm. The 40mm extrusion costs twice as much as the 30mm extrusion series (notably it is twice the weight).

I have a couple of designs in my head:
1. 60x60 for the 1150 long on the bed with 30x60 for cross beams (spacing of ~18cm between centres). Two 60x60 for the cross beam of the gantry. Issue is whether SBR16 can be attached easily. (~$200)
2. Same proportions as 1 but using series 40 pieces - twice as expensive, definitely can attach SBR16 easily. (~$400)
3. 40x80 for 1150 span for X rail mouting. Run a 30x60 1150 span inside it and use 30x60 cross braces joined to this (probably use an end plate to join the 40x80 and 30x60). 2 lengths of 40x80 for gantry cross brace (~$300)
4. All series 40, but use 40x40 for table crossbraces. Would 40x40 be as strong (deflection resistant) as 30x60 (orientated vertically).

Any help is appreciated, I just don't know how strong this gear is. (And I'm no engineer)

[bassdoctor]

Just down load the application from 8020 and it will show you the deflection figures.
80/20 Design Tools - Tech Toolkit™ Introduction
hope this helps, Mark.