Design Help Pt2 Required for CNC design/Build

[Jonathan]

I've not done the calcs but suspect the effect is small so don't panic. Interested to hear if anyone has worked out how much they deflect for a given side load (or vertical in this case) or has experience of this orientation

It's going to be tricky to calculate as it relies on the strength of the bolted joint between the round rail and the support. The aluminium surface at the joint is a V-shape, so the rail only makes two line contacts. There's not many bolts (and if you don't threadlock them they can work loose) which overall means the round bar can, and do, bend in that direction upon the rail. Check it with a dial indicator and you should be able to see the effect.

For the gantry I will be using 20mm plate sides with 120x40mm heavy extrusion (8.8 kg/m) for the y-axis on the basis that the box section resists twisting from the cutting loads better than plate and is lighter, reducing the forces required to accelerate and stop the gantry.

See you mention making the frame very strong, which is great, but with only one ballscrew you're kind of defeating the object of doing that. Not saying don't make the frame strong, as you can't change that later (without wasting material/money) unlike adding an additional ballscrew which is obviously easy enough.

BTW I too am a model flyer (Gliders and power) and have in mind to build a 1:3.5 scale (4.25m) "Reheinland" glider with all the bits CNC cut

I bought a 500 size helicopter recently, so I'm also almost a model flyer. Not dared actually fly it yet! Couple of bits to cut from carbon on my router first. So far I have just stuck to model cars.