Quote Originally Posted by routercnc View Post
Hi Mike
Good to hear someone getting use out of my spreadsheet. Nice to put something back into this forum.
Just a comment on the x axis bearings. When mounted on their side it does make for a neat installation but be aware that because the blocks are open (sort of C shaped) that they will open up slightly due to the gantry mass and to a less extent the cutting forces. 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.

As for twin screw - I have a gantry about 600mm wide with a single ball screw and I can rock the ends of the gantry back and forth by hand up to about 1mm if I push hard. Having said that I can happily machine balsa, liteply and ply and they come out at the right sizes. But I would still say twin screw is better and would like to upgrade when funds allow because I could then up the feedrate.
Thanks routercnc for the spreadsheet and the comment re the X axis bearing placement. I've seen them placed like this on another design, but somehow felt that vertical placement would be better for carring the vertical weight of the gantry and resisting racking. 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.

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 - once I have done my brother's guitars!

Kind Regards
Mike