Initial thoughts on new build

[Neale]

This will be my second CNC router, and is to replace a current JGRO-based design which has a few of my own mods. Fed up with MDF moving every time you look at it, but it taught me quite a lot (and does work!).

I'm requesting a sanity check on my initial thoughts, please. Basic intention is to cut plastics/wood; previous projects have gone from chunky hardwood profiling down to engraving a design on a small wooden box. I shall also need to do some 3D carving in wood. It would be good to be able to do "light" profiling of aluminium, if only to help when I get round to the CNC conversion of my vertical mill, but not a major design driver. I don't want to over-engineer, which is breaking the habit of a lifetime, but I'm trying to be sensible. Initial sketch attached to start dimensioning. I'm thinking 50x50x3 steel welded construction. I might well end up building two, one for me and one for my son, hence the design could sit on a wooden bench (with restricted speed/accel, we realise) for him and a custom floor-standing steel frame for mine. Overall cutting area big enough to go round a 1200x600 sheet, but the spindle will overhang the end of the bed to allow cutting on the edge of panels.

I'm fed up with the DIY approach to rails and leadscrews (although my homemade delrin anti-backlash nuts on the JGRO are one of its finest features!) and intend to use profile rails and ballscrews.

I shall reuse some of the more useful bits of the JGRO. Principally, these are 3x NEMA23 3Nm steppers, M782 drivers (bought shortly before they became obsolete and digital drivers took over), 68V power supply, and ZP5A-INT BOB. I am also using a water-cooled 2.2KW spindle with VFD. The MDF Z platform of the JGRO is sagging under its weight...

First decision to start getting some realistic costs together is about rails and ballscrews. I intend twin X screws outside the upper X rails, single motor with belt drive. I'm thinking 2010 ballscrews for X and 1605 (1610?) for Y and Z. What size rails should I use? 20mm for X and 15mm for Y and Z, or would 15 or 20 do for all 3 axes?


I have been looking at UK suppliers for pricing of rails and screws, as well as BST Automation, although it's quite difficult finding the right bits on the BST site - I shall need to send off for a specific quote once I have dimensions. Chai does not seem to stock profile rail - is that right? Unfortunately my little Myford lathe cannot handle ballscrew diameters like this so I shall have to pay someone else to machine them which certainly seems to put up the UK prices considerably.

All constructive comments welcome! I feel a bit daft asking about something that seems so ordinary compared with a number of the machines described here but I can't really find a "reference" design similar enough to copy, although most of my ideas have come from reading threads on this forum so I don't think I'm ridiculously out of line.