Hey folks, I'm just getting parts together to start a new build. 2400mm x 1200mm full sheet cnc router. I'm thinking SBR16 rails for Y and I'd like to use a ballscrew for the Y also. What would I have to do to eliminate or avoid any whipping issues being that long? Is it do-able? Should I go a different direction? Your thoughts would very much appreciated. PS. I already have a 1500mm CBeam bought from openbuilds, so was going to use that, and an already assembled Z that would bolt on to the C beam.
Doable, but not sensible. I wouldn't go under 16mm for a screw that long, rather 25mm, and at that point the price is rather high. So I agree with Gary, go with a rack and pinion setup.
Point taken guys thanks. In that case, would you also go rack and pinion on the X? or ballscrew? What size? Mod 1.5? 2? I know bugger all about rack and pinion sorry
There are 1.5m axes running with 8mm leadscrews without much trouble, but for beefiness sake, if using the c-beam like in a workbee with the screw running in the "channel", I think I remember somebody managing to fit a 12mm ballscrew there, so I'd go with that (google it first!). But in a machine of this caliber I'd say it doesn't really matter what drive type you use as long as you don't get excessive screw whip.
It's the screw whipping I'm trying to avoid. There was someone (can't remember where I saw it) that had made something to prevent whipping. It was basically like 2 bushes, one on each side of the nut, connected with a rod, centred in between the nut and the ends. Hard for me to describe but apparently it works well. I'll see if I can find a link
I have a 1/2"-10 five start acme screw on my 1500 mm y axis and I do not experience any whip problems. If you plan on ball screws, 12 mm or 16 mm should both work fine for your 1200 mm axis.
And for that, we suggest the rack and pinion solution, which is free from whipping. These things in the hobby scale can usually be figured out to a good degree with common sense. Go to your local hardware store, and find threaded rods. At least here, we have them usually available in 1 & 2m lengths in big box stores. Next, take the desired diameter rod in the length closest to your needs, support one end on the floor and try to buckle it with your hand from the other end. This gives you a basic view of how easily a screw of said size will whip. The 8mm at that length requires very light pressure, whereas a 16mm would be so-so, I'd imagine. This is of course highly dependent on the material to be cut and the rotating speed of the screws, but it gets you into the ballpark. Regards, Will
rack and pinion.. but if you are wanting to use ball screw, make the screw stationary and drive the nut to rotate. This will also eliminate whip.
