So I am trying to design a 3 axis cnc unit. I need to get around 42" on my x axis but only see 40" screws. What options do I have?
The 8mm screws max out around the lengths shown. To go farther you need something larger in diameter. Best suggestion would be McMaster-Carr. Matching anti-backlash nuts can be found at dumpsterCNC - anti-backlash solutions for home and industrial linear motion
What are you trying to turn? The ends define the means here. When you say 3 axis lathe, do you mean X-Z plus a Y, mill-turn style? A moving subspindle? A turret with live spindles (usually in conjunction with the Y-axis mill-turn)? Lots of possible axes here- I think lathes go up to about 9. Personally- even assuming a light duty extrusion-type build for turning plastics- I'd just grab a C7 RM1605 ballscrew and SFU1605 nut, easy to find in the 1000-1500mm range for $50-100 on eBay and Amazon and takes a lot of the component matching and backlash elimination work out of the equation. You could go double-nut to pretty much eliminate backlash entirely, but that increases the cost a fair bit. On a lathe, the Z axis is probably the most critical- you can usually play with a little leeway on turned diameters (except when you're riding the line between slip fit and press fit!), but actual shoulder placements and thread accuracy generally matter a lot to an overall project. Then you could go traditional ACME style on the shorter axi[e]s with smaller thread, brass or Delrin nuts and have an easier time dialling in backlash. Or just ballscrew the whole thing, whatever floats your boat. They're way cheaper than they used to be!
Thank you both for your replies. Something to think about. I had a thought of my own last night, my work Piece Will Never exceed 38 in so the Thousand mm screw works just fine the problem for me is the overall workpiece has to be almost 50 in. If I build a 50 inch table can I use a c arm in the middle and not extend end to end of the table series forgive my terminology,
If your work piece will be 38" the screw needs to be longer than 40", I think. You have to mount the screw, connect the stepper and allow for the y axis assembly and support.
Yeah, even if the 1000mm length is just the screw and not the machined ends (which I'm not 100% sure about), you also have to subtract the length of the nut and the maximum width of your tooling to get the usable working distance. Most of these Shenzhen importers will do custom lengths with custom machining for just a few dollars, though. Just a case of changing a couple of numbers in their ERP system for them. Edit from a lot of ballscrew shopping right now: length is total length, standard BK-style machined end dimensions are available (about 100mm total including nut for RM1204, probably in the 125mm range for 1605)
