Y axis rail- single or double?

[Corvus corax]

I just received a REALLY nice 25mm preloaded STAR rail, with two cars, 51 inches long, which I intend to use on my Y axis. The travel of my ballscrew is about 23 inches, and I had always intended to have Y be around 24 inches travel.
Problem is, I just hate to cut this rail. Its so hard to find a good 50 inch rail, it seems a shame to cut it into two 25 inch pieces. The rail is new, and has two carts.
Is there a significant enough advantage using two sections in parallel for this machine? I intend to cut metals, possibly including some steel. The Z axis will be capable of 12 inch moves.

[jimbo]

Ah, the joys of secondhand components. 25mm is quite heavy duty. I would save it for another project or sell it and buy two smaller rails. If you are going to cut metals, I would definitely have two parallel rails, this would increase rigidity especially with the 12" z. The further apart you space the rails also increases rigidity, as this will conteract the torque from the z-axis. If you are going to cut it, will one truck on each rail be enough to bolt your z-axis to? I would be inclined to have two trucks on each rail, but that will also eat in to your travel.

[Corvus corax]

The carts are pretty big, though not as long as the extra heavy duty ones. The mounting area on each is about 2.5 by 3.5, and my Z axis is fairly light, so I doubt I'd have a problem with torque. I have some more time to look, so I'll be keeping an eye out for some more rails, though I have no idea what I'll use these for if I save them for another project. I've already got a collection of useless ballscrews to store. And a large servo motor, and an Accucoder 1000 line encoder I'll never use...

[2muchstuff]

Don't feel bad about having extra stuff. There will come a day when you will need it, if not sell it here or on the Bay. I have been scrounging up parts for my router for a while now and you wouldn't believe what I've accumulated. I don't know how many times I've changed the design ending up with more extra parts, but every change relates to a better upgrade. Be patient the parts you want will come to you.

[jeffs555]

My 24mm IKO rails have a torque spec of around 80 N-m which translates to a little over 700 inch-lbs. Assuming the maximum distance from the bearing to the end of the cutting tool is 15 inches, that translates to a maximum of 700/15 or about 46lbs of cutting force for a single carriage. The torque specs for your rail are probably higher than mine, but it still sounds marginal for a single rail. You just need to find the torque specs for your rail. Using two rails with a single carriage on each might be better. The moment arm for the torque along the rail would only be the distance from the bearing to the centerline of your spindle, probably only 3 or 4 inches. Still, if you are planning to cut metal, it might be best to have 2 rails and 4 carriages.

PS I am actually planning on only 3 carriages on the Y axis, 2 on the lower rail, and 1 on the upper rail.

[Corvus corax]

Yeah, I went through the calculations and found I have fairly big trouble if I went with a single rail. But compared with my current ballscrew woes, this is minor.