Linear bearings - round or square?

[kerino]

I'm just embarking on my first CNC router table design. The work area will be 3' x 3'. I'm trying to work out the pro's and con's of round vs. rectangular linear slides. From all I've read so far, it seems whatever type I use will need to be fully supported, so it's either round with open bearings or rectangular.
Can anyone explain the advantages of one over the other, to help me make a decision please?
Many thanks
Kerin

[posix]

without delving into the theory of it all just go with round because it's more readilly available (gas/water pipes) and cheaper. and it leaves extra room for the L profile mounting bolts as well.

[Bruggles]

if you are talking about the ballbearing type, the square seem to hold more weight in any given size range, they are also easier to mount in my opinion, but the others are about the same if you get the mounted rails. Thompson super smart round bearings do have impressive weight capacities, for not much additional cost over traditional round bearings. If you are looking at one of these types it seems like square has many advantages, the disadvantage being cost. For round bearings check out www.qbcbearings.com

[Halfnutz]

The square are the way to go if you can afford them. They simply have better specs for a given size, but they cost much more. Start searching ebay for THK, Thomson, IKO, INA, Linear, bearings, linear actuators, CNC, etc. Do your homework now, check out all the DIY builds here, this site is a fantastic wealth of info. First of all define your requirements. If you need to cut heavy aluminum your needs are much different than if your just engraving into wood, of course. If you use a bidnapper service you can pick up linear square rails off ebay for a song. Spend a little time planning and deciding what you really need first, that way you wont be starting your second machine before your first one is done, like I did! Good luck and start a thread when you get started.

[kerino]

Thanks everyone for your advice - it's been very helpful. I need to work out some load factors now. I think I will go with square, as I would like to do some light machining in aluminium, as well as wood. The oppertunity for picking up bargains here in the UK is very limited, compared to the USA, but I will keep scanning eBay and hoping...

[Robyn]

Also check out www.technische-antriebselemente.de for wide variety of components.