What linear rods should i use?

Hello.

I'm designing my own 3D printer, and for that i would need some 600mm long rods to carry X/Y carriages on. I've already tried assembling it with 8x600mm normal steel rods, however, those proved to be too bendable. I need some stronger rods, but the problem is that they are so very expensive. I know the very best would be proper chromed and hardened steel rods, and especially when working in those lengths. Rather than trying to explain the what i need, I have some prictures i took of a sketchup model i made of the printer. It's going to be a cartesian printer, FYI.




In the model, i just put some 8mm rods in (marked with brown), which is the ones i'm asking about.
Roughly, the idea is that there will be belts(The white ones above the rods), driving a carriage on either side. That would move one of the axies, and the same priciple would apply for the other axis. Thats for X and Y, while Z would be moved up and down. You can compare it to the way an Ultimaker works.

So, my actual question is this. What sort of rods would people use for this? I know rods maybe aren't optional at those lengths, but if you had to use a rod, what kind would it be? What diameter, chromed?
Also keep in mind that i care about price, and i would probably have to buy them online(Ebay, Aliexpress, etc.). Europe sellers preferred, if people know any good ones.

Thanks in advance

I would use fully supported linear guides. You can get quality, Japanese and German made, used parts on ebay for reasonable prices. You will have to search through about 10 pages of listings, but keep looking -the deals are there. The size doesn't matter much as long as the length is sufficient.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

The configuration you have in the images, the 8mm rods are spinning shafts, not linear guide rails, you wouldnt really want to spin guide rails in linear bearings, you have some 2020 profile there, maybe you should create a carriage to run on that, then you could probably keep the 8mm shafts, your arrangement needs them, but you could probably get away with only one per axis, the other end is just an idler, but you also need some belt tensioner in there, maybe if the pulleys where rotated 90 deg, you could use short shafts.

but as DD says if you can get some 600mm linear guides it would probably be the best investment you could make, bolt it to your 2020...though might want to use something bigger.

Edited 2 time(s). Last edit at 03/26/2016 07:54PM by MechaBits.

Like MechaBits said, it looks like you are trying to use the rods for double duty - linear guides and power transmission. With a few caveats, you can't do that. The bearings that run on rod won't tolerate rotation.