Profile v Supported Round Rail

[Jonathan]

Profile rails are much more rigid than round rails. Round rails for obvious reasons have zero moment load rating, whereas profile rails with 4 rows of balls have a high rating. The profile rails with 4 rows of balls is what you should look for.

Profile rails are preloaded, so there is no clearance (theoretically negative clearance) which ensures there is no play. This is especially important on the Z-axis where gravity does not effectively preload them.

For the lengths you are suggesting there will be some profile rails on eBay for a good price.

In the end it depends what you want to use the machine for and if you can afford it. Round rails are perfectly adequate for machining wood, composites and aluminium at moderate feedrates especially if they are orientated optimally.

I can't think of any advantages of round rails over profile rails, other than obviously the price!

[Rogue]

The profile rails with 4 rows of balls is what you should look for.

Aha! Now you mention it I seem to remember reading that somewhere. I tried to check out the PDF links from the Zapp website but the links are screwed for that product, I'll have to hunt them down seperately.

Is the number of rows something that is usually advertised with them, or is it a matter of hunting down the specs for each one to check?

[Rogue]

Hah! Just found a pair of 20x400mm Hiwin profile rails on Ebay for £80. Exactly the same thing is less than £50 from Zapp. Unless I'm misunderstanding something?

I have trust issues with Ebay, I always suspect I'm about to be conned :confused:

Edited to add:

Am I being genuinely stupid, or is there a reason why this item (which is current ideal dimensions for one axis) is £200, while the same items from Zapp are just under £150? Is there a subtlety that I'm missing that is going to come back and bite me in the arse later if I don't it into account now?

http://www.ebay.co.uk/itm/HIWIN-x4-1...item3368afd509