Profile v Supported Round Rail

Yes, that's "v" not "vs". Technically correct in this situation? Possibly not, but old habits die hard.

Anyway, the title says it all really. Over comparatively short distances (200mm of travel for any given point on a 200mm table, so estimating 400mm of rail) are there any specific advantages or disadvantages between the two?

For a vertical axis, will they both work as securely as each other?

Thoughts, opinions and wisdom welcome as always! :beer:

Edited to add: I've read elsewhere that for these small-size machine purposes, the difference between 15/20/25 profile rails is almost nothing. At this point I'm looking at the Hiwin rails from Zapp, if it's a matter of brand quality.

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!

Quote:

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Originally Posted by Jonathan

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

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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?

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

have you seen these ??

http://www.ebay.co.uk/itm/AMT-MSA15-...pmod%3D2707044

James

Not bad! Was trying to avoid overseas sellers but even if the rev'noo take their cut on top that will still be a good price I guess.