Bent linear rails - opinions ? Help !

[isvflorin]

I received the rails for the X azis, 1440mm long, used from ebay.
The rails are slightly bent from start to end -about 2-3 mm deflection.
20mm wide rails, 1440mm long. Is that normal and something that can be adjusted while mounting ? Or should I take it with the seller and shipping company ? Sent email to seller but no answer yet. Item description said nothing about bent rails.

Thanks,
Florin

[poordumbbastard]

Florin,

0.01 mm per 450mm is about normal deviation, 2 to 3 mm is a lot.

You could try and mount them by tightening one bolt at a time and nudge rail with rubber mallet and clamps until straight.

If you don't succeed you could always return them but the shipping cost will probably exceed the cost you paid for the rails.

PDB

[isvflorin]

Well, adjusting the rails while mounting might be possible, however accuray will probably suffer. Returning them is not a happy thing either, but since the deviation was not mentioned in the auction details it really bugs me. I wouldn't have bothered to get bent rails from another country for that price.
For bent rails I would have paid a different price. Is it unreasonable to try to settle a partial refund with the seller ?

FLorin

[poordumbbastard]

Florin,

A partial refund with the seller would be fair if you could correct most of the error.

Otherwise returning them for scrap iron would be very painful if you have to pay the shipping charges.

I would contact PayPal or your credit card company and file a dispute.

PDB

[BEARINGMAN]

If you check the installation instructions for your rails from the company web site, you will find that they all require a machined register for one rail to mount against, and the otheer rail is adjusted to be parallel to that. for an explanation see 5bears web site.

[isvflorin]

Thanks, I am aware of that and it is reasonable to me. BUT 3mm deflection worries me a lot, especially if the seller said item is perfect condition for use.
I don't want to make a big deal if it isn't necessary so the question is 3mm deflection over 1440mm lenght is considered ok or very bad ?
How were your mounting experiences with longer rails ? where they perfect straight ? I was looking at the rails again, and some of them have uniform deflection over the entire lenght - like smooth curve, but others have just a bend from where the rails go straight- like a flat V instead of a curve.

The deformation is heightwise also, not just in only one plane.

[isvflorin]

took a pic,
put 2 rails side by side so they can touch ends
in the middle you can see the space, you can see the space to the left side as well (little white from napkin).
the space for these 2 is 2.5mm wide, I can't put rails end to end because of the trucks, if I would do that the space would be bigger.

[rowbare]

It does sounds like more deflection than one might expect but I don't think you will have any problems if they are properly installed. Whether it is practical to do so is another question...

http://www.cnczone.com/forums/showpo...7&postcount=10 talks briefly about this.

The attached image is of a linear stage that was on eBay a while ago. Note the 4 blocks holding the rail against the machined edge.

bob

[isvflorin]

Thanks Bob,

I'm also wondering what abuse it takes to get those 20mm rails bent that way.
Any ideeas ?

[Zumba]

The mounting surface should have a shoulder milled into it, and wedges should press the rail against the shoulder at each bolt location.