How to align ball screw to linear rail?

I understand the method of aligning a linear rail to a length of extrusion, using a dial indicator on the carriage, but I'm having trouble working how I would do the same when mounting a ball screw to extrusion.
How do you move a dial indicator along a ball screw to check its parallelness to the rail? The ball nut doesn't have a flat surface to reference to and if you use a ball nut mount, how do you keep it square as you move it along the ball screw?
I must be completely missing somethng....lol

How do you guys do it? It must be one of the most difficult jobs to do when building a CNC Router?

Steve

Attachment 27939

It's exactly same as the rails. Why do you need a flat surface.? Just indicate off the side of ball nut or screw. Watch this.

https://www.youtube.com/watch?v=TsOPaRAayFk&t=5s

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Originally Posted by JAZZCNC

It's exactly same as the rails. Why do you need a flat surface.?

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So I can get accurate results. That method is like balancing a ball on top of another ball....

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Originally Posted by JAZZCNC

Just indicate off the side of ball nut or screw.

Watch this.

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I watched the video, thanks. It shows the person indicating somewhere around the top of the ball screw and then carefully pivoting the mag base and metal plat up so he can move the Indicator up the other end of the ball screw.............I can't imagine that being good engineering practice.

But if thats the way its done, I guess I don't have other choice.
I just thought there might be a better way.

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Originally Posted by Sterob

So I can get accurate results. That method is like balancing a ball on top of another ball....



I watched the video, thanks. It shows the person indicating somewhere around the top of the ball screw and then carefully pivoting the mag base and metal plat up so he can move the Indicator up the other end of the ball screw.............I can't imagine that being good engineering practice.

But if thats the way its done, I guess I don't have other choice.
I just thought there might be a better way.

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Most screws have a different finish in the vid it shows a ground flat to crests to work from most don't so if you wind the ball nut / housing to one end take a reading then wind to other end take a reading and adjust if needed,

Phill

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Originally Posted by phill05

Most screws have a different finish in the vid it shows a ground flat to crests to work from most don't so if you wind the ball nut / housing to one end take a reading then wind to other end take a reading and adjust if needed,

Phill

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Thanks Phill.

Perhaps I was a bit naive here, but I took a rather more simple-minded approach to ballscrew alignment. Both ballscrew bearing blocks were clamped to adjustable mounts that allowed me to move the bearing up and down, left and right. I left the clamp bolts loose enough to allow the bearing block to move, then wound the ballnut attached to the carriage to that end of the ballscrew. Clamp bearing block in place. Ditto at other end - allow ballscrew to locate bearing block. Tighten. Job done. Didn't need to blow the dust off my DTI...

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Originally Posted by Neale

Perhaps I was a bit naive here, but I took a rather more simple-minded approach to ballscrew alignment. Both ballscrew bearing blocks were clamped to adjustable mounts that allowed me to move the bearing up and down, left and right. I left the clamp bolts loose enough to allow the bearing block to move, then wound the ballnut attached to the carriage to that end of the ballscrew. Clamp bearing block in place. Ditto at other end - allow ballscrew to locate bearing block. Tighten. Job done. Didn't need to blow the dust off my DTI...

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That's problem isn't it. So many way to do it and each machine different so not always possible to do it that way. But end of day it's not rocket science.!

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Originally Posted by Sterob

So I can get accurate results. That method is like balancing a ball on top of another ball....

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Well yes but easy enough, it's just a case of moving up n down to find high point then lock it off.