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View Full Version : Maximum length guideline for a standard 16mm ballscrew?

WandrinAndy
10-10-2012, 11:27 PM
I've previously seen a guideline posted... by Jonathan I think... for the maximum length for a standard 16mm ballscrew assembly, after which whipping becomes a real problem, but I cannot find the posts.

Is 1500mm still ok-ish for a 1610 ballscrew?

Cheers, Andy

irving2008
10-10-2012, 11:42 PM
16mm @ 1500mm long, the critical speed if fixed one end and supported at the other is around 600rpm

http://www.nookindustries.com/ball/BallCalculators.cfm

Jonathan
11-10-2012, 12:39 AM
It depends how fast you need the machine to go. If you're happy with 6m/min, then as irving has said 1500mm is OK. If you need more you either have to use more bearings, use a higher pitch screw, increase the diameter of the screw, or rotate the nut. Which you choose depends on how much faster you need the axis to travel.

WandrinAndy
31-10-2012, 07:23 PM
"Fixity"... now that's a new term!

A-B-C-D-End Fixity - Nook Industries, Inc. (http://www.nookindustries.com/engineering/calculators/Endfixity.cfm) gives "Fixity" definitions and based on these, my interpretation is that for example:

- Fixity-B is the same as using BK12 + BF12..... 16x1500mm = 6.88 m/min critical speed

- Fixity-C is the same as using BK12 + BK12..... 16x1500mm = 10.1 m/min critical speed

And if I want to use BK12 blocks at both ends to get the better speed potential, I need to ask Chai to machine both ends to take BK12 blocks?

Please "holler" if I've got this totally wrong... which as normal is a distinct possibility!

Jonathan
31-10-2012, 09:17 PM
I think you mean m/min not m/s!

On my X-axis I got both ends of the screw machined to match BK12 blocks, but for different reasons. I don't think this increased the price much if at all. It would probably help more if you went for custom end machining and blocks which increase the spacing of the bearings on the 'not fixed' end. Do you need more than 6m/min though? That's a fairly respectable speed, certainly plenty for cutting metals and most things efficiently.

WandrinAndy
31-10-2012, 11:27 PM
Do you need more than 6m/min though? That's a fairly respectable speed, certainly plenty for cutting metals and most things efficiently.

My difficulty was not knowing what speed I need and whether that was a fairly respectable speed or not... But you've clarified that now... Lol.

I will go for the extra BK12 and BK12 end machining anyway.

Btw, I have edited m/sec to m/min... Thanks!