Novice question on ballnuts

[9fingers]

Looking at typical data sheets for 20mm ballnuts, backlash is quoted as 0.05mm (2 thou). Ok fair enough.
The same manufacturer has double ballnuts that are also quoting 0.05mm backlash.

In my novice eyes, I'd expect use of a double ballnut to be able to achieve zero backlash.
So are double ballnuts adjustable when fitting to a machine to get near to zero?

Apologies if this is a daft question but I don't understand - please be gentle

Bob

[pete3000]

Depends on the class of ballnut and the screw used, C7 is a general grade with some backlash. or spend more on C5 grade with preloaded/slightly oversize ball bearings fitted. Double C7 ballnuts will generally have less play than single but you have to ask yourself do you need absolute zero backlash ? and how deep is your wallet?.

[John Stevenson]

Depends on the design of the double nut some are adjustable and some are just advertising hype.
If you want zero backlash then best to use two single niuts back to back and shim them.

However most C7's are better that the absolute resolution of the machine. If they follow spec quoted backlash should be max allowed and is usually better.

Depends on supplier.

John S.

[9fingers]

Thanks Gents

That indeed helps.

As for wallet depth, it is deep enough for me not to want to buy twice but not so deep to automatically opt for the dearest version of everything.

Of course the sensible thing would be to sell my manual milling machine and buy a CNC one but that would be no fun!

Bob