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Question regarding positional accuracy?

Ferdo

Plastic
Joined
Apr 25, 2023
Hi,

I’m looking at purchasing my first CNC mill, which is a used Hardinge GX 1000 and I’m a little confused about the accuracy provided by the machine maker.

They state the following:

Accurate positioning accuracy ISO230-2
- Full stroke positioning 0.01

Accurate repeatability accuracy ISO230-2
- Full stroke repeatability 0.005

Ball-bar accuracy, example accuracy 0.004mm on X-Y plane

The machine I’m looking at has a x/y/z stroke of 1020/540/540 mm

Does this mean that the machine has a positional accuracy of 0.05 over the entire stroke of the x axis, for example? Does this mean that over an 500mm stroke in the x axis it has a 0.005 positional accuracy? Likewise, the repeatability would also be halved if the stroke was 500mm in the x axis?

Sorry if this is a dumb question.

Some clarity on this would be appreciated.

Thanks,
Ferdo
 
Several thoughts:

The best people to ask these questions are Hardinge sales and engineering personnel.

Accurate positioning accuracy ISO230-2
- Full stroke positioning 0.01
This seems to say that the absolute position over your 500 mm stroke is only 0.01 mm, not 0.005 mm.

Accurate repeatability accuracy ISO230-2
- Full stroke repeatability 0.005
This seems to be saying that if you move from a location anywhere in the movement range, go to another position that is also in the movement range, and then return to the first position, it will be within 0.005 mm of where it was at first. And you can do this over and over and always land in that 0.005 mm distance of where you were the first time.

That's my take on it. But often sales people will have different points of view. Just try to buy a real 2x4 in the lumber yard. Or even a piece of 3/4" plywood in today's world.

I suspect your "0.05" number is a typo.
 
My understanding aligns with Paul. Repeatability is coming back to the same place over and over within 0.005 mm.
That spot is accurate within 0.01 mm All of the presupposes a brand-new machine with zero wear and tear.
 
You can buy the ISO 230-2 standard and find out the details. It costs around $170. Whether that is expensive depends on how desperate you are to know the exact answer.
 








 
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