Scanning speeds

[[Pa...]]

Hey everyone.

Piece by piece, I've been disproving anecdotal "rules" about using a CMM that have been passed down through programmers over the last 20 years.  As an aside, I'm really concerned about the way so many people just believe what the last guy said.

What I have not yet found time to test is the scanning speed limit.

If you had a workpiece made of 4140 steel with 4 concentric ground diameters (our grinders are damn good) at Ø18.800", 18.400", 17.900", and 17.350", and each has a diameter tolerance on size of ±.0002", what scanning speed would you use to evaluate the size?  This is a setting standard used to "zero" a 2-point measurement at the grinder.  Pic attached.

If I had the same piece but all cylinders were less than an inch in diameter, what speed would you use here?

If it matters, I've got the workpiece oriented so the normal vector of all cylinders is along the Z axis of the CMM.

I am not using Navigator.

The high limit scanning speeds used in my shop on an operation like this one is 0.590"/s.  As I type this I'm scanning at 1.0"/s just as a test.  Since this piece is a one-off and was ground on my day off, I don't have the luxury of looking for a method that best matches the 2-point measurement from the grind operator.  I don't know what his measurements were.

Feel free to comment on evaluation settings, stylus selection, etc as well.  I like what I have but am always happy to be proven wrong, especially if it makes me look good 😎

 

[[Ma...]]

Well it's depending on what head do you have.

I have tested same path with different speeds and forces. It is pretty obvious that for features of nice form you can go faster with same measuring force, but if you have bumps, then it can airscan. So if you know your surface, you can measure faster, but adjust mesuring force.

For our active head VAST XT i usually measure at 200mN and speeds are up to 10mm/s - on not so precise planes i go up to 15mm/s, but remember - you can have set 0,5s on begining of scan or even before end of scan of eliminating points - so you don't have data in that time - they are filtered and can not be brought back.
Thats why i keep curves without that option.

But doing your research is a best way to know what you can go.

 

[[Pa...]]

Shoot.  I knew I forgot something.

VAST Gold in all cases.

I always test.  I'm just curious what others have learned.

Also curious who else works weekends 😜

[[Ma...]]

Heh i am not working on weekends, but in some sense i work 7d/week.

Now i am figuring out how to construct a measuring device of bended shafts.
Problem: whenever is cylinder bended sideways - result is skewed.
Next problem: measure it in 90° to cover both forging directions, but there is residual flash.

I got into this stage ( i hope i'll find a missing formula to get correct radius ) ( ignore tolerances - not used here )
Key is to have same height in every angle ( constructed up to 2mm bended from axis )