How many hits

[Schrocknroll]

How many hits are needed in a 30 inch diameter that is no more than .005 out of round. I wouldn't usually use more than 16, but the guy I work with uses 90.
He generally likes to keep his hits no more than 1 inch apart. To me this seems like major overkill. I personally believe it's in order for him to keep his his hours at 80 a week.
Seriously, he works from 6 A.M. to 9 or 10 P.M. every day, then from 6 to some time in the afternoon on Saturday, and sometimes Sunday too.

Sounds like a milking job to me.

[kbotta]

30" dia?
I'd use a lot also....

[Schrocknroll]

Could you be a little more specific, maybe a range or distance between hits?

By the way this is post 100

[Paul Sarrach]

3 per inch does not sound that unreasonable, I might even go 4?

Way to go schroknroll,

[Marty Schwab]

more hits = better accuracy.

[bboyd]

90 points is overkill, 16 is not enough. If your part is that round and not filmsy 30 points would seem reasonable.

[mtalla]

30"

goin' for size or form?

[ag162]

Congrats Shrocknroll!!!!!!!!!!! Welcome to the senior Group

A.Gore

[Schrocknroll]

goin' for size or form?

Size mostly.

I've changed from 16 to 30 to 90 and I've never seen a real change more than a tenth or so.

[Paul Sarrach]

try 120. did it get bigger or smaller? did it get closer to nom?

[Matthew D. Hoedeman]

If you are looking for size only, then you are using the wrong tool when you use the CMM. For a 30" diameter, I would use a PI tape. Good luck finding one anymore. This will give you an answer as quick as you can read a vernier scale and it will give you the absolutely BEST number for the size you can get from anything at anytime.

[ag162]

The key to this is the tolerance and feature characteristic. I don't see using 90 in a size case. I would experiment with a 30, 60, 90 and dimension. If the difference was very minimal, then reduce it to a comfortable minimum. BUT, be sure that you can support your decision if you are called to the floor to prove your results.
Increased Speed = reduced labor costs = Happy Mgt

A.Gore

[george frick]

30 inch diameter. i would use 36 for size. 1 hit every 10 degrees calculated @ least squares= average dia. less hits would be acceptable depending on the tolerance. for form more is better. i have used 360 on some applications. 1 hit every degree. i have seen a chart on this forum for suggested # of hits for dias. i'll try to locate it. bear in mind cmm's are not the best tool for checking roundness or for that matter even size. once again depending on the tolerance.

[george frick]

form is everything. that's why when you check a master ring gage the size reports the same whether you use 4 or 400 hits. something to think about. also congrats on your senior member status joining the ranks of the big 4 paul,matt,winston,& CANADIAN JOHN!

[bboyd]

If you are looking for size only, then you are using the wrong tool when you use the CMM. For a 30" diameter, I would use a PI tape. Good luck finding one anymore. This will give you an answer as quick as you can read a vernier scale and it will give you the absolutely BEST number for the size you can get from anything at anytime.

PI tape OMG I forgot what century it was for a minute