True position report for hex

NODOCHAU
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True position report for hex

Post by NODOCHAU » Tue Jul 17, 2018 9:55 am

Hello,
Can some one tell me how to report the true position for the hex. Datum is a cylinder.

Thanks

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medupriest
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Re: True position report for hex

Post by medupriest » Tue Jul 17, 2018 10:47 am

I think I would typically make intersection points at the 6 corners and then construct a centroid point using those six points and that is what I would use to report.

NODOCHAU
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Re: True position report for hex

Post by NODOCHAU » Thu Jul 19, 2018 7:23 am

Thank you for your reply.
So we will report as a point (feature) to a datum (cylinder)? Or construct a circle by using 6 points and report it under MMC condition?
Which method should I use?

Thanks

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Ryan Christopher
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Re: True position report for hex

Post by Ryan Christopher » Thu Jul 19, 2018 11:23 am

ASME Y14.5-2009 also specifies in section 7.3.3.1 paragraph 2 that you can interpret position requirements with a "surface interpretation" so long as the limits of size are maintained.

In other words you are allowed to figure out the minimum and maximum boundaries for the feature and use profile to evaluate.
Ryan Tackes
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http://www.vantagemeasure.com/

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Re: True position report for hex

Post by Greg » Tue Jul 24, 2018 2:19 pm

I am having the same issue currently. Just received a print with a few hex holes and they want true position of the hex holes with MMC. Like the previous post asked, can we just create a circle from the intersection of the hex lines and report the position of that? My boss does not want to report profile because it's called out as TP.

I also have to report the size of the hex. Do I just give them line-line distances three times?

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Re: True position report for hex

Post by NODOCHAU » Tue Jan 15, 2019 8:15 am

I got the issue when try to report the true position for hex.
Measure 6 lines on 6 surfaces, construct intersection points then construct a circle by using those points. Report true position with a cylinder datum.
After finishing the first run, I turn the bolt to another hex side the run the 2nd run and keep doing that to 6th hex side to ensure the reading is repeatable. But All 6 readings are different. The differ is about 0.002 to 0.003. Do you have any ideas??
As I heard that CMM manager is upgrading to a new version to include Hex true position calculation. Do you know when?
I am using 3.6 SP2 version

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CrashN8
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Re: True position report for hex

Post by CrashN8 » Thu Jan 17, 2019 9:47 am

I think you'll need to describe your problem in greater detail... I do not understand what you mean "I turn the bolt to another hex side the run the 2nd run and keep doing that to 6th hex side to ensure the reading is repeatable." What are you trying to do? What do you expect to happen?

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Re: True position report for hex

Post by Murguel » Thu Jan 17, 2019 2:38 pm

NODOCHAU wrote:
Tue Jan 15, 2019 8:15 am
After finishing the first run, I turn the bolt to another hex side the run the 2nd run and keep doing that to 6th hex side to ensure the reading is repeatable. But All 6 readings are different. The differ is about 0.002 to 0.003.
Are you measuring a Bolt? I have a warm feeling that you are trying to validate the centricity between a bolt's hex-head and its body by "mis-using" the "True-Position" feature. As the name states, it is for positions but not for centricity. Centrictiy does have an own GD&T Feature and doesn't require a detour over True-Position.

Question: Do you have a variance up to 0.003 only when you turn and measure the part in different orientation or do you have also a deviation when you re-measure the 1st side?

PS: 0.0051 mm (0.002 inch) doesn't sound much for me though.

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Re: True position report for hex

Post by NODOCHAU » Wed Feb 27, 2019 3:34 pm

Hi CrashN8,
After the first run I turn the bolt's hex head 60 degree and perform the same run and do it 6 times.
Hi Murguel,
Yes I got variance from 0.002 to 0.005 inch.

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Re: True position report for hex

Post by CrashN8 » Thu Feb 28, 2019 2:33 am

Okay... so the bolt head is not concentric with bolt threads, this does not surprise me at all. What exactly do you expect to see here?

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