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Normal member
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posts: 2
since: Jan 26, 2007 |
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I am confused on calculating the total allowable bonus using datum shifting. Bonus applied to the feature is very straightforward, but when the darums are allowed to shift, is there a method of calculating this? There is no way that would be able to just add the difference between the datum holes at MMC and their actual size. Maybe with the secondary, but not with the tertiary datum. Here is my example:
1 hole true pos. dia 1.5m ABmCm. I have a CMM, but the software is not calculating this correctly. Any insight would be great. |
| Date: Jan 26, 2007 on 07:56 a.m. |
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Normal member
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posts: 24
since: Apr 04, 2001 |
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keith (Jan 26, 2007 07:56 a.m.):
I am confused on calculating the total allowable bonus using datum shifting. Bonus applied to the feature is very straightforward, but when the darums are allowed to shift, is there a method of calculating this? There is no way that would be able to just add the difference between the datum holes at MMC and their actual size. Maybe with the secondary, but not with the tertiary datum. Here is my example:
1 hole true pos. dia 1.5m ABmCm. I have a CMM, but the software is not calculating this correctly. Any insight would be great.
You need to consider the virtual condition of the datum
If B(m) is at MMC, you may have no shift. (MMC-V.C.)
If B(m) is at LMC, you should have the maximum shift. (LMC-V.C.) |
| Date: Jan 26, 2007 on 09:26 a.m. |
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Normal member
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posts: 2
since: Jan 26, 2007 |
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| That's fine and I understand that form datum -B-. However, how do you incorporate shifting for datum -C-, on a rotational basis? You can't just do the size of the datum minus the virtual condition for all three; the feature, the primary datum, and the tertiary datum, and then apply that to the tolerance can you? |
| Date: Jan 26, 2007 on 10:15 a.m. |
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Normal member
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posts: 24
since: Apr 04, 2001 |
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keith (Jan 26, 2007 10:15 a.m.):
That's fine and I understand that form datum -B-. However, how do you incorporate shifting for datum -C-, on a rotational basis? You can't just do the size of the datum minus the virtual condition for all three; the feature, the primary datum, and the tertiary datum, and then apply that to the tolerance can you?
In my stacks, the tertiary does not usually come into play. In the couple of instances I have studied it, the influence has been variable depending on how far away the measurement is. Can you present an image of the hole, and datums and their relationships? |
| Date: Jan 26, 2007 on 10:59 a.m. |
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Normal member
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posts: 107
since: Nov 16, 2000 |
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| Take a look at the previous message - http://www.etinews.com/cgi-bin/UltraBoard/UltraBoard.cgi?action=Read&BID=5&TID=115&SID=394977
keith (Jan 26, 2007 07:56 a.m.):
I am confused on calculating the total allowable bonus using datum shifting. Bonus applied to the feature is very straightforward, but when the darums are allowed to shift, is there a method of calculating this? There is no way that would be able to just add the difference between the datum holes at MMC and their actual size. Maybe with the secondary, but not with the tertiary datum. Here is my example:
1 hole true pos. dia 1.5m ABmCm. I have a CMM, but the software is not calculating this correctly. Any insight would be great.
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| Date: Jan 28, 2007 on 07:25 p.m. |
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