# How do I convert inches of mercury to pounds per foot

Q

#### QA GEEK

I work in a aircraft job shop and we recently started using vacuum fixtures to hold parts down during CMM inspection. The problem we are having is converting inches of mercury to pounds per foot in order to meet the 5lbs per foot allowable weight to restrain parts. Can anyone point me in the right direction?

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J

#### Jimmy the Brit

I have this on a reference table:

inches of mercury x 70.73 = pounds/square foot, and
inches of mercury x 0.4912 = pounds/square inch

but it doesn't have any attribution on the table, so probably not solid enough for your needs.

D

#### Dean Frederickson

To convert inches of water @ 4 degrees C into pounds/sq. ft. multiply by 5.202.
To convert inches of water @ 4 degrees C into inches of mercury multiply by .07355.
I know this isn't exactly what you asked for but you should be able to figure out what you want by using these conversions, hope it works for you.
Google "How do I convert inches of mercury to pounds per foot" it will give you a number of conversion charts.

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#### Jim Wynne

Leader
Admin
I have this on a reference table:

inches of mercury x 70.73 = pounds/square foot, and
inches of mercury x 0.4912 = pounds/square inch

but it doesn't have any attribution on the table, so probably not solid enough for your needs.
This source (also of uncertain pedigree) agrees with the 70.7 number you cite.

Q

#### QA GEEK

Wow, I'm impressed with the quick replies. Thanks to all, now I'm off to see how this works out.

Phil

D

#### Dean Frederickson

Google "How do I convert inches of mercury to pounds per foot" it will give you a number of conversion charts.

#### gard2372

##### Quite Involved in Discussions
I work in a aircraft job shop and we recently started using vacuum fixtures to hold parts down during CMM inspection. The problem we are having is converting inches of mercury to pounds per foot in order to meet the 5lbs per foot allowable weight to restrain parts. Can anyone point me in the right direction?
So far all great links and formulas for the mercury conversion.

But.... Have you and your team decided firmly that vacuum holding fixtures is the way you want to go? As you stated your shop recently started using vacuum holding fixtures.

Perhaps due to the nature of the parts handling (aerospace) vacuum holding is the way to go for a cmm inspection to minimize toe clamp nicks etc and cosmetic or plating/coating rework...

Perhaps another post for alternate techniques for holding parts during CMM inspections if you decide that vacuum holding is not the way to go. Maybe due to vacuum fixtures for many part configurations would be costly for non-repeat parts in a job shop vs. typical blocks with many threadded holes for variable set-ups etc...

Also try http://www.cmmtalk.com

Q

#### QA GEEK

So far all great links and formulas for the mercury conversion.

But.... Have you and your team decided firmly that vacuum holding fixtures is the way you want to go? As you stated your shop recently started using vacuum holding fixtures.

Perhaps due to the nature of the parts handling (aerospace) vacuum holding is the way to go for a cmm inspection to minimize toe clamp nicks etc and cosmetic or plating/coating rework...

Perhaps another post for alternate techniques for holding parts during CMM inspections if you decide that vacuum holding is not the way to go. Maybe due to vacuum fixtures for many part configurations would be costly for non-repeat parts in a job shop vs. typical blocks with many threadded holes for variable set-ups etc...

We have run the gambit including having a so called fixturing consultant. We Machine and assemble aircraft doors and window surrounds for several general aviation OEM's so most of our business is repeat. But thanks for the suggestions. I think the vacuum fixtures are the best way we have tried yet but I had to make sure that we were in compliance with the 5lbs per foot max. I ran a couple of the formulas suggested here to my customers engineering and they agreed that any of these would be acceptable so thanks to all for the help. Maybe one day I can return the favor.