Five Foot Caliper vs. Tape Measure - Tolerance issues

H

HMW64

#1
I am new to the "Quality" environment so maybe someone can shed some light for me....I was recently sent a 5ft caliper to measure vinyl cut parts...sizes and style vary....why?? I was told because our tolerances our +/-1/32, our tape measures are not accurate because the operator may have to judge between whether the length is nominal or off by a 1/32, if it is between they feel that everyone rounds it down to the nominal and feels the process is not in control. I don't understand how a 5 ft. caliper will be more accurate??? It seems to be alot of money spent on a possible 1/64th difference. Any comments???
 
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#2
Hello and welcome to the Cove,

A 5 ft calipher instead of a tape measure?

Well, a calipher is usually much more exact than any tape measure, and the trick is to use measuring equipment that is... let's say one decimal more accurate than the tolerance in quiestion. You don't want to round the numbers down.

As for the lot of money spent on a possible 1/64th difference, It would seem that it is considered important to stay within the tolerance ( I know nothing about your product of course, but presume that the tolerance would be wider if it was not important).

/Claes
 
#3
HMW64,
Been there, done that. And you are correct, it won't work.
Yes the caliper is more accurate compared to the tape measure. The problem is you cannot easily use a 5 ft caliper while measuring a flexible piece of vinyl.
I will suggest three alternatives;
1- If you have CAD capability plot a full size pattern, with the +/- tolerance, to be used as a template.
2- I purchased a device called "Scanmaster II" . It's a digital readout with a 0.5" dia wheel. You roll it across the item you want to measure and the results are displayed. It also interfacres with a computer. The only number I have is Tech suppotr, 1-800-854-8075.
3- Purchase a digital readout tape measure.

I prefer method #1. It's quick and easy. You can use irons to hold the fabric down and remove wrinkles. Eliminates the discussion on measurement technique.
 
R

Ravi Khare

#4
It is important to stay within tolerance. It is all the more important to stay at the centre of the tolerance. A 1/64 step in a measurement system will divide the tolerance zone of +- 1/32 into 4 parts at best.

Even if you set the process initially to produce within tolerance, it is bound to drift as all processes do. Even with a 1/64 resolution measurement system, you won't be able to determine the drift until it has already eaten up 1/4th of your total tolerance.

The lot of money you spent on a 1/64 difference is well invested, considering the cost you could otherwise incur on rejects .
 
H

HMW64

#5
Thanks for everyones input...what I will be measuring are vinyl cut lengths for vinyl windows. Lengths can be from 14 inches up to 10 feet, so I will be limited to what I can measure. When I started running capability studies currently I receive a control data sheet per saw and only one employee per data sheet, I do that so I can determine that each saw can maintain tolerance and also the capability of each employee. I am amazed how some employees never differ from nominal but others do, it makes it difficult to know if the employees are performing the checks correctly or at all.... So if I have 10 different saws do I take samples from each saw and measure??? Do I pick samples per employees???? Can anyone relate??
 
C

Connie

#6
CALIPERS VS TAPE MEASURES?

HI HOPE W.

I can't answer for your company since it sounds like your keeping a pretty good quality dept.
But... i worked for a window company here in Minnesota (a smaller company) for 2 years. I operated the sash saw and the frame saw, we cut lengths for double bay and bows, patio windows, brick moulding and more, with lengths up to 16 ft. all we ever used is a tape tht read decimals and with regular checks we seemed to keep the tolerance with in spec we actually had very little scrap. our saws were computerized with offset functions up to .0001 so that might have helped.

The only problem we had was to get everyone familiar with the conversion from fraction to decimals. (the little pocket charts helped alot).
 
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