Calibration of Home Made Gages - Simple go/no-go gages to true position gages

[beaser3]

We have a variety of home made gages that are used on our shop floor. They range from simple go/no-go gages to true position gages. We are trying to get them all on a maintenance and/or calibration schedule. How do you define the allowable inaccuracy on these gages for a lab scope? Any suggestions? Thanks in advacne.

[MysterHK]

Are these similar to production fixture jigs? Or am I thinking of something else?

[beaser3]

I don't think so. These are gages that are used during a production run to validate product. Example: We make a ring that has an open ID of 1.00 +/-.005. We have a gage that has the lowest limit (.995) and highest limit (1.005) set. The part must not pass on the no-go side of the gage and must pass on the go side.

[MysterHK]

Ahh. In that case, I would turn to two references:

American Gage Design standards (B47.1) & ANSI B1.2 gage standard

I would think these would satisfy ISO requirements for allowable inaccuracies.

There's a book I saw that I had a chance to glance over called, "The Handbook of Dimensional Measurement" that has possibly what you're looking for as well.

Hope this helps.

[BradM]

In Reply to Parent Post by beaser3

I don't think so. These are gages that are used during a production run to validate product. Example: We make a ring that has an open ID of 1.00 +/-.005. We have a gage that has the lowest limit (.995) and highest limit (1.005) set. The part must not pass on the no-go side of the gage and must pass on the go side.

Beaser, if I read this correctly.. you are checking a dimension 1.00+/-.005 with a part with +/-.005 limits. What accuracy/resolution is your tool? Have you done any precision studies with your home made gauges?

You stated maintenance and/or calibration schedule. As I am sure you know, there is a difference between the two. Are you wanting to actually have a calibration on the tools, or some maintenance/ verification activity performed on them?

[beaser3]

Beaser, if I read this correctly.. you are checking a dimension 1.00+/-.005 with a part with +/-.005 limits. What accuracy/resolution is your tool? Have you done any precision studies with your home made gauges?

You stated maintenance and/or calibration schedule. As I am sure you know, there is a difference between the two. Are you wanting to actually have a calibration on the tools, or some maintenance/ verification activity performed on them?

The calibration/maintenance will be done for different gages. Some of our gages are holding fixtures only. In that case we will not do calibration, just maintenance to ensure that the holding fixtures haven't rusted, gotten damaged, etc................ We are actually hoping to do calibration on the gages that are being used as limit gages (is that necessary). We have done no accuracy or precision checks as far as I know. Many of these gages have been in existence for years. I guess our thought was that as long as we are using the gages to "verify" product, they should be calibrated.

[Stijloor]

In Reply to Parent Post by beaser3

We have a variety of home made gages that are used on our shop floor. They range from simple go/no-go gages to true position gages. We are trying to get them all on a maintenance and/or calibration schedule. How do you define the allowable inaccuracy on these gages for a lab scope? Any suggestions? Thanks in advacne.

Beaser,

You need to look at this Standard.: ANSI/ASME Y14.43-2003

A description is quoted here:

Document Details
ANSI/ASME Y14.43-2003
Dimensioning and Tolerancing Principals for Gages and Fixtures

Presents the design practices for dimensioning and tolerancing of gages and fixtures used for the verification of Maximum Material Condition (MMC) size envelopes and Virtual Condition boundaries generated by Geometric Tolerances controlled at Maximum Material Condition. These practices focus on the design of receiver-type gages, which collect attribute data when used for the verification of workpieces dimensioned and toleranced in accordance with ASME Y14.5M-1994. For gaging and fixturing principles and practices, see Sections 2 through 6.

The standard can be purchased here.

Hope this clarifies.

Stijloor.

[BradM]

In Reply to Parent Post by beaser3

The calibration/maintenance will be done for different gages. Some of our gages are holding fixtures only. In that case we will not do calibration, just maintenance to ensure that the holding fixtures haven't rusted, gotten damaged, etc................ We are actually hoping to do calibration on the gages that are being used as limit gages (is that necessary). We have done no accuracy or precision checks as far as I know. Many of these gages have been in existence for years. I guess our thought was that as long as we are using the gages to "verify" product, they should be calibrated.

Thanks for the reply. Now note, obviously if you followed my posts I have a certain affinity for the field of calibration. So, when in doubt, calibrate it. Basically, I like the word confidence. If you have any device, tool, etc. calibrated, you have more confidence in it's performance. Now, intervals can be adjusted based on usage, possible wear, etc.

Stijloor provided some good reference material for you. Question: Were you planning on having them done outside, or do them yourself? If you found someone with good standards and such, then you might consider having them do it (at least initially). You could then see what they did on their paperwork to ascertain if you can do it in-house.

I guess I am a little uncertain what level of accuracy you are verifying on the part, and what level your tool is expected to have (and then what level your standard for the tool would need to be). As I am a current student on the Art of estimating uncertainty myself, I do wonder if you try to verify these in-house, if you would have a good enough hold on all your uncertainty to produce measurements you could be confident in.