Calibration of a Width Gage Slot with an Attribute Gage - Maximum Width Condition

drobbins329

Starting to get Involved
#1
I have many width gages on my production floor. Simply checking against a max width condition.

My question is this:
How would I go about measuring the effective size of the slot? I have an ok set of gage blocks to compare against, but I can't get down to .0001" on some arrangements. I have a CMM I can use, but I don't trust it to hit all the possible high/low spots. I don't feel a comparator would even come close.

I attached an image of one of them as an example.

What is best practice on something like this, with the highest accuracy?
 

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ncwalker

Trusted Information Resource
#2
Off the top of my head:

1) I would definitely pass gage blocks through the slot - they have surface. And that will tell you the situation with the whole slot.
2) But you're right about the high and low spots. Lay it on its side and use a height stand and lever indicator to reach into the slot and find the high and low points that way (should be pretty quick). Put a paint dot for marking the location. Flip it over and do the other cheek.
3) With the offending areas marked, you can then switch to pin gages (most people have these in finer graduation than gage blocks) or try the CMM ensuring you probe in the marked locations. If you were really good with the CMM you could load up a matrix of positions from the edge where you could type in locations of the high/low spots and probe there specifically.

Hopefully, that gives you a few things to think about.
 

drobbins329

Starting to get Involved
#3
Absolutely some things to consider. I am pretty handy with the CMM. I use the gage blocks currently. I do not have gage pins in the appropriate sizes to get the resolution I am looking for (.0001).

Now that I am discussing it, I am considering getting gage pins for each width gage, in a go/nogo setup. Custom sizes to match the acceptable wear tolerances of the width gage in question.

Thanks!
 

Eredhel

Quality Manager
#6
Some CMMs can scan the part without lifting off the surface making them able to take as many points as you want. Some can only take one point at a time, they back off the surface for each point taken. Ours is a scanning head that can ride along the surface and take thousands of points along the way. With scanning heads you can do form, contour, and other more complex things.

I was checking to see which type you all used.
 

ncwalker

Trusted Information Resource
#8
Also thought about this a lunch - a profilometer may be able to help, if you have one. They can be very squirrely with their pickups, though, and you may not be able to get one that can access such a narrow slot.

Pin gages are cheap. (Relatively). I'd get them. But lock them up. They have a tendency to wander.
 

normzone

Trusted Information Resource
#9
Buy spares. They will disappear. And if you're concerned about .0001, there may be wear issues if they see a LOT of use.

I would think the gage block/pin method would be more reliable than your CMM, unless you have done this and demonstrated repeatability that supports your CMM data.
 

ncwalker

Trusted Information Resource
#10
Buy spares. They will disappear. And if you're concerned about .0001, there may be wear issues if they see a LOT of use.
Disappear?

I'm at the point where finding a 0.2500 pin in an English set or an 8.000 mm pin in a metric set is harder than finding a unicorn. Not sure such sizes even exist..... I've never seen one ... :)
 
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