Techniques for Measuring Flatness

#21
There are 2 slots of varying thickness (go/no go) in which the product must pass or not pass through. If the product is too thin and goes through the "no go" side, it is rejected. If the product is too thick and won't go through the "go" side, it is rejected. Our assumption was that the maximum degree of unflatness that a part could demonstrate would be the difference between the measurements of each slot.
Ok, I'm going to try a slightly new twist here: As already noted this may not be the best method for measuring flatness, but I wonder if flatness (by itself) is the real issue here? It would seem to me that this is really about how the customer uses your product. I.e: How does it fit in with the mating parts? A reasonable assumption would then be (please correct me if I'm off target) that they put it in some kind of frame, where it needs to stay within certain parameters to fit and function well.

Perhaps you could check its function by using not a toaster but two flat planes (covering the entire surface if that is the equivalent to how it is used), separated by gauge blocks? I used to do this to check that gears to a pump would be neither too thick or distorted by heat treatment (would have caused them to seize up) nor too thin (not enough pump pressure due to oil escaping through the gap).

However, the customer is applying pressure to one side of the filter and measuring the length the other side rises off of a flat surface. I tried to argue that this is magnifying the degree to which the product is not flat but they insist their method is correct.
Yes, it sounds like a strange method, but maybe it is warranted by how they assemble it? Not enough information here, but the key is to discuss this with your customer and agree on a proper specification.

This is getting interesting. Please let us know how it ends.

/Claes
 
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C

Cullet

#22
Thank you to all who responded. After reading your replies, I think I am confusing flatness with parallelism and I apologize for the incorrect usage of terminology in my original post. Our product has a fairly consistent thickness throughout each piece, but tends to get some warping/bowing in the firing process. This warping/bowing is what our customer has an issue with. Is anyone aware of any techniques/gauges/jigs that can be used to check for parallelism in a production setting? Time is an issue here and visual inspection is too subjective. Thank you again.

Regards,
Steve
 

bobdoering

Stop X-bar/R Madness!!
Trusted Information Resource
#23
Is anyone aware of any techniques/gauges/jigs that can be used to check for parallelism in a production setting? Time is an issue here and visual inspection is too subjective.
It really goes back to the function and the correct callout. If the part has to slide into something, true position at MMC (toaster, if you will) will be a good idea. True parallelism will require an overall zone - highest point above the surface plate of the part sitting on the surface plate. Claes had a good description there.

What the customer is doing...I don't know. I can't understand what the point they are trying to prove with that is. If the function needs to duplicate the condition they are generating, then....well, ok. My guess is - and I hate to say this out loud - they just came up with a back yard method that does not measure anything correctly.
 

Stijloor

Staff member
Super Moderator
#24
Assuming that paralellism is the intended characteristic, think about a functional gage. Two plates with a distance between them equal to the MMC condition. But if you produce different products, a functional gage is required for each. Another option could be an indicator on a surface plate. More versatile and you obtain an actual reading rather then a good/bad outcome obtained with a functional (attribute) gage.

Hope this helps a little bit.

Stijloor.
 

Paul F. Jackson

Quite Involved in Discussions
#25
It really goes back to the function and the correct callout. If the part has to slide into something, true position at MMC (toaster, if you will) will be a good idea.
Bob, It wouldn't be true position at MMC, it would be straightness at MMC applied to the thickness specification or flatness at MMC if the newest ASME Y14.5-2009 standard is cited just as I explained earlier.

Paul
 
C

Cullet

#26
I should have given more information in my last post. The customer slides our product into a slot on a trough which metal flows down. They feel that too much warping/bowing will create stress on the filter which could result in breakage when the metal flows through it. What if I made an adjustable "toaster" gauge? I could determine the average thickness for a production run, set the thickness of the gauge to the average thickness plus 1.5mm, and slide the parts through? Since the average thickness of a production run does not vary by more than .25mm, this should eliminate the majority of the warped parts. It would not be perfect but it would improve what the customer is seeing now.

Regards,
Steve
 

Stijloor

Staff member
Super Moderator
#27
I should have given more information in my last post. The customer slides our product into a slot on a trough which metal flows down. They feel that too much warping/bowing will create stress on the filter which could result in breakage when the metal flows through it. What if I made an adjustable "toaster" gauge? I could determine the average thickness for a production run, set the thickness of the gauge to the average thickness plus 1.5mm, and slide the parts through? Since the average thickness of a production run does not vary by more than .25mm, this should eliminate the majority of the warped parts. It would not be perfect but it would improve what the customer is seeing now.

Regards,
Steve
Can you show us a drawing?
 
S

sathis

#28
My company has come across a customer issue dealing with the flatness of our product. We produce reticulated ceramic filters for use in steel foundries. We currently use what we call a "toaster" gauge which acts as a dual purpose thickness measurement gauge and as a flatness gauge. There are 2 slots of varying thickness (go/no go) in which the product must pass or not pass through. If the product is too thin and goes through the "no go" side, it is rejected. If the product is too thick and won't go through the "go" side, it is rejected. Our assumption was that the maximum degree of unflatness that a part could demonstrate would be the difference between the measurements of each slot. However, the customer is applying pressure to one side of the filter and measuring the length the other side rises off of a flat surface. I tried to argue that this is magnifying the degree to which the product is not flat but they insist their method is correct. I was hoping to find some methods other people use to determine flatness. Our current specification is +1.5mm.

Steve
Just to have a insight on this , the attached one will help you.


http://www.mahr.com/scripts/relocat...D=9633&FileID=6191&ContentDataID=32100&save=1


sathis
 

Attachments

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Cullet

#29
A drawing of what? A filter, the issue we're seeing, what I envision the adjustable gauge to look like?
 
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