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Recommendations for detecting "Triangle Effect"

M

MysterHK

#1
What kind of special measuring setups would be good to detect this in a centerless grinding operation?
 

Stijloor

Staff member
Super Moderator
#2
What kind of special measuring setups would be good to detect this in a centerless grinding operation?
A surface scan on a CMM, a roundness tester, etc.
Two-point measurements (micrometers, etc.) do not work.

Is roundness or cylindricity specified?

Stijloor.
 

ASchmidt

Registered Visitor
#4
We have a diameter that is held .562-.563 on a centerless, but customer specification is .5615-.5635. (No other call out on the diameter) We use ring gages to the customer size to check for the lobed(triangle)effect, charting with a digital snap to maintain the .562-.563. I'd love to hear of other options that people are using....

(We don't allow the operators to use the CMM or a circular geometry gage.)
 
C

Craig H.

#5
Being April 1, I am hesitant to post this, but...

What exactly is the "triangle effect" as it is being discussed here? A google search revealed a lot on some sort of psychological research and discussions of the Bermuda Triangle effect.
 

Stijloor

Staff member
Super Moderator
#7
Being April 1, I am hesitant to post this, but...

What exactly is the "triangle effect" as it is being discussed here? A google search revealed a lot on some sort of psychological research and discussions of the Bermuda Triangle effect.
It is also called lobing, a form (out-of-roundness) deviation that can occur as a result of a centerless grinding process. I have seen 3 - 5 - 7 point lobing (and more) effects.

Stijloor.
 

Stijloor

Staff member
Super Moderator
#8
We have a diameter that is held .562-.563 on a centerless, but customer specification is .5615-.5635. (No other call out on the diameter) We use ring gages to the customer size to check for the lobed(triangle)effect, charting with a digital snap to maintain the .562-.563. I'd love to hear of other options that people are using....

(We don't allow the operators to use the CMM or a circular geometry gage.)
How are your operators expected to inspect/verify their work?

Digital snap gages are 2-point measurements that can give false readings; dimensional, and certainly form.
 

ASchmidt

Registered Visitor
#9
I know that the digital gages do not pick up on the lobing that we experienced. But, by having the operators check for it by using the ring gage to the customer tolerance, we have implemented a safe guard. The operators still maintain the grind size to .562-.563, but if it doesn't fit the ring gage in their checks, there is an obvious problem. It was the only solution I could come up with that satisfied the customer.
 

Jim Wynne

Super Moderator
#10
A feature of size may be lobed, and still be "concentric" relative to another feature.

Lobing is a form deviation.
The term "concentricity" gage is misleading. If you look at the picture on the page I linked to, it's a simple set of centers that you can use to rotate the part while applying an indicator--a simple way to check roundness and cyclindricity.
 
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