Implementing a set of bore gages at a machine

[Capskinfan]

Hi All,
I'm looking for advice on implementing a set of bore gages at a machine. Our diameter tolerances are tight (.0008" total). We've inheirited a set of LVDT Kurt gages, and someone else has purchased Fowler Pistol Grip gages, but I'm unable to get a decent GR&R out of them.

I've got a mandate to implement in process checks at the machine, but can't wrap my head around putting gages to the shop floor that aren't accurate enough to do anything.


Thanks

 

[tonefordays]

What bore size are you working with? How deep? Material type?

I'm not familiar with the Kurt gages you mentioned, however we use the Fowler pistol grip bore gages regularly to measure .0005 tolerances. The way we typically set up a gage that needs to be used at one of our machines is to let the tool sit in the shop so it acclimates to the shop temperature. Then use a ring gage in our QC lab that is at 69?F to calibrate the bore gage. Have the operator get a feel for the tool by measuring the ring gage several times. Depending on the size of the bore and how deep it is, you may need to take multiple measurements to check for out of roundness and taper. Also, the gage should be verified against the ring gage throughout the day to verify the calibration. Another thing to keep in mind, the size of the bore and the material type you're working with could be susceptible to temperature change, so depending on the temperature difference between the shop and quality lab, you may need to compensate for this slightly.
It helps too, if there are going to be multiple tools being used to check the bores, that all the tools are calibrated to the same ring gage, and everyone is on board with how the part will be checked and with what tools. In my experience, when you start using too many tools to measure the same feature, you will likely get slight variations that can start adding confusion and doubt to the processes. So I suggest keeping it as simple as possible.

Hope this helps.