Help with measuring a .0005 bore

[Jeff Andresen]

I am measuring a .250 +.0005 -.0000 bore in the side of a chassis( looking from Y+). The CMM tells me the size is .2494 and I checked it with plugs and it measures .2502. The CMM also says the form is .0025. My alignment does not include the bore. I am actually measuring the size and location of the bore from the side of the chassis. Any help...

[Matthew D. Hoedeman]

Well, this one will come back to the specs of your machine and equipment.

IF your machine specs are 0.0005" (which is pretty good), it is NOT good enough for that tolerance.

If you are using a TP2, you will not be able to check that tolerances on a hole.

AND, if you are looking for size and shape on something like that, you WILL need to eb aligned to it to ensure that you are getting proper comp for the probe hits.

[William Johnson]

Depending on what your cmm is capable of, most cmm's will not do that close of a tolerance on a diameter.

[Wingman]

Yes to all above.
Bore Gage / Intramic / Plug the bore. Use CMM for location.

[Jeff Andresen]

I know you have been through this before with others, but how do I align to the bore (level etc)?

[Matthew D. Hoedeman]

Measure the bore as a cylinder, then simply LEVEL to the cylinder, measure a place on the face, intersect the cylinder and plane, set your XYZ origin to the intersection point. No rotation is needed since it is a round feature. I much prefer to set all 3 axis to a point not the cylinder alone since the axis of the length of the cylinder can then change with the measurements.

[Jeff Andresen]

Thanks again...

[mattfurtaw]

I measure the diameters of bore weekly and Hoedeman stated it correct. You must align to the bore in order to measure the diameter accuratly. Otherwords you get false information.

[Paul Sarrach]

I measure the diameters of bore weekly and Hoedeman stated it correct. You must align to the bore in order to measure the diameter accuratly. Otherwords you get false information.

http://www.websophist.com/Pat_On_Back.jpg

[spazus_maximus]

What kind of math are you using for your diameter? Leastsqrs,maxinsc??

[bob mappes]

use Deltronic pins for the size

[1CMM4ME]

Jeff, as stated by everyone else, use the cmm for location purposes. We have alot of small bores we have to measure, as we use Federal air gaging systems. You can check the size and roundness easily. However, if this is a one off deal, then you may just want to stick with gage pins, or bore mics. Air gaging systems get kind of costly and are not cost effective if you don't use them all the time.
Just my .01$

Note: If you have to check big bores ( like supervisors or bosses) a cattle prod works quite well.