We have a machine that drills 5 holes in an item with a single head which steps across to each individual hole position and drills the hole.

Would it be OK to combine the measured sizes of hole diameter onto one chart, or should these be charted seperately - I cannot see how the indexing of the machine would affect the hole diameter when drilled.

Also could we combine the positional measurement for these holes onto one chart if we simply plotted the variance from nominal rather than the actual position from a common datum end face ?

You may be able to combine them. The easiest way to determine this would be to plot the holes individually on the same graph. If you cannot distinguish a pattern, you should be safe combining them. If you do see a pattern, chart them separately until you can correct the cause.

Hi Martin :bigwave: . It's been a awhile.

I like Miner's response - "You may be able to". I'm just looking from a die casting view. If we are drilling through a thicker, solid area of the casting, there could be some variability intoduced from porosity (tool "wander"), some anomaly in the metal, or the drill starts on a seam line. Normally I would chart each hole by itself for this example - depending on the size tolerance. If the tolerance is pretty tight and you need to show capability to a customer, it could be necessary to show each hole's capability because the combination of holes could push you under an "acceptable" index number.

We "almost always" :rolleyes: use a bore gage with a master ring when measuring a machined hole size. It's more intuitive to know what the size is compared to zero than looking at the actual dimension.