Finding Center

I manufacture sight pushers for auto pistols. Most of my designs require a series of holes drilled on the centerline of 1-1/2" bar stock. In reality, the same sizes of steel and aluminum are several thousandths different in width. When mating the two, the holes really need to be centered.
Anyway, I have a Grizzly 1007 equipped with a DRO Pros glass scale 2 axis DRO. A friend who is a professional machinist helped me set it up. We tramed the table and the vise and found it to be durn near perfect. Out less the than .001 for 360*.
When I use the DRO to find center I use an electronic edge finder mounted in a collet. When I drill a hole, I also use a collet. I'm still ending up 10-15 thousandths off center.
Any idea what I'm doing wrong?

I want to talk to you. I am a gunsmith and most of the sight pushers are not what I call "good or universal". I have spent well over $1000.00 on pushers and I still don't like what I have. Please text me at 336-325-6938. Thanks, Phil (Ustawuz)
 
The 10 -15 thou off sounds like it could be a backlash problem if your wiggler is being used alternately on each side of the piece. You could try wiggling one side and then instead of going to the other side wiggle to to a straight edge clamped against the other side. You would be moving the work in the same direction each time and than when you halve the readings take care to also move the work in the same direction.
Cheers
Frank W.
 
The DRO should be mounted so that it measures the table poison & not the lead screw. Back lash can't affect this unless he has lash in the scales. I have one scale I need to fix that has lash in it so this is posable.

It doesn't sound like he has a wiggle style center finder. I'd like to see a picture of it myself so we have a better understanding.
 
Here is a tool I made over 40 years ago to mark the centers of shotgun ribs for putting in beads. It would only work up to 1/2" but you can make one large enough to accommodate whatever stock you need to find the center of. As you can see the pins on the outside are roll pins and the center punch is stepped and held in with another roll pin.

RIMG0032.JPG RIMG0033.JPG
 
Here is a tool I made over 40 years ago to mark the centers of shotgun ribs for putting in beads. It would only work up to 1/2" but you can make one large enough to accommodate whatever stock you need to find the center of. As you can see the pins on the outside are roll pins and the center punch is stepped and held in with another roll pin.

That is very cool. I never thought of doing that, and have never seen one before.
 
Stricktly old school, lol. just have to be precise when you measure out for the pin placement.
 
That's a pretty nifty looking tool for marking the shotgun ribs.

Thanks, if you are making a lot of those sight pushers you might want to make one about 2" between the pins I think it would save you a lot of time.
 
I have a jig that locates the holes for the production pieces that are done on a drill press. I need to be able to produce a good accurate jig on the mill for when the jigs wear out or I want to change a dimension.
 
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