[rezcar]

Hi all,
I'm trying to enlarge a 1/2" hole about 1" deep. I have a Grizzly boring head and am having a hell of a time getting to setup concentric to the hole.

First I found the center of the hole with a macro in Mach 3 (thanks Hoss!). I adjusted the boring head dial to "0" and found it was off. So I setup a DTI to indicate off the boring bar shaft and turned the dial every which way to get it to read as close to zero but the smallest I could get was 0.006" of needle movement.

Is my cheapy boring bar just too cheap? Were my first two steps correct?
Thanks.

[RICHARD ZASTROW]

I ASSume this is a single point off-set boring head.

If this is securely attached to the spindle, the tool tip is rotating concentric to the spindle bearings.

If your indicator is attached to a non-moving object, you should be able to bring the bar to "0". If not, something is not tight. Could be the boring head, tool attachment or even play in the spindle bearings.

Is it possible your boring bar isn't straight? If it isn't the indicator will change over the length.

Actually, all that matters is the circle the tip of the tool is inscribing.

Dick Z

[rezcar]

Thanks, yes it is a single point, offsetting boring head. I didn't indicate off the shank or body but off the boring bar itself, hoping that I could bring it to zero via the adjustment dial.
http://grizzly.com/products/Boring-Head-Set-R-8/H5679

The "9/16" hole offset" mentioned in the description is the spacing between the two boring bar holes right?

[RICHARD ZASTROW]

I believe you are correct on the hole spacing.

Are you indicating the hole? If so, I doubt if it is actually round. If you have enough stock in the hole, you might spray some blueing (bluing?) into the hole, bore it out till cleaned up (no blueing left in the hole), then see if it indicates true "0". If not, something's loose and/or moving.

Another possible problem could be the indicator itself. I had similar problems with cheap wobbly indicators.

Dick Z

[rezcar]

I have indicated the hole, and it is round. I have also indicated off the spindle and it is out by 0.001".

It just baffles me that I can't turn the dial on the boring head to get it to at least 0.001", as if aligning something in a chuck with independent jaws. Well, it is a cheap import, so it doesn't REALLY baffle me!

I'm going to do some drilling with a center point and then switch to the boring head without moving the table to see how off the two are. Another problem could be the tram of the head, I did get it spot on at one height but didn't do the full range of motion. This will mean that even if I do get it centered, I may not be boring straight down.