Best way to adjust a boring bar bit is to clamp a depth mike to the bed,
over blocks, with the mike spindle centered at same hgt as the bar and
square to the lathe axis. The overall position of this rig is close to
the work. Tye bit is then bought into position and the mike set to
refer to the tip position. Then yu loosen the clamp screw for the bit
and dial off your new setting. It's wise to check that after clamping
the bit again. The mike gives you a means of making very small
adjustments to the bit position relative to the bar axis. If you're too
ham-fisted to get it exactly right, you can set out a bit more and them
stone the bit edge back to spec.

I use this trick often enough when boring in my hor mill, for which I
have no indexing boring bar holder. I have never had any trouble hitting
..0005" on dia, or less.


Regards, Hoyt McKagen

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On pp.85-96 of Gingery's book, he explains how to bore the holes in the
headstock of the lathe. Basically, he installs a temporary lathe on the
ways, the spindle of which lathe is a boring bar in which a cutting tool
is embedded. The future headstock of the real lathe one is building is
them moved along the ways towards the boring bar and the tool bores the
correct hole in the headstock. He mentions that one could also do this
with the tailstock but it is better to use the headstock as soon as it
becomes available.

On pp.94-96, he explains how one can advance the cutting tool .010 inch
to enlarge the hole a little at a time. He does this using a feeler gauge
and an adjustable gauge that one needs to build and which attaches to the
boring bar.

I would just like to be clear about the use of this adjustable gauge.
For example, is it supposed to remain attached to the boring bar while
one is boring the hole and the motor is turning? That seems to present a
possible hazard, in that the adjustable gauge could come lose and come
flying at you. On the other hand, if one removes the adjustable gauge,
maybe reattaching it could be a source of errors in the diameter of the
hole one is boring. But maybe that doesn't matter, since Gingery only
says it has to be about a .010 inch cut each time, not exactly a .010
cut each time, and one also has adjustible calipers to check the final
result.

So, is Gingery assuming the reader has enough common sense to remove
the adjustable gauge? Or is one not supposed to remove it?

Ignorantly,
Allan Adler


************************************************** **************************
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* Intelligence Lab. My actions and comments do not reflect *
* in any way on MIT. Moreover, I am nowhere near the Boston *
* metropolitan area. *
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************************************************** **************************

"Allan Adler" wrote in message
...
snip
On pp.94-96, he explains how one can advance the cutting tool .010 inch
to enlarge the hole a little at a time. He does this using a feeler gauge
and an adjustable gauge that one needs to build and which attaches to the
boring bar.

I would just like to be clear about the use of this adjustable gauge.
For example, is it supposed to remain attached to the boring bar while
one is boring the hole and the motor is turning?

No, it is removed after each use.

That seems to present a
possible hazard, in that the adjustable gauge could come lose and come
flying at you. On the other hand, if one removes the adjustable gauge,
maybe reattaching it could be a source of errors in the diameter of the
hole one is boring.

The adjustability of the fixture is to establish a relative reference point.

The shimstock allows relatively precise *relative* adjustment without
needing to know the absolute position.

A parallel: standing on the ground, if you wanted to position your head
exactly 1/4 inch higher all you would need to do is stand on a 1/4 inch
plate.

But maybe that doesn't matter, since Gingery only
says it has to be about a .010 inch cut each time, not exactly a .010
cut each time, and one also has adjustible calipers to check the final
result.

So, is Gingery assuming the reader has enough common sense to remove
the adjustable gauge? Or is one not supposed to remove it?

Ignorantly,
Allan Adler



StaticsJason