Why would it matter how you got to the other side, either by raising
the quill, removing the edgefinder or running the table left/right to
clear the end of the part/vise and moving the table back into
position? Once one edge is found, the table dial can be reset to
zero (or DRO if you have one), then what I do is move the table 1/2
the dia. of the edge finder probe, and reset the dial/DRO to zero so
the centerline of the spindle is centered over the edge of the part
just "found". Then, it is an easy matter to move into the part
whatever the distance is that you need to drill/mill. In this case
its half the dia. of the part. Measure the part to determine its
diameter and do the math. It is also sometimes possible to "edge
find" on the corresponding vise jaw face, the jaw holding the
opposite side of the part. I don't think this is as accurate as
measuring the part directly, but its probably close enough for lots
of situations. If you are lucky enought to have a DRO that does the
centerline computation for you, its a snap to edge find both sides
and use the DRO to do the math.
I use a DRO so backlash is not an issue as far as locating centers or
other points. It is an issue when milling, and I tend to account for
it in positioning the table even for drilling, but this occurs after
the "position" is located using the edge finder & DRO.
Another way to end drill the center of a round part held vertically
in the mill is use a stop on the side of the jaw, such that a 90 deg
corner is formed (one that reaches the centerline of the stock),
edgefind both surfaces of the jaw and stop, set both to zero,
establishing a 0,0 datum at the corner of the jaw/stop, then dialing
over 1/2 the stock dia. from both axes. I use this ALL the time, for
nearly all my milling/drilling. When I'm done with one
operation/part, I return the spindle to the 0,0 datum location and
lock down both table directions and turn the DRO off. Then, when I
return for another operation (hours, days, weeks later), I have the
same 0,0 datum to start from. (Often I verify this if its been more
than a short time between). The DRO maintains is coords. even when
off, but even if it doesn't, just resetting zero on both axes before
moving the table re-establishes 0,0.
Another way to do the end center drilling would be to set up a rotary
table with a 3-jaw chuck, center it by whatever method you like (I'd
use a piece of tubing and a test indicator, but have used a dead
center in the spindle held firmly into the centerhole of the RT
for "less accurate" needs). Then put the round part in the chuck and
drill away. This takes some setup time but works very well,
especially for multiple parts.
--- In GrizHFMinimill@yahoogroups.com, "Jim E." <jim0000@a...> wrote:
> Many of the recommendations you're receiving will only give
> approximations if the sides or end edges of the workpiece aren't
smooth. Running any device, no matter the type, across rough or non-
trued surfaces will give only approximations. Question is, to what
level of approximation can you live with?
> Plus, to those who are advocating the use of an edge finder to
locate the center, whether while flat or on end: how do you do so
> a: lifting the spindle to get the finder over to the opposite
> b: removing the finder from the collet, then re-inserting it after
> moving the piece to the other side of the spindle?
> Lakewood, CA
> All Hail Rube Goldberg!
> dswr@w... wrote:
> > Bill, you are right... about the assumption of a diameter of
1/2". I was thinking of the original post where the question was
about drilling a 1/4" hole through the side (diameter) of a 1/2"
round bar. Sorry 'bout
> > that!
> > Also, the diameter of the Edge finder can be some dimension other
> > Leo (pearland, tx)