On 2008-08-30, Michael Koblic wrote:

"DoN. Nichols" wrote in message
...
If you add a V block to the vise to keep things from shifting.
upright round objects are difficult to clamp reliably in a vise, but add
a V-block and you can do a better job with a cylindrical item. However
a live center typically has a Morse taper shank, so you'll need some
extra tricks to make up for the taper itself.

My vise has a sort of vertical v-block incorporated. My "live centre" really
only remotely resembles a proper lathe live centre.

O.K. The v-groove in the vise (likely not a very deep one, but
something to help) is a start. Ideal depth of V-groove would be such
that the two sides of the 'V' are tangent to the diameter of the thing
being held. If it is shallow enough so the tops of the V touch the
circumference of the workpiece it will cut grooves into the workpiece
and will not be as good a grip. Of course, some vises (e.g. toolmakers
vises) have deeper grooves than others do.

As for your "live center" -- is it at least a pointed part held
in bearings so it is free to rotate? That is a start. If it is not
free to rotate, then it is just a center, not a *live* center.

Of course -- way back before bearing mounted centers in the
tailstock became common, the center in the headstock was called "live"
(because it rotated), and the one in the tailstock was called "dead"
because it did not. And the point of contact between the tailstock
center and the workpiece was lubricated with "white lead" (a lead oxide,
IIRC) -- something considered a hazardous material these days. :-) There
was typically a small well in the tailstock casting, and a plug which
would dip out some and could apply it to the center/hole interface.


I was just thinking what kind of rotation will happen to the
piece if its so bent that it moves the centre around when *not* clamped.
I
guess it will find a way...

It is used with a face plate, to impart rotation to a workpiece
suspended between centers. The one in the headstock spindle rotates,
but it does not have enough contact area to really drive the workpiece,
so the dog is clamped onto a part of the workpiece which you are not
(currently) changing, and its tail is driven by a slot in the faceplate
(if a bent-tail dog), or by a bolt through the faceplate (if a
straight tail dog). These do not wag. :-)

For that you need a wiggler?

Well ... actually a "wiggler" is an indicator used for moving
centers of the workpiece over/under the axis of the lathe, mill, or
drill press spindles.

If you are trying to drive something with a drill chuck which
has a poor enough finish on the end so you can't clamp it and prevent it
from wobbling, then you clamp the drill chuck onto some steel rod, take
a file to it while it is rotating to form it to a point (60 degree
angle), and use this to hold the upper end of your workpiece. You will
then need to clamp a bent-tail dog onto the upper end of the workpiece,
and a collar of some sort around the drill chuck to drive the dog's
tail.

OK, now I found some nice pictures and I understand it. Sort of.

Good -- pictures do help a lot. You know -- there are
downloadable PDF files of various old books (out of copyright) which are
very good things to have for what you are trying to do -- or for anyone
with an old manual lathe, mill, and other such tools.


Another thing to worry about is that most drill presses don't go
slow enough, and if the workpiece, collar, and dog are not fairly well
balanced, the drill press will try to walk around the floor (or the
workbench, if it is a benchtop drill press).

At this point using the canine arrangement on my drill press fills me with a
sense of dread. Also, the parts I am turning are very small, so a really
small dog would be required. A chihuahua...

I've got one of those -- a dog which came with my Unimat SL-1000
back around 1970 or so. Hmm ... a pity that Unimat of that vintage are
now being treated as collectors items on eBay. Otherwise, it could be a
reasonable lathe for making your gnomen, albeit a bit small for turning
the scale ring (whatever it is called).

Yes. If you had a lathe, you could make a disc shaped dog, with
a disc to hold the "tail" and a setscrew from the other end, and you
could add bolts to the side opposite the dog to balance the tail.

You could also make something which would clamp on the bottom
section of the chuck (after it was tightened) which had two or three
evenly spaced slots to engage the dog tail -- and not need to worry
about its balance. This would leave only the workpiece itself, and if
it is as small as you say, it probably would not have any significant
problems with balance.

*But* -- if you had a lathe, you would not need to do all of
this anyway. :-)

How large a diameter of center drill? The proper speed for one
is a function of its maximum diameter -- and the metal into which you
are drilling.

1/8"

O.K. Yes, that would want to run fairly fast. 2000 RPM would
be only slightly over 65 SFM (Surface Feet per Minute -- the measure
used for determining the speed of the workpiece/tool interface. (take
the diameter in inches, multiply by Pi, divide by 12 to give the
circumference in feet, and divide that into the RPM. That is a fairly
conservative speed for HSS (High Speed Steel) in brass.

To avoid snapping off the point, you need a way to prevent the
workpiece from tilting in the drill press. Also, a proper
coolant/cutting fluid would help them to survive. But center drills
(like all drills) are "consumables" so keep spares on hand.

I swear the first one snapped just by me looking at it...

It feels like that sometimes. Were you using it in a drill
press, or in a hand drill? The drill press is the better bet. And
don't just keep pushing it in -- go a little way in, then back the
spindle up to let chips clear, then in again, etc. Normally you don't
need cutting fluids on a free-machining brass, but I don't know what the
characteristics of the cast brass which you are working with might be.
I wonder whether it could be a bronze? Not likely, as those are more
expensive, but they are tougher alloys.

I just took apart a very old Sears cordless drill and liberated a 12V motor
as well as a 3/8" chuck and a whole bunch of cool little gears. Also I found
an old 12V motor with some strange reduction gear which, many years ago was
going to be a pottery wheel for kids. Some of this stuff has got to be
useful even though 12V is not exactly ideal.

An old automobile battery and a battery charger to keep it near
full charge and you should be fine. And that would be a lot cheaper
than a lab power supply of sufficient capacity to handle your tools.
(Hmm ... if it is small enough, perhaps a motorcycle battery would be
sufficient.

If it was straightforward it would not be fun...

:-)

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---