On 2008-08-30, Michael Koblic wrote:

"Jim Wilkins" wrote in message
...
On Aug 28, 11:51 pm, "Michael Koblic" wrote:
"Jim Wilkins" wrote in message

[ ... ]

A large pointed setscrew held by nuts and washers might work.

Setscrew pointed upward for the center, nuts and washers to hold it
tight in the hole.

I see. I could actually clamp the "live center" in a drill press vise and
position it.

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 typicaly has a Morse taper shank, so you'll need some
extra tricks to make up for the taper itself.

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...

:-)

[ ... ]

http://www.lindsaybks.com/bks/advmach/index.html

Don't be put off by its age. Production techniques may have improved
dramatically since then but manual lathe operations are still the
same.

For that I thank you. In fact I have been actively looking for older texts
which are more in keeping with what I am doing. I think I mentioned the old
blacksmith book with wooden bearings etc. He goes into lathes a bit but not
in enough detail (where, as far as I am concerned, is where the God is).

I am waiting for my first order from Smartflix so I can see these things
actually happening. They have some extensive courses on milling and lathing.

Hopefully, they will also tell you that while you are using a
lahte, you are *not* "lathing", but rather "turning". :-)

If it works out renting from them I should move forward more quickly. In any
case, I have ordered the book you recommended.

If the chuck doesn't hold the part straight you mount it between
centers and drive it with a dog.
I think a 4-sided pyramidal point held in the drill chuck is enough to
drive brass without a dog if you take light cuts. You don't need to
make the point run perfectly true as long as you mark it so you can
remove and replace the work.

Does the dog not object? Juvenile humour aside, now I have to study how to
use a dog! I thought a dog was a sort of bent thing which held parts to a
face plate if you did not have a chuck...

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. :-)

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.

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).

[ ... ]

That's a good idea I hadn't seen before. Then again I have a collet
lathe which is the perfect machine for making small round parts. Mine
would be a little more perfect if it hadn't been abused in trade
school. A small lathe with a 3-jaw chuck is close.
http://www.mini-lathe.com/

Ha! You heard it here first! I have never seen it myself elsewhere, it just
came to me when I was trying to drill centre hole in the end of a 3/16"
copper rivet to stick on the end of my gnomon. I had to make another jig to
hold the rivet in the drill press vise but it works just fine.

The ability to make fixtures is an important one in any kind of
metalwork, and some woodwork as well.


Maybe with a centre drill you do not need to punch? Am I right in that?

See the center/spot/stub drill thread. With less rigid equipment like
your drill press and my 50-year-old milling machine you have to learn
what works and what doesn't. The punch mark is to align the drill bit
with your hand layout since it's very difficult to position the center
of the drill bit directly.

I have been following that thread - and I was not sure. I bought a centre
drill and promptly broke one end. The other end worked well, but I used a
punch. I believe you have to run them quite fast.

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.

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.

Good Luck,
DoN.

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