A question re eccentricity (re the blank, not the turner)
 

I'm wondering about making a simple device for holding blanks with
adjustable and repeatable eccentricity. Consider cutting a 2 in. length
of 4 in. diameter steel or aluminum bar into two halves at an angle like
a large set of wobble washers used in cutting dados. One half to be a
faceplate with an angled face. The other half to hold the blank as a
rotatable faceplate ring.

Armchair machining is confusing, so would some engineer-turner or maybe
somebody who uses wobble washers please explain, so I don't waste time.

As the angle-faced ring is rotated on the angle-faced faceplate, does
the angle of a blank fixed to the ring increase from in-line (axial) to
maximum at 90 deg. then back to axial with further rotation? IOW, does
90 deg. provide all the adjustable eccentricity I can expect? Will this
work? Has some turner already tried and used it? Who? Where? Why?
TIA, Arch

Fortiter,


http://community.webtv.net/almcc/MacsMusings

Hello Arch

This might sound harsh but it is not meant to be.
You out of wood ??
To much time on your hand ???
Or just plain bored ????
Sorry I do not really know what wobble washers are, except maybe when
the wash load is not balanced with the spin cycle (G)
But if I see this right, to get more than 90 deg. you could turn the
blank around 180 deg. and.....
I'm stopping with this, it looks to much like a smart aleck reply, which
it isn't.
Whatever Arch, you keep well and get some more off us confused and stir
up some of that gray matter, like to read some more of your posts

Have fun and take care
Leo Van Der Loo

Arch wrote:
I'm wondering about making a simple device for holding blanks with
adjustable and repeatable eccentricity. Consider cutting a 2 in. length
of 4 in. diameter steel or aluminum bar into two halves at an angle like
a large set of wobble washers used in cutting dados. One half to be a
faceplate with an angled face. The other half to hold the blank as a
rotatable faceplate ring.

Armchair machining is confusing, so would some engineer-turner or maybe
somebody who uses wobble washers please explain, so I don't waste time.

As the angle-faced ring is rotated on the angle-faced faceplate, does
the angle of a blank fixed to the ring increase from in-line (axial) to
maximum at 90 deg. then back to axial with further rotation? IOW, does
90 deg. provide all the adjustable eccentricity I can expect? Will this
work? Has some turner already tried and used it? Who? Where? Why?
TIA, Arch

Fortiter,


http://community.webtv.net/almcc/MacsMusings

"Arch" wrote (clip) As the angle-faced ring is rotated on the angle-faced
faceplate, does the angle of a blank fixed to the ring increase from in-line
(axial) to maximum at 90 deg. then back to axial with further rotation?
IOW, does 90 deg. provide all the adjustable eccentricity I can expect?
(clip)
^^^^^^^^^^^^^^^^^
Arch, I believe the angle of the work increases until you reach 180 degrees
of rotation, and then starts decreasing again. The maximum angle will be
twice the angle of your original bevel cut.

If you want to visualize this, imagine that you make the bevel equal 45
degrees. If you rotate the loose piece one half turn, you will get a 90
degree miter.

In article ,
(Arch) wrote:

I'm wondering about making a simple device for holding blanks with
adjustable and repeatable eccentricity. Consider cutting a 2 in. length
of 4 in. diameter steel or aluminum bar into two halves at an angle like
a large set of wobble washers used in cutting dados. One half to be a
faceplate with an angled face. The other half to hold the blank as a
rotatable faceplate ring.

Interesting... certainly seems to be workable to me. The next step would
be to figure out how to connect the two angled faces and also have the
tailstock end one rotatable around a center axis. The connection would
also have to be pretty secure once you get the wood out on the end
whipping around.

You might check out the Escoulen chuck for ideas. It uses a ball and
socket to achieve eccentricity.

Be careful. Things can get pretty wild when turning the far end of a
12-inch piece.

Slowly I turned...
Randy


Owen Lowe wrote:
In article ,
(Arch) wrote:


I'm wondering about making a simple device for holding blanks with
adjustable and repeatable eccentricity. Consider cutting a 2 in. length
of 4 in. diameter steel or aluminum bar into two halves at an angle like
a large set of wobble washers used in cutting dados. One half to be a
faceplate with an angled face. The other half to hold the blank as a
rotatable faceplate ring.


Interesting... certainly seems to be workable to me. The next step would
be to figure out how to connect the two angled faces and also have the
tailstock end one rotatable around a center axis. The connection would
also have to be pretty secure once you get the wood out on the end
whipping around.

Randy, I cobbled up a cheap 'n dirty version of the too expensive
Escoulen chuck using a trailer hitch ball and pipe nipple & cap welded
to a faceplate. So far, a flop in progress, but pregnant with
possibilities. :)

Actually, I've had best results using an old cheap & worthless
independent 4 jaw chuck with a short pipe nipple cut into 4 quadrants
for jaws. I rounded the blank's end a little so it moves easily at
angles in the chuck and the nipple's threads added a secure bite. I
just wanted to simplify. Did I hear someone say, "cheapify?"

Leo #1, Messing around my shop is never boring. For me, making things
for a lathe is almost as much fun as making things on a lathe. Even tho
neither ever works out, my old schnauzer doesn't care and life in the
shop goes on. :)

Leo #2 (not necessarily in that order) Thanks, as usual, you are right
and I'm 90 deg. behind what's going on.

Bill, I really want to turn at an angle to the lathe's axis, eccentric
as opposed to off center. I may have my terms confused. I did make an
adjustable off-center chuck by setting a small rotatable disc in an off
center shallow hole in a larger face plate. The disc carried a small
bolt-pinchuck arranged so that its turning radius swept thru the lathe's
center to give me a concentric option. The disc was fixed with a long
setscrew from the periphery. A Sorby infringement, but I'm not selling
any.

Owen, Thanks for the encouragement. If it works, I'll borrow your pen
and burn my name in it. :)

Every one else, Hope this thread hasn't
taken us too OT from rcw's sacred mission of arguing the color wheel of
lathe white vs blue vs black vs gray vs plaid vs polka dots. Arch

Fortiter,


http://community.webtv.net/almcc/MacsMusings

"Arch" wrote: (clip) I cobbled up a cheap 'n dirty version of the too
expensive Escoulen chuck using a trailer hitch ball and pipe nipple & cap
welded to a faceplate. (clip)
^^^^^^^^^^^^^^^
Arch, let me tell you about the chuck I cobbled up afterI saw Escauen demo
his chuck. I starts with vacuum chuck setup, using a large, thick wooden
disk, mounted on the spindle. Turn the face of this wooden disk to a
concave spherical surface, of (maybe) 10 or 12" radius*. Mount your work on
a circular bowl shape chunk which can be stuck to the large spherical
surface, being held on by vacuum. You can offset the axis by any amount
that still covers the central vacuum port, and here's the beauty of it:

Unlike the Escaulen chuck, this one orbits the part of the wood closest to
the headstock, while the other end stays on axis, because every radius of
the spherical surface describes a cone whose tip is 10 or 12" from the
vacuum chuck*, and on the lathe centerline. This has the following
advantages:

1.) The part of the wood that is farthest off axis is firmly held by the
chuck.

2.) The part of the wood that is farthest from the chuck is spinning on
axis, so it does not take much of a beating as it is being turned, and you
are not "cutting air."

3. If you are careful to match the size of the work to the radius of the
spherical vacuum chuck*, you can use the tailstock for additional support.

4. There is very little chance of having the whirling end of the work whack
your fingers, or catch the lathe tool.

*If you want to take the trouble, it is possible to make chucks of various
radii, to match the requirements of different jobs.

"Leo Lichtman" wrote:.(clip) Turn the face of this wooden disk to a concave
spherical surface, of (maybe) 10 or 12" radius*. (clip)
Just in case I have creatred some confusion--the *radius* I am referring to
here is the radius of curvature of the concave wooden chuck. (If it were a
reflector, it would be the focal length.) It is NOT the radius of the wood
spinning on the spindle.

Arch,

I think you are on the right track with the hitch ball. Too bad you
aren't in the North Texas area; I enjoy "reinventing" things and this
sounds like an interesting project.

If the "Archoulen" chuck doesn't work out, you could use the components
to make a pneumatic device to hold your turnings while you enhance them
-- carve, burn, etc.

Slowly I turned...
Randy

I have got to start paying attention to which message I am "anchored" to
before replying. Should have posted the above a little higher in the tree.

Slowly I turned...
Randy

Moving my confusion right along:

I had thought that displacing the drive center in the same plane
radially from the lathe's center axis was 'off center turning' and
changing the drive axis to an angle from the lathe center was 'eccentric
turning'. Thinking about Bill and Leo's posts, I've had it wrong. In
my concept of 'offset' the turning cone's base is at the headstock and
its point is at the tailstock. In 'eccentric', it's the reverse, but
there's no essential difference. Right?
Funny how wrong ideas get fixed in the mind.

Leo, practically, how forgiving is your chuck re different blank lengths
while keeping the tail-points reasonably true? Can you cut all blanks
to the same 'focal' length and vary the waste for different pieces?
Sort of like the myth about Procrustus who made all his coffins the same
short length and cut off the deceased legs to fit. ;)

For some this may be a bit tedious and it sure isn't earthshaking, but I
urge Leo, Bill, Randy and others to comment and in particular on the
terms; 'offset' and 'eccentric'. Our archives have enough errors
already.

Arch

Fortiter,


http://community.webtv.net/almcc/MacsMusings

----- Original Message -----
From: "Arch" (clip) I've had it wrong. In my concept of 'offset' the
turning cone's base is at the headstock and its point is at the tailstock.
In 'eccentric', it's the reverse, but there's no essential difference.
Right?(clip)
^^^^^^^^^^^^^^^^^^
Arch, as far as I know, the accepted method of turning a piece at an angle
to the lathe axis uses the Escaulen chuck, or equivalent, which holds the
wood on-axis at the chuck end. I don't know of any authoritative definition
of this as "off axis" or "eccentric". As far as I know, a piece remaining
parallel to the axis, but supported off axis, could also be called "off
axis" or "eccentric"

You are not wrong--you are exploring no-mans-land.
^^^^^^^^^^^^^
Leo, practically, how forgiving is your chuck re different blank lengths
while keeping the tail-points reasonably true?
^^^^^^^^^^^^^^^
As long as some part of the wood is on axis, regardless of the distance from
the vacuum chuck, it seems to me that a live center could be brought up for
support. If this ends up being part of the turning--good. If not, you can
always turn it away just as you would a little remnant on the bottom of a
bowl. Many of these "off-axis/off center" turnings end up kind of weird, so
the decision of what to do with the end where the live center touches may be
made at the last minute.

To answer your actual question, the actual tolerance will depend on the
diameter of the piece, and the angle, since that will determine the range
over which some wood still crosses the centerline. Believe me, this becomes
clearer after you have played with it some. Failure is a good teacher, if
you can remain calm :-)