The usual way to do segmented turnings is to cut trapezoids and glue
them up in a ring then stack the rings up to make the vessel.
Typically, one cuts the same angle at both ends of the segment.

When doing reverse segments, one cuts one end to the appropriate angle,
and leaves the other end at 90 degrees. The angled edge of the segment
is oriented outwards rather than inwards. See my facebook post for an
example of a ring being glued up:
https://www.facebook.com/media/set/?...l=f 7a342b1e7

When cutting normal segments, one sizes them for a given outside and
inside diameter. There's lots of segment calculators on the web that
will give you the width of the board to use, and the length of each
segment. However I can't find any calculators that will determine the
dimensions for a reverse segment except I have a spreadsheet that
calculates the width and length for an eight sided ring using the
following formula:

OR = outside radius
IR = inside radius

Width = OR - (.924* IR)
Length = (.541*IR+Width)/.707

The segment length seems to come out a little long but that gives some
fudge factor so that's fine.

What I'm looking for is the formula to enter the number of segments, the
inside and outside diameter and for it to calculate the length of the
long edge of the segment. Any math whiz out there that can clue me in?

Thanks...

....Kevin
--
Kevin Miller - http://www.alaska.net/~atftb
Juneau, Alaska
In a recent survey, 7 out of 10 hard drives preferred Linux
Registered Linux User No: 307357, http://linuxcounter.net

Rather than doing calculations I find it easier to make full size
drawings. What is the advantage of your way of making rings? I see
what I believe to be disadvantages. Trapezoids are more efficient in
wood use and there is not much end grain to contend with.

Ray

On Sat, 10 Dec 2011 19:10:48 -0900, Kevin Miller
wrote:

The usual way to do segmented turnings is to cut trapezoids and glue
them up in a ring then stack the rings up to make the vessel.
Typically, one cuts the same angle at both ends of the segment.

When doing reverse segments, one cuts one end to the appropriate angle,
and leaves the other end at 90 degrees. The angled edge of the segment
is oriented outwards rather than inwards. See my facebook post for an
example of a ring being glued up:
https://www.facebook.com/media/set/?...l=f 7a342b1e7

When cutting normal segments, one sizes them for a given outside and
inside diameter. There's lots of segment calculators on the web that
will give you the width of the board to use, and the length of each
segment. However I can't find any calculators that will determine the
dimensions for a reverse segment except I have a spreadsheet that
calculates the width and length for an eight sided ring using the
following formula:

OR = outside radius
IR = inside radius

Width = OR - (.924* IR)
Length = (.541*IR+Width)/.707

The segment length seems to come out a little long but that gives some
fudge factor so that's fine.

What I'm looking for is the formula to enter the number of segments, the
inside and outside diameter and for it to calculate the length of the
long edge of the segment. Any math whiz out there that can clue me in?

Thanks...

...Kevin

On 12/11/2011 11:04 AM, Ray wrote:
Rather than doing calculations I find it easier to make full size
drawings. What is the advantage of your way of making rings? I see
what I believe to be disadvantages. Trapezoids are more efficient in
wood use and there is not much end grain to contend with.

Full sized drawings are easy with trapezoids. Not so much with reverse
segments because they don't intersect the center of the ring. But even
with a trapezoid approach all one needs is the length of the outer edge.
Much easier to just use a segment calculator and set my jig accordingly.

To me, here isn't any particular advantage to one way versus the other.
It's a design decision. I like regular segmented turnings but reverse
segment vessels have visual "movement". The goal is to create an
artistically pleasing piece, not just a functional bowl. A trapezoidal
ring may use a bit less wood than a reversed segment, but not that much
really. End grain isn't that muhc of an issue - I'm still mostly
turning side grain. I'll post a photo later showing the effect and what
the rings look like after they're trimmed on the bandsaw & lathe. It
makes more sense when you see the destination...


....Kevin
--
Kevin Miller - http://www.alaska.net/~atftb
Juneau, Alaska
In a recent survey, 7 out of 10 hard drives preferred Linux
Registered Linux User No: 307357, http://linuxcounter.net

On 12/11/2011 01:23 PM, Kevin Miller wrote:
really. End grain isn't that muhc of an issue - I'm still mostly turning
side grain. I'll post a photo later showing the effect and what the
rings look like after they're trimmed on the bandsaw & lathe. It makes
more sense when you see the destination...

OK, I take back what I said about end grain. Good catch Ray.

Over in a.b.p.w I posted a couple new shots. One is a bowl I finished
the other day using the reverse segment method, and the other is the
glue-up that I posted yesterday. I must have done them slightly
differently, as the glue-up clearly is going to yield a lot of end
grain, whereas the bowl has side grain. Go figure.

This is the first time I've tried doing the reverse segments, so there's
a learning curve. I'll have to go out to the garage and cut some more
segments and play with them to see what I did differently. I suspect I
didn't 'reverse' the segments on the bowl - that is, the angle faced
toward the center rather than the outside, and on the glue-up I did
reverse them.

I'll take some shots of my experimenting and post the results...

....Kevin
--
Kevin Miller - http://www.alaska.net/~atftb
Juneau, Alaska
In a recent survey, 7 out of 10 hard drives preferred Linux
Registered Linux User No: 307357, http://linuxcounter.net

I added a reverse-segment calculator to my web site:

http://www.delorie.com/wood/revseg.html

Try a 2"id 3"id three-segment one :-)

and yes, it properly handles both "thick" and "thin" ring math ;-)

The math looks like this:

# angles
$a = 180 / $nseg;
$a2 = 360 / $nseg;

# ID triangle
$b = $ir * dcos ($a);
$ie = $ir * dsin ($a);
$ie2 = $ie * 2;

# outer radius cutoff for equations below
if ($a2 = 90) {
$rc = $or*2;
} else {
$wc = $ie * dtan ($a2);
$rc = $b + $wc;
}

if ($or $rc) {
# a thin ring. width is limited by the perpendicular radius

$w = $or - $b;
$l = $ie2 + $w / dsin ($a2);
$cutlen = $l;
if ($nseg 4) {
$cutlen += $w * abs (dcos ($a2));
}

} else {
# a thick ring. width is limited by the intersection

$lo = sqrt ($or * $or - $b * $b);
$w = ($lo - $ie) * dsin ($a2);
$l = $lo + $ie;
$cutlen = $l;
}

On 12/11/2011 11:18 PM, DJ Delorie wrote:

I added a reverse-segment calculator to my web site:

http://www.delorie.com/wood/revseg.html

Righteous, thanks! You and Dan (over in a.b.p.w) rock...

....Kevin1
--
Kevin Miller
Juneau, Alaska
http://www.alaska.net/~atftb
"In the history of the world, no one has ever washed a rented car."
- Lawrence Summers

On Sun, 11 Dec 2011 21:02:51 -0900, Kevin Miller
wrote:

On 12/11/2011 01:23 PM, Kevin Miller wrote:
really. End grain isn't that muhc of an issue - I'm still mostly turning
side grain. I'll post a photo later showing the effect and what the
rings look like after they're trimmed on the bandsaw & lathe. It makes
more sense when you see the destination...

OK, I take back what I said about end grain. Good catch Ray.


...Kevin

If what you are looking for is the pinwheel effect you might consider
cutting like for trapezoids but making one angle 90 degrees and
doubling the angle for the other end. I have been doing segmented
bowls for about a year. Some of my projects at

http://ray80538.home.comcast.net/~ra...l/segbowl.html

Are the black lines between segments an inlay or wide glue lines. The
way you glue up looks like it might be difficult to get tight joints.

On 12/12/2011 03:19 PM, Ray wrote:

If what you are looking for is the pinwheel effect you might consider
cutting like for trapezoids but making one angle 90 degrees and
doubling the angle for the other end. I have been doing segmented
bowls for about a year. Some of my projects at

I think that's what I ended up doing on the bowl I posted, where the
side grain was showing rather than the end grain. It tightened up
nicely on itself and doesn't have the end grain exposed.

When I did the other one, you'll notice the cross brace in the middle -
it kept the segments from all sliding in. Exactly right though - it is
a pain to clamp when they're glued up that way.


http://ray80538.home.comcast.net/~ra...l/segbowl.html

I've been to your site before. I'm curious - have you had any
expansion/contraction issues with the segments in the bottom such as
with image
http://ray80538.home.comcast.net/~ra...l/P1240146.jpg
(about half way down the page)?

Are the black lines between segments an inlay or wide glue lines. The
way you glue up looks like it might be difficult to get tight joints.

LOL. The black lines are a strip of teak glued between the segments.
I'd be way too embarrassed to post if my glue joints were anywhere near
that bad! :-)

....Kevin
--
Kevin Miller - http://www.alaska.net/~atftb
Juneau, Alaska
In a recent survey, 7 out of 10 hard drives preferred Linux
Registered Linux User No: 307357, http://linuxcounter.net

On 12/11/2011 11:18 PM, DJ Delorie wrote:

I added a reverse-segment calculator to my web site:

http://www.delorie.com/wood/revseg.html

Dan posted this over in a.b.p.w:

"Great. I see that he implemented both sets of equations along with the
test for when to use which set. (And they appear to work. It is always
nice to see things when they work.)

I see two red circles and two blue circles. The red circles are the
inner and outer radii. One of the blue circles shows the inner edge of
the segments. However the purpose of the other blue circle is a mystery
to me.

What is the purpose of the second blue circle?"

I wasn't sure so figured I'd ask here...

--
Kevin Miller
Juneau, Alaska
http://www.alaska.net/~atftb
"In the history of the world, no one has ever washed a rented car."
- Lawrence Summers

On Mon, 12 Dec 2011 18:31:36 -0900, Kevin Miller
wrote:



http://ray80538.home.comcast.net/~ra...l/segbowl.html

I've been to your site before. I'm curious - have you had any
expansion/contraction issues with the segments in the bottom such as
with image
http://ray80538.home.comcast.net/~ra...l/P1240146.jpg
(about half way down the page)?

That one was done last March. I have been turning for less than a
year so it might be too soon to judge stability. In that bowl the
grain of the wood runs mostly tangentially to the bowl so any
expansion / contraction should be radial. I can't feel any
unevenness. I have had cross grain problems in the past and tend to
avoid it.


Are the black lines between segments an inlay or wide glue lines. The
way you glue up looks like it might be difficult to get tight joints.

LOL. The black lines are a strip of teak glued between the segments.
I'd be way too embarrassed to post if my glue joints were anywhere near
that bad! :-)

Your finished bowl looks nice. Sometimes photography does not do
justice to subtle detail. How did the end grain piece turn out?

Ray

...Kevin

In article ,
Ray wrote:

On Mon, 12 Dec 2011 18:31:36 -0900, Kevin Miller
wrote:



http://ray80538.home.comcast.net/~ra...l/segbowl.html

I've been to your site before. I'm curious - have you had any
expansion/contraction issues with the segments in the bottom such as
with image
http://ray80538.home.comcast.net/~ra...l/P1240146.jpg
(about half way down the page)?

That one was done last March. I have been turning for less than a
year so it might be too soon to judge stability. In that bowl the
grain of the wood runs mostly tangentially to the bowl so any
expansion / contraction should be radial. I can't feel any
unevenness. I have had cross grain problems in the past and tend to
avoid it.

Most of the "top" segmented turners I've talked with say to avoid
cross-grain.

--
--------------------------------------------------------
Personal e-mail is the n7bsn but at amsat.org
This posting address is a spam-trap and seldom read
RV and Camping FAQ can be found at
http://www.ralphandellen.us/rv

On 12/13/2011 10:13 AM, Ray wrote:

That one was done last March. I have been turning for less than a
year so it might be too soon to judge stability. In that bowl the
grain of the wood runs mostly tangentially to the bowl so any
expansion / contraction should be radial. I can't feel any
unevenness. I have had cross grain problems in the past and tend to
avoid it.

It's always a hard one - seems like there's always some contrary
expansion that goes on no matter what you do. :-) Glad those are stable.


Your finished bowl looks nice. Sometimes photography does not do
justice to subtle detail. How did the end grain piece turn out?

Thanks Ray. The end grain piece is the lid to the bowl, the darn day
job has prevented me from finishing it! (Not that I'm complaining -
plenty of guys out of work that would love such "troubles".)

I'll post a nicer photo of the bowl when I get the lid done. I think
it'll be interesting to see how seasonal humidity changes affect it...


....Kevin
--
Kevin Miller - http://www.alaska.net/~atftb
Juneau, Alaska
In a recent survey, 7 out of 10 hard drives preferred Linux
Registered Linux User No: 307357, http://linuxcounter.net

On 12/13/2011 10:35 AM, Ralph E Lindberg wrote:
Most of the "top" segmented turners I've talked with say to avoid
cross-grain.

Always a good idea. If the pieces are narrow you may get away with it.
We'll see on the piece I did. If the segment isn't too wide there
won't be much movement. One thing I usually do also is to anchor the
pieces with a ring of solid wood, (ex: the ring of cherry around the top
of my bowl).

--
Kevin Miller - http://www.alaska.net/~atftb
Juneau, Alaska
In a recent survey, 7 out of 10 hard drives preferred Linux
Registered Linux User No: 307357, http://linuxcounter.net

On Mon, 12 Dec 2011 18:19:06 -0600, Ray wrote
(in message ):

http://ray80538.home.comcast.net/~ra...l/segbowl.html

well, Ray, I went to your comcast site and looked around. Seldom at a loss
for words, I am now. I kinda feel like selling my tools and taking up tearing
pieces of paper into little bits, or something.
tom koehler

--
I will find a way or make one.

Kevin Miller writes:
Dan posted this over in a.b.p.w:

I see two red circles and two blue circles. The red circles are the
inner and outer radii. One of the blue circles shows the inner edge of
the segments. However the purpose of the other blue circle is a
mystery to me.

What is the purpose of the second blue circle?"

I posted over there, here's it is again: the outer blue circle is where
the math changes, and you start to get end grain tear-out issues. For
an OD bigger than the blue circle, you're cutting into end grain no
matter which way the ring is turning (much like solid-blank bowl
turning). For OD smaller than the blue circle, if you mount the ring
the right way you're always turning "downhill".

For an OD the same as the blue circle, the OD is tangent to the edge of
one segment at exactly the spot where it intersects the adacent segment.

The inner blue circle is how big your clamping block needs to be.