I need some large quarter-round molding. The finished size must have
have a "radius" of 3" - that is, the distance from the point to the cut
edge must be 3". I thought of turning a 6 1/8" cylinder, and losing an
eight to the kerf on the TS. Then I remembered it'd be quartered, so
I'd lose another eight. Then I realized that as I take the kerfs I'm
actually shortening the legs by somewhat more than an eight due to the
curvature of the piece. I haven't done a google search and I haven't
made any effort whatsoever to do the math. Anyone up to the task?
tia
JP
************************************************** *****
I'll be on the rowing machine if you need me.

Jay Pique wrote:
I need some large quarter-round molding. The finished size must have
have a "radius" of 3" - that is, the distance from the point to the cut
edge must be 3". I thought of turning a 6 1/8" cylinder, and losing an
eight to the kerf on the TS. Then I remembered it'd be quartered, so
I'd lose another eight. Then I realized that as I take the kerfs I'm
actually shortening the legs by somewhat more than an eight due to the
curvature of the piece. I haven't done a google search and I haven't
made any effort whatsoever to do the math. Anyone up to the task?

A cylinder of 6 1/8" *will* give you sections with radius 3" when
quartered, assuming a 1/8" kerf.

Molding? That's a log!

Jay Pique wrote:
I need some large quarter-round molding. The finished size must have
have a "radius" of 3" - that is, the distance from the point to the cut
edge must be 3". I thought of turning a 6 1/8" cylinder, and losing an
eight to the kerf on the TS. Then I remembered it'd be quartered, so
I'd lose another eight. Then I realized that as I take the kerfs I'm
actually shortening the legs by somewhat more than an eight due to the
curvature of the piece. I haven't done a google search and I haven't
made any effort whatsoever to do the math. Anyone up to the task?
tia
JP
************************************************** *****
I'll be on the rowing machine if you need me.

draw a cross section on a piece of paper to see your errorw.

61/8" diameter , one cut at 90degrees to diameter leaves you a length
of 3" for a 1/8"kerf
after the first cut, you have two half round pieces, 3"high and 6 1/8"
across
make a second cut and you have two quarter round pieces 3" radius. more
or less.

I believe but have not drawn it , that the curve will not be a 3"
radius , but will be the remainder of the 6 1/8" curve. And not a
proper 90 degree circle segment.

Probably close enough for a moulding though.

wrote:
61/8" diameter , one cut at 90degrees to diameter leaves you a length
of 3" for a 1/8"kerf
after the first cut, you have two half round pieces, 3"high and 6 1/8"
across

But not quite 6 1/8" across, because I've lost the 1/8" section from
the middle.

snip
Probably close enough for a moulding though.

It's to sit vertically below another, smaller quarter-round piece. The
whole assembly is for a corner detail on some wall panels.

I know I can sneak up on it, and I could rip in on the band saw for
less loss, but I'm sort of keen on knowing the math behind it. Time to
start digging.
JP

Jay Pique wrote:
wrote:
61/8" diameter , one cut at 90degrees to diameter leaves you a length
of 3" for a 1/8"kerf
after the first cut, you have two half round pieces, 3"high and 6 1/8"
across

But not quite 6 1/8" across, because I've lost the 1/8" section from
the middle.

snip
Probably close enough for a moulding though.

It's to sit vertically below another, smaller quarter-round piece. The
whole assembly is for a corner detail on some wall panels.

I know I can sneak up on it, and I could rip in on the band saw for
less loss, but I'm sort of keen on knowing the math behind it. Time to
start digging.

There's hardly any math involved. Quarter a 6-1/8" cylinder with a 1/8"
kerf, and you come out with 4 quarter-rounds, which, when you gang them
together, make a 6" cylinder.

You *do* come out with a proper 3" radius and a 90-degree arc.

Every point on that arc is 3" from the center of the new circle or the
vertex of that 90-degree angle. So we say you have a 3" radius there.

Nothing to see here.

In article om, "boorite" wrote:


There's hardly any math involved. Quarter a 6-1/8" cylinder with a 1/8"
kerf, and you come out with 4 quarter-rounds, which, when you gang them
together, make a 6" cylinder.

You *do* come out with a proper 3" radius and a 90-degree arc.

No, you don't. It's pretty close, but not exactly. The radius of curvature is
3-1/16", not 3", and the arc does not meet the flat quite at 90 degrees.

Every point on that arc is 3" from the center of the new circle

Not correct. But close enough it doesn't matter.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

There's hardly any math involved. Quarter a 6-1/8" cylinder with a 1/8"
kerf, and you come out with 4 quarter-rounds, which, when you gang them
together, make a 6" cylinder.

Not exactly. Yes, the cylinder will be 6" in diameter when measured
across the cut lines, but it won't be a perfect cylinder. The radius
on the outside curves will still be half of 6 1/8" - JP is right. Take
it a little further - say you start with the 6 1/8" cylinder, and keep
cutting 1/8" sections off until the straight parts of your "quarter
round" are only 1" long. Then you put the 4 quarters together, and you
do NOT have a round 2" diameter circle - you have pieces with a 1" flat
face, but the radius of the outside curve doesn't change. So, Jay, the
question is whether it's more important that you have a radius of
exactly 3", or flat sides of exactly 3". If you start with any
diameter cylinder, and remove any material at all for a kerf, you can
not end up with 4 pieces with 3" faces AND a 3" outside radius. Unless
you're up for a lot of sanding... I hope I explained that well enough
- draw it out, and keep taking away kerfs until it makes sense.
If you're looking for opinions, I'd say that nobody could tell the
difference between a 3" radius curve and a 3 1/16" radius curve, so I'd
say the 6 1/8" cylinder would probably work. It would be even closer
to use a bandsaw for the thin kerf and reduce the cylinder diameter
accordingly.
Good luck and let us know what works,
Andy

Subject

Ever consider 1/4 circle from plywood.

3" radius is NBD.

If interested, check out Anderson International here in SoCal.

Lew

A 6 1/8 cylinder has a radius of 3 1/16. Quarter it and each piece still has
a radius of 3 1/16. You could use a 1/2" blade to cut it. The radius still
won't change.


"boorite" wrote in message
ps.com...
There's hardly any math involved. Quarter a 6-1/8" cylinder with a 1/8"
kerf, and you come out with 4 quarter-rounds, which, when you gang them
together, make a 6" cylinder.

You *do* come out with a proper 3" radius and a 90-degree arc.

Every point on that arc is 3" from the center of the new circle or the
vertex of that 90-degree angle. So we say you have a 3" radius there.

Nothing to see here.

Jay Pique wrote:
I need some large quarter-round molding. The finished size must have
have a "radius" of 3" - that is, the distance from the point to the cut
edge must be 3". I thought of turning a 6 1/8" cylinder, and losing an
eight to the kerf on the TS. Then I remembered it'd be quartered, so
I'd lose another eight. Then I realized that as I take the kerfs I'm
actually shortening the legs by somewhat more than an eight due to the
curvature of the piece. I haven't done a google search and I haven't
made any effort whatsoever to do the math. Anyone up to the task?
tia
JP
************************************************** *****
I'll be on the rowing machine if you need me.

You could do it as a glue up, using paper as a release between the
quarters. Turn to 6" and separate along the paper.

OR

Fasten 4 pieces together with screws at each end, outside the area to be
turned. Trim the unturned ends off. (Note: I have never tried this but
it should work.)

Jess.S

I need some large quarter-round molding. The finished size must have have a "radius" of 3" - ...

Make a split turning --- Glue up 4 pieces of 3"x3" stock (or slightly
over sized). Glue paper between the joints. This will act as a
separator. Turn a 6" cylinder and split the four quadrants along the
paper seams with a tap of a chisel. It's done frequently.

Doug Miller wrote:
In article om, "boorite" wrote:


There's hardly any math involved. Quarter a 6-1/8" cylinder with a 1/8"
kerf, and you come out with 4 quarter-rounds, which, when you gang them
together, make a 6" cylinder.

You *do* come out with a proper 3" radius and a 90-degree arc.

No, you don't. It's pretty close, but not exactly. The radius of curvature is
3-1/16", not 3", and the arc does not meet the flat quite at 90 degrees.

Every point on that arc is 3" from the center of the new circle

Not correct. But close enough it doesn't matter.

Yeah, I wasn't thinking straight. Of course the *arc* still has a
3-1/16" radius, i.e., bisect the 90-degree angle, and the distance to
the point on the arc is 3-1/16". But the distance from either leg of
that right angle is only 3". I swear I got honors in plane geometry,
but that was a long time ago. I was thinking more in terms of getting
the piece he wanted.

So the answer is, there's really no way to section a cylinder and get a
quarter-round of radius X that's exactly X on each side. You'd have to
live with an arc whose radius is X + .5*kerf, or start with an X by X
section and cut radius X onto it.

wrote:
I need some large quarter-round molding. The finished size must have have a "radius" of 3" - ...

Make a split turning --- Glue up 4 pieces of 3"x3" stock (or slightly
over sized). Glue paper between the joints. This will act as a
separator. Turn a 6" cylinder and split the four quadrants along the
paper seams with a tap of a chisel. It's done frequently.

Now THAT's what I'm talking about. Thanks to you two for bringing it
to my attention. I'm not a turner, but I have heard of it. I'll
definitely relay the message to our lathe guy. I'm a little surprised
he hasn't thought of it. He does turnings for us from home. Is there
another use for this trick that I would have used myself, but not
involving a lathe? For some reason I vaguely remember knocking apart
some pieces that had been glued up in this manner.

JP

The commercial technique for turners of the early part of the 20th century
was to take four pieces of 3 1/8" square wood and glue them together with
kraft paper (heavy paper bag materail) between. Cup centers, a dead one in
the head stock and a live one in the tail, were used to turn the piece as
they would hold the center tight without splitting the glue line. The
cylinder was turned, split along the paper joint, sanded to tremove the
paper and it was done. Today I would use hot glue to hald the wood together
and separate it with paint thinner when done but the same procedure.
______
God bless and safe turning
Darrell Feltmate
Truro, NS, Canada
www.aroundthewoods.com
"boorite" wrote in message
oups.com...

Doug Miller wrote:
In article om,
"boorite" wrote:


There's hardly any math involved. Quarter a 6-1/8" cylinder with a 1/8"
kerf, and you come out with 4 quarter-rounds, which, when you gang them
together, make a 6" cylinder.

You *do* come out with a proper 3" radius and a 90-degree arc.

No, you don't. It's pretty close, but not exactly. The radius of
curvature is
3-1/16", not 3", and the arc does not meet the flat quite at 90 degrees.

Every point on that arc is 3" from the center of the new circle

Not correct. But close enough it doesn't matter.

Yeah, I wasn't thinking straight. Of course the *arc* still has a
3-1/16" radius, i.e., bisect the 90-degree angle, and the distance to
the point on the arc is 3-1/16". But the distance from either leg of
that right angle is only 3". I swear I got honors in plane geometry,
but that was a long time ago. I was thinking more in terms of getting
the piece he wanted.

So the answer is, there's really no way to section a cylinder and get a
quarter-round of radius X that's exactly X on each side. You'd have to
live with an arc whose radius is X + .5*kerf, or start with an X by X
section and cut radius X onto it.

Jay Pique wrote:
wrote:
I need some large quarter-round molding. The finished size must have have a "radius" of 3" - ...

Make a split turning --- Glue up 4 pieces of 3"x3" stock (or slightly
over sized). Glue paper between the joints. This will act as a
separator. Turn a 6" cylinder and split the four quadrants along the
paper seams with a tap of a chisel. It's done frequently.

I'll definitely relay the message to our lathe guy. I'm a little surprised
he hasn't thought of it.

Just called him. He said "oh I know that" and seemed to think it
wouldn't work. The typical way we make large turning blanks is to glue
four pieces of thick stock into long square tubing using 45d miters.
So it's hollow in the middle. I don't know, he was pretty dismissive.
In any event, if I want to hop on the lathe at work (after I dig it out
from under two tons of crap), is this the process by which I should do
it.....

I need (4) three foot lengths of quarter round with a 3" radius. So I
take (4) 3 foot lengths of 3.125"x3.125" stock and glue them together
with a piece of grocery bag in between. Then I screw on a faceplate,
being sure that it's centered on the intersection of all four pieces.
Then I mount it on the lathe, and align the interesection at the other
end with the tailstock center. Then I turn it round to 6". Once done,
I simply take it off the lathe and split it apart - I'm assuming with a
chisel pounded into the glue joints?

Sounds very nifty. Have I missed anything?
JP

In article .com, "Jay Pique" wrote:
[...]
In any event, if I want to hop on the lathe at work (after I dig it out
from under two tons of crap), is this the process by which I should do
it.....

I think the *first* step in your process should be to crosspost this thread to
rec.crafts.woodturning . You're likely to get more ideas from the folks over
there, and probably better ones than you're going to read in my post...

I need (4) three foot lengths of quarter round with a 3" radius. So I
take (4) 3 foot lengths of 3.125"x3.125" stock and glue them together
with a piece of grocery bag in between.

OK so far, AFAIK...

Then I screw on a faceplate,

... but I don't think I'd do that...

being sure that it's centered on the intersection of all four pieces.

... owing largely to the difficulty of being sure that it's centered. If it's
not centered *exactly*, you're not going to have quarter-round when you
separate the pieces.

My first thought is to grip it in a four-jaw self-centering chuck. If you
don't have one that opens wide enough, use stock an inch or so longer than
needed, and mill a stub tenon on one end, small enough to grip in whatever
chuck you do have.

Or you could use a steb center in the headstock. (Yes, that's spelled
correctly.) Probably work better than a spur center.


Then I mount it on the lathe, and align the interesection at the other
end with the tailstock center. Then I turn it round to 6". Once done,
I simply take it off the lathe and split it apart - I'm assuming with a
chisel pounded into the glue joints?

Sounds ok to me... but I've only *read* about doing this. Never actually did
it. Ask over at r.c.w .

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Jay
Not a face plate, use centers, but otherwise, okay. Tell your lathe guy
there is no reason for it "not" to work unless he cannot get the centers in
the right place. The intersection is hard to miss though. This is one of
those cases where "we have always done it that way" because it works :-)

______
God bless and safe turning
Darrell Feltmate
Truro, NS, Canada
www.aroundthewoods.com
"Jay Pique" wrote in message
oups.com...

Jay Pique wrote:
wrote:
I need some large quarter-round molding. The finished size must
have have a "radius" of 3" - ...

Make a split turning --- Glue up 4 pieces of 3"x3" stock (or slightly
over sized). Glue paper between the joints. This will act as a
separator. Turn a 6" cylinder and split the four quadrants along the
paper seams with a tap of a chisel. It's done frequently.

I'll definitely relay the message to our lathe guy. I'm a little
surprised
he hasn't thought of it.

Just called him. He said "oh I know that" and seemed to think it
wouldn't work. The typical way we make large turning blanks is to glue
four pieces of thick stock into long square tubing using 45d miters.
So it's hollow in the middle. I don't know, he was pretty dismissive.
In any event, if I want to hop on the lathe at work (after I dig it out
from under two tons of crap), is this the process by which I should do
it.....

I need (4) three foot lengths of quarter round with a 3" radius. So I
take (4) 3 foot lengths of 3.125"x3.125" stock and glue them together
with a piece of grocery bag in between. Then I screw on a faceplate,
being sure that it's centered on the intersection of all four pieces.
Then I mount it on the lathe, and align the interesection at the other
end with the tailstock center. Then I turn it round to 6". Once done,
I simply take it off the lathe and split it apart - I'm assuming with a
chisel pounded into the glue joints?

Sounds very nifty. Have I missed anything?
JP

Darrell Feltmate wrote:
Jay
Not a face plate, use centers, but otherwise, okay. Tell your lathe guy
there is no reason for it "not" to work unless he cannot get the centers in
the right place. The intersection is hard to miss though. This is one of
those cases where "we have always done it that way" because it works :-)

Should I be concerned about the points on the centers acting as a wedge
to split the blank prematurely? Stebcenters, as someone said, would
probably prevent this. Not sure we have them though.

JP

In article . com, "Jay Pique" wrote:

Should I be concerned about the points on the centers acting as a wedge
to split the blank prematurely?

Nope -- not if you drill a little recess right at the center for the point to
slip into. It's *much* more important to avoid lining up the spurs on a spur
center with the joints in your glue-up. :-)

Stebcenters, as someone said, would
probably prevent this. Not sure we have them though.

Cup centers would work too.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

Glue solid blocks to the ends and put our centers in that.

"Jay Pique" wrote in message
Should I be concerned about the points on the centers acting as a wedge
to split the blank prematurely? Stebcenters, as someone said, would
probably prevent this. Not sure we have them though.

JP

Jay Pique wrote:
wrote:
61/8" diameter , one cut at 90degrees to diameter leaves you a length
of 3" for a 1/8"kerf
after the first cut, you have two half round pieces, 3"high and 6 1/8"
across

But not quite 6 1/8" across, because I've lost the 1/8" section from
the middle.

snip
Probably close enough for a moulding though.

It's to sit vertically below another, smaller quarter-round piece. The
whole assembly is for a corner detail on some wall panels.

I know I can sneak up on it, and I could rip in on the band saw for
less loss, but I'm sort of keen on knowing the math behind it. Time to
start digging.
JP

Jay,

If I do the math, I get 2.99936..." for the radius. Kind of hard to
explain without using figures. If you're seriously interested, I can
make an attempt, as it takes time to write a text-only explanation.

Regards,

Mark

Forget trying to explain your math, what is it your trying to figure out?

"redbelly" wrote in message
oups.com...
If I do the math, I get 2.99936..." for the radius. Kind of hard to
explain without using figures. If you're seriously interested, I can
make an attempt, as it takes time to write a text-only explanation.

Regards,

Mark

"redbelly" wrote in message
oups.com...

CW wrote:
Forget trying to explain your math, what is it your trying to figure
out?

I was figuring out Jay's question, given in the original post: take a
6-1/8" diameter cylinder (or circle) and saw it into quarters, where
the saw kerf is 1/8". What is the size of each quarter, measured
across either of the flat faces?

You gave that number as a radius rather than a side length. That didn't make
sense.


At least, that is my understanding of what was asked in the original
post. As a math question, the answer is 2.99936...". As a
woodworking/carpentry question, 3" will suffice. Who here can position
a piece to better than 0.001" on their table saw?

There was a puzzlemaker on here some time ago that claimed .0002 accuracy.
After considerable time expaining why he was full of it, he finaly gave up
and left. He still claims this in other places and on his website though.

CW wrote:
"redbelly" wrote in message
oups.com...

CW wrote:
Forget trying to explain your math, what is it your trying to figure
out?

I was figuring out Jay's question, given in the original post: take a
6-1/8" diameter cylinder (or circle) and saw it into quarters, where
the saw kerf is 1/8". What is the size of each quarter, measured
across either of the flat faces?

You gave that number as a radius rather than a side length. That didn't make
sense.

Sorry about the confusion.

It's "almost" a radius, and would appear to anybody to be a radius for
all intents and purposes. But it's **not** a radius because it doesn't
originate from the center-of-curvature of the rounded face (the center
of the original, uncut cylinder).

The original post even used the word "radius", but in quotes since it's
not **really** a radius. I just figured people who had read that, and
have been following this thread, would know what I meant.

Mark

At least, that is my understanding of what was asked in the original
post. As a math question, the answer is 2.99936...". As a
woodworking/carpentry question, 3" will suffice. Who here can position
a piece to better than 0.001" on their table saw?

There was a puzzlemaker on here some time ago that claimed .0002 accuracy.
After considerable time expaining why he was full of it, he finaly gave up
and left. He still claims this in other places and on his website though.

In article .com, "redbelly" wrote:
Who here can position
a piece to better than 0.001" on their table saw?


Steve Strickland. g

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.

redbelly wrote:
It's "almost" a radius, and would appear to anybody to be a radius for
all intents and purposes. But it's **not** a radius because it doesn't
originate from the center-of-curvature of the rounded face (the center
of the original, uncut cylinder).

Yeah, that's what I was trying to convey. Sorry for the confusion.
I'm now going to turn, or have turned a segmented blank that will yield
true quarters with 3" radii, thus eliminating the need for mental
gymnastics. Thanks all for the input.

JP

By product of the job I guess (machinist). When someone says radius,
"almost" never enters my mind. It either is or isn't.
"redbelly" wrote in message
oups.com...


It's "almost" a radius, and would appear to anybody to be a radius for
all intents and purposes. But it's **not** a radius because it doesn't
originate from the center-of-curvature of the rounded face (the center
of the original, uncut cylinder).