any tips for cutting centering rings?

any tips for cutting centering rings?

Post by Brian Sipo » Sat, 29 Apr 2000 04:00:00



I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
cardstock. I use a compass to mark the exact diameters (or as close as I can
approximate) and then use a hobby knife to cut a little outside the inner
ring, and inside the outer.
The problem is that I can't get anywhere near good curvature with my knife
because the paper is so thick that it takes more than one cut to go through,
and I don't want to go through the entire thing the first time, because then
I end up cutting more straight lines than curves. The other thing is that
trying to oversize it and sand down isn't too effective either, because it
crimps the paper.
Anyone have experience with this?
 
 
 

any tips for cutting centering rings?

Post by Conner » Sat, 29 Apr 2000 04:00:00


Have you tried cutting with a pair of heavyduty sissors?

Connery Carroll
NAR #77226 L1

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any tips for cutting centering rings?

Post by Paul Alber » Sat, 29 Apr 2000 04:00:00


Quote:

> I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
> cardstock. I use a compass to mark the exact diameters (or as close as I can
> approximate) and then use a hobby knife to cut a little outside the inner
> ring, and inside the outer.
> The problem is that I can't get anywhere near good curvature with my knife
> because the paper is so thick that it takes more than one cut to go through,
> and I don't want to go through the entire thing the first time, because then
> I end up cutting more straight lines than curves. The other thing is that
> trying to oversize it and sand down isn't too effective either, because it
> crimps the paper.
> Anyone have experience with this?

If you can find a good art supply store, they will probaby have a
'compass cutter' or similar tool.  It's like the compass you use to
draw the circles, but with an exacto blade instead of a pencil.  

Paul

 
 
 

any tips for cutting centering rings?

Post by bob fortun » Sat, 29 Apr 2000 04:00:00


Hey Brian,

Maybe you're trying too hard to get it perfect.  The ring doesn't need
to touch every single part of the tube, its really not that critical as
long as the bt60 is centered within the bt80 tube.

Here's a test:  If you dry fit the rocket parts together and upturning
the assembly causes all the parts to fall out on the floor, the pieces
and parts are probably cut a bit too generous.  If everything stays
pretty much in place then yellow glue will hold everything together.

Add little blocks of balsa standing on end around the ID of the c-ring
so that it butts the bt60 if you are concerned.  Or wrap some light
cotton string, like kite string, around the joint where the 60 meets the
ring then saturate the string with glue.

Good Luck!

Bob

Quote:

> I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
> cardstock. I use a compass to mark the exact diameters (or as close as I can
> approximate) and then use a hobby knife to cut a little outside the inner
> ring, and inside the outer.
> The problem is that I can't get anywhere near good curvature with my knife
> because the paper is so thick that it takes more than one cut to go through,
> and I don't want to go through the entire thing the first time, because then
> I end up cutting more straight lines than curves. The other thing is that
> trying to oversize it and sand down isn't too effective either, because it
> crimps the paper.
> Anyone have experience with this?

 
 
 

any tips for cutting centering rings?

Post by bob fortun » Sat, 29 Apr 2000 04:00:00


Hey Brian,

Maybe you're trying too hard to get it perfect.  The ring doesn't need
to touch every single part of the tube, its really not that critical as
long as the bt60 is centered within the bt80 tube.

Here's a test:  If you dry fit the rocket parts together and upturning
the assembly causes all the parts to fall out on the floor, the pieces
and parts are probably cut a bit too generous.  If everything stays
pretty much in place then yellow glue will hold everything together.

Add little blocks of balsa standing on end around the ID of the c-ring
so that it butts the bt60 if you are concerned.  Or wrap some light
cotton string, like kite string, around the joint where the 60 meets the
ring then saturate the string with glue.

Good Luck!

Bob

Quote:

> I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
> cardstock. I use a compass to mark the exact diameters (or as close as I can
> approximate) and then use a hobby knife to cut a little outside the inner
> ring, and inside the outer.
> The problem is that I can't get anywhere near good curvature with my knife
> because the paper is so thick that it takes more than one cut to go through,
> and I don't want to go through the entire thing the first time, because then
> I end up cutting more straight lines than curves. The other thing is that
> trying to oversize it and sand down isn't too effective either, because it
> crimps the paper.
> Anyone have experience with this?

 
 
 

any tips for cutting centering rings?

Post by Scott Hamilt » Sat, 29 Apr 2000 04:00:00


If you're planning on having to make very many of these rings it might
pay to have a single custom one made from thick plywood, then use it as
a guide for making your cardboard ones.

Scott Hamilton
BAR #????
Up, Up, and Away!!

 
 
 

any tips for cutting centering rings?

Post by Dan Kir » Sat, 29 Apr 2000 04:00:00


Balsa will give you a better strength/weight ratio.  Rough-cut
the piece like you said, then sand to fit, stopping frequently
to check the fit.

If you must use cardstock, mark the piece out with a compass,
then take a pin and make a series of holes as close together as
possible all along the pencil line.  To cut the piece free, just
connect the holes with your X-Acto knife.  If the holes are
close enough together, you'll have sort of a saw-tooth edge.
Not perfectly smooth, but if you cut for a tight fit,
the "teeth" will bend flat against the body tube, giving a near-
perfect fit.

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any tips for cutting centering rings?

Post by The Silent Observe » Sat, 29 Apr 2000 04:00:00


Quote:

> I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
> cardstock. I use a compass to mark the exact diameters (or as close as I can
> approximate) and then use a hobby knife to cut a little outside the inner
> ring, and inside the outer.
> The problem is that I can't get anywhere near good curvature with my knife
> because the paper is so thick that it takes more than one cut to go through,
> and I don't want to go through the entire thing the first time, because then
> I end up cutting more straight lines than curves. The other thing is that
> trying to oversize it and sand down isn't too effective either, because it
> crimps the paper.
> Anyone have experience with this?

I've recently found a really useful technique for making centering rings
-- one that I suspect may be new.

First, I start with shirt cardboard -- the stuff that keeps a new shirt,
in the original packaging, in an attractive shape.  I use my computer
and a drawing program to draw the ring templates, and then glue them to
the shiny side of the cardboard with *** cement (so I can peel them
off the finished ring at the end), but you can just as easily make them
with a compass.  I make twice as many rings as I will eventually need,
because I glue two layers of the cardboard together to get rings just
the tiniest bit stiffer than the Estes fiber rings used for centering a
BT-50 or BT-20 in BT-60 or BT-80.

Once the templates are in place, I use scissors to cut the outside of
the ring and, like you, I cut them the tiniest bit oversize --
typically, I get them about the same as the tube O.D. (where the I.D.
will be the eventual dimension).  Then, however, I use an ordinary hole
punch (the sort that will put a 1/4" hole in most paper or light
cardboard) as a nibbler to nibble out the interior.  Don't worry about a
few "bumps" on the I.D. of the ring; we'll take care of those further
down.  Once I've got all the centers nibbled out, I glue the rings
together in pairs, with the dull (brown) side of the shirt cardboard
together, taking care to align the O.D. edges.

When the glue dries, I test fit the inner tube and use an X-acto knife
or similar to skeeve off the bumps on the I.D. until I have a snug fit.
I wait, however, to trim the O.D. until I've glued the double weight
rings to the inner tube and that glue has dried, then sand the rings to
fit -- with the double weight ring, and if I sand along the edge instead
of across it, I find I can pretty quickly sand half a millimeter off,
evenly, all around the ring, and get it to fit the outer tube.

FWIW, on the 24 mm Bertha I'm working now (a replacement for my Bertha
24, that flew at NSL 98 on an E6 and was retired after 50 total flights
from A8 to D12-0/D12-7 as well as the E6), I was able to do the ring
set, ready to glue, in about fif*** minutes, including drawing and
printing the rings on my computer (but not including glue drying time).

I also used this technique to make a bulkhead for my reproduction Cobra
-- I didn't like the look, or the remembered mess, of using the
tissue/glue "putty" to seal around the motor mounts in this cluster
bird, so I made a bulkhead to go on the forward end of the motor mount
-- and was able to cut all three holes cleanly, to the I.D. of the 520
centering rings that act as thrust blocks, in just a few minutes per
hole.

Yes, you might have to buy a tool -- check your local grocery store, in
the school supplies aisle, and you can probably get a simple hole punch
for about $3.50.  Be sure you get the one built like a pliers, not the
one that looks like a little steel block with a button on top; that one
doesn't have the reach needed to be used this way.

--
 WARNING!!  This area has been designated an official DOPE FREE ZONE!!

      If you're going to be a dope, please do it somewhere else!

Donald Qualls, aka The Silent Observer           NAR # 70141-SR Insured
Rocket Pages                http://www.FoundCollection.com/
Telescope Pages            http://www.FoundCollection.com/

Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.

 
 
 

any tips for cutting centering rings?

Post by Tom » Sun, 30 Apr 2000 04:00:00


How about connecting it to a Moto-Tool on lowest speed. Then just hold
the tip of the knife first against the outside line, then when that
separates, the inside line. Voila! A ring.
Quote:

> I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
> cardstock. I use a compass to mark the exact diameters (or as close as I can
> approximate) and then use a hobby knife to cut a little outside the inner
> ring, and inside the outer.
> The problem is that I can't get anywhere near good curvature with my knife
> because the paper is so thick that it takes more than one cut to go through,
> and I don't want to go through the entire thing the first time, because then
> I end up cutting more straight lines than curves. The other thing is that
> trying to oversize it and sand down isn't too effective either, because it
> crimps the paper.
> Anyone have experience with this?

 
 
 

any tips for cutting centering rings?

Post by Darren J Longhor » Sun, 30 Apr 2000 04:00:00


What I do is cut only sraight lines around the circumference, using a steel rule and x-acto knife. You end up with a plyhedron, not a circle, but if you draw enough lines it's close enough. This method also works for balsa, and with balsa you can sand away any inperfections.
Quote:

> I'm trying (unsucusfully) to cut BT-80 to BT-60 centering rings out of thick
> cardstock. I use a compass to mark the exact diameters (or as close as I can
> approximate) and then use a hobby knife to cut a little outside the inner
> ring, and inside the outer.
> The problem is that I can't get anywhere near good curvature with my knife
> because the paper is so thick that it takes more than one cut to go through,
> and I don't want to go through the entire thing the first time, because then
> I end up cutting more straight lines than curves. The other thing is that
> trying to oversize it and sand down isn't too effective either, because it
> crimps the paper.
> Anyone have experience with this?

 
 
 

any tips for cutting centering rings?

Post by MikeTEAC » Mon, 01 May 2000 04:00:00


For D/E engine mounts; I use corrugated cardboard. I trace the circles; use a
heavy duty scissors to cut outside; and Xacto to cut out the inside.
For each ring; I use *two* pieces of cardboard. Corrugated cardboard has a sort
of 'grain' to it; the corrugations run paralell. So I epoxy two pieces of
cardboard; rotating one 90 degrees, so the corrugations cancel each other out.
The epoxy stiffens the cardboard enogh such that a dremel tool can be used to
shape the inside/outside. I apply epoxy liberally on the side of the rings when
they go into the body tube and the engine mount tube; and the exopy seeps into
the corrugations; and I get a great; tight fit.
Mike
 
 
 

any tips for cutting centering rings?

Post by Bob Kapl » Mon, 01 May 2000 04:00:00


Quote:

> If you can find a good art supply store, they will probaby have a
> 'compass cutter' or similar tool.  It's like the compass you use to
> draw the circles, but with an exacto blade instead of a pencil.  

The typical compass geometry doesn't work so well, with both the point and
knife at non vertical angles to the cardboard. Look for a "Matte Cutter"
which is designed more like the fly cutters we use in a drill press. Some
are pretty flat and sit on what is being cut, others use a long arm with a
point and knife.

BTW, a drill press and fly cutter WILL cut nice cardboard rings, but it's
certainly overkill. I use s***corrugated cardboard to make test cuts to
get the correct ring size before attacking the plywood.

        Bob Kaplow      NAR # 18L       TRA # "Ctrl-Alt-Del"

Kaplow Klips:   http://www.FoundCollection.com/(baffle too!)
NIRA:           http://www.FoundCollection.com/  NAR:    http://www.FoundCollection.com/

 
 
 

any tips for cutting centering rings?

Post by Bob Kapl » Mon, 01 May 2000 04:00:00


Quote:

> How about connecting it to a Moto-Tool on lowest speed. Then just hold
> the tip of the knife first against the outside line, then when that
> separates, the inside line. Voila! A ring.

Thew slowest speed on a motor tool is WAY TOO FAST for doing something like
this. ANd the knife pressure will more than likely just deflect rhe
cardboard rather than cutting it.

        Bob Kaplow      NAR # 18L       TRA # "Ctrl-Alt-Del"

Kaplow Klips:   http://members.aol.com/myhprcato/KaplowKlips.html (baffle too!)
NIRA:           http://www.nira.chicago.il.us  NAR:    http://www.nar.org

 
 
 

any tips for cutting centering rings?

Post by Tonya & Jame » Mon, 01 May 2000 04:00:00


Wal-mart, in the past week or two has started selling a circle mat cutter in
the arts and crafts department, it's near the popsicle sticks. Adjustable
cut sizes, and a very reasonable price too.
Jamey #5295


Quote:


> > If you can find a good art supply store, they will probaby have a
> > 'compass cutter' or similar tool.  It's like the compass you use to
> > draw the circles, but with an exacto blade instead of a pencil.

> The typical compass geometry doesn't work so well, with both the point and
> knife at non vertical angles to the cardboard. Look for a "Matte Cutter"
> which is designed more like the fly cutters we use in a drill press. Some
> are pretty flat and sit on what is being cut, others use a long arm with a
> point and knife.

> BTW, a drill press and fly cutter WILL cut nice cardboard rings, but it's
> certainly overkill. I use s***corrugated cardboard to make test cuts to
> get the correct ring size before attacking the plywood.

> Bob Kaplow NAR # 18L TRA # "Ctrl-Alt-Del"

> Kaplow Klips: http://www.FoundCollection.com/(baffle
too!)
> NIRA: http://www.FoundCollection.com/ NAR: http://www.FoundCollection.com/


 
 
 

any tips for cutting centering rings?

Post by Essenc » Mon, 01 May 2000 04:00:00


What sizes does the Walmart one cut?

Budget Rocketry sells one that cuts 1 3/4 to 8 1/2" up to 7/16" thick.
I have successfully cut 1.9" centering rings for a recent project out of
3/16" bass wood.

- Nick

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