Choosing paper for round shell pasting

[AdmiralDonSnider]

I still wonder how thick a kraft paper to buy for round shell pasting.
Unglazed virgin kraft is pricey, so I best reflect about my choice
before buying. I heard about 40 pound kraft being popular, not sure if
this is true. On the other hand my local supply sources what is about
a 47 pound (80gsm) only; will this make a difference? What makes me
doubt it´s fine is a line from Hardt: "As a general rule, two or three
complete layers of 30- to 40-pound paper will be required for each
inch of shell diameter (...) Fewer layers of thicker paper may be used
to save time, sometimes with a sacrifice in the regularity of the
shell walls." (p.222)

As far as I know the desired thickness of pasting (amount of layers)
is calculated using a formula given by Shimizu; at the same time this
formula calls for a known or estimated mean value of tensile
strenghts, not for a paper´s gsm or pounds. Do you guys measure these
values?

What thickness paper (pounds) is a traditional or suggested choice for
traditional paper pasting? What about my 80 gsm? Feel free to
enlighten me in case I´m taking things too serious ...

Thanks a lot!
Admiral

[boom.armstrong]

I use 70 pound Kraft for my pasting applications. Depending on your
shells diameter you will want to adjust the width of each strip.
Properly broken in it will lay down quite flat. The number of layers
used will depend on what type of break you are seeking, as well as the
type of break charge. A Poka shell may only require 3 layers of paper
with a weak BP break. A 6 inch Warimono will require 12 to 14 layers,
with a coated hull burst. If using a KP break or booster you will
need to dial in the number of layers. Since the confinement will
determine the strength of the burst.

Post by AdmiralDonSnider
I still wonder how thick a kraft paper to buy for round shell pasting.
Unglazed virgin kraft is pricey, so I best reflect about my choice
before buying. I heard about 40 pound kraft being popular, not sure if
this is true. On the other hand my local supply sources what is about
a 47 pound (80gsm) only; will this make a difference? What makes me
doubt it´s fine is a line from Hardt: "As a general rule, two or three
complete layers of 30- to 40-pound paper will be required for each
inch of shell diameter (...) Fewer layers of thicker paper may be used
to save time, sometimes with a sacrifice in the regularity of the
shell walls." (p.222)
As far as I know the desired thickness of pasting (amount of layers)
is calculated using a formula given by Shimizu; at the same time this
formula calls for a known or estimated mean value of tensile
strenghts, not for a paper´s gsm or pounds. Do you guys measure these
values?
What thickness paper (pounds) is a traditional or suggested choice for
traditional paper pasting? What about my 80 gsm? Feel free to
enlighten me in case I´m taking things too serious  ...
Thanks a lot!
Admiral

[AdmiralDonSnider]

I focus on Chrysanthemum shells with their heavy pasting.

As far as I know there is some overlap in pasting, I guess Hardt
thought the wall would become quite irregular if these overlaps are of
thick paper too. But when I hear you words, this seems to be less of
an issue in practice. So my 47pound would be right too?

[boom.armstrong]

There are a few different pasting methods. Some people use gummed
tape, others even use a WASP which is machine pasting using tape.
Being a traditionalist and not turning out large numbers of shells, I
still prefer to hand paste with
strips of Kraft. Using a paper like you have may require more
layers. But the overall thickness should be relatively close. By
changing the orientation of the poles while you are pasting you can
eliminate any "bulging" due to overlap.
One thing many neglect to do is to break the paper in. I find this is
important for better breaks and symetry. You are actually working the
paste into the papers fibers. This creates a much stronger and
brittle shell.

Post by AdmiralDonSnider
I focus on Chrysanthemum shells with their heavy pasting.
As far as I know there is some overlap in pasting, I guess Hardt
thought the wall would become quite irregular if these overlaps are of
thick paper too. But when I hear you words, this seems to be less of
an issue in practice. So my 47pound would be right too?

[maxx4671]

First off I want to tell you Im a beginer and Ive only pasted ten
shells but I thought I had something that would be able to help you
I use fifty pound kraft paper that I found at Hobby Lobby made by
Pacon corporation out of Appleton
It says natural craft on the pack cost around five bucks for thirty
feet by thirty inches
I found this video very helpful

One thing I do diffrently is the v's that I cut from the Kraft are a
lot shalllower then on the video
and I make sure the grain is going the right direction
for a three inch shell six layers seemed to work good for me
when i paste I have a caliper thingey close by to check the diameter

Hope this helps

Maxx467
Proud to be a new PGI member

[AdmiralDonSnider]

Thanks both of you.

Concerning breaking paper, I´ve never heard this to be used in case of
spherical shells. While I expect it to give a better look, as the
strips are like cloth and will adhere very closely, I can´t help
thinking that the paper also looses some strenght, as you actually
break the fibres. May be wrong on that one.

I´m still interested in how you determine the layers. If you´re using
Shimizu´s formula, you must measure the tensile strenghts somehow. Now
how do you do that?

[HiNRG61]

Post by AdmiralDonSnider
Thanks both of you.
Concerning breaking paper, I´ve never heard this to be used in case of
spherical shells. While I expect it to give a better look, as the
strips are like cloth and will adhere very closely, I can´t help
thinking that the paper also looses some strenght, as you actually
break the fibres. May be wrong on that one.
I´m still interested in how you determine the layers. If you´re using
Shimizu´s formula, you must measure the tensile strenghts somehow. Now
how do you do that?

When I first began building shells in the mid 80's I tried to copy
recipes exactly to the letter, searching everywhere for some
particular weight and/or brand of paper. It was sometimes very
frustrating.
I had been attempting to follow someone else's "formula", rather than
understanding the principle involved.

After attending several PGI conventions and discussing shell
construction with other pyros, I realized that virtually any paper
will work just fine as long as you adjust/adapt it to your particular
situation: the speed and energy of your burst material, the
construction and thickness of your shell hemis, and the type of paste
you're using.

While you could probably rig up some kind of tensile strength
measuring device, ala Shimizu, using clamps and a spring scale, most
of us probably rely on the tried and true method of trial and error.
The key is to keep careful notes (and video if you can) of each
attempt, and then to remain consistent in your technique, once you are
satisfied with the results.

At the factory, we used the aforementioned gummed paper tape, which is
a convenient way to work. Tape is obviously more expensive than kraft,
but in the commercial world, labor is more expensive than paper so it
made sense to speed up the process with the costlier material. The
paper tape yielded very satisfactory results, producing hard,
symmetrical breaks. Another advantage of the tape is rapid drying
time; we could paste wrap a (small, 3 to 5 inch) shell in the morning,
and shoot it that night.

One other thing to consider is the intended end-use of the shell. If
you're building a matched pair of shells for a PGI competition, that's
one thing. If you're constructing a flight of three inchers for a
finale chain, no one's going to notice if the densely packed bursts
are shaped more like an egg than a basketball!

I wish you well. Kurt

[boom.armstrong]

Like Kurt said, you can measure the tensile strenght of the paper.
How much trouble that may be is a matter of opinion.
With all the other factors involved, you are more likely to achieve
success by experimentaion and good record keeping.

As far as breaking the paper is concerned. You are not weakening the
fibers. You are essentially impregnating them with paste which
increases the dried strength. Think of it this way. If you merely
swipe some glue over a piece of paper only the surface will be
bonded. Now work it through the paper and fibers and you have a solid
mass.

Post by HiNRG61

Post by AdmiralDonSnider
Thanks both of you.
Concerning breaking paper, I´ve never heard this to be used in case of
spherical shells. While I expect it to give a better look, as the
strips are like cloth and will adhere very closely, I can´t help
thinking that the paper also looses some strenght, as you actually
break the fibres. May be wrong on that one.
I´m still interested in how you determine the layers. If you´re using
Shimizu´s formula, you must measure the tensile strenghts somehow. Now
how do you do that?

When I first began building shells in the mid 80's I tried to copy
recipes exactly to the letter, searching everywhere for some
particular weight and/or brand of paper. It was sometimes very
frustrating.
I had been attempting to follow someone else's "formula", rather than
understanding the principle involved.
After attending several PGI conventions and discussing shell
construction with other pyros, I realized that virtually any paper
will work just fine as long as you adjust/adapt it to your particular
situation: the speed and energy of your burst material, the
construction and thickness of your shell hemis, and the type of paste
you're using.
While you could probably rig up some kind of tensile strength
measuring device, ala Shimizu, using clamps and a spring scale, most
of us probably rely on the tried and true method of trial and error.
The key is to keep careful notes (and video if you can) of each
attempt, and then to remain consistent in your technique, once you are
satisfied with the results.
At the factory, we used the aforementioned gummed paper tape, which is
a convenient way to work. Tape is obviously more expensive than kraft,
but in the commercial world, labor is more expensive than paper so it
made sense to speed up the process with the costlier material. The
paper tape yielded very satisfactory results, producing hard,
symmetrical breaks. Another advantage of the tape is rapid drying
time; we could paste wrap a (small, 3 to 5 inch) shell in the morning,
and shoot it that night.
One other thing to consider is the intended end-use of the shell. If
you're building a matched pair of shells for a PGI competition, that's
one thing. If you're constructing a flight of three inchers for a
finale chain, no one's going to notice if the densely packed bursts
are shaped more like an egg than a basketball!
I wish you well. Kurt

[Lloyd E. Sponenburgh]

Post by boom.armstrong
Now work it through the paper and fibers and you have a solid
mass.

Generally called "a composite".

LLoyd

[AdmiralDonSnider]

First I´d like to say thanks for the interesting information. Thanks
HiNRG61 for pointing me towards understanding the principles rather
than imitating others, I´d just been unsure...´
I´ll go with my 47 kraft and optimize by trial.

In the meantime I´d like to hear your opinion about homemade newsprint
hemis. These are held in high esteem by Shimizu and other Japanese
shellmakers and are said to be superior to strawboard ones.
As far as I remember they are slightly different in size than their
strawboard relatives and are made thinner; is that right?
What are the things to look for when using these?

[HiNRG61]

Post by AdmiralDonSnider
First I´d like to say thanks for the interesting information. Thanks
HiNRG61 for pointing me towards understanding the principles rather
than imitating others, I´d just been unsure...´
I´ll go with my 47 kraft and optimize by trial.
In the meantime I´d like to hear your opinion about homemade newsprint
hemis. These are held in high esteem by Shimizu and other Japanese
shellmakers and are said to be superior to strawboard ones.
As far as I remember they are slightly different in size than their
strawboard relatives and are made thinner; is that right?
What are the things to look for when using these?

If you don't already have it, I highly recommend David Bleser's "Round
Stars and Shells", which I believe is still in print and available
from American Fireworks News. IIRC, Dave includes some very good
information on making your own newsprint hemis and how to use them.

He suggests using standard plastic shell hemis as forms, covering them
with Saran wrap, and pasting on strips of newspaper with thinned
Elmers white glue.

This will work, but you have to keep in mind that your newsprint hemis
will have nowhere near the rigidity of commercial strawboard. You may
need to use smaller diameter stars,or use a small particle size burst
material, in order to minimize interstitial space and maximize the
integrity of the shell. In other words, you have to depend on
consolidation of the contents, rather than the strength of the
container, to form a solid shell.

Also, your end product will probably be larger diameter than normal
if you're using plastic (or strawboard) hemis as case formers, as
their O.D. is larger due to shell wall thickness. This can actually be
a benefit, as it means increased volume for contents inside (bigger
burst), and a tighter fit in the mortar (less lift-gas blow-by) for
higher altitudes, or you may be able to use less lift than usual.

I tried this a couple of times back in the day, but decided the
results (at least in my case) weren't worth the added hassle. But
don't let that comment discourage you from trying it yourself. Your
results may be quite different from mine.(Not to mention bragging
rights for "doing it all from scratch"!)

Hope this helps and I wish you well.

Kurt

[J***@icloud.com]

What is the width of gummed paper I should use for a 3" shell I was thinking maybe 1" or 1 1/2"

[The best news in machining]

Post by J***@icloud.com
What is the width of gummed paper I should use for a 3" shell I was
thinking maybe 1" or 1 1/2"

3/4" works well. For 1.75" shells, we have to use 1/2" tape. 1" is too
wide - it tends to wrinkle badly on small shells.

We 'WASP' a LOT of small shells. It was a learning exercise, since most
folks don't make really little ones.

Lloyd

[d***@gmail.com]

Post by Lloyd E. Sponenburgh

Post by boom.armstrong
Now work it through the paper and fibers and you have a solid
mass.

Generally called "a composite".
LLoyd

That's something that's long confused me, so glad to see this old thread come up. On the one hand there are instructions on orienting strips according to the grain on the device. OTOH, the same set of instructions may refer to soaking the paper in paste and rubbing it to "break" the grain, which I took to mean making it less grainy and closer to isotropic. Is that actually what goes on? If so, are these instructions at cross-purposes?

Getting my hands & table covered in paste is one of the more fun aspects of shell building for me. I'm still a kid at heart. But it does call for some set-aside of time & facilities. I usually don't try to preserve my paste, so that calls for even more planning.

Robert

[The best news in machining]

Post by d***@gmail.com
That's something that's long confused me, so glad to see this old
thread come up. On the one hand there are instructions on orienting
strips according to the grain on the device. OTOH, the same set of
instructions may refer to soaking the paper in paste and rubbing it to
"break" the grain, which I took to mean making it less grainy and
closer to isotropic. Is that actually what goes on? If so, are these
instructions at cross-purposes?

It _sounds_ like they are, because the old-timers called it "breaking the
grain", "breaking paper". But, with virgin kraft, it doesn't really
break anything. It just softens all the fibers, and impregnates every
pore in the paper with paste.

By virtue of that, it tends to _behave_ more like it were 'grainless', so
long as the paste is still wet, although it's still more dimensionally-
stable along the length of the grain.

It shouldn't require _too_ much 'planning', just because you don't save
your old paste. It's only a two-minute job to make a new bowl of paste,
and it doesn't have to rest more than about 20-30 minutes before it may
be used.

L