CA cements and solvents - 2012/08

Q552: I find that my CA cements tend to thicken and become
unusable with time. I tried adding some CA solvent to the
cement and it came back to its original consistency. It seems to
work okay, but I’m afraid to put it to the test and actually use
it on my airplanes. Do you know if this restored cement can
be used reliably, and if not, what is the best way to keep CA
cement over a long period of time so it will not thicken?
A552: Although I have some suggestions of my own, I asked
this question of a true expert, Pat Tritle, who is a model
airplane kit manufacturer as well as a columnist for Flying
Models magazine. He gave me his thoughts about this question
and a related item, both of which use common acetone as the
solvent.
Pat stores his CA cement in a refrigerator in a large 12-
to 16-ounce bottle. He dispenses this refrigerated cement
first into a 2-ounce bottle and lets that come up to room
temperature. From there he transfers the CA into a 1-ounce
bottle for actual use. If the CA tends to thicken in the heat of
summer, he thins it with a little acetone.
Because the acetone is a solvent, you have to be careful how
much you use. That’s why
it is good to try the CA on a
test strip, to make sure it still
cures properly when the accelerator is applied.
Pat went on to say that a big complaint with using CA
cement is that the tips get easily clogged. Many modelers
insert pins into the tips to unclog them. Often, if the pins are
contaminated, this tends to cure the CA, making the clog even
worse.
To solve this problem, Pat suggests that you remove the
tip from its container after each use and place it in a bottle
containing acetone. Let that tip soak at least overnight.
In the meantime, substitute a newly cleaned tip and
continue building. The next day remove the clean, unclogged
tip and let it thoroughly dry. If anything is caught inside the
tip, use a can of compressed air to blow it out. Don’t even think
of using your mouth.
The key point here is that you are using a solvent. Residual
solvent might prevent the CA from curing, so make sure the
acetone has completely evaporated before placing it back on
your CA bottle.
Thank you, Pat. This was helpful. I do caution my readers to
test their CA cement on some scrap balsa before using it on a
model.
Q553: I enjoy flying RC model aircraft, but would still like to
revert to my childhood start in the hobby when I built and
flew rubber-powered models. Can you recommend a good
book to get me started once again?
A553: One that I recently got my hands on was written by
longtime Flying Models columnist, Don Ross. The title is
Rubber Powered Model Airplanes. It is available from CarstensPublications, and the website is listed in the “Sources”
section.
Don did an excellent job with his 168-page book. It
provides plans, enabling you to build two different all-sheetbalsa
models in a matter of hours. Many techniques to help
simplify model construction are provided. I have included a
photo of a figure that appears in this book.
This simple technique uses a couple of rubber bands and
several scrap sticks to help the initial framing of a built-up
model fuselage. I tried this approach on my next model and
was really impressed. Good job, Don!
Also of interest, and reported on in my “FAQ” column
that appeared in the September 2008 MA (page 71),
is Ron Williams’ book titled Building and Flying Indoor
Model Airplanes. Although the emphasis in this case is
Indoor flying, there are many references to rubber-power
techniques. This book can be obtained from AeroCraft RC.
The website is listed in the “Sources” section.
Q554: A friend told me that some brushless outrunner
electric motors allow for the quick change of a bent motor
shaft right at the flying field. Is that possible? How do you
do it?
A554: I only discovered this trick from AMA Hall of Famer
and Northeast Electric Aircraft Technology (NEAT) Fair
director, Tom Hunt.
I had accidentally bent the shaft on my little E-flite Park
180 motor. That would have been the end of my flying day,
except that Tom came up to me and asked if I had another
Park 180 motor with me. My other aircraft had the same
motor.
Tom quickly grabbed the propeller on the motor with
the bent shaft and pulled with a good amount of force. To
my surprise, the outer barrel of the motor popped off, along
with the bent shaft, propeller, and adapter.
Next, Tom went to the “good” motor and repeated the
process, except now he had an outer barrel with a straight
shaft. He slipped that barrel over the motor’s armature and
the magnet “sucked” the barrel in place. Believe it or not,
that magnetic action was the only thing holding that barrel
in place.
The propeller now turned over smoothly and I was able
to continue flying. I’ve since done this with several other
brushless outrunner motors and, in each case, the repair
process worked. I now keep several spare motors in my field
kit just in case. I keep the complete motor, but I’ll bet if you
ask your motor manufacturer, it can supply just the barrel
with the shaft to be used as a spare. Give it a try! Q555: Years ago I used a popular cement of the day called
Ambroid. It was slightly orange and took a while to cure,
but it was strong and all model builders used it. Although
I’ve gotten modern and use CA cements, I’d love to try to
build a new model using only Ambroid cement. Is it still
available?
A555: Using the Internet, it didn’t take long to find a source
for Ambroid cement. The company that makes it is still alive and well in the town of Swanzey,
New Hampshire.
I found a distributor that carries the
3.2-ounce tubes of Ambroid for $5 each.
With a minimum shipping and handling
charge of $5, it isn’t cheap, but it is
comparable to a 2-ounce bottle of CA
cement.
The company is called the
Northwoods Canoe Company of
Atkinson, Maine. I’ve listed the website
and telephone number in the “Sources”
section.
Q556: I had a recent situation where one
of my small Spektrum AS2000L linear
servos appeared to be stalled. It was new
and it had worked on my test bench,
but when I installed it in my model, it
stopped moving. What did I do wrong?
A556: I’m glad you ended on that note,
because you did do something wrong
during the installation process. In
answering this reader, I contacted him.
What he did was install the Spektrum
microservo using double-sided tape.
That is okay, but he allowed the tape to
project out from the servo’s PC board.
The one main gear on this particular
servo hangs off of the PC board. As you
can see in the photo, the gear can be
easily pinned by the protruding doublesided
tape. When that happens, the
gear is stopped, which in turn stalls the
motor, meaning the servo can’t move.
I had this reader cut off the tape, so
that it was clear of that main gear. As
soon as he did that the gear was able
to rotate without effort and the servo
worked normally. It was a minor
point, but it did stop the servo.
The message is clear; always make
sure that moving parts on any servo
are free to move. The tip-off here was
that this servo worked on the bench,
but not when installed in the aircraft.
This same situation can result from
control rods that fit too