lotus



previous page: 7.4 What other scale/sport scale kits are available? I'd like to build another kit or two before tackling a scratch scale project.
  
page up: Model Rockets FAQ
  
next page: 7.6 What tools do I need?

7.5 O.K., I've done all my research, collected all the data I can. I've even built a couple of scale kits a a warm up. Now I'm ready to build a model I can be proud of. How do I...?




Description

This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.

7.5 O.K., I've done all my research, collected all the data I can. I've even built a couple of scale kits a a warm up. Now I'm ready to build a model I can be proud of. How do I...?

Get rid of body tube seams:
Use silkspan, applied with clear dope, or .5oz. - .75 oz. fiberglass
cloth applied with epoxy. Silkspan will require a number of
subsequent coats of dope or primer to seal the surface and fill in
the fibers of the material, while the fiberglass should only require
a few coats of primer to fill in the weave. Really deep seams in the
tube should filled with your favorite putty beforehand. Tubes covered
with silkspan/fiberglass will be less likely to have the seams pop
later on.

Sand sharp break lines in fins with diamond cross sections, like those
used on Nike motors:
You can't...use a built-up fin instead. Use 1/64 ply or thin plastic.
Cut out mirror images of the fin pattern, then score the breakline
with the back of an Xacto knife, being careful not to cut all the way
through. Gently bend at the break line. Use a spar under the breakline
to provide support and give the proper root to tip thickness
distribution. Glue the three pieces (two fin halves and spar)
together, and fill the open ends with wood and/or putty.

Form sharp edges on nose cone, transitions, etc. (when turning your own):
The most common material to turn these items, wood (balsa, bass)
just won't take a very sharp edge. Try forming the piece slightly
undersize, then apply several coats of epoxy (try to get the coats
as even as possible). Then use a sanding block to sand the surface
smooth, but don't sand all the way down to the wood. These steps
should be done without removing the part from the lathe. The epoxy
will hold a better edge than wood, and the resulting surface will
have a plastic-like feel. Make sure the epoxy you use will cure to
a hard surface in thin films...5 minute epoxy often remains somewhat
rubbery.

Simulate weld lines:
Thread can be used, but something with a flatter cross-section
usually looks more realistic. Try cutting very narrow strips
of thin plastic using two X-acto or razor blades glued together (may
need a plastic spacer between the blades to get the desired width).
The width and thickness of the strip will of course depend on the
size of the weld to be simulated, but a 2:1 or 3:1 width:thickness
ratio is about right. Paint the model body tube with primer
let dry and apply the plastic strip with a _small_ amount of liquid
cement. Use a strip of frisk film or masking tape to provide an edge
to insure the plastic strip gets applied straight. Then apply several
coats of primer to fair in the edges, sanding between coats. If
AmSpam ever gets around to publishing it, a future "Art of Scale"
will cover this in more detail.

Simulate screws, bolts, and rivets:
For large-scale models, you may be able to find small screws in sizes
0-80 or 00-90 that will do the job that will do the job (Small Parts,
Inc, P.O. Box 4650, Miami Lakes, FL 33014-0650 is one source). On
smaller models you can simulate screws by embossing slots into Sig
"scale rivets" with an X-acto blade. Sig scale rivets are available in
both round and flat-head varieties (Sig Manufacturing Co., Inc., 401-7
South Front St., Montezuma, IA 50171). To simulate really tiny screws,
emboss the shafts of the scale rivets. Socket head screws can also be
simulated using scale rivets by drilling or punching a hole in the
center of the head. Rivets can be simulated in a variety of ways. On
large scale models, Sig scale rivets may be appropriate. For small
models, the best (and most difficult) way is to emboss thin sheet
material (aluminum or plastic) using a punch and die. This method gives
very sharp definition to the rivet heads. An easier way that produces
less definition of the rivet head is to simply punch from one side of
the sheet only - no matching die is used. This allows the use of a
small spur gear (e.g. a watch gear or pounce wheel) as the punch,
thereby allowing a whole row of rivets to be punched very easily.
A sewing machine can also be used to punch a whole row in short order -
just grind down a needle to produce the correct size rivet head. Model
airplane types often use tiny drops of glue to simulate the rivet
(RC56 glue supposedly works well).

Make multiple copies of parts:
Often, an number of identical parts appear on a prototype, and it is
usually tedious to make just one of them. RTV rubber is a two-part
rubber compound that cures at room temperature. Space does not allow
a detailed discussion of the method here, but basically a high-quality
master pattern is made, over which the RTV is poured. When cured,
the rubber mold is removed. Epoxy or urethane resin can then be
poured into the cavity to make as many copies as desired at a small
fraction of the work needed to make the master. Fiberglass parts can
also be laid up in RTV molds (another yet-to-be published AmSpam/SRM
article). Check out back issues of "Fine Scale Modeler" magazine
for a number or articles on casting parts in RTV molds. This is an
extremely valuable technique for the serious modeler.

 

Continue to:















TOP
previous page: 7.4 What other scale/sport scale kits are available? I'd like to build another kit or two before tackling a scratch scale project.
  
page up: Model Rockets FAQ
  
next page: 7.6 What tools do I need?