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December 9, 2007:
Frank Pittelli, Marty Hayes and Joe Sommer visited Charlie
Mann in Severna Park MD to try vacu-forming
the turret top for a Tiger I. Charlie and his friends
vacu-form helmets, armor and equipment for
Star Wars reenactors.
Frank took some "battle" photos that are posted below.
Joe will post photos of the molds, raw parts and finished
parts after they are cleaned up.
The attendees are still undecided about the efficacy of
the concept. However, they had a great time
learning about vacu-forming and talking with
fellow modelers.
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Click Photo For Enlargement (72 Kb) |
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The Star Wars modeling experts prepare to form .080 plastic over a couple
of their molds and over some simple cupola and toolbox molds that Joe
brought. The larger items are coated with some talcum powder and placed
on the vacuum table. Charlie has a very nice rig, which incorporates an
old 50 gallon water tank to hold the "vacuum charge". A pump sucks a strong
vacuum in the tank (about 15 PSI) and then a 1 inch ball valve is thrown
to quickly draw the plastic down to the table and molds.
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Literally all hands on deck when the plastic is drawn down to smooth out
any wrinkles and press out any bubbles. Since the plastic is heated before
the draw, everyone wears gloves to protect their hands and long sleeves
to protect their arms.
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Click Photo For Enlargement (91 Kb) |
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Click Photo For Enlargement (80 Kb) |
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Marty and Joe anxiously await the forming of the 1:6 scale Tiger turret.
Charlie (the guy mugging for the camera) says that they've formed some helmets
about the same size, so he isn't worried about covering everything.
Ultimately, the biggest problem is extracting the plug from the molded part.
Shortly, both Marty and Joe will perfect the "curbside extraction method".
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A very nice draw of the Tiger turret using .118 plastic which forms well after
Charlie determined the proper heating time, which is more of an art than a
science. Heat too little and the plastic won't form well; heat too much and
the plastic will stretch too thin and break. Joe will extract the turret
back at home, will clean up the edges and, of course, take some point blank
shots at it to see how well it holds up.
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Click Photo For Enlargement (82 Kb) |
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Click Photo For Enlargement (91 Kb) |
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A 1/6 scale mold for a Tiger I turret was constructed
using 1/2 inch thick plywood for top and bottom plates,
and 3/4 thick pine for vertical studs and the straight
sidewalls. The nose and sidewalls were sheathed
with 1/8 inch thick high density fiberboard. The mold
was hollow to allow future vacuum ports for details
if needed. All molds were placed on 5/8 inch thick
riser plates with beveled edges made from medium density
fiberboard to facilitate release after forming.
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Molds for the early commander's cupola and the aft
turret tool box were also constructed at 1/6 scale.
One tool box mold included the cutout for the rear turret
lift trunnion. The cupola mold was made from a PVC pipe
fitting. Tool box molds were made from 2x4 pine.
Small 1/16 inch DIA vacuum port holes are visible in
the top of the cupola mold and near the trunnion cutout
on one tool box mold.
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Click Photo For Enlargement (108 Kb) |
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Click Photo For Enlargement (83 Kb) |
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Two different thicknesses of black ABS sheet were vacuformed
over the turret mold - 0.090 inch thick and 0.118 inch
thick. Both thickesses pulled well with no tearing and
minimal webbing at the corners. Both had a small amount
of flare at the bottom edge that can be removed by improved
riser design. The front corners of the sheet were cut
to allow extraction of the mold from the sheet in that
the lower half of the nose must be removed for the gun
mount. Making the lower half of the nose in the mold
beveled out rather than vertical should fix this problem.
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White 0.090 inch thick ABS sheet was vacuformed
over the tool box molds. The tall thin tool box
molds had moderate webbing at the corners but the
trunnion cutout formed surprisingly well. While
folded webbing appears ugly it was not a major
problem. Fusing the inside corners of folded
webbing with standard PVC/ABS cement and filler
allows it to be cut and sanded smooth.
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Click Photo For Enlargement (58 Kb) |
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Click Photo For Enlargement (71 Kb) |
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Webbing for the second tool box mold appears better
but was actually worse in that it was open rather
than folded. The second tool box also had moderate
flare at the bottom.
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The cupola was also vacuformed using 0.090 inch thick
ABS sheet. The indentation in the top came out very
well.
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Click Photo For Enlargement (54 Kb) |
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Click Photo For Enlargement (66 Kb) |
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The turrets were rough cut by hand from ABS sheets
using a Roto-Zip saw. The Roto-Zip was also used
for final trimming. The 0.118 thick material
trimmed nicely but the thinner 0.090 material
vibrated more and produced a rougher edge. The
corners of the lower half of the nose were glued
back together with PVC/ABS cement. Even subtle
imperfections in the surface of the mold transferred
with surprisingly fidelity to the outer surface of
the parts.
Both turrets were taped to a fitted base plate made
from 5/8 inch thick medium density fiberboard.
Both were shot multiple times at point-blank range
with a standard 0.68 caliber marker. No damage
was incurred in either turret.
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The cupola and tool boxes were also rough cut
using the Roto-Zip. The cupola was trimmed with
the Roto-Zip and the tool boxes were trimmed
with a band saw. The cupola only had minimal
flare. The tool box with the trunnion cutout
turned out very well, while flare and webbing
problems were present in the second tool box.
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Click Photo For Enlargement (40 Kb) |
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Click Photo For Enlargement (65 Kb) |
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The cupola and toolbox were taped to the turret
for this preliminary photo. They can be cemented
together using standard PVC/ABS cement for simple
construction.
Current efforts are focused on building a light
turret base similar to Tiger #T001 and Cromwell
#T040 along with methods to attach/pivot the ABS
turret top to the turret base.
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Lesson Learned About Vacuforming Turrets
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Minor changes in mold and riser design should
remove flare and extraction problems. Webbing
will still be present for the tool box but may
be trimmed later.
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Using a Roto-Zip only required about 5 minutes
to cut the turret from the sheet and perform final
trimming.
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Both 0.090 and 0.118 inch thick ABS turrets
will withstand paint ball impacts. The thicker
material is recommended for easier trimming.
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Vacu-forming is an art. Charlie Mann is a
master of this art.
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