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R/C Combat Vehicles

Vacuforming Turret Parts

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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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.
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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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".
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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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.
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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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.
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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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.
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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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.

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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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.

Lesson Learned About Vacuforming Turrets
  1. 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.

  2. Using a Roto-Zip only required about 5 minutes to cut the turret from the sheet and perform final trimming.

  3. Both 0.090 and 0.118 inch thick ABS turrets will withstand paint ball impacts. The thicker material is recommended for easier trimming.

  4. Vacu-forming is an art. Charlie Mann is a master of this art.