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Vaccum forming truck bodies 101

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Old 07-16-2008, 12:36 PM
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jdiamond
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Default Vaccum forming truck bodies 101

Ok as promised, a step by step tutorial. I'll post the pics in order as they are described and reference them.

Materials needed: 24x24x1/4" plywood(3 sheets), 1x2x6" oak(2 pieces), indoor/outdoor clear silicone caulk(2 tubes), 8 flat L brackets, 16 non-flat L brackets, 8 3 inch screws with wingnuts, 1 inch weather stripping, 8 lbs of sculpey modeling clay, plaster of paris(amount may vary), wood putty(or spackel), four bricks, and plastic of your choice(I used PETG, which I will explain why later on).

Tools needed: Power saw, drill, sandpaper and block, screwdriver(powered is prefered), oven, and vaccum cleaner(you'll need 2 unless you are using a shop vac).

Step 1: Building the box. This needs careful attention to getting a perfectly sealed box. You'll want to make this box 24x24 and 4 inches deep. Using the non-flat L brackets, bolt the whole thing together, and use the caulk to seal it. Make sure you seal it very very good, I suggest sealing both the inside and out, as well as putting it in the joints when you are putting it together. Cut a hole in the side of the box for your vaccum to connect. This should be a very tight seal. If you are using two vaccums, cut two holes.

Step 2: Build 2 frames with the outer dimensions being 23x17. Most ovens are 24x18, and you'll need a little room to get it in there and out easily. Use the flat L brackets, and keep them towards the outer edges of the frames. I suggest strongly using caulk to seal the joints. Place the two frames together, with the non-bracketed sides facing each other, and drill 8 evenly spaced holes for your 3 inch screws to go through. Drill this the exact diameter of the screws. There should be 2 screws per side. Now, take the upper frame, and drill out those holes a size or two larger, to make pulling the frames apart easier. The lower frame will have the tighter fit and hold the screws in place so they aren't falling out(you can also glue them as well).

Step 3: Place your frame on your box, centered, and trace the inner outline of it onto the box. Then draw a grid with lines spaced 2 inches apart. At the intersections, and inside of the outline, drill out 5/16 inch holes. Now take the weather stripping, and on the outside of your frame tracing, place it, preferably two rows deep to give it a perfect seal.

Step 4: Build a mold. For my example, I used Parma's replica of the Predator. This is more easily done if you have a body that hasn't been cut, but if not, don't worry, Sculpey to the rescue! You can make molds any variety of ways. It may be easier for some to just take an uncut body, and fill it up with plaster. Plaster isn't as durable though, and also that won't work with a body that is already cut, or if you are looking to modify it signifigantly. In my case, I needed to use sculpy to make my mold. The trick is, to do it slowly, knead the sculpy into a 1/8" sheet like a pizza, the bigger you can do this the better, and you'll see why. Use that "pizza" and put it in in the inside of your truck body, and work it into all the crevices, and details. After you've done this, and the body surface is fully covered, you'll want to start adding sculpy thoughout, to build it all up to about 1/2 inch of thickness. The reason for doing that first layer like a piece of pizza, is to minimize gaps and crevices. I learned the hard way, and wound up having to fill up alot of defects.

Now, with your body and sculpey upside down, and still soft, fill it with some plaster, as much as you can. You can use some wood blocks to take up some space as well. Your goal is to make something that gives the soft sculpy some support when you remove the body to bake it. If you do use wood blocks, or other materials, make sure they are NOT touching the sculpy(I learned this the hard way too) as if it is, when the sculpy is baked, then cools, it needs to be able to contract some. The plaster should compress a little, but the wood will not, and your mold will crack. There may be better ways to fill the mold, and I can't guaruntee that it won't crack, but, if it does crack, you can fill it later on as I did. At the very bottom of the mold, you'll want a block of wood that will keep the mold off of the ground, and it should be only a couple of inches wide, to allow for suction under the edges of the mold.

Next, back it according to the instructions Sculpy has. Given it's large size, I wound up baking it for a longer time than they suggested, I believe I baked for 30 minutes instead of 15. Let the mold cool overnight. If the mold cracks, fill the cracks in with CA glue, and sand. You'll likely have a number of imperfections you'll want to fix, and you can use wood putty or spackel to fill them in and sand them down. When done, you'll have a strong, permanently constructed mold that should hold up to repeated use.

Step 5: Lets make some bodies. First, you'll want to select a material. I used .040 PETG, which has the same basic qualities as Lexan, except that it is less resistant to UV rays(it'll yellow a bit if left out in the sun, in otherwords). It also forms at a lower temperature, which can be pretty important. Set up your box, and attach your vaccum. Place the mold in the most central area of the box, and coat the mold with cooking spray. In your oven remove all of the racks except the lower one, and line it with tinfoil(this will save you from getting in trouble with the wife should you overheat your plastic. Place the bricks on the rack against the sides, with two bricks stacked on top of one another. they should be place lengthways, and on their sides. Now cut your plastic into a sheet that will fit in the frame, and tighten the frame very tightly. Place in the oven on top of the bricks, which if using PETG should be preheated to 325 deg or so. Close the door and watch through the window with the light on, for the plastic to begin to sag. Once the plastic has sagged to the bottom edge of the top brick, quickly remove it, and place the the frame down onto the box, and turn on your vaccum. Try to be sure to drop the frame *Straight* down, so that the plastic dosn't wrinkle, and so that the thickness is even on both sides. It's best to have a helper that can switch on the vaccum as soon as you give the signal, because the plastic cools very fast. As the vaccum is turned on, use your hands(wearing gloves of course) to help push down stubborn areas. Allow a few minutes to cool, then remove your body from the mold and frame.

I ran into a number of snags along the way. First, make sure the frame is make of a wood that can withstand some heat. Oak worked well for me. Pine will incinerate. If you use two vaccums, it's probably a good idea to have them on opposite sides of the box. I noticed my bodies are slightly thinner on the side that the vaccums were, presumably there was a bit more suction going on or something. As far as the mold, there are probably a number of methods, choose whatever is easiest, and still strong enough to withstand some abuse.

Pics below: forming box, frame, mold, underside of mold, original body, formed body, painted body (patterned after http://www.offroaders.com/directory/...ks/Pouncer.htm )
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Old 07-22-2008, 09:41 AM
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Default RE: Vaccum forming truck bodies 101

omg amazing idea amazing body you man deserv an award it is simply fantastic
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Old 07-22-2008, 01:23 PM
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Default RE: Vaccum forming truck bodies 101

Great job....I am thinking of doing this myself to try and fit a MT body on a Truggy with some artistic flair.

What size of frame would be the smallest that you could use to do a 1/8 scale truggy? The dimensions are W - 410 mm (16.1") L - 170 mm (6.6") H - 152 mm (6"). I notice that you use a 23" x 17 " frame. I assume that the inside dimensions are 17" x 13" using 1x2's? What size of plastic sheet do you use for this? I am just trying to figure out how many pc I could get out of a 4x8' sheet.

Once again...great job...thanks for posting!!!
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Old 07-18-2019, 07:34 AM
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Ancient thread, but I have been expanding upon the original premise, creating a new body form from a 3d printer and making a silicone mold to create a silicone form for vacuum forming. Will update soon with some pics and instructions...
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Old 07-19-2019, 04:47 AM
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Steps thus far:

1. Designed the body using Blender and Autodesk Meshmixer. Make sure you measure and scale correctly!
2. Printed out the body with a 3d printer. Because mine is fairly small, I had to print it out in a number of blocks and glue it all together, and smooth out the seams. Took two spools, cost approximately 60 dollars. (Farming it out I could have done it in two sections, but the cost would have been 400 dollars for this 1/8th scale body).
3. Built a mold box out of cardboard. You definitely want to fill some of the void areas around the body with foam or wood to minimize the amount of silicone you will use. In my case, I still wound up using 3 gallons. Cost around 400 dollars! Pro tip - coat your printed body with oil or Vaseline - I didn't do this, and paid the price. Demolding was a nightmare, and I had a lot of trouble getting it out. Most likely you'll need to cut one end of the mold vertically to aid you in getting it out. You can reseal it back together if you want, but I'd recommend clamping it back in some fashion because you're gonna need to demold again and it makes it much easier.

Upcoming steps:

4. Coat the mold with Vaseline and/or oil, and pour silicone into the mold. My guess is looking at it, typical 1/8 scale is gonna take about 2 gallons or close to it.
5. Demold, and now you have your form!
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Old 07-24-2019, 05:06 AM
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I have completed the creation of the form! Pics coming....
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Old 08-14-2019, 05:59 AM
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Bad pull, but painted anyway as a trial run.
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Old 08-14-2019, 06:34 AM
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I'll post pics of the form, former and all that soon, still a few things to clean up overall.

This pull got messed up. First, when dropping to the platen the frame got cockeyed, and the resulting twist to reposition caused several wrinkles. Also, I think I got it too hot and caused it to get the bubbly, lumpy look. I'm refactoring the way I'm dropping the frame, which is really tricky because this form is so large that it barely fits on my platen. Most likely I'm going to ditch the "lower from above on cables" method to lowering it by hand. I might put some guides in as well.

There has been a ton of trial and error for sure(and dollars spent), but I can see the light at the end of the tunnel. I have some concerns that I didn't do the mold as good as I could of, in terms of smoothing it out, as I'm seeing some of the imperfections of the mold in my pulls. Though the first pull didn't show them - most likely because it wasn't hot enough - the second did(but that pull was too hot).

Some notes about this particular body and form:
1 This thing is pretty large, and unlike most truck bodies it is undercut, that is the bottom of the truck is narrower than the mid section. This fact really rules out using anything other than silicone as the form. Even with silicone, getting the pull off of the form requires some wrestling moves!
2. The side fins and tail fin are 3 printed and screwed into the body. I cannot imagine there is another way to do it, trying to form over those would be near impossible I think. In this pic I haven't put the clearcoat over those parts yet, but once I do it should blend very seamlessly into the body.
3. I used .060 PETG for this. The shell is very hard, and much more durable than my previous work using .040 PETG.

About the former(I will post pics when I clean it all up!)
1. I bought a 36x24 steel cart from Global Industrial, with two trays. The top tray I assembled upside down in order to help contain the heat.
2. I bought 3 1500W garage heaters, that are 24x12. I removed the mounting brackets(using a sawsall, lol), and used wire to hang them inside the upside down metal tray.
3. The frame is hung using wire running up through the top tray to a sheet of plywood that was supported by a box. Once heated, I removed the box and lowered the frame onto the form. This doesn't work well enough, so I'm changing that.
4. I likely will frame 3 sides of this cart with plywood to keep the heat contained, and to then use lower settings of the heaters for a more gradual uniform heat.
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Old 08-14-2019, 12:29 PM
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I was wondering if you'd be willing to make a Airplane canopy for me.. It was damaged in shipping, Its a about 18" long 6"wide 6" tall.. Thx
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Old 08-15-2019, 05:26 AM
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Originally Posted by Sylvestercds1 View Post
I was wondering if you'd be willing to make a Airplane canopy for me.. It was damaged in shipping, Its a about 18" long 6"wide 6" tall.. Thx
If you provided the form, sure. However, making a form of that size is not so easy, or cheap. You may be much better off just ordering a new one.
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