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Old Dec 14, 2013, 04:15 PM
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Query about lexan moulds.

Any advice on what materials are the best to use (and shape!) when making a mould for fairings? My M5 Komrade has got his vac former working and produced a prototype KTM 990 fairing for the M5 but it needs refinement. Any suggestions?
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Old Dec 14, 2013, 04:30 PM
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You can make a plug from easily shaped foam with a surface of bondo and primer or sculpt it in sulphur free clay like Chavant NSP. Cast it in rtv silicone (Smooth-on) and cast the the final plug in plaster.

After that it's building a vacuum form machine and using Polycarbonate to make the final piece.

If you don't want to go through all of that. You can make the piece in foam as i suggested earlier with the bondo primer surface. Wax it up REALLY well and then lay down fiberglass.

In short it depends on just how many you need and what trouble you are willing to go through to make what you need.

Other ways are shaping it in basswood (or something equally hard and then vacuum forming it as before.
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Old Dec 14, 2013, 04:48 PM
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What is the best plastic to use for vac forming at home i tried the coke bottle stuff PTFE i think it was, it formed well but when i painted it with a lexan paint it goes that brittle it shatters, i tried forming lexan & it did not form as well & had bubbles in it, from what i read you need to bake lexan in an oven for hours to get all the moisture out of it as it absorbs moisture.
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Old Dec 14, 2013, 05:42 PM
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http://www.eplastics.com/Lexan_Clear...arbonate_Sheet

This is what's used on rc bodies.
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Old Dec 14, 2013, 06:02 PM
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Quote:
Originally Posted by Throttlejunkie View Post
What is the best plastic to use for vac forming at home i tried the coke bottle stuff PTFE i think it was, it formed well but when i painted it with a lexan paint it goes that brittle it shatters, i tried forming lexan & it did not form as well & had bubbles in it, from what i read you need to bake lexan in an oven for hours to get all the moisture out of it as it absorbs moisture.
I made a homemade vac former a year or so ago, I tried both materials PTFE and Lexan. PTFE formed easy and like you found it would shatter on impact. Lexan will form to a shape just as easy if you get the temperature perfect, if you do a few trials you will find the sweet spot.

The moisture problem is the hard part, The missus wasn't to keen to have a sheet of lexan in the oven for hours.
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Old Dec 14, 2013, 07:04 PM
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Quote:
Originally Posted by rcmotogp View Post
I made a homemade vac former a year or so ago, I tried both materials PTFE and Lexan. PTFE formed easy and like you found it would shatter on impact. Lexan will form to a shape just as easy if you get the temperature perfect, if you do a few trials you will find the sweet spot.

The moisture problem is the hard part, The missus wasn't to keen to have a sheet of lexan in the oven for hours.
Lol, I did not bake the Lexan when i tried it, i found out about the baking after i tried it & have not tried again since, but i think i may have went a bit thick at 1mm, what thickness do you find best to use, i was looking at another plastic called H.I.P.S, high impact plastic sheet which is colored so you would not need to paint it & just use decals but i have not got around to it yet
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Old Dec 14, 2013, 07:08 PM
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The basic rc body shell is .030. The heavy weight ones are .040.
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Old Dec 14, 2013, 07:30 PM
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I used 1mm Lexan. It gets stretched a fair bit so its no where near that thick once its formed
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Old Dec 15, 2013, 04:44 AM
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Hello,

Lexan is hard to mould it makes some bubbles !
I used PETP which is really easy to mould, but it broke easy ...


More pics here on facebook : MOTO RC BIKE :

https://www.facebook.com/pages/MOTO-...63638403777267
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Old Dec 15, 2013, 08:41 AM
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He's using PETG apparently.

Whats the best for the actual plug itself? I wouldn't mind trying to make the nose fairing and have something a bit more Dakar rep.
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Old Dec 15, 2013, 12:06 PM
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The reason Lexan, aka polycarbonate, can have bubbles is moisture. Sheets have to be kept in a warm dry environment or they absorb moisture. When heat is applied bubbles will form in the sheet.

The best material for a tool is aluminum but thats mainly for high volume production. The next best is aluminum filled epoxy which is cast in a mold made from the master model. For a few parts you can use plaster of paris as long as the mold geometry doesn't have undercuts or fine detail.

For the master model you can make that cheaply by using automotive bondo cut with "honey" which makes it thinner and pourable. If you cant find honey then just use less catalyst. Make a smaller armature or rough shape from a stable hard material like hard wood. Apply the bondo on top of that and sculpt it to shape.
We normally use Renshape or another tooling foam for a master model but bondo is as close and as cheap as it comes. If you have access to 3M micro balloons (micro glass spheres used to fill in epoxy and other applications) you can add that to the bondo paste to change its shrink rate and working properties.

Its possible to get a couple pulls off the bondo master model but the heat and stress will damage the model. Take care not to expose it to high heat because it will shrink or change shape and possibly detach from the armature if you used one.

The master model orientation is also critical and you have to consider the machine your using to form bodies. If you know this then you know your sheet size and max draw height. Its the difference between a two piece body or a one piece.

Some stats;
Lexan 0.020 - 0.035in is good to about 4-5in high tooling.
Lexan 0.060 - 0.065in is good to 6in high tooling
The cut line of the part should be 6mm above the plane (floor)

Ive been making vacuum for tooling for special effects one off models, production car body tooling for HPI, Maxtec, Venom/Atomik for about 20 years. If you want to learn just ask me and post pics of your project so I can guide you through it if you like. Its fun and interesting with plenty to learn every time.
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Last edited by Chris Nicastro; Dec 15, 2013 at 12:18 PM.
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Old Dec 15, 2013, 12:21 PM
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I used Plaster of Paris, its cheap and easy to use. As Chris said its ok but you wouldn't want to use it for high volume runs.
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Old Dec 15, 2013, 12:42 PM
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I loved working with Renshape!. Expensive, but man it did everything you wanted it to do.
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Old Dec 15, 2013, 05:04 PM
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Last time I checked Renshape was about $0.35 a cubic inch! Who knows now. Ciba was the parent company but things have changed over the years and there are other rapid prototyping foam boards now. I love the material and still have a chunk lying around for a rainy day. At HPI our master models were worth thousands of dollars when they were finished in materials and man hours.
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Old Dec 20, 2013, 09:30 AM
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Description: A metal mug in there for scale. A 1/8 buggy shell JUST fits nicely.

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Description: Made from four thick wedges of MDF. Turned out quite nicely. A shame the photos didn't!

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Description: The first test piece.

I'll paint the first shell up and see how it looks. It's all still at the crude stage, but having the potential to bash out new riders and fairings for the M5 will be handy.
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