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Vacuum-forming query

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#1 slotbaker


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Posted 17 May 2019 - 07:37 PM

Curiosity question: Has anyone tried vac forming into a negative mould to get sharper detail?



The thought crossed my mind looking at the blow moulded MDI McLaren Elva that Jairus is building.

It has great/sharp detail.


I'm guessing there would be plenty of problems to get a good result, like;

- The deeper the mould, the thinner the material gets at the bottom

- Small details (door handles, gas caps, tail/head lights, etc) would have to be vented

- Making the mould

- etc


If it could be done, the result might rival (or get close to) resin cast or injection moulded bodies for detail.


Maybe not worth the effort, but someone smarter than me might be able to make it work.

Steve King

#2 swodem


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Posted 17 May 2019 - 07:51 PM

That idea sucks ;-)

Sent from my iPhone using Tapatalk Pro
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Steve Meadows

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Posted 17 May 2019 - 07:58 PM

Steve, I think you should post your thread in "The Body Shop & Paint Booth" forum also  :) 

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Paul Wolcott

#4 Brian Czeiner

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Posted 17 May 2019 - 09:05 PM

I have dabbled with the process. Results have been promising. Venting every detail has been the biggest hurdle. Particularly with side details. As for getting thinner, I have found the sides actually stay thicker and thins out toward the top creating a lower center of gravity body without reducing body pin area strength. It's all about how the air flows. Another hurdle is the vent hole size. Too big and you get dimples all over. I haven't given up on it yet. Just too many other things to develop.

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#5 Ramcatlarry


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Posted 17 May 2019 - 09:29 PM

Find an old Mattel HO vac former - might be good for interiors, but not much bigger.

Larry D. Kelley, MA
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#6 Gene/ZR1


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Posted 18 May 2019 - 09:28 AM

Yes it can be done.
I have played with this for quite awhile.
As far as vent draw holes it's a unique setup consisting of a female mold that sites in a bucket or box arrangement with the perimeter top edge sealed and vacuum is all drawwed from the bucket or box bottom.
When my time permits I will get back into this. So far small prototype molds have worked.
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Eldon Adams AKA Gene/ZR1
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#7 Dave Crevie

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Posted 18 May 2019 - 09:32 AM

The venting is the main problem. It is almost impossible to get all the recessed areas properly vented. That is why

the plastics industry still uses the positive-mold approach. Blow molding works very well, but most blow molders

are set up for larger parts like bottles. Back when the Austin-Healey club had their national meet in Rockford, one

of the activities was an R/C car race. I built a blow mold to produce an Austin-Healey BJ-8 style body, and had

some guys that worked for Container Corp run the bodies. The bodies were 1/8th scale, and came out very well

using PTG. Container Corp was one of the larger customers of the shop I worked for at the time, and I queried their

engineers about the possibility of doing slot car bodies. Their general opinion was that you couldn't get a thin enough

cross section of the sides to make it feasible. Plus the size of the "torpedeo" style injection system made the inlets too

large. It was a good idea from the standpoint that two bodies could be made with each machine cycle, being joined

around their bottom edges. 

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