Airfix 1:72 scale Blohm Voss BV-141

[N4521U]

Airframes. this is more or less my first attempt following your instructions. The difference being I cast the positive out of plaster based on the mold I made wit latex making the result slightly larger than the original but figuring I could trim it down enough to make it fit, not happy with the results so far.

I used to attend meetings in San Jose with Rodney Williams, Google his name. What He and others used to do is make a plaster mold from the INside of the kit canopy and use This for the male part of making a clear sheet molded canopy replacement..... Don't know if this would help what you are trying to do..... Bill

***I must add, they used to sand and clear coat the plaster till it was glass smooth before plunging into the plastic. I believe one of them had a little vacuum frame to pull the plastic over it, but the method for the glass on this seems to work a treat. Bill

 

[A4K]

Great results mate! Have to learn vac forming (and casting...) myself.

 

[Wurger]

 

[Airframes]

Looks like it worked out well, nicely done.
Bill, the method you described can work well. However, it all depends on the thickness of the part into which the plaster is poured, as this will determine the size of the plaster mould. The thickness of the material to be moulded has to be allowed for also, and also the amount of shrinkage/stretch whilst mouldiing. Of course, if the original part is thick, then the male mould will be very much under the required size. And if the original part is inaccurate (one of the main reasons for replacement in the first place) then only an inaccurate duplicate will be produced!
Busted, I'd be interested to see which way you made the vacuum equipment, using the vacuum cleaner. bear in mind my mechanical ability these days is limited due to Rheumatoid Arthritis.

 

[A4K]

With Terry - would be very interested to see your vac set up!

 

[aircro]

Great job with kit and vacuforming BW . Did You sanded over ribs on canopy(matrix), can't see on that photos?

 

[Crimea_River]

Good work, and also curious about the vac-form rig. I've seen a few on the net but never had the balls to go build one.

 

[Lucky13]

Glad to see this thread up and running again...

 

[N4521U]

I think I need to make a couple of things a little more clear, then.

This is Not molding Liquid plastic! This is forming pretty much like the method shown with the balsa block.

The only difference is using the INside of the kit canopy for making the plaster shape. The vacuum formed canopies like the Squadron stuff I find a little too thin to work with. But when forming by the block and opening method as shown in this thread it's probably 3x the thickness of the cellophane aftermarket stuff. More or less the thickness of the kit canopy, so building up is not all that critical.

Picture a box thick enough to put the hose of a vacuum cleaner in a hole in the side. The top would be drilled with a bazillion holes, 1mm, 1/16" holes about 15mm, 3/4" apart in a grid pattern maybe 150mm, 6" square. Add a bit to the bottom of the plaster model to make the sides a bit longer for trimming, double stick tap it to the middle of the grid. Heat the plastic for the canopy in the oven till soft, wear bl00dy gloves, drop this over the plaster model and turn on the vacuum. If the model is reall big, usually thru holes, itty bitty ones, are drilled thru it to help the vacuum around the model.

There are commercial vacuum tables available. This is a general description of them. Hope this helps.

 

[Bustedwing]

I farted around with plaster and wax molds for a while and I finally ended up using the glazing that came with the kit. In this case the glazing is a poor fit in that it's a bit to small. The pieces I made as a result only need a bit of sanding around the edge and they fit like a finger in a bum ! I actually used a flash light sans the innards as a shell or case for the vacuum chamber. Then a piece of expanded wire mesh where the lens would normally go. Then I cut a hole in the side of it to attach to the vacuum. I made a wooden frame with a handle to clamp the piece of styrene in and used a kiln I have for copper enameling to heat the plastic. I'll post a pic of the setup later tonight. Works like a hot dam !!

 

[Wayne Little]

 

[Bustedwing]

Here's a picture of the deal I made up, The flashlight body works as the suction device. The wooden frame holds the clear plastic. the small kiln is what I use to heat the plastic. Heat the plastic, hit the vacuum button and lay it down on the flashlight

.

 

[Bustedwing]

The black pipe out of the side of the flashlight is hooked up to a Canadian Tire Shop vac that could suck start a 747 !

 

[A4K]

Cheers mate! Will give that a go myself!

 

[N4521U]

Well ain't that the go!
Now I would call that Innovating!

 

[Airframes]

Good stuff.

 

[Matt308]

The black pipe out of the side of the flashlight is hooked up to a Canadian Tire Shop vac that could suck start a 747 !

I know that chick!

 

[N4521U]

If the Vac is That strong........... why heat the plastic?
The air rushing past it would create enough heat eh?

 

[Crimea_River]

I know that chick!

Got a number?

 

[Matt308]

No.. but I can direct you to the stall. If I recall correctly you could get her number and a dental dam in the same location.