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Old Feb 23, 2002, 12:19 AM
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Edinburgh Turnhouse, Great Britain (UK)
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Super light canopy process

Hi folks
Everyone has been so friendly here I wanted to see if i could contribute something useful. Probably Ill be teaching grandmother to suck eggs but here goes a wee tip from Scotland

This is a technique for making surpisingly strong but incredibly lightweight canopies and other details. Comes from the model boat world where it is normally used to make much thicker things.

Basically you get oasis or other carvable water retaining foam used by flower arrangers and carve it into any desired shape such as a canopy for a heli iether two halves or a nose only type.

Then you varnish the foam a couple of coats then put on mould release wax or just spray with a silicon household polish like "Mr sheen" (do this well away from electronic conectors cost that stuff migrates!) wait till it dries then spray with polyurethane varnish preferably piano grade gloss. spray as many coats as you want it to be thick two is about minimum 3 to 4 about normal. wait till it dries then slip the varnish off the foam mold you now have a very fragile but incredibly light moulding. next spray the inside with letraset fixative and sprinkle with eccospheres
available from http://www.emerson.com/ if you want you can use a peel off rubber maskol on the window areas before letraset spraying. shake out the eccospheres and then lay beads of cyano as ribs wherever you want some strength then springle more eccospheres on to the cyano. dont use to much cyano at a time becuase the occospheres cause it to cure lightening fast and slightly exothermic. lay down two or three layers on any ribs you want a bit stronger. paint as desired with marker ink the eccosphers will have made all but the masked windows white.

It is possible to make a quite large moulding this way that wieghs less than a gram it wont survive a crash too well but you can make several in an afternoon off the mold.
eccospheres are tiny 20 to 200 micron glass balloons and make a phenominally strong but light structure with cyano. You can use a flexible cyano if you want a bit more resiliance but then you can het distortion in the molding in warm weather.

If youve heard this before then sorry to bore you
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Old Feb 23, 2002, 12:31 AM
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Scott,

Cool, Ill have to try that out.

Bill
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Old Feb 23, 2002, 12:57 AM
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Vicksburg, MS
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Yea, for real .... VERY cool idea. Why didn't I think of that

Thanks for sharing
John

PS, got to ask, how did you know about this trick?
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Old Feb 23, 2002, 03:06 AM
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Edinburgh Turnhouse, Great Britain (UK)
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Well saw the original oasis carving idea at the Glasgow model boat club for hull moulds. Then later I was involved in the develupment of ultrasonic transiducers and high power "tweeters" for hi fi and used the idea plus the eccospheres to make cones and domes. Later a friend wanted a way of making lightwight pilot for his indoor scale model Free flight and we tried the method described. a couple of things to add though. it is important to make sure the draft of your mold is free or the urethane wont come off and so it is a good tip to spray the sealing varnish (not the polyurethane you use for making the canoly but the ordinary aircraft varnish) while the mould is hanging draft side down so any drips go with the draft. This is only important if you want to re use the mould as otherwise you can just carve out the oasis from the finished canopy. good mold release or lots of sloppy "mr sheen" is important too.

The oasis flower foam is incredibly easy to carve especially if you use a slightly wet knife. a proper set of wood carving tools allows quite high detail to be done. You can of course also use plastiscene or any modeling clay for a higher detailed mold the oasis is just dead quick to carve and of course is much cheaper.

Hints for copying other moldings

suppose you have moulds from an plasic kit.. Just spray with mold release and then spray with polyurethane varnish release the polyurethane by cutting allong the edges of the plastic model part and it will pop free the urethane will tear sometimes but usually it can be persuaded free. do the eccosphere fill and ribbing procedure as above and you just reduced a 10 gram revell part to a 0.1 or 0.2 gram replica. but with almost all the detail intact!

Suppose you want to make a replica but increase / decrease the scale? You can do this by making a pantograph and lead screw arrangment. you make a pivot for the pantograph which you can make up with any DIY tube contructor set. pivot it between two boards that you set braced on the table. you get two lengths of screwed rod and a 2 to 1 gear set. gear the two lead screws to gether and pass them through nuts in each of the two boards. In this way one turn of the larger gear adbances one board by one unit and the other by 2 units. You mount a dremmel with tool bal cutter roughly the size of 3 units and you mount a felt tip or free inking ball pen on the other. bond oasis to the 2 x board and bond the master molding to the 1 x board. follow the profile of the master with the pen ans the dremmel will merrily chew the oasis (make sure the wife is in Argentina if you do this indoors) as everything will be green for sime weeks!
adter each pass has clearly marked the master with the felt tip pen advance the lead screw ha half turn or so and repeat this moves the oasis twice as far as the model and of course in the opposite direction so you get x y and z mutiplication by two if of course you remembered to set your pantograph to 2 to 1!
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Old Feb 23, 2002, 03:07 AM
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Edinburgh Turnhouse, Great Britain (UK)
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I was going to post a sketch here but cant figure out how
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Old Feb 23, 2002, 03:19 AM
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It seems I can only post images here with a hyperlink so Ill have to upload them to my home page first will do so if anyone is interested. In the meantime the one critical thing not explained above is that the master board and copy board are braced vertically on the table and the master is on the front of one board and the copy on the back of the other with the panograph passing through between the boards with a bell crank shape clamped in a tight horizontal pivot. No doubt though you guys will have used pantograph 3D coppying before.
Im glad the other tip was of use to some anyway especially Johtbyrne who has been so helful to me
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Old Feb 23, 2002, 11:19 AM
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Aubrey;


I am interested ,, Go ahead and post it please.

Bill
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Old Feb 23, 2002, 11:52 AM
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Here is a "sketch" of a vertical pantograph copy system as described above. When setting the ratio dont be confused by the bell crank the ratio is the distance from the pen tip to pivot versus the dremel tip to pivot measured as a straight line. The gear ration must be the same as that distance ratio.


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Old Feb 23, 2002, 04:29 PM
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Now there is something to try when making a pattern for a plug.

Thanks Aubrey


Bill
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