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Hot wire patterns from double skinned cardboard

Saves on cost of ply wood - or - metal for patterns and quicker to make

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Mark Kettle 102/09/2014 07:54:40
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2227 forum posts
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Hot wire patterns made from quality double skinned cardboard -from newly delivered cycle bike boxes- with the popularity recently of cycling these are freely available from your local shop just ask.

Draw on your pattern allowing for width of edging with bike bowden cable 1.2 - 2 mm est this is for the hot-wire to work up to, available again free from the bike shop, glued on with super glue with the help of masking tape, pin to foam and hot wire cut, easy and cheaper than ply wood or metal.

If the pattern gets a bit narrow and floppy say for a wing section just support via a spine of 3 mm ply glued on.

To cut the cable I've invested in a bike cable cutter, it squeezes the cable when cutting, you could just quality pliers but may have to neaten up the end with super-glue before use.

cardboard patterns.jpg

bowden cable from bikes.jpg

bike cable cutter and other tools.jpg

cardboard edge.jpg

Finished part below :

finished part.jpg

rear top decking cut from a big chunk of foam.

Edited By Mark Kettle 1 on 02/09/2014 07:57:29

TigerOC02/09/2014 08:52:02
308 forum posts
13 photos

Clever idea Mark. Thanks for your input. Many cardboard boxes and pretty sturdy and could be used the same way.

Rob

Mark Kettle 102/09/2014 09:03:09
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2227 forum posts
1309 photos

Yes your right Rob.

Mark Kettle 102/09/2014 09:07:23
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2227 forum posts
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So made from cardboard and supporting balsa - bowden cable attached to balsa - the fin slot pattern.

fin slot pattern balsa support and cardboard .jpg

fin in slot.jpg

Olly P12/02/2015 15:51:22
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3215 forum posts
181 photos

That's a great idea - far easier than the wood I'm using at the moment, how do you get the ribs to align at each end of the block of foam?

Mark Kettle 112/02/2015 22:10:15
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2227 forum posts
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Olly you can put a pin in the section / pattern you have made and rest this against the work for reference, as in this picture :

44 inch span epp foam avro vulcan section location pin edge of foam.jpg

Happens this is bowden cable is edged light ply section however you could do it on card or cardboard because the super glue harden the card edge, when I have done it Olly with card you can support the thin trailing edge of the section with a spine of wire let in.

44 inch span epp foam avro vulcan wing section like gazelles section b on plan.jpg

The pin here is on the front of the section because the trailing edge was to thin for the pin.

jp mid wing section cut.jpg

This is on the Jet Provost wing.

Been using cardboard patterns to cut models for quite a while now......

top side pattern -sides and engine pod.jpg

Above you see the top pattern which is the general outer shape and not used for any cutting, the middle one is the side pattern for the fuselage from foam 15 mm thick see how ply or balsa supports the thin card in some area's. And these sides are edged with 20 mm top and 10 mm foam the patterns seen below bottom for the top and bottoms. The 3rd bottom pattern ( seen above ) is the side engine pod made from 20mm foam

bottom and inner fuselage.jpg

....and you end up with a Jet

27 oz with the filler on and all gear in .jpg

Olly the pattern you seen at the beginning of the thread the 'bowden edged cardboard' was used the cut the turtle deck and fin slot for this Folland Gnat. Cardboard for patterns has been used for years by engineers especially sheet metal workers when planning there work.

I hope Olly this helps with your planned foam modelling. Kind regards Mark.

Mark Kettle 112/02/2015 22:36:51
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2227 forum posts
1309 photos

Cardboard again. Shame I can't use the bike box brand name for this model - Cannondale would be a great name and decorate the side the same way.

baggu or cannondale plane pattern.jpg

Olly P13/02/2015 07:22:37
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3215 forum posts
181 photos
Hi Mark, I get the attachment to the foam, nice and simple. I have used card for test runs on laser cutters before now. My question is a bitmore general I suppose.

My centre section is a simple constant section so how do I ensure that the ribs line up at each end of the block of foam,I.e. the spars will be aligned and the ends wull be square to the span?

Then I have to do it on a tapered dihedral section, 4 times!
Olly P13/02/2015 07:22:39
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3215 forum posts
181 photos
Hi Mark, I get the attachment to the foam, nice and simple. I have used card for test runs on laser cutters before now. My question is a bitmore general I suppose.

My centre section is a simple constant section so how do I ensure that the ribs line up at each end of the block of foam,I.e. the spars will be aligned and the ends wull be square to the span?

Then I have to do it on a tapered dihedral section, 4 times!
Mark Kettle 113/02/2015 21:18:37
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2227 forum posts
1309 photos

Ok - Olly, see the yellow wing section it has two rectangle holes in with a centre chord line marked on, if a line was marked on the foam by scribing / or pen mark on the the edge of your if your cut pattern in foam of the wing plan (the shape you want) this would help you line up your sections either end of your foam wing blank, and before cutting just 'mark-one eyeball' by check that they are in the same plane / level.

However often the wings sections I cut and fly are done in a simpler way, this is done by having the rear half of the under wing section flat, and have a front raising 'phillips entry' from the mid-bottom of the wing to the leading edge. I'll see if I have a picture to illustrate:

jp angle on wing to help section.jpg

the front of the foam is cut off, then with a bar / wire rod a small triangle is cut off and the resultant of this is stuck back on the wing, the front piece of foam is cut off square in this jig I've made and the same jig holds the metal bar to cut off the small triangle off foam.

making 30 mm square blocks for body.jpg

This method allows me to keep a flat reference from the work bench and knowing the foam is flat and level, the 'phillips entry' shape to the section - brings the simple section I cut into the 21st century, and Olly if you also use the pins on the section to help with line up. I end up with wings that fly well without much trimming needed. Whilst flying the Jet Provost the model raised up on the wave lift and I got to the same height as a JP model with a wing built in balsa.

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