Radders Posted November 30, 2012 Share Posted November 30, 2012 Hi guys, Been thinking alot lately about vacs since I got started on the Hudson. I'm going to attempted at making my own master, unsure of what aircraft yet, but it's going to be fairly large. I've got the balsa wood sorted with thanks to my dad, but I've got a question. Say i'm making a 1/32nd scale aircraft, do you have to take into account the thickness of the plastic used when vacforming (the final scale), so really I'd make the master slightly smaller? Or is that me being silly. I've no idea what i'm going to do, i'm weighing up my options with regards to engines etc to see what would be best as I wouldn't want to make engines etc! Thanks all, Radleigh. Link to comment Share on other sites More sharing options...
tigger Posted November 30, 2012 Share Posted November 30, 2012 HI Radleigh you are pretty much on the mark but be aware that you will need to reduce the size in all three dimensions due to the thickness. Don't forget I am here and can offer any assistance you may need? I would also recommend that you make it the thickness of the plastic included on the bottom of any part to raise it above the level of the outside of the pulled sheet . I hope that makes sense? Regards John Link to comment Share on other sites More sharing options...
radial Posted November 30, 2012 Share Posted November 30, 2012 Not silly. I reduce my plans by 1-2% to make up for skin thickness. But,make sure you clearly mark your 100% plans and reduced plans. Can be confusing. BTW balsa is a good choice. Link to comment Share on other sites More sharing options...
Radders Posted November 30, 2012 Author Share Posted November 30, 2012 Yeah I think I get that, so it's got to be wider\deeper so that it sticks out of the vacform. When I'm nearer the time John, i'll drop you an email as I was also going to ask about getting it vacformed Link to comment Share on other sites More sharing options...
Radders Posted November 30, 2012 Author Share Posted November 30, 2012 Not silly. I reduce my plans by 1-2% to make up for skin thickness. But,make sure you clearly mark your 100% plans and reduced plans. Can be confusing. BTW balsa is a good choice. Cheers Radial. Link to comment Share on other sites More sharing options...
tigger Posted November 30, 2012 Share Posted November 30, 2012 No problem Radleigh just give me a shout when you need me? Regards John from my ipad Link to comment Share on other sites More sharing options...
Iain Posted December 1, 2012 Share Posted December 1, 2012 Radleigh - i recon you should knock up some nice masters for a Shackleton, or Victor in 1:32 - just sayin! Iain Radders 1 Link to comment Share on other sites More sharing options...
ssculptor Posted December 1, 2012 Share Posted December 1, 2012 Radleigh - i recon you should knock up some nice masters for a Shackleton, or Victor in 1:32 - just sayin! Iain I'd like to have vacs of all three of the V bombers. They were beautiful aircraft. Stephen Link to comment Share on other sites More sharing options...
Radders Posted December 3, 2012 Author Share Posted December 3, 2012 Radleigh - i recon you should knock up some nice masters for a Shackleton, or Victor in 1:32 - just sayin! Iain Lol, Iain I'm starting with a Skyvan, something a little easy to break me in. But i'm looking at certain fighters that haven't been produced in 32nd if I can master my first master. Work is starting on this after xmas, as I'm not down my dads until then. (He has the Balsa wood!) Link to comment Share on other sites More sharing options...
Thomas Lund Posted December 3, 2012 Share Posted December 3, 2012 Did a little thinking and sketching a few years back (not that I finished it, but that may come) with regards to the correction for thickness issue. What I was thinking: If you imagine a fuselage being completely circular then the circumference (spelling) would be pi * diameter and a half fuselage would then be pi * diameter / 2. Since the sheet you vacuform is flat from the start the piece that is drawn around the fuselage would be the diameter from start and then extended to pi*diameter/2, eg 1.57 times longer and thus 1 / 1.57 = 0.64 times thicker. So I thought I'd reduce the cross sections by 0.64 the thickness of the plastic i intend to use. The fuselage is usually not completely circular, but this should be close enough. Maybe I'm over-thinking here - cannot help doing stuff like that :-) Link to comment Share on other sites More sharing options...
wunwinglow Posted December 3, 2012 Share Posted December 3, 2012 You are over-thinking it Thomas! Practical experience shows that the stretching isn't uniform, as the plastic stops thinning as much when it touches the mould, so the worst thinning happens as the last area of plastic finally makes contact with the mould. With a cylinder or hemisphere this is quite even, but the more irregular the shape, the more the extremities thin out, until sometimes the plastic gets so thing it pops through rather than makes the final shape. It also makes a big difference if you are forming over a male master, rather than into a female one. Over a male, the plastic starts to get pushed together as it passes around corners, and you can get ridges forming off the corners. Into a female cavity you don't get this so much, but you do have to vent the moulds so the air is drawn away right into the farthest parts of the cavity. We sometimes use a material called Metapor, (http://www.portec.ch/) which is a porous aluminium-filled resin, but you need to CNC the shapes, and it is horrendously expensive. But you can make pretty much any shape you want, it self-vents so no need to drill holes everywhere, and it will take thousands of moulding operations if needed. Oh, finally, you will need to factor in some shrinkage overall, usually about 1 or 2 %, as the plastic cools from forming to room temp. The only way you can find this out exactly is to do some formings with the machine and material you intend to use. Tim Link to comment Share on other sites More sharing options...
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