Search the Community

Nearly 4 years ago I started an attempt at scratch building a Short Sperrin (scale 1/72) using CAD modelling, my CNC-machine, 3D printing and Vacuum forming. I got as far as a nearly finished CAD model and a few moulds made in the CNC-machine, but life got in the way, so the project ground to a halt. I recently felt the urge to take it up again but I quickly realised what a big project the Sperrin is regarding the number of moulds required (at least 18), so I decided to pause it again. Instead, I am doing something much smaller and more simple but using the same techniques. I have always had the ambition to model the most important planes of my real world aviation career, so I thought why not start at the beginning. I started to fly gliders when I was 14, and much of my training and my first solo was in a Grob 103 Twin Astir registered SE-TZL. Thus, SE-TZL will be the subject of this build. Here is my plan, process and progress so far: I started off by collecting as many images and references of the Twin Astir as I could. These were used in trying to create accurate drawings/profiles. The profiles were then imported into the 3D modelling program Blender where I created an accurate (hopefully) 3D model of the Twin Astir. Here is a simple render of the 3D model: The 3D model was then chopped up and turned into moulds (still just on the computer) and scaled to 1/72. I decided to create female moulds in order to get the dimensions accurate when vacuum-forming. The 3D moulds are then sent to my kit-CNC machine which will mill the moulds for me. And here it is milling the left-hand side fuselage mould. I have managed to mill the moulds for the stabiliser and the two fuselage halves, so that leaves the wings and canopy moulds to be milled. I will hopefully get that done over the weekend. Here is a picture of the right-hand side fuselage mould and the stabiliser mould. I have also vacuum-formed the right side of the fuselage and the stab. It really is a small model, and I think it is going to be a little tricky to build, especially since this is my first vacuum formed model! This is my very simple homemade vacuum-forming machine: And here is the right-hand side of the fuselage vacuum formed together with the stabiliser:

I recently won this on ebay for the grand total of $11 ..... yup, it's a toy - but I am hoping it will come in useful in my future scratch building efforts. Way back in the 60's, kids all over the USA were getting this treat from Mattel - I don't ever remember seeing this as a kid in the UK..... either we were too safety conscious or I was too busy playing with my Johnny Seven OMA Given the current litigious behavior in the US it's hard to imagine a toy like this ever been sold at all. Here we are encouraging kids to heat up sheets of plastic over an unguarded heater plate, then risk repetitive strain injury by pumping frantically on the vacuum chamber, followed by handling possibly hot plastic while trying to carve out the shapes with sharp scissors and knives. It's a miracle any American children survived the 1960's at all! Anyways..... This is what it looks like out of the box On the right, we have the heater plate, and on the left we have the vacuum plate. Originally I thought the vacuum area was about 4" x 4", (or 100 mm x 100mm Nigel), but it turns out to be around 3¼" square, but I think that will be large enough for my purposes. It also came with all these goodies - a whole bunch forming tools, ranging from race cars to numbers to little boats and even included this highly detailed fast jet !!! How does it work ? There's a hinged two piece handle which swings over both the heater plate and the vacuum plate. First, the handle is swung over the heater section (leaving the second part of the handle back over The vacuum section) The plastic sheets are placed in a recess in the handle (I plugged it in when I got the unit and the heater started warming up immediately, which was good!). There are a few companies still producing sheets which will fit this, so materials are no problem. Then the second part of the handle is swung over and that clicks into place, locking the plastic sheet in position Like so..... and just for scale value - that's a 1/48 Wessex nose sitting on the vacuum plate When the plastic sheet has softened enough, the handle is quickly swung over from the heater side to the vacuum side...... ... and you start pumping frantically on the vacuum handle...... Here is a view of the highly technical vacuum mechanism.... Heater plate on the right, vacuum chamber on the left. You can see the rod connecting the handle to the vacuum - simply a greased section of tube with a rubber washer helping to create the vacuum - if you look at the second photo at the start of this post, you can just make out the single hole through which the vacuum is pulled. Very simple, but effective. I have already ordered an upgrade set which includes a blade valve to help increase the vacuum and some other parts to help improve performance, and from numerous posts I have read, the upgrade kit seems to really improve the Vac-U-Form. These can be had on ebay quite readily - I've seen them go from $5 to $50 depending upon condition and what's in the box. This one is in surprisingly good condition and a complete bargain at $11. Of course, sods law.... right now, I have nothing that I need to vacuform. I shall add some more info and photo's when I get the upgrade kit and get that stuff fitted - and maybe even vacu-form something!