Vacu-forming Vexations

I framed up the Judy in “record time” – about three days from sticks to frame.  Since then, time has been dragging on that model.  I’ve been trying to figure out how to color it, how to make the canopy, and how to make the spinner.

I am probably just going to go with green and white tissue for the colors – differences in shading is about the only difference  between the Esaki Green and White and WWII Japanese Green and Gray.  Here is an example of what I mean; just basic green and white:

Full-size Yokosuka D4Y in Japan. (Is that a full-scale motor peg location???)

Before I start covering, I have to figure just what is and isn’t going to be covered in the canopy area.  That means making the canopy.  In the short kit, I will be providing templates for the canopy cross section at the major stations.  I used those to create not one, but three canopy sections.

I did this for two reasons:  I wanted to show the canopy somewhat like the original: 1) it is in sections that slide fore and aft over each other and, 2) it will fit in my vacu-former.

I’ve never been much of a vacu-forming modeler.  To me, it is a lot of work to create a blank, make it presentable, and then pull a canopy.  For me, the process sucks – pun intended.

I was looking around my shop the other day and noted that I have misplaced the canopy for my 24″ Comper Swift (yes, I am modeling a version with a canopy).  That one had caused me much grief because the plug looked good, but when I pulled it, the plastic looked terrible. I tried to fix it, smoothing the plug with CA, with clear paint, and such, only to have those either stick to the plastic and pull away or de-gas and cause bubbling in the plastic.  I had done three or four to get the “good enough” version and now it was missing.  I can’t understand where it might have gone, but others might understand if they saw the terribly messy condition of my workbench.

the now-missing “good enough” canopy

So, now I had four canopies to pull.  What a fun time for me.  And right I was!  It took me the majority of my free time yesterday to get four pieces that are “good enough”, although now “good enough” is a factor better than it was.

I had to pull FIVE Comper canopies before I fixed all my issues.  Firstly, you have to know that I tried to simplify my process about a year ago.  I had been using one of Chris Boehm’s vacu-formers and that worked satisfactorily, except that I had to set up a vacuum, tape the box to my counter next to my stove and heat the plastic over a gas range – all a little bit work-intensive and fiddly.  So I decided to buy a Chinese dental vacu-former after reading some mailgroup comments about one by Dave Gee (of Black Sheep Squadron and AMA Model Aviation fame).  For about $80+, I got a compact all-in-one setup that has about a 4.5″ square working area – Simple.

Except…the vacuum will pull your teeth out (again – pun intended).  The heater works well, and the mechanism works well and it will pull that plastic (when heated sufficiently) right down so tightly that a) it is hard to get the plastic off the plug and b) the plastic shows every dimple and open grain and whatever defect and c) the combo of the hot plastic and the tight pull adheres to anything on the surface – balsa dust, or filling material, or whatever.

they look good, right?

So my pulls yesterday were failures.  I spent much of the day finely sanding and filling the Comper plug again and again.  I started trying release agents, but I was fearful of the gassing I had experienced before.  I went with a light oil on the surface (fail); I went with candle wax on the surface (fail).  I finally decided to use the obvious – the Dow 33 industrial grease I use for rubber lube.  I put it on rather generously and pulled – and discovered that I left too much grease on.  I wiped the plug down, leaving it slippery but not overly greasy – SUCCESS!

the set from the above photo in the front and the rear set is the good set.  Notice the grain pattern and all the dust in the front set – bad, bad, bad.

So, now I am on my way again.  Now I am venturing into another area – canopy frames.  I am using something new to me:  Transfer Tape.  This is a ultra-thin double-sided tape; about 0.002″ thick.  I stick one side on the back of tissue, and then use a sharp x-acto blade to cut narrow strips, peel the back off the tape and stick it to the canopy.  I know Paul Boyanowski has used this stuff and I know Winn Moore has and I asked Winn what I needed.  I am using 3M ATG 924 tape.  Here’s how that is proceeding.

starting to look good!

Did you know that some AMA/NFFS/Duration-type Free Flighters says that us FAC-Scale modelers are nuts?  They might have a point – scale details take time (and might cause mental-stability issues!)

P.S. No, I will not be providing canopies for the Judy!

 

969 total views, 9 views today

This entry was posted in Builds, Products. Bookmark the permalink.

4 Responses to Vacu-forming Vexations

  1. Richard Ranney says:

    And I thought it was difficult heating the plastic in the oven, and using my household vacuum cleaner setup. Actually it is kind of difficult. And there is that anticipation of a perfect canopy when having only one piece of plastic to pull down. The answer… is that my standards were not very high.

    I enjoyed your story, and I hope that you get this all figured out… that your efforts and business are successful.

  2. Simon Blake says:

    I enjoyed the story too. However, it seems like a lot of work. I haven’t made a canopy in years because I haven’t built a scale model in years. But when I did, I just carved the plug with an extra eighth inch or so depth on the bottom, traced around the bottom of the plug on a piece of 1/8 or so plywood and cut it out so the plywood was a loose fit over the plug. Then I heated the oven, put the plug on a sheet of wood in the oven, laid a sheet of clear plastic over the plug and when it started to droop I forced the pattern I had cut out down over the plug so it pulled the plastic down. I remember making the canopy for my Keith Rider Suzy this way and it turned out quite well. I hope to get back to building scale models soon, after I have all my power models fixed up for the Nats, and I will try this again on the Elemdorf Special kit I bought from you at last year’s Nats.

  3. Lane Cobb says:

    George, I have never tried molding a canopy but when I do, I will:

    1) Click on your How-To Links
    2) Click on the 850 Free Flight Ideas PFFT link
    3) Scroll down to Canopy Molding Simplified

    Let us know how that works!

    PS – Thanks for your site and for that link in particular. There is a mind blowing amount of ideas contained there-in.

  4. Mark Fineman says:

    George: Hope I’m not bragging, but I’m pretty good at vac-forming model parts, including canopies. I have several vac formers, including a big one that was written up in Model Builder magazine years ago. They’re all just boxes with a perforated surface and an attachment point for a vacuum cleaner. Here are some tips, in no particular order:
    1. Finish the plug with vinyl spackling compound. Sand it smooth with successively finer grits of sandpaper. Don’t dope it, epoxy it or use any other finish. The smooth, spackled surface will pull smoothly from the canopy.

    2. Raise the plug with scrap balsa so that the plastic can “drape” around the base of the plug. Use CyA to glue the scraps to the bottom of the plug.

    3. Sometimes the base of the plastic piece may not adhere to the lower part of the plug. Leave the plug in the vac-former, still drawing a vacuum, and go around the base with an electric hair dryer (set on high) or electric heat gun (set on low), coaxing the plastic against the plug with a pointed or rounded dowel.

    4. If you’re using a vacuum cleaner as part of your set-up, make sure it has a new bag, or at least has been emptied. You want the strongest vacuum you can get.

Leave a Reply

Your email address will not be published. Required fields are marked *