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Sanger Vacuum Form Bristol Beaufort


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Vacs can seem intimidating, but it's really just a matter of using a few new techniques that are not really difficult. To begin with, start like you would with any kit: study the plans and instructions to get entirely familiar with them. Make notes (mentally or in writing) about areas you need more info on (research) or any steps you may want to rearrange while building. It's also best to make a firm decision on the exact model you'll build if there are any options as to "types" and/or armament. Also, decide what vac parts you can replace with items from the spares box or aftermarket. This improves model quality, saves work, and saves time.

 

Since you say you're a beginner at vacs, start by gathering the things you'll need particular to building a vac:

1) A few big sheets of 100-320 grit wet/dry sandpaper. I usually get the 3M packs (most any hardware dept. or store) and use the full size sheets. You can use tape (doubled up on the back of the sheet) to stick it down.

2) A smooth flat surface to stick the sandpaper to. I have a 2ftx3ft sheet of glass on my bench top, but any completely smooth, hard surface will work. (tip- when you place the sandpaper on the surface, make sure the closest edge of the paper is along the closest edge of the working surface. This allows you to hold parts easier when working on a single edge of a plastic part)

3) Plenty of new knife blades! #11 blades seem to work best, but use whatever you're comfortable with.

4) Black marker with a medium or fine point

5) Coarse and medium sanding sticks. I get mine at Sally's Beauty Supply as they're larger and cheaper than the "hobby" brands

6) Liquid 5-10min epoxy and/or epoxy putty

7) Contour gauge

8) Brass tubing and wire

 

Before removing any parts, look at them to see if any of them are VERY thin, and/or deformed (vac prop spinners are notorious for this!). Deformed parts can be gently pushed back out using a well rounded (not pointy) paint brush handle. These, and other very thin areas can then be re-enforced using some epoxy putty or glue. If you try to use super glue, do it in small amounts and DO NOT use any accelerator, as that causes heat which may melt or further deform the part.

 

Ok, to start with, lets get the parts off of the backing sheet..

1) Use the black marker to outline each part on the sheet as close to its edges as possible

2) Holding your knife blade at a 45deg (or so) angle, SCORE around (but do not worry about cutting through) each part as close to its edge as possible. Go lightly at first and score multiple times to avoid cutting into a part or any slippage that might make you cut yourself!

3) Bend the plastic backing around each part back and forth until it snaps away, leaving the basic part. It's usually easier to cut sections of the sheet plastic up so you can do this 1-2 parts at a time rather than trying to manipulate and handle all the parts on the sheet while doing this.

4) You can do this as needed for each part, but I usually do them all at once since it's a "chore"

5) SAVE the backing sheet plastic, you may need it later!

 

The next chore: SANDING the parts. Again, you can do this as needed, but doing them all at once gets it out of the way and also allows you to remove the sandpaper and free up work bench space.

1) Always sand mating parts in pairs. This because you have to sand, check their fit with each other, sand some more, check fit again, etc., etc.. Remember, it always easier to sand away more plastic than to fill gaps later!

2) You can wet sand or dry sand depending on whether you prefer sanding dust or "sludge". In general, sand with a circular motion and even pressure throughout your hand holding the part. Regrip the part once in a while to change and even out the pressure points while sanding.

3) Sand each part until the black marker line on each edge disappears. You can go fast at first, but slow down and pay more attention as you get closer to finishing. This is where you should be switching back and forth between the two mating halves of an assembly, checking their fit to each other as you go. When you get the fit you want, STOP (black lines gone or not).

4) Very flat parts like horizontal stabilizers can be held by making tape "handles". Take a LONG piece of tape (7-8in) and put on top of the part while making 3-5 "fingers" of tape stick up as you place it across the top. These loops that stick up will fit between the fingers on your hand, allowing you to hold it and sand it (bit watch your hand pressure and go easy!).

5) Trailing edges of wings and stabs need to be much thinner than they're molded. This is where you use the close edge of the sanding surface. Simply hold the part and you can work the edges of the parts along the edge of the sandpaper, sanding only the area you want.

6) Sometimes it's easier to use a coarse sanding stick or the edge of your knife blade to finish up areas like trailing wing edges where you need more control. A knife blade can scrape away plastic faster than sanding it away. Use whatever tool/method seems best to you.

7) SCISSORS often work better when cutting vac clear parts. Clear parts usually seem to be a tougher plastic that takes more scribing and cutting with a knife, which leads to the possibility of mistakes. Small cuticle scissors usually work very well instead.

 

Here's some more general tips/techniques that you'll need to note as you go along...

1) Do NOT cut out "openings" (for cockpits, wheel wells, doors, etc.) until AFTER the complete part has been removed from the sheet and sanded down.

2) When you do cut those apertures open, only do it roughly. Do not worry about cutting them exactly to shape until you can do so while matching any opening to its mate in any other part.

3) Cut and sand your clear parts to fit the fuselage without worrying too much about any "cut" line on the part. Be sure your fuselage halves are mated (glued or simply taped together) so you can test fit each clear part where it goes.

4) If you need to replace a yellowed vac kit clear part AND you have a vac machine, simply fill it with Plaster of Paris and you can use that as a new master to make a new part.

5) Depending on the thickness and rigidity of the parts, you may need to add interior bulkheads to strengthen a fuselage or other cylindrical part.

6) You'll probably need to make spars for the wings/tail planes. While you can make them from sheet plastic, brass tubing works well too.

7) Almost all vac parts are designed to be "butt" jointed, so you'll probably need to use the brass wire to make locator pins for some parts.

 

and the last major difference is in how you glue up vac parts....

1) You need to buttress seams on fuselage halves, cylindrical, and conical parts because the edges of these parts are too thin to get them to mate up like an injection kit does. You do this by placing interlocking strips of sheet plastic (made form the backing sheet leftovers or any other spare sheet plastic) along the interior undersides of the mating edges. These strips only need to be about 1/4"-3/8" wide, and you can make their length convenient to where they're being used on the model (usually 1-2in. or less). Be aware of things like interior bulkheads or other parts that may come into contact with these strips, as that may cause fit problems. Glue several of the strips on the top and bottom interior edges of the fuselage lengthwise, allowing 1/2 of the WIDTH to stick out past the edge of the part. Do the same for the opposite fuselage half, BUT be sure each of them is "staggered" in position to the strip it's nearest to on the first half. In other words, they should fit between each other when you put the halves together, interlocking with the other fuselage half and interlacing with the other strips (though they do NOT need to be so close as to touch) so that you can hold the halves together without the mating edges slipping up or under each other.

2) You may need to bend a buttress strip into a "U" lengthwise IF the curvature of the parts is great. Otherwise, the straight edge that extends into the opposite parts may not fir well and will also leave a gap under it instead of following the curvature of the part.

3) Superglue and epoxy usually works best on putting vacs together. You can use liquid glue (Tamiya, Testors, Weld-On, Tenax, etc.), but use care as the thin plastic is more prone to damage from them. I do not recommend using tube type cements. Instead, use epoxy putty/glue in those areas.

4) Be wary of using superglue in LARGE amounts (liquid or gel) because it does heat up as it cures!

 

That's most of the general knowledge for building vacs. It'd be a good idea to go to You Tube and look at some videos on building vacs. Seeing those will probably make what I wrote make a lot more sense, as well as expose you to other ideas and techniques to get the job done while also making it easier. They should also ease your apprehensions about building vacs.

 

Hope this helps!

 

GIL :smiley16:

Edited by ghodges
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