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Mike

Building Vacformed Models

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John Adams of Aeroclub fame has graciously posted his tutorial on how to build vacform models on this forum before, but unfortunately during our various moves the thread seems to have got lost in the sands of time. I managed to find a copy the other day, so am pleased to re-post it, along with my personal thanks to John for this, as it probably saved me from disaster when I decided to do my first vacformed model back when I hadn't even completed an ordinary injection moulded kit yet! Anyway - here it is. I've added a bit about Zip Kicker from my experiences, but other than a few typos and some reformatting, it's almost untouched :)

VACFORM MODELLING, a new approach?

by John W.Adams


Models featuring the vacuum formed method of construction have been around for a long time. However, many people who consider themselves to be competent modellers, will still not attempt this form of construction. Also I speak with an equal number of modellers who have had a go at vacuum forms and made (what appears to them) to be irredeemable mistakes and given up in disgust. Why? Do they lack confidence, patience or skill? Perhaps the answer lies in the traditional techniques.

These vary slightly on the theme, "cut out and sand down parts using an abrasive covered board either wet or dry". Some advise modellers to leave a rim of waste plastic around the part. The theory here being that when this rim wears down to a thin membrane and breaks off, the correct thickness has been achieved. In fact, if the average wall thickness is 1mm and a rim of 2mm has to be sanded away, that to me spells 3 times the effort.

Let us look at the problems.

1. Vacforms are difficult to cut out
2. I can't see how far to sand down
3. My fuselages end up like bananas
4. Parts are difficult to hold whilst sanding down

And some common mistakes.

5. My trailing edges end up too thick and the wing appears flat
6. I make a mess of cutting out cockpits and wheel wells
7. I have taken too much plastic off


Now let us look at some answers.

Start off with the right tool for the job, a good knife with a replaceable blade is essential. I always use a straight edged blade such as a Swann Morton 10A pointed blade with a No3 handle. (The No 11 blade can be too fragile). This type of blade is good for most jobs, but knives such as Edding and Stanley are best for heavier work. Olfa and Scribe 'N' Cut, make tools whose primary purpose is scribing panel lines but can be used to score through very thick material. I use blades with a curved edge, only for scraping.

Hold the scalpel comfortably like a pen and angled away (about 45 deg) from the piece to be removed. Score all around the part using reasonable pressure.

1. The first myth to dispel, is that vacforms are not cut out by brute force, but merely scored around with a sharp blade. Once the surface of most sheet material has been broken by a cut or score and that sheet is then stressed by bending so as to open the cut, the sheet will invariably break along the cut, no matter how wiggly the score line. Always take some cuts out to the edge of the sheet and start the break-out there. Practice on a piece of waste plastic.

2. Before scoring out the parts we must have a marker to show how much plastic will require removing by scraping or sanding (abrading) so the parts will fit together. We can use a fine (0.1) pointed marker pen, preferably permanent ink. A soft sharp B pencil will suffice. I find the best results are with a Rotring .25 (or similar make) drawing pen ideally filled with the type of ink specified for use on plastic drafting film (I use both Red and Black ink for contrast). Simply draw around each part where the part meets the backing sheet. This ink line shows us where we score and where we need to remove plastic. Be accurate. The ink line is King.

The part when broken out is then sanded down to the pen line (more anon).

3. Fuselages end up like bananas, because, when using the traditional techniques any pressure on the centre of the fuselage will cause the part to bow, and as this is usually at the widest/deepest part, the wall plastic will be thinner. The waste plastic at the ends of a tapered fuselage, drop tank or nacelle or wing tip (where a mould cavity narrows) will be thicker. Consequently the centre edges of the part abrades away more quickly than the ends. Also slight 'moulded in' stresses can cause a part to bow when released from the constraints of the backing sheet.

Obey the ink line and the parts will straighten and fit, when taped together.

Paragraph 4. should provide a solution.

4. When using the traditional abrasive paper covered board the following formula applies. ‘Finger ends tend to disappear at the same rate as the plastic’, or when the water turns red, that's far enough! Also parts are slippery and tend not to want to move against the drag of the abrasive. There is nothing to grip, on such as tailplane halves or wheel halves.

We need some form of adhesive tape which is resistant to shear (drag) loads, and tacky enough to grip on a curved surface, and yet peel off easily when required. Also something to hold the part in comfort.

A method often employed to hold parts whilst sanding is to use some ordinary kind of sticky tape, either made into a loop or of the double sided variety, often using a piece of wood as a handle.

These tapes are not made for the job and are either too strong or too weak. The part keeps falling off or will not come off easily. BluTak is equally uncooperative when used for this purpose.

The answer is Sticky-pads and Tee-Al. (If this just sounds like a blatant advertisement, the simple truth is - they work)! Sticky-pads measure 12mm x 25mm and have a fabric base coated with a high-tack but highly peelable adhesive which is very resistant to side loads. Tee-Al is simply handy lengths of Tee section aluminium extrusion used as handles, other materials can of course be used.

When these two items are combined, handling of vacform parts becomes very easy. A suitable piece of Tee-Al has one or more Sticky-pads removed from the backing strip and positioned on the top face of the 'Tee' and then the protective wax paper is removed from the pad. The vacform part to be worked on is simply pressed into place and abrading or scraping can begin.

Even small curved or rounded parts can be secured by this method. In trials I have easily held and sanded down the mating surfaces of small difficult to hold parts such as drop tank and wheel halves. Highly curved parts like propeller spinners can be held by drilling a hole (in a piece of wood) and cover it with a Sticky- Pad, cut radial slits in the Pad and push in the spinner. A pair of wheel halves took a mere 3 minutes including cutting out.

Sanding down the parts.

For sanding (abrading) the parts I prefer to make my own handy sanders by affixing abrasive paper of the required grit (80!) to a piece of Tee-Al (or wood, even tube) with ordinary double sided tape (I recommend the new Sellotape range). Thus a whole range of sanding tools can be created for little cost.

Alternatively you can use a Sandvik Handy Sander fitted with a medium Sandplate. Sandplates are rectangular metal self adesive plates (110x60 mm) with a pin point textured surface fitted to an orange plastic, comfortable handle. It is an excellent tool and widely available. Sandvik also produce a smaller tapered Hobby sander which has its uses. Sandvik also make a larger type but beware as I have found the moulded plastic handles may have a slight curve, and so the plate is not truly flat, however the self-adhesive plate (220x60mm) suitably mounted can be very useful (I have one on the bench top). I sometimes use a 10 inch single cut File (Farmers friend) of the type sold for sharpening lawn mowers (the handle is forged on the blade).

Leading and trailing edges can be reduced most effectively by scraping, using a heavy duty craft knife blade (Stanley knife). This is held almost at right angles to the surface and scraped to and fro along the wings inner surface. Use the curved type for single surface biplane wings. If you want to use two hands, then Tee-Al can be easily held in a small vice. Scraping is by far the best method and is a very fast way of removing material. You can scratch build wings this way.

When a Polyhedral wing (cranked or gull) is encountered, just treat the wing in separate stages.

There are other advantages to using this system. Work can be carried out at a convenient eye level thus enabling closer monitoring of the plastic removal. Parts such as wings are kept flat. You can work over a sink wet or dry so the dust can be washed away. Dust is the enemy of the tacky surface. Once adhered to a dry surface, Sticky-Pads will remain in place even under water. If water gets between the pad and the part, adhesion will cease, but can be reactivated by drying.

Trailing edges must be treated separately to the leading edges, which is the answer to problem no 5 (flat wings). If you draw a chord line through a section of vacform wing (representing the flat abrasive board) it should be noticed that the leading edge meets this line at a much steeper angle, presenting a smaller area to the abrasive than the trailing edge. This means that more plastic will have to be removed from the latter. So if the old abrasive board method of sanding is employed, it's all too easy to take off too much of the leading edge whilst concentrating on the trailing edge, if both edges are in contact with the board at the same time.

Let us now take a look at cutting out waste areas such as wheel bays cockpits or windows.

As a general rule I do not remove waste areas until I have most of the mating surfaces sanded down, unless they project in some manner as to be a nuisance to progress. Whilst still in place, waste areas help with maintaining rigidity.

With a cockpit, or nose wheel, or gun position cut-out such as on the conventional fuselage split line, it is best to line up the two halves and secure them with a little tape. When you are satisfied that all is correct, score around the matching waste areas to be removed.

Now separate the taped halves and where the score lines reach the edge of the part, make a positive nick with the knife.

Now support the fuselage at the nick with the finger and thumb or a small pair of pliers, and then start to shear the waste with the other thumb nail or a second pair of pliers. When the waste part is beginning to move, change to the other side of waste bit and start off the shear there. Within seconds the tear should follow round the score line and the waste part should break cleanly out. When pressure is first applied some distortion may be apparent but you will notice it springs out.

For rectangular areas in thicker material, make two cuts with a fine razor saw, the ends of which are joined with a score line and then cracked out.

When an aperture needs to be made in in a fuselage side or a wing surface we apply a slightly different technique.

Score around the area accurately and carefully. It does not matter if the shape is rounded or square, but if the shape of the required cut-out is complex (for instance a Spitfire wheel bay) divide into separate areas, i.e. a circle and a rectangle. Now score diagonal lines across the waste areas within the scored outline and at the intersection of these lines make a hole by forcing in the scalpel tip or if the plastic is too thick make a hole with a small drill. Using the scalpel tip, start to apply a cutting pressure along each diagonal in turn. It will be noticed that the little tri-angular pieces are starting to curl inwards shearing along the scored lines. Now, take a blunt instrument like a small screwdriver, simply push in the triangles one by one. They should drop out like petals, with moderate force. A pair of needle nosed pliers may be helpful in removing the waste and it actually takes less time than reading this paragraph. For very thick plastic, use a fretsaw / piercing saw.

If you do not possess either of these useful saws, or a razor saw, you should!

Glues
For vacuum forms use the thin liquid solvent glues. These are often Methyl Ethyl Ketone based. The correct method of use is to hold the parts together and apply the glue to the joint with a brush or Touch 'N' Flow solvent applicator. Capillary action will take the glue through the joint while light pressure is applied. I do not recommend solvent glues for laminating plastic sheet (use slow set Cyano).

Always work in a well ventilated room when using any solvent based glue and keep the glue covered when not in use.

The wide family of Cyanoacrylate or more commonly called 'super-glues' are best used when small or dissimilar materials are to be joined, or reinforcements or instant results are required. If cyanos are used on canopies a white 'blooming' of the transparency may occur. This is caused by the 'gassing' cyanoacrylate reacting on contact with the hygroscopic plastic surfaces, and being clear you can see it. Do not remove the top of your cyano bottle and dispense glue straight from the bottle, the tingle in your eyes is the same effect as on your canopy!

Buy a small glass mirror or culture dish lid and dispense a drop of glue at a time, dip a pin or a cocktail stick into this to apply the glue. For a measured drop try breaking off the tip of the eye of a small needle so as to produce a fork (be careful of your own eyes when doing this). You will need to clean out the fork with the tip of a blade occasionally. An excellent way of dispensing along “run” of cyano is to use an old fashioned draftsman's bow pen, just load with cyano instead of ink. No it won't work with a Rotring type pen.

There are a number of accelerators (often called "kickers") on the market which speed up the setting rate of cyanoacrylate glues. These can contain 1.1.1. Trichloroethane, so treat with caution. They can also cause the plastic of your model to become brittle and craze, or even crack if put under any pressure, so use sparingly.

Ordinary Bicarbonate of Soda has a similar effect, and can be used for building up areas quickly. I will expand on this later.


Transparencies

These seem to give more than their fair share of problems. I seldom put a knife anywhere near a canopy, instead preferring a small very sharp pair of scissors. Buy high quality. Next, can you see what you are doing. I find that working against a mono coloured background a help. You will find the background required varies according to the light. If the frame lines are indistinct, then cut strips of masking tape and use them to define the no - go areas. Work carefully, trim the waste off a little at a time, Flex-I-files are good for sanding the edges, but remember to remove the dust and most importantly do test the fit of the canopy to the fuselage frequently.

When you are finally satisfied with the fit, hold the canopy in place. Now run a brush full of liquid glue around the edge, then apply slight pressure. Repeat with the glue and hold for a minute. If you allow the glue to dry you will find that the canopy is nicely bedded in. It can be easily removed for painting and may be finally affixed using Krystal Klear. P.V.A. base glues such as Kystal Klear are the best for affixing transparencies. Apply with a small brush or cocktail stick. Any excess can be cleaned off with a damp cloth. P.V.A. can also be thinned with water.

If there is no moulded rim on which to seat the canopy then glue strips of thin plastic card to form a rim around the inside of the cabin opening. Should you then find that the fuselage plastic is of thicker gauge material than the canopy, then simply build up or pad out the rim with narrower strips, until the canopy is flush with the fuselage surface.

This is fiddly but not difficult, but remember if you have over sanded the fuselage, your canopy will not fit!


Battle Damage Repairs
Or, "I've taken off too much plastic". It's not the end of the model, we can repair most mistakes. Most initial problems are caused by failing to mark or score out accurately. So if for instance an inconsistent score line has caused a piece to stay with the backing sheet when breaking out, simply retrieve it and glue into place using super-glue, then sand down as normal. If it's a large tear/spilt then you might want to reinforce with a piece of plastic card.

All repairs are best carried out using super-glue (CA, Cyano, Cyanoacrylate), because you get instant strong joints, which sand well.

A more common mistake is, over sanding of parts - especially on fuselage halves. Usually this is caused by not obeying the ink line or by being over enthusiastic when sanding down and not checking often enough. If one fuselage side has had too much removed from the middle (banana) then the answer is to assemble the parts together with tape and assess how much is missing. Once this is ascertained, glue some suitable strips (taper if required) into the gap, gluing only to the wounded side. Gap filling cyano can be used but if this is not at hand, use super-glue and bi-carbonate of soda (baking powder) to bridge the gaps. You just apply super glue and then a pinch of bi-carb, this soaks in the glue and instantly sets hard, Repeat the process until the wound is filled. Then restore the contours using a tool such as Flex-I-File or Flex-I-Pad.

The result will be a strong hard repair much quicker than using two part or tube fillers.

If the case is a trailing edge with a large piece missing, then the best approach is to cut out the area and square it up, then glue into place a piece of suitable size plastic strip, use super-glue and/or baking powder again and file to shape.

When damage occurs to a corner of a wing tip, prop blade or something like the end of a tip tank or radome, simply apply super-glue and then dip in a small pile of bicarb, this will harden immediately. Repeat the process until a suitable sized blob has formed and then file back to shape. If you have to use those vacform props then this is the solution for filling the blades.

When joining fuselage halves it is usual to strengthen the joint with strips or tabs of plastic card glued into one half so as to form a rim on to which the other fuselage half fits. A better fit will be achieved on very curvaceous fuselages if these tabs are placed at intervals and stick outwards, 10 thou card is best. It is a tedious job cutting a number of these tabs, so I use an office paper punch to produce a load of little plastic discs which will contour nicely around the inside of a fuselage half, even if the half fuselage does look temporarily like a Viking ship.

Perhaps here a word of caution about choosing your subject. Vacuum form kits vary in quality. If you have never before attempted a vacuum-formed kit please don't be tempted to go out and buy that 15 year old Scruggs Four Engined Wonderplane kit. Instead try a few simple exercises, get some plastic card and make a new tailplane for that damaged Mustang, or practice making holes in a piece of plastic card. There are lots of cheap vacuum formed kits around often from Eastern Europe, and they can be picked up at model shows. Examine the kit and if it's crisp and cleanly moulded it will probably fit together well, If it looks blobby and ill defined, don't buy it.

If some items like spinners or wing roots are thin and crushed then reinforce with Milliput or bicarb but never use tube type fillers (most tube type fillers are only good for shallow surface blemishes as they usually work by solvent evaporation).

Milliput if properly mixed and placed on a storage heater or hot domestic radiator (below 70deg) will harden very quickly and not affect the kit plastic. (Here’s a tip, mix and heat the Milliput before applying it - it will harden just as fast, but use it quickly. It is advisable to wash your hands immediately the putty is mixed and again after the application is completed.

The following useful tip came via one of my customers.
To fill well-fitting joints such as leading edges and fuselage centre lines scratches or panel lines, use Tippex Correction fluid, Note it must be the bottle which incorporates a Red oval 'Perfect' design in the label and not the one with a Green oval. The environmentally friendly one may do wonders for typists but it's no good for modelling. Tippex bonds very well, dries quickly and sands beautifully.

White metal
Most recent vacuum formed kits contain detail parts cast in white metal, or suitable parts can be purchased to improve older kits. The best adhesive is cyanoacrylate. White metals usually contain a proportion of lead, (Those called Pewter should not) so don't eat when working with it and do wash your hands.

Blow holes or any deficiency in the castings are best repaired with the super glue and bicarb combination. Milliput or Plastic Padding car body fillers also adhere well to white metal.

If a hole in a propeller or engine is too big then bush it with a piece of plastic or metal tube. Household pins make good strong prop shafts.

However the occasion often arises when there are no under carriage legs available for that old large kit. The solution is Aluminium or Brass tube. This can be bought in a variety of concentric sizes with which you can fabricate oleo legs. If you cannot find it in your local plastic kit store, then make a visit to a Model Railway shop or one specialising in flying models. You will be amazed what goodies you will find. It does puzzle me still just how parochial many 'plastic kit bashers' are!

Tube can be easily cut with a fine saw or even with a heavy duty craft knife by rolling the tube back and forth with the blade as you apply pressure. Plastic card fillets or fairings can be stuck on to the metal with super glue or 5 minute Epoxy, then filed to shape. Brass has the advantage of being soldered for greater strength (exit plastic modeller-stage left).

Axles can be glued to the end of the tube, or drilled right though to accept a piece of wire (a section of sewing pin) which can be sleeved up with metal or plastic tube to scale size.

If you are boxing in a wheel bay, make the top from thick plastic card or if it is a kit vacuum formed item, strengthen it so that it can be drilled to take the under-carriage leg.

Metal tube can be utilised for wing spars, and when threaded through a fuselage it can be bent either side to set the dihedral angle.

Jigs
The assembly of any type of kits can be facilitated by making jigs. A jig can be as simple as a piece of plasticine, or an elaborate affair constructed from plastic card. With only a little imagination, a few pins, cocktail sticks, plasticine, right-angled triangles cut from card and a square of card with lines drawn on to it, for a base even the most complex biplane can be set up for accurate final assembly. There is now my purpose built metal Biplane Jig only available from me.

Vacuum formed models do require some hand and eye skills but remember these can only be discovered or improved upon if you are prepared to have a go, the hardest part is picking up the scalpel and making that first cut (sorry, score). If this article fires some of you to stretch your horizons or provides a solution to a particular problem then it has achieved its aim. If on the other hand you are going to sit back and wait for the Big Injection Company to produce that Scruggs Wonder plane, I have it on good authority they never will. So you might just use your time while saving up for the resin from Blob-o-Kit (who probably nicked it from the vacuum form anyway), to have a go, and find as my youngest daughter used to say the World can be your Lobster!

Copyright . John W. Adams.

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Good clear points on this. I have a couple of vac form planes. My first and only one built so far is a 1/72 A-12, but have a 1/72 Vanguard and C-133. I made the A-12 just for practice, of course much smaller, but you still get a bit of the feel for vac models.Need to make some more space in my "skunk works" before starting those big ones.

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Good read.

 

 

Been a while ...

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Something I found out purely by chance that maybe of use,I have recently been attempting a vac 1/72 DH Comet airliner,its really rough and although the manufacturer states it is pre cut,it still need a ton of sanding,Well I get the fuselage pretty close but I am having trouble keeping the sides aligned when I am checking the sanding.(I have worked out the outside diameter of the Comet in 1/72 ,so I have used a compass cutter to cut a hole in plastic card and this is my guide).I need something ridged to put in side the fuse to support it whilst I am checking.Off to B&Q to see what tubing they have,nothing doing in the rather odd size I want,but then I come across water pipe insulation.its just about the the right size ,a little bit big but thats good.Less than a pound for about 5ft.Result.

I slice a section out of it and trim  around the wing cut out and put the fuselage halves together and I get a ridged supported fuselage.This stuff is easy to cut and when I was sanding the wing cut out area,it sands as well.

Obviously it may not work for everything but its worth checking out.

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Thanks for finding this and reposting Mike

 

Bruce

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I'm just glad it's still proving useful to folks, and it's a tribute to John's experience that it is :)

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