Techniques and tricks: SPECIFIC TECHNIQUES

This section discusses specific aspects of scratchbuilding applied to the slot. In other areas of modeling, the mechanics of the models is a nonexistent problem, but is essential in the slot models.

CHASSIS ADAPTATION

Sometimes we need a new chassis for our car because we did not find a commercial one that fits the dimensions of the body or because the resin kit has no chassis, for example, or simply because we want to make one.
In the latter case, we can start from scratch or adapt a commercial chassis that would have. I personally like the second option because it saves a lot of work, usually gives good results and the cost is low.

We are going to shorten the distance between axles of the chassis to reduce the wheelbase, we want the car also have four-wheel-drive. To do this, we start from a chassis that originally had four-wheel-drive, in this case, the Tecnitoys Hyundai Accent WRC chassis.

We need to shorten almost 10 mm. but maintaining the four-wheel traction. The best part for cutting is beween the motor and the front axle, as it is the least affects the mechanics of the car. Ideally, you do not have to touch the engine pod and rear axle. It will save us many problems. It is also much easier to change the supports of a axle without drive.

When going to paste the two cutted parts is interesting to help us with other pieces of plastic that serve to strengthen and guide to set the axes the same distance on both ends. In this case I used a pair of evergreen plastic strips glued with bicomponent glue. When hit, we must check that the distance between the ends of the axles on both sides is the same.

The engine is very simple to adapt, because being a SCX RX81 just have to cut the front axle lenght and fit the gear assembly between the crown and the pinion. If instead of having four wheel drive by gears, had we chosen a chassis with all-wheel drive by belt (e. g. a Ninco Peugeot 307), would have to find a belt to the appropriate dimensions to the new length of the chassis.

And once we put the plates that connect the braids with the engine already have a chassis with the wheelbase to suit our needs.

In the former case we have shortened the chassis wheelbase, but suppose we need to lengthen the wheelbase. We begin cutting the chassis like in the previous case, where possible allways cutting between the engine and front axle.

Once cut, we would paste the two stringers, one on each side of the chassis to connect the two parts into which we have divided.

We must be very careful that the axes are the same distance at both ends at the same height. To do so, hitting the chassis on a flat surface like glass or a piece of pottery can be of great help.

Finally, for the union to be hard enough, we will strengthen it with bicomponent glue once we are sure all the measures are correct.

Thus, with a little work will have a chassis set to the wheelbase of our model. Maybe to finish the job we must cut the sides of the chassis or front and rear ends, or maybe not needed. In any case, those will be minor modifications.

WHEEL RIMS ADAPTATION

Probably many of you may have a large collection of spare parts for slot cars. In slot racing, wheels and tires are changed by others more adequate or of better quality, engines changed by more powerful ones, cables, braids, more or less straight axles... How many times have we bought a car to compete and we had to change the axles or wheels? or certainly more than once you change the tires to a car because there are better looking another on the market. The result is a small (or large) collection of material that will probably never use it. Well, we can use the tires we have in store for our models in a fairly simple way. With a little patience, we will achieve some tires that fit well with our model, and without spent noney.

I´m making a new wheel rim from six-spoke wheels that mount many car from the Altaya collections (such the Ferrari F40, Ferrari GTO ....), which are these:

The first is to clear the inside of the rim. In this case, with the help of a mini drill and a small cylindrical grinding wheel we remove the central butterfly nut. It should be emptied with care to avoid damaging the inside of the rim and the axle coupling.

Once the interior emptied, we have to tweak the channel of the rim to fit properly the tire chosen. In this concrete case I use tires from Scalextric, called type 9, which assembled the Renault 8, Alpine A310, Seat and Fiat Panda Abarth among others. We measure the dimensions of the original tire channel, in this case 4 mm wide and 15 in diameter, which would be the ring of the rim should be about 12 millimeters, which would correspond with a tire at 15" at 1/1 scale. With patience and care we go making the channel with a square file and grain 180-220 sandpaper. With a little patience, the result looks like this:

Once we have the channel of the rim well defined and finished we put the resin insert who fits the tire model chosen, in this case, the insert corresponds to the tires assembled in the Renault 8 TS.

When we put the inserts, we must be careful with the depth of the rim troath. If we went too far emptying the rim, we can use plastic pieces of different thicknesses to fill the gap until the rim be to our liking, and then glue on them trying to keep centered the resin insert. Once we have finished the tires, if we want to reduce its diameter without deforming much, we can mount ir on a axle, place them in a chassis with the engine fitted and make them turn on over an sandpaper for iron until get the desired diameter. It would the same technique that used to center a bit defective tires. However, in most cases we won´t how much the wheells where center because the slot cars won´t be to roll down the track but if we want to roll, the better they doit right, does no?

The previuos would be the most extreme case, where we have to change virtually all dimensions of the rim, most of the times, with empty the rim and put the insert inside we´ll get the tire we want, and with the advantage of reusing material that already we have purchased.

As you can see, it isn´t difficult to reuse material we have in our drawers, in this case abandoned tires, and get very good results. At the end that´s the essence of scratchbuilding.

WIDENING A BODYSHELL

Within scratcbuilding works, one of the most typical transformation is to widen the body, or more specifically, the wheel arches. The work is very simple but very heavy. I´ll show you the technique normally i used to widen the wheel arches of a slot car, that can be applied to both plastic and resin bodies.

Lets supposed we want to widen with putty the wheel arches of a car a given dimension. The model that I´m going to use for this explanation is a Altaya Porsche 911 SC bodyshell with the paint completely removed:

Over a cardboard mark lines with the width of the car, the new width that we want to obtain, the imaginary longitudinal line that would separate the car into two halves, or any other line or notation that can be a help to us. In principle, markink the current width and the new one would be enought. The cardboard chosen should be one with sufficient thickness to withstand the putty that we will hit without deforming excessively. I usually use cardboard about a 1 milimeter thick.

As I said, the marks on the cardboard are simply to position it well in the wheel arch. This, though it seems obvious, will save us much work when adjusting the width and final shape of the putty. When we have it well positioned, glue the cardboard to the body with instant glue on the inside of the wheel arch.

Once well pasted the cardboard, proceed to stick the putty we want. For these cases I often use the Pattex Repair Express stick, but you can use any putty always taking into account whether their properties following the work that we perform. For example, I can´t think of ever using Tamiya Putty for this job because a piece so large would be very difficult to mold and very fragile at the same time. From all I´ve used, the Pattex Repair Express stick offers the best compromise between hardness and elasticity. For me the ideal one.
We will apply the putty into the approximate shape about the wheel archs. Obviously it isn´t going to be right the first time, probably have to paste more putty to form either the wheel archs but it is important to ensure appropriate forms.

Once the putty thoroughly dry, we pull out the carboard that has been the putty support and cut off the ends to give the body the proper width. The graph paper at this point is almost essential if we want our model symmetrical. Over paper we mark all the lines that could be convenient for us to fit centered the bodyshell and the lines thar would mark the ends of the body. With a sharp cutter cut the excess from the ends of the wheel arches and with sandpaper glued to a wooden block sand the edge to leave it well finished. This part of the work is very bored, because continually we must be sanding and re-positioning the car over graph paper to check the measures, but a good work always takes a good amount of hours.

Depending on the type of cardboard used as a support, the inside of the wheel arches will better or worse finished. The rougher the cardboard the harder the work to leave it well finished. And always something of cardboard will be attached to the body, which we must remove with a gentle sanding. In this case I´m going to use an iron pipe of about 18 mm in diameter wrapped with a sheet of used sandpaper although I have other pipes of different sizes for other cases.

Gently I pass it inside the wheel arch to left ir completely clean. Once clean, we can sharpen the inside of a wheel sticking plastic strips of the appropriate thickness according to:

• We just want to sharpen the inside of a wheel arch. With a thin strip (about 0.3 mm) will be enought.
• We want to change the interior of the wheel archs to get a smooth curve or slightly modify it. The strip pasted in the interior must be thicker who later could be easily sanded at points that would be necessary. This often I do when for example have to make smaller the gap between wheels and body, or if the shape of the wheel arch isn´t correct and there is much gap between the wheel and the top of the pass, for example. Stick on the inside a plastic strip with instant glue and once the glue has dried I give the shape with the metal pipe wrapped in sandpaper. The thickness of the plastic strip will depend on how we want to close the hole. I use strips than 1 millimeter thick.

In the example I show you I´m not going to hit any strip on the inside because it will be partially fairing and it isn´t going to see, so it is not necessary. That if, in this case try to make it the best sanding possible.
In the next picture the two arrows show where should be glued the plastic strips to which it referred:

The final step would be to give shape to the exterior of a wheel arch with sandpaper, file or any tool needed. If we have applied enought putty we only had to sand/file to get the right shape. If at any point we have fallen short on the putty will stick more over the previously applied and we will continue work as usually do.
If we want to outline fully the outside of a wheel arch, we can make a paper template with the shape and then cut it in a plastic sheet the thick that we want, always bearing in mind that the thickness of the sheet must be added to the total width of the car, if we mind that dimension...

Paste the resulting piece carefully in its place, ...

...fill the gap with putty,...

... and we have the wheel arch done, in absence of some pass with sandpaper to finish it off.

If the wheel arch that want to expand has its limits well-defined the work is greatly reduced. For example, we will broaden one where the back is a straight line almost perpendicular to the ground. If we wanted to do it with putty, which can do it, it would take us a lot of work to leave right the straight part and both sides symmetrical. In these cases it is best to glue a strip of evergreen or plasticard to define the edge perfectly. In the example I show, hit a strip of plastic of a an approximate shape to the wheel arch that fit the best over the surface of the body. To ensure the strength of the joint use bicomponent glue:

With the piece secured, stick the putty filling the resulting space.

When the putty is well dryed it only takes to work energetically with lime and sand until we left the wheel arch to our liking:

The trick to define the surface where stick the putty with a plastic strip save us lot of work, material (we spend less filler), allows us to define perfectly the edge, with exactly the right shape and at the same position on both sides of body if we are careful when whe paste the strip.
This trick not only can be used for widening wheel arches, but whenever element od the body we want to make perfectly shaped, such as an air intake or anything else that comes to mind.

PREPARING A RESIN BODYSHELL FOR DECORATION

Prior to working with them, the resin body seemed somewhat mysterious to me and gave me much respect, but once I started using them for my scale models, I realized that it wasn´t that bad. Clearly they need some preliminary work before decorating but not much more than when we worked with a plastic body. If you haven´t decided to decorate a resin because don´t know very well where to start the following lines can guide you.

The quality of the reproductions in resin cover a spectrum ranging from excellent (in quality craft vendors) to "things" that one make at home with more faults than good parts. Within this range we can find everything. In general, the quality of the resins that have passed through my hands has been increasing, partly because manufacturers of resin body have better products and also because cloning techniques are better, but it doesn´t mean that we don´t find models with faults, and is that the molds for resin bodyshells (which are made of silicone) loose quality and definition as they are making copies of a model. If we have the luck that our model is one of the first copies made from the mold will have less work to do on the bodywork.

The steps to leave prepared to decorate a resin body are:

Fit car mechanics. I am in favor of allways manipulating the body before decorating to avoid damaging the paint or something, when we have bare the bodywork there´s no problem to brush the paint, for example. So when to the model I have removed the most obvious failures (mold burrs) I adjust the chassis. Usually I use a commercial chassis that fits well with the width and wheelbase of the body, and whenever possible, I joint it to the body by evergreen lugs stuck to the body using bicomponent glue as seen in the following photos:

Special care will must have with the interior of the model, maybe the engine can now touch with the drivers tray. As always, lime, sand and patience will help to bodywork, drivers tray and chassis fit perfectly.

Adjust the glass and the rest of the body elements. If our model has vacuform acetate crystals is interesting to try to fit them as much as possible before decorating the body. It´s difficult to fit the windows perfectly, but you can always improve the fit by sanding the inside of the body, for example. It´s a nuisance to have the car painted and decorated and see that the front glass doesn´t fit well into its hole as we can spoil the decoration trying to adapt if we aren´t careful. The same applies to accessory elements of the body, such as mirrors and bumpers .. You may also have to open the windows that appear sometimes closed by a thin layer of resin, with a cutter will open the holes carefully and we will review again with fine sandpaper. The task of adjusting the glass is usually heavy but the end result is worth it.

Retouch the body. After the mechanics and glasses, we will do the finishing touches to the bodywork:

• Remove any burrs with a smooth sanding. Carefully go deburring the burrs the mold has left with a fine sandpaper, a 220 grit for wood could be fine, being careful not eat more than necessary. If the body is of very good quality this work is limited to few points.
• Add material where missing. Due to the manufacturing process of the body, there are times when air bubbles are trapped between the mold and resin, which make holes in the bodywork or some parts appear incomplete. Depending on the size and the area containing the hole, we can cover it with a bit of putty (Pattex stick or similar), stick a piece of plasticard/evergreen, or both.
  
• Remove air bubbles. Sometimes small resin bubbles will appear over the surface, especially in vents and fissures of the body, such as those who appears next to the hood latch in the following photo.
  
  With a pin or a thin needle can be safely removed.
  
• Retouch the bottom of the body. The bottom of a resin body are likely to be poorly reproduced by failure to manufacture the bodywork. They may be lack of material, can be bubbles, might not be properly outlined the shape of the body ...., failures that will require that part get retouched. Sometimes with a little putty solves the problem, but if the problem is more serious, we must rebuild the bottom. In the example below the front and rear of the car has some faults and their shape is not correctly defined, so let's fix it.
  First paste a thin strip of evergreen/plasticard with bicomponent glue on the inside. The intention is the strip to support the putty applied later.
  
  Once well glued the strip, apply bicomponent putty. For these cases I often use Nural 41. If were a car used to run on track better use other putty, which is more flexible and impact resistant, even it is worked worse.
  
  Once dry, with sandpaper will give the proper shape to the putty.
• Cover the pores. Rare is the resin body that doesn´t have a pore, but there are some who have many... Here is an example:
  
  To cover them, the best way is dilute a bit of Tamiya Putty with pure acetone and apply the mixture with a brush as if we were painting the area. The mixture will become more dense as the acetone will evaporate. Depending on the depth of the pore, we can apply the mixture more diluted or thicker:
  
  When the cputty is dry we will match the surface with some smooth past with used waterproof sandpaper, for example 220 grit. Finally, after a thorough cleaning with water and dishwasher, a coat of primer will allow us to see faults that had gone unnoticed and as a basis for painting:
  

Thus we will have a resin body ready to decorate. As you can see, the work does not have any complications, .just the bodies of resin has a little more preparation before decorating than a plastic body, but little more.

CREATION OF A COMPLETE INTERIOR FOR A SLOT CAR

The changes or improvements in our slot cars don´t need to be limited to the body or chassis of the car. If weight is not a problem in our model and if we go a step further in the reproduction of the car, provided that the provision of car mechanics allows us, we can make a complete interior and not just a flat drivers tray.
Indeed, to make a complete interior of a car will depend critically on the arrangement of the engine in the chassis. If the model has central transverse or front engine we can fit a complete interior, however if the arrangement of the engine is central longitudinal or "anglewinder" we probably can´t make it due to lack of space.

In this case, I'll do a full background to a ProSlot Porsche 911 GT2. First, the engine layout (central trasnversal) allows me to fit together well and for the other part original drivers tray is horrible:

To make the new cabin we need to know the measures of the body interior where it´s going to be embedded. We will use squared paper or, better still, graph paper to graph the drivers tray that will serve us as a starting point, assuring the correct fit. The advantage of doing it on paper is that is that we can repeat all times we need to get the appropriate template, and if it is graph paper instantly know the right dimensions.

When we have the definitive template we cut the plasticard sheet, in this case 0.75 mm. thick. The sheet may be somewhat thicker or thinner, but the 0.75 mm. sheets have a good compromise between rigidity and lightness.

We already have the piece that defines the interior of our model, we now have to cut from the plastic sheet the other pieces that forms it:

The pieces are glued together making a kind of box:

When we have the box made, we glue it to the tray and see if fits well into the body and doesn´t touch with any mechanical element (cable or motor) and the chassis is well embedded into the bodywork. Having made the findings, glue all the pieces of the interior with a strong glue, I always advise bicomponent glue who once dry will allow us to manipulate the piece without problems.

The dashboard is a very important part of the car if we do a complete interior. As we have space, we can actually enjoy doing one with strips of plastic and putty or copy in resing the dashboard of another scale model, for example. In this case I chose the second option. From a 1/32 scale model car I get the dashboard, I make a mold with clay and filled with poliuretane resin. After drying the resin we have something like this:

Some faults and imperfections but is more than enough for what we want to do.
After adjusting the resin dashboard, we glue it to the interior that we have done, being careful with the adjustment of the crystals and the interior within the body is correct.

Finally, if space permits, we can make a roll cage for our car. With plastic rod glued together and reinforced with bicomponent glue can do whatever we want:

To finish the work, as is enough space, place a seat and a full body driver. The drivers are easily available to get and the seat can be done with evergreen or plasticard sheets, or buy too.

And that´s all. With the interior done what we can decorate to our taste. Never be lacking the steering wheel, shifter, seat belts and a fire extinguisher, but we can always recreate more decorous, for example, with the wiring inside the car made with guitar strings of different thicknesses or anything else that comes to our mind.