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Scratchbuilding pt. 1: Material Choice

I've been asked many times about the tools, techniques & materials I use in my RC car projects & scale accessories - I've replied where I can but this (and future articles) is intended to be a more definitive and in-depth answer.

Everything I've learned has already been documented in the forums over the last few years (apart from the plastic kits and RC cars I build as a kid in the 1970s and 80s), but I can appreciate it may be a little intimidating if you only came in towards the end & the first thing you see is a truck built from 1500+ bits when all you really want to know is where to start ... (answer - with something simple, like I did - basic toolboxes & so on - one of my early creations was an "instrument case" which was two bits of styrene & a little bit of a weathering effect in the paint).

I will warn you that the first two parts of this series will be mostly theory - but I do plan to write up some worked examples for later instalments.

 

Let's take a look at our options for materials:

Wood - it's not the 1950s any more so this is no longer the default for model making - though it's still popular in boats and planes (Image 01). Obviously there are a huge number of options, but the most obvious ones are balsa and thin plywood. Balsa sands easily, but to get a fine finish where it doesn't appear fibrous anymore takes a lot of sealing and resanding, and I don't really see much of a use for it in RC cars. Plywood on the other hand has distinct possibilities for some details: planking (Image 02) in a pickup bed, or panelling in a garage diorama for example.

 

jr scratch pt1 01 jr scratch pt1 02

 

Brass - available as various rods, tubes, strips and sheets, it would be perfectly possible to construct just about anything you want. In practical terms it's really best kept for parts you want to look scale but would be too vulnerable in styrene, such as mirror supports, roof racks & external ladders (image 03). Other metals - such as the very thin steel biscuit tins are made from can be used in a similar way.

jr scratch pt1 03

PVC Foam Board (e.g. Foamex - and not to be confused with "foamcore", which is styrene or card outer faces & expanded polystyrene foam on the inside). Theoretically this has a lot of advantages: it's cheap considering its thickness, light weight, and it responds well to rapid shaping with power tools and knives - but can also be sanded to leave a decent surface. Not something I've got into (yet), I don't think it'll ever become my #1 choice due to its comparative lack of rigidity & not being able to build up multiple layers of fine detail, however it does have the distinct advantage of the ease with which complex curves can be made - I can quite see me using it for a curvy bonnet (hood) on an otherwise fairly square vehicle.

Card is not something I use a lot of - but it does have its uses. It's the obvious choice for making scale cardboard boxes (fake oil / air filter boxes etc to populate shelving with, and the ability to get the same thin stuff (160 to 200 gsm) through a printer makes it ideal for quickly translating drawings to a 3D mockup. Generally not suitable for RC car bodies (or anything fitted on/in them) due to not being in the least bit waterproof.

jr scratch pt1 04

Styrene (also known as ABS or plasticard) sheet is available in many sizes & thickness, I generally use 0.25mm to 3mm thick in "A4+" and "A3+" sizes. I use 1.5mm and 3mm the most, but I'm trying to move to 1mm and 2mm as some of by scratchbuilt vehicles have turned out a bit on the portly side.

As a material it has some major advantages - the main one being that it's the same stuff Tamiya make their "hard" bodies (and driver figures) from, so you can incorporate sections of Tamiya bodies/accessories and/or modify parts - and easily bond yours and their bits together.

Even if that wasn't the case, it cuts, sands & bonds well, is very receptive to filler, it takes scoring very well, paint bonds well with the correct prep, and it can even be heat formed - for me that means heating & bending sections, but full on vacforming is possible too. There is also a huge range of tubes, rods & sections available.

 

jr scratch pt1 05 jr scratch pt1 06

 

Note: image 05 shows relatively simple scale ammo boxes, each made up of around 20 pieces, painted. Image 06 shows some of the 1,500 parts going into a current project. Ignoring the wheels & driver, all this was once styrene sheet.

HIPS (High Impact Polystyrene) sheet has one matt side & one shiny, but apart from remembering to use it all the same way up & removing the protective plastic film it, doesn't really seem to have any practical differences in use & bonds well to regular styrene. My preference is still to avoid it if possible though, it just doesn't feel the same.

Many "found" parts have been included in my scale model/body work - sewing pins (see image 07), 12g CO2 sparklet canisters, paper clips, 1/48 truck wheels & tyres, small bore rubber pipe, stretch insulation, small fasteners (M2 cap head especially), studding, rubber bands, costume jewellery chains, etc etc (see image 08 for most of that).

jr scratch pt1 07 jr scratch pt1 08


Other materials I've used include Nylon bar (needs machining, and it can be surprisingly difficult to hide the fibrous nature of the stuff when it comes to painting - see image 09), GRP sheet (glass reinforced plastic - most useful for hidden structural parts, e.g battery holders, chassis & extensions), Aluminium sheet, plate & bars (again generally hidden small bit like servo posts, brackets - but also sometime very visible stuff like machined scale beercans - see image 10), and Polycarbonate (lexan) sheet (just windscreens & light lenses for me so far, but the obvious next step is vacuum forming).

jr scratch pt1 09 jr scratch pt1 10

Short version - I mostly use styrene sheet for my projects (and other stuff finds its way in too sometimes) but there are other options :)

 

Before I end this part, I do want to mention bonding - obviously you need something to hold together the parts you've made.

For styrene, traditional "poly" glue still has its uses (for instance positioning very fiddly bits), but has some major drawbacks - the stink, the constant drying up & blocking of nozzles, and the fact it doesn't seem to want to bond premade forms such as tube and rod that well. I'd recommend EMA Plastic Weld (as long as you decant it into a smaller pot - the bottle is top heavy and liable to spill) applied with a brush, or, if/when you find you need larger quantities, Dichloromethane, which can be bought in bulk.

For card, paper, tissue, balsa & most woods I don't think you need to look much further than white PVA glue - though Molak "Dur" will give a tougher joint on balsa. Both types have a long setting time.

For brass, soldering is the easiest way to tackle joining it at home.

Cyanoacrylate (Superglue) has it's uses (especially when bonding two different types of material) but does have problems too - primarily the fact it'll bond skin to itself very effectively and quickly, but also you have to be cautious on fibrous materials as it can heat up alarmingly. The main reason I don't like it is that it works very well up until the point it completely fails - and you're left with two parts and a separate fillet of glue. I really prefer 2-part epoxy glues to CA, despite the fiddly/time consuming preparation and overnight setting times.

 

Next time I'll cover tools.

:)

 ________________________
Written by TB member Jonny Retro

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