The right tools for the job
Building in twinwall will be a new experience for most modelers. New experiences generally require new skills and new equipment. Fortunately, most of the kit you will need for twinwall should already be in your toolbox. This section is therefore perhaps aimed at those new to the hobby, but it may also be worth a read for seasoned 'balsa bashers' and 'foam fanatics' - you won't be needing that sandpaper or hot wire!
Sharpen that knife
Better yet, buy a new blade.
The most precise type of knife for modelling is generally a surgical scalpel. These are available in most craft shops and can be fitted with a whole host of different shaped blades, the best of which is usually the straight type.
Scalpels are great but if you are having trouble finding one then you might find that a pack of spare 'Stanley' knife blades make very useful cutting tools. In fact, you can get away without fitting them to a handle if you promise to be really careful. Generally, the handles are quite clunky and can get in the way of some of the more fiddly cutting jobs.
These blades tend to be very cheap and can be bought in packs of ten. Remember - if you feel your knife dragging in the material then it's probably time to change/sharpen blades. It's certainly a lot less hassle than slipping and ruining either the component you're working on, or your fingers!
Cutting straight lines and saving your fingers
The ability to draw and cut a straight line is essential to making accurate twinwall models.
I've found that the best cutting guide by far is a 1000mm length of aluminium U-section channel from your local DIY superstore. The U-section measures something like 20mm wide by 10mm tall.
At around £5 GBP it's not the cheapest ruler you'll ever buy, but the fact that you can press down with your fingers safely concealed within the U-section away from the blade will hopefully make it a wise investment.
Save your bench! buy a board
Working with twinwall, especially the translucent colour, we can use the semi-opaque nature of the material to make our lives much easier.
You can now draw designs straight onto your building board and then cut out shapes directly over the designs. We don't need to transfer measurements or use stick on patterns.
Obviously you won't want to be cutting directly onto your workbench, and a typical cutting mat is not big enough to maneuver a twinwall sheet, so a perfect solution can be found in pre cut MDF (Medium Density Fibreboard).
You can buy a sheet 600 x 1200 x 10mm for around £5 GBP and the surface can be drawn on and even cut on without too much damage. Eventually you will wear the sheet out but since each sheet has two sides and plenty of room, by shifting your drafting/cutting area around on it periodically, you should be able to make a single five quid sheet last years!
The right glue
Perhaps the most widely available glue choice for twinwall is common Impact adhesive or contact adhesive. It's the glue that you spread onto both surfaces, wait five minutes then press together.
If you make a mistake, you can often peel apart the two surfaces, remove the glue using 'white spirit' and start again.
A popular brand name in the UK is Evostik - easily recognised by its trademark red and black tube.
Twinwall also sticks very well with a 'hot glue' gun, but it's heavier than the contact adhesive and can be a bit clumsy to work with.
Double sided tape
Double sided tape is also a very useful way to stick two twinwall surfaces. It's got a bit more initial 'grab' than contact adhesive and so is very useful in the construction of fuselages, for example, where you may not be able to apply direct pressure to the join.
However, in my experience, double sided tape does not have as much long term hold as the glue and where I've used it on a trailing edge, the join has crept apart over the space of a few days. Not ideal for trailing edges perhaps but a useful tool nonetheless, especially for very rapid prototyping of new designs.
Self adhesive clear tape
Clear tape is a very good way of finishing your twinwall models. It has many uses from covering the exposed flutes on leading edges - thus improving aerodynamics - to strengthening fuselages.
We've found the best brand to be 3M Pressure Sensitive tape - 25mm width. This has excellent adhesion to the polypropylene, is highly water resistant and does not leave residue when removed from most surfaces.