Summary of thoughts on foam modelling

25 May 2021

• Sanding is unavoidable in most instances. Protrusions outside the intended outline can be sanded away slowly until it fits exactly. To minimise sanding, cut to the edge where possible to have a vertical cut. 
• Straight lined cuts are the easiest to control using straight edge and it is easier to judge whether the cutter is held vertical even though the cutter is held at an angle to the direction of cut.
• Segmented lines will approximate curve.

As an example, it is easier to make flat discs resembling wheels by dotting the the centre point of the blank and use a straight edge to make straight cuts around the wheel outline. Alternatively, a simple tool can be fabricated to pivot on the centre point.

Sounds a lot of work, it would be best I suppose, if I have a suitable 'wheel-template', such as a coin or washer that is of the diameter desired. I could then use double side tape to fix it to a blank, slice with cutter since the cutter can not cut through the template. And the sanding finish would be easily performed. Once the template is removed, place the disc in a suitable sized circle template and mark out the center. 

18 September 2018

It is good advice to think things through, and writing the thoughts down helps to consider any issue objectively. That is, except when I start to over-think and complicates matter simply because what I thought was logical can be so impractical. Well, that's the way I am. Less think more action might be an improvement but I still like to write about it, isn't this what a personal blog is for? A diary of thoughts. Here's how I am thinking of modelling foam. Nothing on wings, they are quite straightforward.

Fuselage

1. Measure the length of the nose to the extreme tail end of the fuselage. If there is a spinner, exclude it. If the rudder shall form part of the tail end, include that in.
2. Measure the maximum height (depth) of the fuselage. If I will be using sheet foam for fin and rudder, than they shall be ignored.
3. Mark out the measured length and height on a polystyrene foam board that is thicker than half the fuselage width. In this case, the foam fuselage shall comprise of a left handed half and a right handed half.
4. Cut two rectangular blanks. To make them identical, use squares and hotwire cut. Mark the datum line on the left and right blanks.
5. Glue the plan view of the fuselage onto thick cardboard. Cut only one side of the curved planform so that there is one convex edge and the opposing edge is straight and parallel to the centre line and to the full depth of the foam board. Make 2 sets if the foam will be cut free hand using a hotwire bow. If a table hotwire is used, it might be possible to use only one set.
6. Tack/pin the top template/s against the datum line to cut one side of the fuselage. Pay attention that the centerline on the template is positioned between the two sides, the nose is at the squared edge. After one side is cut, the templates are flipped over for the cutting of the other side.
7. Make 1 or 2 sets of side profile template/s. Pay attention that they are placed over the datum line, the nose is at the squared edge. Hotwire cut along the side profile.
8. Cut the slots for wing seat, tail seat on the side profile template/s, cut out these slots on the whole foam assembly. 
9. For decks and turtledecks, cut slit/s on the side profile template/s, cut out these slits on the whole foam assembly. Make the section templates, position them into the slits, hotwire cut and remove the section templates.
10. Cut away cavity in the foam model.
11. Reinforce areas and points, install RC gears etc, glue together, sand external smooth, cover with tissue, paint and apply markings.
12. Attach pre-finished wings and tail pieces.