Utskjæring av balsa spanter. Hvordan?

[zabbe]

Heisann
Har begynt å bygge meg et nytt fly fra tegning. Denne gangen tenkte jeg at jeg skulle være noe mer nøye under byggingen. Så nå skal jeg spørre om tips når jeg støter på dem, istedet for å bare jukse ivei

Her er problemet. Når det skal lages spor til lister i kroppspantene, så knekker balsaen imellom sporene. Noe vanskelig å forklare kanskje, se tegning...

Hvordan ungår jeg dette?

[Motorboy]

Skjær etter farger jeg har markert i rekkefølgen i farget tall, ikke skjær alt på en gang, skjær flere ganger på samme stedet slik du kommer dypere til bunnen er nådd.

Jens Eirik

[Celtic-Griffin]

I have several tips & comments to offer:

1. As the former is drawn, the grain in the balsa is running the wrong way.

2. The best method is to cut semi-circular formers from laminated balsa - take two balsa sheets, each one half of the thickness of the former and glue them together under press with their grain directions crossing each other. This is best done with ordinary white glue thinned with a little water (about 10%) to make the glue penetrate the balsa better. The result is a balsa laminate which is strong in all directions and will not crack across the grain when cutting.

3. If you are building a scale model or 'scale-like' model, the bits between the former and the fuselage stringers serve no purpose and the former can be cut to the inner radius without the slots. If the former is cut as shown in your sketch, the bits between the stringers only show through the covering material and destroy the smooth finish - check typical full size aeroplanes.

4. It is important to use very sharp cutting blades - a simple tool can be made with two fresh razor blades (the single edge hard back type are best) and cyano them together with a small piece of the stringer material in between. This way you cut slots which are always the correct width for the stringers. Otherwise the best cutting tool is Nr. 10 medical scalpel blades which can be bought in boxes of 100 - these are much sharper and a better format than the usual 'x-acto' hobby knife blades - change them often for best results.

5. If you do use formers with slots as you have sketched, make sure to use a glue on the stringers which can be sanded as easily as the surrounding balsa otherwise you will get the 'starved horse' effect (high points) which will spoil the finish. In this respect, good old balsa cement is still the best (UHU Hart), cyano is not.

Good luck with your project, its good to know that there are still model builders out there...

[zabbe]

Takker for tips.
Når det gjelder "grain-retningen" så er de tegnet opp slik på tegningen. Jeg bygde en glider i fjor vinter med vertikal grain, disse knakk/sprakk når jeg klemte sammen halen og nesa under bygging. For meg virket det derfor fornuftig med horisontal grain.

Det er bare noen spanter som har disse hakkene og de er skjult under balsaplanking. Hakkene har vel ingen annen funksjon enn å passe på plasseringen av listene.

Hmm. det ble litt vanskelig å skrive dette på norsk, siden jeg tenker engelsk når jeg leser engelsk...