Hi All,
Im interested in knowing what different ways people have gone about making an bulb plug for making a plaster mold to cast ballast. Especially how to make the plug accurate per a template.
Last time I carved one out of balsa for an RG65. It worked pretty well but isnt perfectly symetrical, nor is it a perfect torpedo NACA profile shape.
Any ideas better than the balsa method? Im sure one of the regulars on here has something useful.
Thanks in advance.
Barbera
You may read here :
http://www.onemetre.net/design/bulbcalc/bulbcalc.htm
and here for one method of construction :
http://www.rcsailing.net/forum1/show…79-Ac100/page2
See Post # 15 and Post # 16
Claudio D has posted the method that uses thin sheets of lead (from roofing contractors) and the bulb is drawn in multiple levels. Cut out the levels, and glue them together to form rough bulb shape, then fill with thick epoxy and shape to final shape, then paint.
While it takes a while to print each bulb template, and then glue up - you don’t have any issues with melting/pouring molten lead with possible “blowbacks” if it hits a plaster mold with moisture.
For a torpedo shaped bulb, they can be turned on a lathe. I have a couple that are delrin, but wood is a good option as well. I would use silicone instead of Plaster as it will hold up much longer and allows more detail to be added to the mold. Silicone is flexible so it will allow some die lock conditions to exist in the mold. Also it will compress so make sure you support the mold when casting.
If you use plaster, let it dry for a couple of months. Really. You will get a better finish(no bubbling) and fewer scars on you hands.
Don