Now, try and figure out the quantity (by weight) of resin you will need by calculating the volume of the box, subtracting the volume of packing blocks, then subtracting the volume of propeller, mandrel, plasticine & the whole lot… quite messy, isn’t it? Anyway, try and come up with some kind of reasonable figure, then multiply by your favorite K factor (bigger than 1) and start mixing up.
Once you are REALLY convinced
is looking right, that the release agent has been applied properly,
you have mixed enough resin, and that one day, you WILL positively have
your propeller back, then you can start pouring:
Pour just enough resin as to obtain this nice "bulge" over
the edge of the box.
Of course you’ll need to set the mold exactly level, otherwise resin will spill all over the place.
What? After all your calculations you ended up
a lot of resin left in the can?
Don’t worry: this always happens to me too! Next time decrease that K factor.
|Now it is quite possible that you really
so, set the mold aside for a couple of days, depending on the type of
resin you used, and forget everything about it. More than anything
don’t spend all your time wondering if you’ll ever see your precious
When the resin is properly set, the top of the mold –that nice bulge- can be finished flat by filing, grinding, planing, or whatever you like: I use a Stanley Surform rasp for this job. Remember that this will be the side the mold will lay on while you’ll be laminating the propellers, and this also will be one of the sides that will take the big squeeze once you close the mold; so it’d better be nice and flat.
Finally, unscrew the base plate from the box and remove the packing from the mandrel, then a light tap should be enough to separate the half mold from the plate….
and you will be staring at this mess:
If you like chinese food, choose a restaurant
still gives you bamboo sticks, and not ugly plastic ones.
Ask then for a fork and a knife and pocket some sets of sticks.
||Use those sticks with
shaped points, to remove all the plasticine from the cavity of the
use only wooden tools so as not to damage the propeller.
Don’t worry: all this will come out one day!
Take your time, and work with patience, DO NOT
any reason, move the propeller from its place: if this happens you’ll
to restart again from the beginning.
The propeller is held there (strangely enough) only by the release agent,
so avoid using solvents to remove the plasticine and go gently with those chinese sticks.
Cotton buds will also help in the final cleanup, until you obtain this result:
When you are satisfied of this first
of the mold, and you're quite sure that the propeller is stil solidly
inside the cavity, apply again your release agent, one or two coats.
Caution: the bottom spacer does NOT need the release agent: you will instead degrease it properly,
and slide it back onto the stem of the spindle, just before pouring the resin.
The top box can now be securely screwed
onto the female mold, after a coat of release agent on the mating
only. You didn't forget to predrill the holes and mark the position,
Here again, if you wish to save resin,
you can add some blocks
of scrap wood inside the box
Just in case, it is better to seal the
outside of the mating surfaces with plasticine or/and a layer of
|By now you might get the feeling
this will probably end up a nice piece of work, therefore you will not
feel happy if you have to bash it with a hammer in order to take it
This is why, at this point, I place some simple extractors on the inside of the male mold.
||Extractors are made
8mm i.d. threaded bushes of the type used in making furniture, holding
a flat point grub screw just long enough to protrude past the edge of
Do not use conical pointed grub screws, they will damage the male half of the mold; grind them nice and flat.
The bushing is held in place with cyano, while the screw must be well waxed, otherwise you'll leave it there forever!
Two of these units, placed at diagonally opposite corners of the male box, will generally suffice for a 6-7" prop.
|Once again, try and calculate how much
need to fill the box, remember that K factor?
And when ready, pour!
Obviously, you are dead
the release agent is all where it has to be,
Well, it's time to relax: set that sticky thing
and forget it for at least 48 hours.
Oh, yes, your beloved master prop is definitely buried in that epoxy!