Then build the outer box for the first casting:
and obtain a suitable base plate for mounting all the hardware on.
||The base plate can be
provided it is strong, flat, and well waxed.
This one shows that it was, several times.
Slide the mandrel into the propeller, front side
up, then the bottom spacer onto the mandrel,
and the mandrel through the base plate in this fashion:
||Yes, the prop is not
the same as
the one in the whole story, because I screwed up the original photo
Anyway, this is also to show that a master prop can be readjusted if necessary before copying.
This one in particular, had the hub reshaped and an aluminium front plate fitted to make things really nice and square, and to cancel usage marks.
Propeller courtesy of Parent & Kelly (circa 1974)
Securely fasten the whole lot to the base plate by suitably packing the protruding stem of the mandrel (with the bottom spacer, or anything else, as in this case) and tightening
the 4 mm socket screw
(you did tap the hole, in the mandrel, didn’t you?)
Aligning the propeller
marks you will have traced on the base plate will help afterwards,
Once satisfied with all this, start packing up
back of your prop with plasticine,
taking care not to warp the blades upwards by packing too tight:
Then scrape away the excess plasticine by running a 20 degree template all around the leading and trailing edges of both blades (unless you are making a single blade...)
The tricky story will begin around the hub, when the template switches from a trailing edge, which is on the bottom, to a leading edge, which is on the top.
reduced to an extremely thin blade, which will then be the same thin
blade on the male mold and I always thought it would break, therefore I
prefer to make the transition by packing up more plasticine and trying
to guess the correct separation line.
In the end, you should come up with something like this:
|Once you are satisfied with the finish of
and convinced that there are no undersquares, it is time to give a good
coat of your favorite release agent, including all of the base
And maybe another, after a while.
Be extra careful at this point: the release agent will bring your precious master prop
back to you, when all this mess is over!
||Next, when the release
nice and dry,
and polished if necessary,
mount the upper aluminium plate on top
of the mandrel cone with another 4mm
socket head screw
(you tapped that hole too, hopefully…).
To give access to the screw once everything is buried solid in resin, you’ll have to install a piece of tubing over the screw head, long enough to protrude over the edge of the box.
Fasten the tube from the inside with a well packed blob of plasticine.
After all this, you might as well fasten the box to the base plate with 4 wood screws driven through from the bottom of the base. A good idea is to pre-drill both pieces before starting with all the plasticine stuff.
Don’t forget to mark the relative positions!
To save resin I usually cyano some blocks of scrap wood inside the box, about 5 mm below the edge. Personally I don’t believe in making the box much shallower than about 50mm, as this will be the part of the mold in which most of the work will be done while making the props, therefore I like it to be rather solid and stable.
Once ready for the first casting, the inside of your job will look like this:
||The scalpel marks on
of the box are there to give a better grip to the resin.
Actually they are just useless: that damn’ stuff will grip to about anything!
While on the outside, it will be better to seal the joint
between box and base with some nice fillets
of finger-smoothed plasticine.
It is very unlikely that
will seep through,