By
Gil
Lamothe
This article
describes a process which I used to re-build several rows
of broken threads on a boxwood screw arm of a Casey Clark
& Co. plough plane. The process involves casting replacement
threads out of epoxy cement, which is tinted with earth pigments,
in order to match the color of the original threads. The results
I obtained were very good from both a mechanical and visibility
standpoint.
I began
collecting old tools several years ago, and find great satisfaction
in restoring them to working order, then using them in my
shop. The plane in question was found at an outdoor farm
auction in the fall. It was a drizzly rainy day, and all
of the non-furniture items were layed out on hay wagons
in the rain. There were several tools, and when I spotted
a screw arm plough plane, my heart began racing. This type
of plane had been on my wante
d list for some time. I gave it a
quick but thorough going over, and everything was perfect.
One of the locking nuts was seized, and there was a small
chip in one thread near the tip of one arm. The thought
of this tool sitting out in the rain was very disconcerting,
and I casually mentioned to the owner that all of his nice
wooden tools were getting wet. "Oh, they'll be O.K. once
they dry" was all I got, so I left it at that, and kept
my eye on the plane. My wife and I wandered around some
more, grabbed a coffee, then moved back in once the auction
was about to start. I took another quick look at the "my"
plane, and sure enough, some bungler had forced the seized
locking nut, stripping three rows of threads. My heart sank,
I kicked myself for not insisting that it be taken out of
the rain, and eventually bought it for $75. Once at home,
I decided that I wanted this tool to be usable, and that
I had to figure out a way to re-build the missing threads.
The fresh break stood out like a beacon from across the
room. Here's what I did.
I purchased some "Rubbertex Molding Compound" and mould release spray
from the Lewiscraft craft store, some plasticine, some two
part epoxy cement (the squeeze tube kind, avoid the fast
setting 15 minute epoxy, you may need the open time), and
a selection of earth pigments from Lee Valley. Using the
good screw arm, I selected an area of threads that matched
up with those that I wanted to re-build. These threads were
given several coats of paste wax. A "dam" was then built,
using plasticine, around the area from which the mould would
be lifted (note: you're working with the good screw arm,
not the one needing repair). The exposed area within the
"dam" was at least 2 threads wider than the area needing
repair, and no more than half the circumference of the screw.
The area within the dam was lightly
sprayed with mould release. Using a soft artist's brush,
a thin layer of the Rubbertex compound was painted onto
the threads within the dam. Once dry, another layer was
painted on, and so on, until the compound was about 1/8
to 3/16" thick. This took 24 to 36 hours, as approximately
2 hours drying in was required between coats. Once dry,
the thread mould that was created peeled away smoothly,
without leaving any traces. The plasticine was trickier
to get off. I used a dental pick to clean it all out.
Next, I drilled three anchor holes (1/16" bit) in the area needing
repair. Because this was a large area I felt the repair
would need the extra grip, and yes, I cringed at having
to do this. For smaller areas or single threads this would
not be necessary. I then mixed up some test batches of epoxy,
mixing in various combinations a earth pigments to try and
match the color of the boxwood threaded arm. In the end,
the yellow ochre pigment alone gave the best match.
The inside of the mould was sprayed with mould release. A small
amount of tinted epoxy was mixed and applied (I used a toothpick
as an applicator) to the area needing repair, as well as
to the mating surface inside the mould. I found it easier
to repair a small section at a time (90 degrees of circumference).
The mould is pliable enough that you can "roll" it on, beginning
off of the repair, and rolling towards the repair. This
will push the excess epoxy out of the end of the mould.
The excess squeeze out was allowed to set for 15 minutes
or so, then picked off with a dental pick. Allow everything
to set 24 hours, then peel away the mould. Voila! You have
casted replacement threads. In my case, three castings were
required to repair damage that was three threads wide and
270 degrees of circumference. The match is so good that
it is only noticeable if you are looking for it.
When filling the mould, try to eliminate all air bubbles by running
the toothpick right down into the threads. Any air bubbles
in the moulded threads can be disguised as small chips,
by shaping with an x-acto knife. A word of warning regarding
the rubbertex compound. It will slightly darken the wood
of the area where the mould is created. Next time I will
give a third or fourth coat of wax before making the mould.
You may also wish to try dental putty, if you have access
to it. It is faster setting and is likely to be less reactive
with the wood. I could not find a supplier nearby, but would
have tried it had it been available.
The
best part about this re-build is that the plough is now
completely usable, and I don't have to worry about the damage
spreading. Now if I could only find a set of plough plane
irons.
