108 CLASSIC BOAT AUGUST 2016Boatbuilder’s Notes
CRAFTSMANSHIP
Timber holdfast
Plane with the grain
Before launching a plane on to a timber surface it is
important to study the grain. The difference between planing
against the grain and planing with it is the difference
between stemming a foul tide and being carried along
smoothly on the flood. Wood is made up of long fibres which
come to the surface like a cat’s fur, so if you plane against the
grain you will not so much smooth the wood as aggravate it,
potentially tearing out chunks as the blade skitters, digs in
and levers up the fibres instead of slicing cleanly through
them. Notice how the grain runs gently uphill across the face
of this oak board to run out at the edge, so that the plane
makes easy progress in the direction shown. Change
direction around knots, which create whirlpools of grain.TEXT AND PHOTOGRAPH ROBIN GATESThe inherent strengths of grown timber which serve the
wooden boat in floors, frames and knees can also be
applied at the bench. A branched ash bough from the
woods has the makings of an excellent holdfast.
The hook-shaped holdfast has a shank which passes
through a hole in the bench and a beak which bears down
on the work, clamping it. It’s based on Newton’s third law.
When you hit the holdfast on the head, the beak exerts
force on the work, the work exerts an equal force on the
beak and as it does so causes the shank to lean backwards
in the hole. The leaning shank then jams between the hole’s
edges. A knock on the back of the shank loosens it. More
versatile than a vice and quick to set up, the holdfast has
been around the boatyard for centuries.
To make a timber holdfast, find a straight ash bough of
3.5–4cm diameter with a branch at 45 degrees. Tough and
shock-absorbent ash is well-suited to the purpose. Strip the
bark with a knife, going beyond the sticky green cambium
before rounding with a draw knife or spoke shave.
The shank of an iron holdfast is usually 1.5–2cm diameter
but considering timber is less rigid than iron a shaft diameter
of 2.5cm to fit a 2.75cm hole will provide a solid equivalent,
given a bench thickness of about 4cm. Use a brace and
centre bit to bore the holes, and leave final shaping of the
shank until the holes have been bored. Friction between the
oversize shank and the hole will create shiny high spots
showing where to plane. Lastly, cut the end of the beak to
be parallel to the bench top when the holdfast is jammed
tight. Use a timber scrap to stop the beak marking the work.(^1)
The beak clamps
the work to the
bench for sawing
(^2)
Cut away the
bark and
cambium
(^3)
Bore a 2.75 cm
diameter hole in
the bench
(^4)
Plane the shank
to 2.5 cm
diameter
(^5)
A sharp tap on
the head tightens
the holdfast
The bicycle spoke drill bit
Some homemade tools can be more effective than shop-built alternatives. This
is a perfect example. Fine wooden boats often require drilling small holes of say
(^1) / 8 th of an inch or less, often through two or three components that are jiggling
around. A sure recipe for getting through a lot of fragile little drill bits! On the
banks of the Thames the solution was the humble bicycle spoke. In about 14
years of boatwork I may have bent a few, but you have to do something really
wrong to snap one. I make them in two ways, the one in the picture on the left is
just filed down to a point with three flat surfaces. The second method on the
right is like a miniature flat bit, the end is flared out with a few whacks of the
hammer on a metal surface, the end is then filed from each side at 45 degrees to
meet at a tip in the middle. I don’t anneal these, so they do go blunt after a while,
but they can be easily sharpened with a pass of the file. So a word of warning; if
you find you need to push too hard they may be blunt and may buckle. It’s
always prudent to keep your fingers out of the way. Ryan Kearley
ROBIN GATES
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