Practical

Making the

perfect

scarf joint

Chris Hawes designed and built a jig for

making multiple perfect scarf joints

I

built my first boat at the age of 15

largely on my bedroom floor. It

was an International Moth made

from 3mm exterior plywood held

together with fishing twine and glass

tape – much the same construction as

the Mirror Dinghy.

One of the things I needed to do was to

end-join the plywood to make an 11ft

length, as ply was only affordable in 8ft x

4ft sheets at the time.

I designed this jig to ensure I made a

good straight scarf joint. I am sure it is not

unique and many cabinet makers will

have much the same design.

Having read the article about scarfing

the stringers for the project boat in PBO,

here’s a tip to make the job simpler.

1

Basic jig construction

Almost all woodworking jigs are

simple, cheap and very quick to make,

and this one is no exception.

A: The main support board. I used MDF.

It needs to be about 100mm wider than

the width of the set of timbers to be

planed and about 1200mm (3ft 11in) long

to give good support. It should have a

good clean square edge.

B: A longitudinal clamping piece. This

should be screwed and glued to the

underside of A with its edges parallel. It is

used to clamp the jig into a Workmate.

C: Stop end support. An offcut from B for

supporting the temporary end stop.

D: Stop end hinge support. Another

offcut from B fixed flush to the end of A.

E: End stop. This is used only when

loading the jig with the timbers to be

planed. It is screwed into D such that it

can be swung out of the way whenever

work starts.

2

Finalising the jig

Turn the jig over and clamp it into the

Workmate, or overhanging the end of your

workbench. You will need two pieces of

the timber to be planed, each about

100mm long, to use as side stops, plus a

thin piece of material to be the plane

bearer. The thinner this is, the shorter can

be your plane. I used a piece of 5mm wall

cladding. A piece of thin plastic (a ruler) or

Tufnol would do.

The longer the scarf the stronger it will

be, but also the longer the plane you will

need. Multiply the thickness of the timber

you will be planing (in this case 15mm) by

the slope, ie if you want a 1:10 slope,

mark a pencil line 150mm in from the end

of the jig.

Fix the first side stop such that the edge

facing the end of the jig is on the pencil

line. Measure off the number of pieces of

timber you want to process at a time and

fix the second side stop.

3

Positioning the plane bearer

Place a straight edge on the arris

(corner) of the jig base board and the side

stop. Slide the plane bearer on the side

stop until it just touches the edge. Mark it.

4

Fixing the jig

Place the plane bearer on the side

stops on the pencil marks. Ensure it is

parallel to the end of the jig and screw it

down. Do not glue; you might need to

loosen the bearer to load the jig.

A traditional

long plane

Step

by

step

A

B

C D

E