Practical Boat Owner – May 2018

The next stage is filleting the inner radii. I
always used to use Plasticine for this but
after more than 40 years in the game have
started using pattern wax. Both are
compatible with polish and polyester resin.
If it’s cold, warm the ‘dough’ a bit, which
makes it much easier to use.
Sets of mini-sized dumbbells for filleting
good, reliable contours are available from
various GRP suppliers (around £38 for a
set of three) while pattern wax costs about
£11 a kilo.
Clean up ‘wax swarf’ at the sides of your
fillet with a simple plastic tool or your
fingernail. The wax polish tidies up the rest.
Once I was happy with the shape, I
applied several coats of silicon free wax
polish and a coat of PVA release agent –
then the plug was ready for its coat of
pigmented gelcoat.

I made a rough model from scrap wood
and hardboard to ensure my idea would
fit, then used the dimensions to make the
plug for the mould. The best material for
this was 15mm melamine-faced MDF,
cheap and readily from hardware stores.
When making plugs, extend the edges
where they’ll need trimming so you’ll have
consistent thickness and some room for
error, and remember your mould will have
to come off the plug so make sure you
have a sufficient release angle.
For shaping this plug I used a router but

if you don’t have one you can hand cut

and sand rounded edges smooth.

Once the whole thing was assembled (I

didn’t use glue) I filled all the countersunk

screw recesses with car body filler. Next I

flattened off and lightly painted and sealed

the now exposed routed edges with

polyester resin (not gelcoat as it will set

sticky unless Paraffin wax is added) and

sanded these off.

When filling holes, less is more! The first

sanding will show the dips and another

one or two coats will do the job and be

quicker in the long run and you don’t want

to sand through the Melamine.

As the completed unit was not going to

be high gloss and was in a light colour

(light colours don’t show marks as much

as dark) the finish didn’t need to be finer

than 240-grit using a random orbital

sander, or 400 by hand plus buffing, but

again, don’t sand through the Melamine.

Once the plug was assembled and

sanded, I buffed the edges while they

were easily accessible – very fine lines are

lost after polishing.

Screws and fixings were countersunk to

be filled later

To start with I made a rough model from
scrap wood and hardboard

Make routed edges and recesses for door

flap sections before assembly

Fillet balls and pattern wax

Special pattern wax can be used for filleting – or Plasticine, as in this case

A modified spatula will clean up ‘wax swarf’ Finished plug ready for the mould gelcoat

Practical Boat Owner t http://www.pbo.co.uk 73

BUILD AN INSTRUMENT CONSOLE

Making the plug for the mould

Filleting inner radii

Waste material

can be cleaned

away with a

fingernail or a

plastic tool