M-Power
Perfect Butt
Profile Scriber
by Stuart Duffy
The manufacturers of the Flat Lying
Trammel Set (which was reviewed in
A WW # 149) have released a Profile
Scriber. As with its other products,
M-Power seeks to develop handtools that
make common tasks easier.
When mating a board to an uneven
surface, the standard method is to draw a
line on the board parallel to the other
component. This can be done with a
compass or with a pencil stuck in a homemade
guide.
The problem with both these tools is
that it takes a lot of care to keep the tool
exactly at right angles to the irregular profile
while drawing the line. Any significant
inaccuracy will result in a gap in the
finished joint or a 'bump' that will prevent
the two sides of the joint mating.
Design
M-Power's solution is a spring-loaded
pencil in a round insert.
The insert fits into one of four discs,
giving an offset (radius) of 14.Smm,
2Smm, 3Smm or 4Smm respectively.
For a smaller offset, the pencil can be
reversed in its holder - the metal cap
screws off, releaSing the pencil and the
spring. This provides an offset of 8.7Smm. However, the cap does
not have a rolling action, unlike the guide
which is fitted with a ball bearing for
smooth operation.
What happens when the pencil gets
shorter? There appears to be a fair amount
of travel in the spring. However, if you like to use most of the pencil, you may have to in sert a piece of dowel as a spacer.
Operation
For simpler marking out tasks, the
Profile Scriber is very easy to use.
Choose the offset you require or prefer.
In most cases the smaller wheels work
better but if for any reason you can't get
the workpiece close enough to the mating
surface, you do have the option of the
larger wheels.
You can also make your own wheels
with a hole saw, bandsaw or on the lathe.
The main criterion is that the wheel must
be perfectly round to give an accu rate
marking. The manufacturer's web site
gives the centre hole as 0.92S" dia. which
we expect is a very difficult drill size to
source. However the Metric equivalent is
23.5mm which should be a bit easier to
purchase.
With the wheel fitted, position the
Scriber on the board. I held the barrel
close to the wheel (base) to avoid accidentally
tipping the tool as I ran it along
the profile being copied. Not only was the
process very easy but the marking is completely
repeatable. Mark out the profile a
dozen times and each marking will be
exactly the same, due to the constant
radius of the wheel.
Accuracy
It might be called the Perfect Butt, but
the geometry of the Profile Scriber is not
perfect.
The Scriber marks a line parallel to the
immediate face of the profile. However
what is actually required is a line parallel
with the joint.
The discrepancy is very obvious in Photos.8 & 9. Along the sides of the recess,
the line is equidistant to the sides whereas
it should be flush.
Initially I thought that the Scriber
would be quite sensitive to curves in the
joint, but Photos.4-7 show that this is not
the case. Where the radius of the curve is
smaller (ie. there is greater curvature), a
smaller wheel is more accurate. However
even the larger wheels will provide a
good join.
There's also the question of how much
accuracy is actually required. Being precise
to 0.1 mm is of no great use if you
can't cut the material to that accuracy.
From my observations and using the
Scriber on-site, the tool is ideal for marking
any out-of-alignment in built-in work.
Complex joints Method Two
Where there is a major change in the
line of the joint such as the one in
Photo.8, the Perfect Butt Profile Scriber
can still be used, but a two-step process is
required. This process is outlined in the
instruction leaflet that accompanies the
tool.
The idea is to create a template with
the Profile Scriber. Then, using the template
and the Profile Scriber with the same
wheel attachment, a line is marked on the
board (Photos.10-12). Most of the errors
introduced by the Scriber in the first step
are removed in the second.
About the only problem left is inside
corners. In Photo.11, I formed them by
extending the sides until they met at a corner.
This method, while being more
tedious because a temp late has to be
drawn and cut, does have the advantage
of producing very accurate joints when
the profi le is very irregular (photo.12).
While the Scriber will mark out both
simp le and complex outlines, it is not suited
to profiles where there are small narrow
changes. Even the smallest wheel will
tend to produce smooth flowing lines
rather than pick up any small gouges in
the mating surface.
Other Uses
With a little thought the Perfect Butt
can be applied to other tasks. For example,
if you are laying up a component in
laminations, you can make full size templates
using the Scriber to mark the offset
formed by each layer of wood.
The Tool
Manufactured in England, the Perfect
Butt Profile Scriber is made from solid
brass, as is the smallest wheel. The three
larger wheels are made from a durable
plastic.
It's a well-engineered, well-manufactured
marking tool designed to provide
repeatable accurate markings.
The Scriber can't be applied in all situations
but it will work on most joints and
make the job much faster and easier.
Macwood International, Ph: OB 8363
4666, sells the Perfect Butt for $62.8O.
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