On Sun, 26 Sep 2004 13:48:59 GMT, Michael Baglio
wrote:

I'm trying to put a _very_ subtle curve on the bottom of some table
aprons. I've placed some nails in the apron templates at the
appropriate points and used a piece of 1/8th" thick wood to try to
draw a fair curve but, (whether I drink to much coffee or I'm just not
good at drawing), I'm not liking the resulting lines, so I'm hoping
I'll get more perfect results by using a (_very_) long trammel arm on
my router to do this.


The height of each arc will be 1/4" above the baseline of each apron.
The center point of the long aprons is 25-3/8ths from each end, and
for the short aprons the center is 9". Like I said, these are going
to be very subtle curves, but visually important and I want them
perfect. ;


How would I compute the radii of the circles I would need to give me
the arcs for each apron?

(Alternatively, is there another method that doesn't rely on how
steady my drawing hand is in order to do this?)

Michael "Shakey" Baglio


The fairing strip is the right idea, Mike but it needs to be thicker.
An eighth inch strip will kink at points where the grain rises to the
face.

Half inch ply or MDF works better but half inch solid stock can be
used if it is straight grained and quartersawn.

I would use this to describe the line and make a pencil line on the
template material, by clamping the straight piece onto the material
and clamping it with moderate pressure at the two outside points.
Then I would take a block and clamp it behind the center point of the
fairing strip.

Tap the block towards the strip until the curve looks good to your
eye. Although math is useful in cabinetmaking, the eye rules.

When you've struck a pencil line on your fair curve you should rough
cut the line to within an eighth inch or so of the finished line.
Then move your fairing strip back the distance that is described from
your router base to the edge of your trimming bit, trying to maintain
a measured distance from the faired curve at all points.

Now block your fairing strip at enough points that it can resist the
force of your pushing the router base against it to trim to the pencil
line. I use hotmelt glue but you could just pin it or screw it.

At this point you should have a template that can be used on multiple
pieces.

I have to say that I only use this method when I have to make a lot of
repetitive pieces. If I was only doing a few I would use the firing
strip to describe the line, cut close to the line, and clean it up
with any of a number of techniques/tools.


Regards,
Tom.

"People funny. Life a funny thing." Sonny Liston

Thomas J.Watson - Cabinetmaker (ret.)
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1