Pattern Following Jig for Bandsaw.
Overview.
Read through the entire article before starting to make the jig. You need
information under the heading Using the Jig which you may not understand
until you know how it is to be used.
The shape of the pattern follower is a capitol letter T. The crossbar of
the T clamps to the table parallel to the blade. The bottom end of the stem
of the T is rounded and there is a rectangular notch cut in the center of
the end. When the jig is clamped to the saw table the stem is parallel to
the table and floats above it by the thickness of the crossbar.
Construction.
There were no dimensions given because the jig is unique to each bandsaw it
is used with. The stem appears to be 1/2 thick by 3/4 inch wide. It may
not be that wide, you may have to make a couple of them to get the feel of
it. The crossbar is about 1-1/2 wide and a little thicker than the
workpiece. The workpiece must be able to slide under the stem without
getting stuck.
The crossbar is as long as the table is wide. The stem is long enough to
reach from the back edge of the table to about 1/16 past the blade. use a
drum sander or what ever you have to round over the corners at the bottom of
the stem. Do not round over all edges just two of them. Then cut a notch
in the end that is just a little wider than the blade and about 3/16 deep.
Cut this notch parallel to the rounded corners.
Now find the point where the stem must be fastened to the crossbar. This is
the point directly behind the blade. No fancy joinery is required here.
Set the stem on top of the crossbar and fasten it with a little glue and
brad nails.
Using the Jig.
To use the jig clamp the crossbar to the back of the table and adjust it so
the blade passes through the slot and is 1/16 to 1/8 inch deep in the notch.
Now you need a pattern. if I had a pattern I could make a pattern. If I
had a pattern I could use it to make a pattern to make a pattern to make an
arm for an Adirondack chair. That's known as recursion. Well, we'll assume
you got the pattern made somehow.
Now here is that information I mentioned in the very first paragraph. The
end of the stem must be high enough to allow the work piece to go under it
but not so high that the pattern also goes under it. Or to say it another
way the pattern must be thick enough to ride on the end of the stem but not
slip under it. Obviously a cardboard pattern won't work here.
Fasten the pattern to the blank with double sided tape. The pattern is on top of the blank. At some point on the pattern the edge of the pattern should be close to the edge of the blank to allow for starting. It is recommended that this be the beginning of a straight line or a line with a very shallow curve.
Start feeding the blank through the blade starting at the point you set up as the start. As you feed the blank through the blade the edge of the pattern should be touching both sides of the notch at all times. If the stem was made too wide you might have trouble following inside curves.
This leaves the workpiece a little bigger than the pattern. There seem to
be two possible solutions to this problem. 1. You can make the pattern
undersized. 2. You can use a flush trim router bit to trim off the
workpiece to match the size of the pattern. I'm sure number 2 is the best
solution because the bandsaw cut is not likely to be perfect enough to be
seen by the general public.
Do not remove the pattern from the workpiece. Turn the work over so the pattern is on the bottom. Set up your router with a flush trim bit. Run around the work piece with the bearing in contact with the pattern.
Question. Why can't I just use a router to cut around the pattern and skip the bandsaw all together.
Answer. The amount of wood to be removed is too much for all but the most powerful routers. Even if you have one of those monsters the bit would wear out quickly and the edge of the workpiece would likely be burned. It would not be safe to use such a powerful router as a hand held machine. While the work could be done in a router table there is still the problem of bit life. I don't know exactly how many arms for Adirondack chares you could get out of one bit but I'll bet it might be only about one chare's worth.
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