DIYbanter - View Single Post

writes:
what incra do you use?

I have the incra 5000. However, even after aligning the angle with
feeler gauges to within a few thousanths of an inch over the 18"
length, it still wasn't accurate enough to get it "just right" for
wide rings, so I use the half-ring-trim technique.

The flip stop comes in handy for segments, though. I use a two-phase
technique for cutting segments:

Phase 1 - rough cutting. I use a drafting triangle clamped to the
waste-side sled (the one that doesn't slide, for incra) as if it were
a rip fence. To set this up, I measure a segment on the stock,
position it for the cut, and use a t-track clamp to clamp it to the
sled. Then I position the sled so that the point of the stock is at
the near edge of the waste side sled, and clamp the corner of the
triangle at that point. I push the sled forward so that the point of
the stock is now near the tip of the triangle and clamp the far corner
down. Now I have the triangle clamped along the leading edge of the
waste side sled, and one edge is parallel to the cut and the right
distance away. Note: the triangle is short enough that the stock
leaves the triangle before beginning the cut, like any good crosscut.

Ok, now that I have a stop, I cut a dozen blanks. Cut, flip, cut,
flip, etc. Now I have a dozen trapezoids slightly longer than needed.
I run a pencil line down all the angled edges of the trapezoids so I
know which ends I've trimmed.

Now I set up the flip stop. I set it for 1/32 long and trim one end
of each rough trapezoid. Set four of them aside. Move the stop to
1/16 long (note that the incra stop makes this easy - it's moved one
notch each time) and trim the other end of the remaining 8.

The reason for this trimming step is that the trimming is done with
the SAME long edge against the SAME part of the fence each time, and I
don't have the rest of the stock influencing the angle at all. It
results in fairly precise cuts that way, and I don't have to worry
about how parallel the long edges of the stock are.

Ok, so now I have parts for two half-rings with slightly long ends.
Use one of the short trapezoids to mark the long ones with a marking
knife so you know where to trim them to later. Glue up the half
rings, leaving the marked ends unglued. Lightly sand. Use t-track
clamps to clamp the half rings to the crosscut sled, aligning the
marks you made with the edge of the sled, and trim them. Note which
side is "up" for each half, when you glue them together keep one half
up and the other half down, so any inaccuracy in the blade's angle is
cancelled out instead of doubled.

Now, sand the whole rings on the disk sander. I make pencil marks on
that side first so I know when I've sanded just enough.

As I glue each layer on to the form, I let it dry enough so that I can
true it up and thickness it on the lathe. I use a ruler across the
ring as a reference, and a second ruler from that to the bottom of the
form to check the "height" of the ring, since in my cases I'm usually
following a plan and it's the absolute height of the ring that's
important and not the relative thickness of it; I can't allow for
accumulated errors in ring thickness.

I use a long block and sandpaper to do the final flattening and use a
straightedge to test for flatness.

When clamping each ring on, also, I turn the ring relative to the form
after the tailstock is brought up to squeeze out any excess glue.
This seems to get rid of the dark glue lines, since bubbles of excess
glue can keep the rings apart.

Ok, this answer was longer than I expected ;-)