Here’s some photos of my process;
I only had enough time to do a two-ring knot, but it’s
all the same to make a four-ring knot accurately if you follow these steps.

This shows the miter sled, the length of contrasting wood for the slices, and the bloodwood blank I’m going to use.

I’ve already squared the blank so that all four sides are the same size.
I randomly pick a side and mark it 1.
Side 2 is 180-degrees to (or, opposite of) side 1.
Side 3 is one of the two remaining sides and side 4 is 180-degrees (opposite) side 3.

This photo shows I’ve marked the blank where the slices
will go and clamped a stop block in place along the fence.

Now, I clamp the blank tight to the fence and the stop block.

Here we’ve cut thru the blank. That’s NOT my hand in the photo—it’s part of the clamp.
My hands are safely distant from all spinning metal at all times while doing this.

After gluing in my slice (Goncalo alves and aluminum, in this case),
I place the blank back on the sled clamped tight to the fence and stop block again.
This time, side 2 is up and I’m going to cut thru the first slice that was glued in.

From here out, it’s just more of the same until I’m ready to cut the blank to length.
Since we’ve marked the blank 1, 2, 3, 4 and the stop block makes repeated positioning a no-brainer all we have
to do is follow the numbers and glue in the contrasting material for each cut in turn.
Then I switch to a cut off sled that’s 90-degrees to the blade and clamp the blank on the mark.

The zero-throat on the sled keeps everything in place and accurate.

Once the pieces are glued in and you’ve drilled thru the center of the blank,
it’s just a matter of turning it to the desired shape.
Here’s my upper barrel:

I hope y’all find this useful and make many beautiful pens. As I’ve learned from many here, share and enjoy.