The saga of the Bird Mouth Bit #3: Assembly with a clamping jig

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Blog entry by splintergroup posted 01-08-2021 08:00 PM 597 reads 0 times favorited 3 comments Add to Favorites Watch
« Part 2: Last preps for the cut Part 3 of The saga of the Bird Mouth Bit series no next part

The bird mouth has been cut and now it’s time to section the sides and assemble the hexagon ring.

Recall that I had used strips of veneer versus using a full-width or spliced together sheet. This is where things would be easier if I had done that 8^)

My target side height was about 2” so I aligned the gaps between the veneer strips to that value, The trick is to also get the strips similarly aligned on the opposite side.

I now want to cross cut the panel but I need to take precautions for tear out on the veneer and try not to damage the sharp bird mouth edge.

Since the veneer will not ride flush with the saw surface due to the walnut strips, the best thing to do would be place a bit of hardboard, as a backer, that fits tightly in the panels recess. The problem is I still want the sharp edge of the bird mouth to ride on something to prevent it from tearing. This would require making the backer the same thickness as the recess. Doable but since I know the veneer does ok when cut with its grain, I’ll just cover it with masking tape and use my routing guide hardboard as a backer for the walnut.

Cross cuts are made:

They look fine from the side, no visible veneer tearing. You can see the layer of tape is only slightly frayed.

A panel with no walnut rails would have been much easier 8^)

Inevitably, the saw kerf will still leave some areas where the gaps between the veneer strips do not align.
Since I’m not dead set on 2”, I’ll just trim off the bald spots and make all pieces the same height after the narrowest piece is fixed.

Backer board comes off and the tape is removed:

I also ran a rabbet down the bottom of each side piece for an inset bottom panel on the completed hexagon.

Glue and clamps

The whole reason I wanted to use the BM bit was the design makes the miters not slip ‘n slide around while clamping and I get a true, factory accurate 30 degree miter without fuss.

I still need a clamping jig since the entire hexagon can distort while clamped. This jig uses a single clamp.

Some math:

If you know the length of a side, you can calculate the span across the flats.

Span = sideLenght x squareRoot (3)

or span = sideLength x 1.73

After all the trimming and other work, the sides came in at 5.825” (measured with calipers on the outer side), the span across the flats then calculates out at 10.09”

With the recessed parts lying 1/16” deep, I subtract off that amount to compensate on both sides to get the span across the hexagon to these two surfaces

10.09 – 1/16” – 1/16” = 9.964”

I cut a setup spacer from hardboard to this exact width using the same technique used to get the perfect width of the side strip groove in the last blog entry (cut slightly over sized, measure and use the dial indicator to adjust the fence).

I also cut two blocks of wood, as square as I could so the length fit snugly between the walnut rails.

Initially cut slightly long, I then stick a feeler gauge between my stop block and workpiece to get an exact fit.

I then attached the two blocks to a flat board with double sided tape such that their ends are even with each other and they are spaced apart by the just-cut hardboard spacer.

I used my long combo squares ruler for the end alignment.

A couple of wood screws are driven into the blocks from underneath to lock them in place. The tape keeps them still while drilling and placing these screws,

Two of the side pieces are then slid over the blocks, effectively locked into place.

With this jig, the ideal dimensions of the hexagon are set and the other four sides may then be glued and a clamp applied to ”gently” close the gaps.

With the clamp in place, the angles are checked

After drying overnight, I sand the top/bottom flat on a piece of melamine with 20” sanding disks applied on each side (120 & 180 grit)

The miters look great!

And with some trim and a finish, a few trays emerge

If you made it this far, thanks for following along 8^)

3 comments so far

View JimYoung's profile


399 posts in 2563 days

#1 posted 01-08-2021 08:39 PM


Thanks again for sharing.

-- -Jim, "Nothing says poor craftsmanship more than wrinkles in your duck tape"

View mikeacg's profile


1808 posts in 2034 days

#2 posted 01-09-2021 10:46 AM

Thank you for taking the time to explain this whole process! I have new toys on order…

-- Mike, A Yooper with a drawl,

View Peteybadboy's profile


2873 posts in 2926 days

#3 posted 01-09-2021 01:32 PM

Split, thanks for posting.

I will add that glue up jig is awesome!

-- Petey

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