Monday, October 10, 2016

The Anatomy of a Rounded Laminated Gun Belt - Part 1 - The Jig

I'm looking into making laminated belts glued up on a round form with a kydex center ply. The kydex ply will add rigidity and keep the belt from curling over.  Laminating in the round will keep the belt from distorting due to the inner ply of a curve being shorter than the outer ply.  I've estimated that there can be about a 1 inch difference in length in a 41 inch belt depending on thickness.  The distortion in a belt after use, I believe, is due to the two plys working against each other.  I came up with this idea for a curved laminating jig.  I'll mostly be making 1 1/2" wide belts, so above the base, the form will be 2" in height.

Not wanting the finished belt radius to be too tight, a 41" belt circumference will be the size for the first attempt at this jig.  Doing the math, that is approximately a 13" diameter.  If the belt is to be about 1/4" thick, I'll make the base 14" to provide a ledge 1/2" deep.  The ledge will act as a guide to keep the belt edges even.

With a lot of scrap plywood lying around the shop, I decided to put it to good use.

Had to biscuit join two pieces for the base.

The circles will be cut with a table saw.  Using a sled (this one I've had for over 20 years) mark two radius points, one for the 13" diameter forms (6 1/2" radius) and one for 14" diameter base (7" radius).  Do this perpendicular to the blade.

Pilot drill and drive a screw into the sled.

Mark the center of the boards.

Drill a larger hole in the wood for the forms and the base to be a friction fit for the screw from the sled.  The wood should not have any play on the screw, but should be able to rotate freely.

To keep the screw from protruding through the bottom of the sled, use shim washers.

For the first cuts, the wood should be screwed down so that there is a fair amount of friction preventing the wood from rotating as it comes into contact with the blade.  Start by cutting off one of the corners.  Hold the wood firmly, any rotation of the wood during the cut will cause the wood to bind against the blade.

Continue cutting off the facets.

Continue cutting off facets until fairly round.

Now loosen the screw so that the board turns freely on the screw.  Holding the wood against the sled, bring the sled toward the blade until the wood engages fully with the blade.  Slowly rotate the wood into the blade (not with the rotation of the blade) until you have a circle.  Do this for all of the form pieces.

For the base, move the screw into the 7" radius hole on the sled and proceed as before.

Once all of the circles are cut, its time to glue, nail, and clamp the form boards together.  We'll use the sled screw to align each circle to the other, one at a time.  Before gluing, rotate the two boards until they edges are most even, then mark with a pencil.  Now remove the screw.

Spread a good woodworking glue on the mating surfaces of the first two boards.  This is the best use for credit cards that I've come up with.

Place the mating surfaces together and drive the center screw back in, align the pencil reference marks, and then nail the boards together.  I always toe-nail when pinning things together.  The outer row nails angle toward the center and the inner row nails angle toward the outer row.  Remove the screw.

I used three form boards which yielded about 2" of height.  Once all three pieces are nailed, clamp the assemblage all around.  This will ensure that all surfaces are flat and well glued.

After a couple of hours of dry time, use 60 grit sandpaper on a block to smooth any irregularities in the rounded surface and then ease the top edge to prevent the surface veneer from chipping.

Sand the curved edge of the base board and ease the top and bottom edges.  Then layout your screw locations for mounting the base to the form.

Center and mount the base to the form again using the sled screw.  Then drill pilot and countersink holes.  Use flat head construction screws.  I decided to screw the base on in case there is a need to increase the height of the form or to increase the diameter of the base.

Top portion complete.

I center drilled the jig and used a through bolt to secure it to a board that can be fastened to a bench to create a stable lazy suzan.  I then bored some holes with a forstner bit deep enough to use a clamp to hold the ends of the leather together as the plies are pressed together while rotating the jig.

The ledge on the bottom of the jig indexes one edge of the leather straps.  Once dry, the belt will be run through the strap cutter again to flush the top edge prior to belt sanding.

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