Adjustable Comb by Scot Heath

Adjustable Comb by Scot Heath

Introduction

Here's a brief tutorial on installing an adjustable comb. I made the hardware for this install but you can purchase very similar HW from Brownell's (Graco). Here's the base plate:

Page 1 of 7Adjustable Comb Install

3/31/2007http://home.comcast.net/~scot_for_sale/guns/comb/index.html

The plate is 1/8" x 1" 6061 Aluminum. The recesses to keep the nuts alligned are .025" deep. After installing the posts and nuts on screws that are too long, I cut the screws flush with the nuts then sand flat on a vertical belt sander to remove any excess and flatten the nuts to remove any bevel at the corners. Finally, I reverse the nuts so the flat, sanded side is against the bottom of the slot in the base plate. I only slot in one direction but make the plate symetrical so it can be reversed for cast-on or cast-off.

The posts are 3/8" 6061 round bar stock, drilled for #8-32 clearance and countersunk on the top. I've used flat head socket head screws but the slots allow a little more tightening. All the screws and nuts are stainless to prevent rust on those rainy days.

Cut the Comb

I start by completely covering the stock with masking tape. This helps prevent "oops" on the finish, gives me something on which to draw the cutout and helps prevent splintering during the sawing operation.

I built the jig in the following photo to allow me to:

� Hold the stock securely during sawing � Allign the cut perpendicular to the vertical axis of the stock



I like to lay out the cut so that:

� The bottom is flat and perpendicular to the butt � The entry and exit of the saw are perpendicular to the stock surface � The corners are radiused enough to use a drill mounted sanding drum to smooth the saw cut. If you use this method, make sure you angle the drum so it doesn't follow the saw cut marks up and down as you sand. Also, take care to sand the entry and exit areas such that the drum is running in the direction so as to pull you down and not up the slope. If you get close to the lip being pulled up, the drum will "run" onto the finished portion of the stock and even with the tape, could cause a bit of a scuff.

Some folks make a large radius cut from front to back, making the bottom of the comb rounded. This is nice because you don't have to be so "straight" when sawing and smoothing. It's difficult on shallow shotgun stocks like the one shown because the stock bolt hole is so close to the cut. I use a 1/4" wide, 6 tpi blade on my band saw running as fast as possible.

Inlet the Base Plate

I built a jig which clamps to my mill table and has holes/slots to allow the stock to be mounted by the pad holes:



If you were careful to get the pad holes horizontal when you cut the comb, the cut will be nice and parallel to the table. If not, you may need to shim the jig a bit. An alternative to the jig is just a plate that cam be clamped in a mill vise. I use a straight flute 1/4" carbide tipped router bit and run the mill at 3000 rpm. This makes the corners nicely rounded and I round the base plate to match on my vertical belt sander. Of course, you can always inlet by hand with a chisel.



Note the deeper sections for the nuts. One of them has broken through into the stock bolt hole at the front, it's close! Also note the inserts for the mounting screws. This is an early stock and I used cast zinc inserts but I have since found brass inserts and use them now. They have wood threads on the OD and machine screw threads on the ID. I use #8-32 flat head screws here as well.

Install the Bushing

I use a Forstner bit for this, I go as big as possible up to 3/4" but typically don't have enough room so end up at 5/8" or so OD. Make the center hole a bit larger than 3/8" to allow the drop to be adjusted differently at the front and at the rear. The closer the posts are together, the more this can be done:



To position the bushings, I install the base plate then just hold the comb against the posts all the way down in the saw cut. Mark the post position on the tape and just "eyeball" them. I measure to the center of the comb and make sure the spacing is perfect for the second bushing from the first. To hold the comb while drilling, I use leather faced boards in my mill vise. I put a 1/2" dowel pin behind the center of the board on one jaw so the board can pivot to allgn with the comb. Drill slowly with very little pressure to keep the comb from slipping down, if the wood is hard, I sometimes put a wedge in from the front and rear under the comb. I leave the OD of the bushings rough via a sharp, pointed lathe tool and then epoxy them in place.

Once the bushings are installed, you can use the same mark to install the set screws. I do this by placing the comb in my mill vise with the flat bottom on the jaw towards me just high enough to allow the busings to be visible over the top of the jaw. This makes the hole nice and perpendicular to the bushing. I go 1/4" to 3/8" up from the bottom of the comb to the hole and drill and tap for a #8-32 screw, then open the wood up to #8 clearance size:



As you've probably noticed, this stock also has an adjustable length of pull and in fact, is cut very short. I use this stock as a try stock when fitting shotguns for customers. I've since gone to a bushing style design for the adjustable length as well, this allows me to use thinner plates (much easier to fit!) and doesn't add as much weight. To cut the stock for length, I clamp it in a rubber lined jig which mounts to the back of my mill table, index and shim until it's flat then mill the end of the stock off with a 3/4" straight flute carbide router bit, again at 3000 rpm. I always take a climb cut and have found this to be the absolute best way to prevent splintering.

Questions? Comments? Please, drop me a line.

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Adjustable Comb by Scot Heath