Repeat Performance For
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SEPTEMBER 2001 / VOLUME 53 / NUMBER 9 cover story ❿ BY TECHNICAL EDITOR CHARLES M. BOYLES, CPE Repeat Performance The art of machining classic shotguns. thaca Gun Co. has reintroduced a classic shot- again. This action empties and feeds the shells gun: the National Wild Turkey Federation Lim- into the breech. Iited Edition, Millennium Commemorative, For the Model 37, the pump-activated slide Ithaca Model 37. The pump-action, repeating pushes the breechblock to the rear, cocking the shotgun is a reproduction of an original 1911 John hammer while the breechblock extracts a spent Browning design, which was marketed by Rem- shell. As the breechblock travels toward the back ington Arms as the Model 17. This particular de- of the receiver, the shell ejector on the breech- sign allows loading and ejecting shells through the block directs the spent shell through the hole in same hole in the bottom of the receiver. the floor of the receiver. While this is occurring, another shell is indexed from the spring- loaded tube magazine and is positioned to be chambered. As the slide reverses di- rection and moves the breechblock for- ward in the pump cycle, the new shell is fed into the chamber as the breechblock moves forward and locks in place. xxThe receiver—the section of the shot- gun housing the trigger, breechblock, shell carrier and feed-ejector slide as- semblies—is made from a 7-lb. block of 1137 steel measuring 7"✕4"✕1.35". It’s a resulfurized, free-machining alloy that All photographs: Ithaca Gun Co. yields small, curly chips when machined. The Ithaca Gun National Wild Turkey Federation Model 37 shotgun illustrates the The 1137 has a hardness of 197 HB, artistry, quality and craftsmanship of today’s high-end gunmakers. machinability rating of 70 and requires moderate power for machining. It can be finished to a smooth, satin finish, which Though developed 90 years ago, the piece il- is important for obtaining a lustrous, deep-blue lustrates the timeless appeal of an elegant design. finish. Today, Ithaca Gun, Kings Ferry, N.Y., can barely keep up with demand for the shotgun. The com- Machining pany manufactures the shotgun in 20, 16 and 12 A fair amount of the machining Ithaca Gun gauges. does is performed on specially designed, single- function machines. The production sequence be- The Action gins on a machine for deep-hole drilling. It pro- Operating a pump shotgun involves sliding duces a hole straight through the square block on back a wooden handle, which encloses the tube the long axis, where the barrel and magazine tube magazine to the rear, then pushing it forward mount on the front of the receiver. This hole cre- See related story, last page must hold between 0.001" and parts that make up the operating com- 0.0015" tolerance from end to end in ponents for the pump action. For shell the receiver.” stops, a T-slot cutter—specific to the xxFor the next machining operation, particular shotgun—is used to create a the receivers are fixtured vertically 0.880"-wide T-slot for the slide. in standard jaw vises on a vertical The receivers then return to the sin- machining center, the Monarch gle-function machines. A bolt-notch cut VMC 75. In this position, a bottom is made by a machine that can get inside plate—with a point on the front the receiver; it’s equipped with a special end—locates the two receivers for head that cuts the bolt notch on an machining. The front face of the re- angle. Making the bolt-notch cut is a ceiver is milled and squared using a critical operation since it sets the head 3"-dia. facing mill with eight dia- spacing for the gun. mond-shaped inserts turning at 16 Then the receiver moves to a special rpm. Then a hole for the magazine shaper, which is a vertical-motion ma- tube is drilled next to the barrel hole chine having a single-point cutting tool and milled to the finished size. that shears off the metal from the part’s Again, this hole can be set for one of interior. The shaping tool is set for a three sizes, depending on the speci- 0.11" DOC and a 0.700" to 0.800" Internal cuts, such as the slide way, are milled fied gauge. on a vertical machining center. xxNext, the receiver’s interior is roughed and holes are drilled for the ates the clearance for the other machin- carrier screws, carrier locking screws and ing operations and the radius on which trigger-plate screws. These locking the circular breechblock rides when the screws retain the carrier screws in the receiver is finished. sides of the receiver. A shallow, counter- The hole is drilled using a special car- sunk hole is drilled and tapped next to an bide-tipped, through-coolant tool man- existing screw. The countersink cuts a ra- ufactured by Niagara Cutter, Amherst, dius into the circumference of the head of N.Y., and standard cutting oil. the existing carrier screw. When the lock- The diameter of the holes vary, de- ing screw is installed, it prevents the orig- pending on the gauge. For example, a inal screw head from rotating. Tapping is 12-gauge has a 0.729" ID and a 16- performed with special 6-48 taps. gauge has a 0.662" ID. After these operations, the receiver According to Terry Whiffen, plant blocks are transferred to a second manager, “the machining processes Monarch 75 for milling of the internal surfaces. At this machining station, The gunmaker uses special cutters in the six receivers are mounted in hori- manufacturing process. zontal vises for milling. In this ori- entation, the cutting tools machine WOC per pass. Another machine makes the bottom, inside and back of the the stock cut. This operation cuts the receivers. stock tang, which protrudes from the xxInitially, the slide-way cut is for back of the trigger plate. This is for the slide mechanism that extracts, mounting the wooden stock. ejects and loads shells and cocks the Next, the receiver is faced off on an hammer in one smooth action—typ- angle for the cant of the stock. At the ical of a Browning design. Then the next machining station, the top and bot- trigger way is cut for a subassembly tom of the receiver are shaped with a that includes the trigger guard, trig- spiral-type form cutter, which creates ger, trigger spring, safety button and the top and bottom radii. hammer with the sear on the back. The trigger subassembly slides into Tooling the receiver from the back on two A lot of the equipment and tooling at machined side rails and comes to rest Ithaca is highly specialized and manu- on the trigger-assembly stop, where factured specifically for making shot- it is retained by a screw. guns. “Although we use some standard Shown is one of a series of special, single- xxNext, there are seven machining 0.750"-dia. endmills, much of the tool- purpose machines Ithaca Gun uses to produce operations, each involving a special ing is specific to Ithaca’s products and the Model 37’s receiver. cut to accommodate the moving machining processes,” said Whiffen. locking thread is 0.065" and the grooves are 0.150". Additionally, there is a lug on the barrel that helps hold it in place so it won’t move, even if it’s not tightened. Finishing After a receiver is milled completely, it’s finished by hand. The inside, top and external edges are hand filed and deburred, as are the barrel threads and trigger-plate components. When debur- Hand fitting (left) and hand finishing are ring is completed, the receiver goes to a two of the critical tasks in the manufac- Blanchard grinder to be sized to a thick- ture of the Model 37. ness of 1.335" and then to the polishing department for finishing. On a 12-gauge gun, for instance, the Machining that configuration makes Ithaca uses belt and wheel machines barrel threads call for 1.125" angular it possible to remove the barrel. With for finishing. Polishing jacks elevate the grooves, which are cut with a special the angular grooves, the free-floating receivers into the belts for roughing and form tool from Niagara Cutter. The ti- barrel drops inside the receiver and truing the radii. The sides and tops re- tanium-coated, HSS groove cutter is locks into position on rotation. It’s sim- ceive a fine polishing. sent back to the factory for resharpening ilar to an interrupted-step screw. The At that point, machinists roll various and recoating, which extends tool life to thread configuration ensures the barrel scenes into the receiver sides. As the en- 4,000 parts. is always in the same position. The graving-machine roll transverses the side of the receiver, it displaces metal, leaving an imprint of the desired scene. John M. Browning’s enduring influence (One scene, for instance, depicts Annie Oakley.) Like burnishing or thread ou may be familiar with the name Model 94. (The Winchester 94 is the rolling, the process increases material Y Browning, which is synonymous saddle gun often seen in Western strength, leaving the surface harder and with high-quality sporting goods— movies.) And, the Belgian company with increased fatigue strength. especially over-and-under shotguns. Fabriqué National produced many Afterwards, the receiver goes for final But you may not know the influence Browning-designed firearms. buffing to give it a nice appearance. John M. Browning had on the design With over 25 firearm patents, After stamping the serial number into and manufacture of firearms.