Howdy Again
Time to talk about frames. Here is a photo of both revolvers stripped of all components. Except the rear sights. To tell you the truth, I forgot to take off the rear sights, I was more intent on the guts of the guns. No matter, the rear sights are identical on both guns, the standard micrometer click rear sight that S&W has been putting on their target revolvers since the early 1940s. I also did not disassemble anything that was pinned together at the factory, I never do. So the extractor rod latches under the barrels are still in place, as are the front sight blades. Of course I was not going to drive the pin out of the barrel of the Model 17 and remove it. Sharp eyes will notice the Model 617 barrel is unpinned. I left the strain screws in place on both guns, just a precaution against losing them.
I took a tour of the Smith and Wesson factory three or four years ago. At the time, the old hammer forges were still in operation, I assume they are still in use today. S&W has always forged their frames, rather than using Investment Casting technology the way Ruger does. The hammer forges are huge machines with a solid bed and a heavy 'hammer' that drops straight down onto the work piece. One 'mold' is mounted on the bed of the machine, and another mold is mounted to the hammer. A hot blank of round stock is placed on the mold on the bed, and the hammer then strikes the blank with tremendous force, causing the metal to flow into shape between the two molds. This process not only reshapes the metal, but causes the internal grain structure to reorient itself to the new shape of the part. Reorienting the grain adds to the strength of the part. Forged parts are not finished parts, there is a great deal of work that has to happen to finish the parts. The forgings are placed on another machine that stamps away most of the extra metal around the perimeter of the part. Then the parts are ready for further processing.
The day I visited the factory, there were bins and bins full of forgings for the huge frames for the 50 caliber revolvers. They were ready to move onto the next steps.
After forging and trimming, the frames roughly resemble the finished parts, but there is still a great deal of precision machining to be done to finish the parts.
I think this would be an appropriate time to bring CNC machining into the discussion. Computer Numerical Control (CNC) is the name given to the process that is used to control automated machine tools, as opposed to controlling equipment manually through the use of hand wheels and cranks. The advantages of CNC are accuracy, repeatability, and the equipment's ability to run continuously for long periods of time. This last attribute means that fewer operators are needed with CNC dominated shops than with manually operated equipment, cutting down on labor costs. One CNC program can perform many operations while the workpiece is on the machine, rather than moving the workpiece from machine to machine, each manually operated and set up to perform a single, specific operation. CNC equipment can also generate complex tool paths impossible to produce on conventional hand operated milling equipment.
But there are also disadvantages with CNC equipment. One is high initial investment cost. Accuracy can only be maintained on CNC equipment as long as the components are in good physical condition and there is no significant wear, no different than hand operated conventional equipment. Dull or worn tools will also cause accuracy to suffer. And it is always possible for an operator to push the wrong button, or fail to align a workpiece properly on a jig or fixture.
The point is, the layman often thinks that CNC is the end all of manufacturing equipment and can do anything. The reality is there are limits to what CNC can do.
My own experience with CNC goes back to the 1980s when I was programming and operating a pair of ancient CNC Bridgeports that had been manufactured in the late 1960s. These machines were from the punched paper tape era. I was programming using a dedicated CNC programming language, then running the program through a paper punch machine to create the punched tape which I fed into the machines. Later we modernized a bit and I was using floppy disks.
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As I have said earlier, this Model 17-3 was made in 1975. I do not know when S&W first started using CNC, but the beautiful semi-circular tool path around the hammer stud tells me the main cavity of this frame was machined out on CNC equipment. A lot has been written about the lack of quality in the Bangor Punta days, but the machining on this frame is nothing short of exquisite.
I was surprised by the quality of the machining inside the 617 frame. Really first rate. There is a circular, slightly raised surface around the hammer stud that serves as the bearing surface for the hammer. There is also a slightly raised area around the trigger stud and the cylinder stop stud that serves as the bearing surface for these two parts. On the Model 17, the studs themselves have larger diameter bosses standing slightly proud of the floor that serve as bearing surfaces. So the studs of the Model 17 would have been more expensive to make than the straight studs of the Model 617. Notice too that the Model 17 studs are rounded on top, as opposed to the Model 617 studs being flat on top. Again, less expensive to make.
Yes, I left the lock components in the frame of the 617. I did remove the 'flag', but not having the 'key' to reposition the lock, I chose instead to leave the lock parts in place and I popped the flag back in position. Yes, the flag is a MIM part, we will talk about MIM later. The little stud projecting up from the surface of the flag engages features on the hammer to lock the gun. Incidentally, there is a tiny torsion spring on the underside of the flag, keeping it normally in the unlocked position. I know plenty of testing has been done with the lock, and it is very reliable, but it would not take much to mash that little spring and, in my opinion, make the lock unreliable. But messing with it would probably void the warranty anyway.
By the way, yes, the reason for the slightly different shape of the Model 617 frame in the hammer area is to provide room for the lock parts.
Here is a closeup of the tool path around the hammer stud of the Model 17. Notice how even the spacing is between adjacent swirls left behind by the endmill, indicating the constant feedrate of a CNC machine.
This closeup of the machining on the Model 617 frame reveals the closely spaced tool marks left behind by the endmill. With CNC equipment it is possible to program a finishing pass, usually a very light cut, sometimes at a slower feed rate, that leaves a very fine finish behind. I suspect this was done with the 617 frame.
After final machining parts would have been placed in a vibratory tumbler, like a giant version of the tumblers reloaders use to polish their brass. I saw one of these tumblers working while I visited the S&W factory. They used conical ceramic beads to polish the parts. The longer the parts stay in the tumbler, the smoother they get. I suspect part of the lack of tooling marks on the 617 frame is due to a good soak in the tumblers.
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So how were frames machined before CNC?
No discussion of CNC machining would be complete without mentioning the pattern following equipment that preceded it. Pattern following machinery made possible repeatable, complex, precise machining. Pattern following equipment used a stylus to follow a pattern. The operator manipulated handles which kept the stylus pressed against the pattern. The workpiece was fastened to a table and as the operator manipulated the handles, the workpiece moved past the cutter, duplicating the shape of the pattern. The precision of parts made on pattern following equipment often depended on the skill of the operator. The development of pattern following equipment goes as far back as the 1840s, developed at the Robbins and Lawrence Armory in Windsor, Vermont. Smith and Wesson was one of many Connecticut Valley manufacturing firms to pioneer the use of pattern following equipment to mass produce precision parts, right up until the age of CNC.
Here is the frame of a K-38 made in the late 1940s. This frame would have been hogged out on a pattern following miller. Yes, the surface is rough, but it is flat. I have seen better examples of frames made before CNC, I chose this one because the manually generated tool paths can be easily seen.
The frame of this little 32 caliber Tip Up was machined out in the 1870s using pattern following equipment. The point is, all that rough surface of the 1940s K-38 was clearance area. No moving parts, other than the rebound slide, touched that rough surface. The lip that surrounds the side plate would have been done as a later operation, also on a pattern following machine, but probably with a finer touch.
Here are a couple of interesting photos. The first is of the grip frame of the Model 17. Notice the diagonal chatter marks. To me, that indicates that this portion of the frame was hogged out in a separate operation, with a rotary tool that was spinning on an axis parallel to the chatter marks.
The 617 frame has no chatter marks on the grip frame area. I suspect that is because this area of the frame was machined away with an end mill while the frame was on the CNC machine for the milling of the main frame cavity, not done on a separate machine with a separate set up the way the Model 17 frame was. More cost savings.
