Linstrum
09-25-2009, 07:01 AM
Nipples have machining on both ends, which is a hard trick to accomplish on something that has a taper on one end, easily-damaged threads on the other, is too short to chuck up in a lathe so it is square and on center, and if you manage to get it chucked-up square with the world your first cut will knock it out of alignment from the force of the tool bit against it.
I had to make up a new set of six nipples for one of my Italian-made replica 1858 .44 Remington cap and ball revolvers because they were so badly rusted they might blow out, plus make six more nipples for my brother-in-law's replica 1851 .36 Navy Colt because his little nephew dry-fired the revolver and mushroomed them over. The nipples that the local gun shop had in stock weren't the right thread size and they said nipples from Midway, Cabella's, Bass Pro, etc, were a special order that could take three months, plus they had had a lot of trouble in the past with getting the wrong size thread. While I was at it I removed all the nipples from all my replica revolvers to see what size threads they have, and no two guns used the same thread! They were all metric as well, which didn't surprise me since they are all Italian. While I was at it, I decided to make new nipples for all of my pistols to have on hand because of the problems with ordering new ones.
Metric thread pitch notation is not given the same way as in the English system, the metric sizes are given in the distance from one thread crest to the next measured in millimeters instead of how many turns per millimeter or centimeter, while English engineering it is the number of threads per inch, or tpi, which is the mathematical inverse used for metric engineering The thread sizes I found were the following, given in both metric and inches:
6mm x 0.75mm, 0.236” x 33.87 tpi
5.5mm x 0.95mm, 0.217” x 26.73 tpi
5.2mm x 0.9mm, 0.205” x 28.2 tpi (this thread is close to the U.S. #12-28 thread, but the body of the #12 thread is 0.216” and too big to fit)
I'm sure there are other thread diameters and pitches as well, so you will need a set of metric and inch-size thread gauges to determine exactly what you have.
When I machined the thread bodies, I made the diameters the exact metric measurements even though the original nipples were under-size, some by quite a bit. When I installed them, they all fit fine. My lathe has metric conversion gears plus eight different thread pitch switch gears that came with the lathe and go in the gear train from the headstock spindle to the carriage feed screw gear ratio selector box. Using the switch gears I was able to duplicate all three thread pitches even though the gear ratio box for the carriage feed screw supposedly couldn't do the 0.95 mm thread pitch. The 0.9 mm thread pitch is close enough to 28 tpi so that I just used that inch-size thread.
The important thing with making nipples is to be sure that the nipple length from its tip to where it tightens up against the cylinder body is not too short, if it is too short the pistol hammer will not strike the cap hard enough or won't strike it at all. If it is too long the hammer won't strike the cap squarely and possibly peen the end over at an angle and close up the flash hole.
I used a medium carbon steel (probably AISI 1045) that will harden up to somewhere around 40 Rockwell C so the nipples will resist mushrooming and have a long life. The bar of steel I used is a new 3/8” X 12” bridge spike that I tested for hardenability, it hardened up nicely so I used it as bar stock for the project. After all the machining was completed I heated up the nipples to bright cherry red with a propane torch and quenched them in plain water to harden them, then I tempered them to a dark straw yellow color so they won't fracture. Before tempering they need to be sanded a bit with fine sandpaper to remove the light coating of fire scale. I don't use sandpaper in my lathe so I turned the nipples with an electric drill motor for light sanding.
The metric thread profile is very similar to the United States thread profile. They both have 60° sides with truncated crests and roots, but I ignored the exact amount of truncation and simply machined my tool bit to a sharp 120° point, which for an application like this works okay. I followed standard thread-cutting procedure, setting the compound feed at 60° and used the compound feed to advance the cutting depth. The ultimate depth of cut, as measured on the compound feed dial, was somewhere around 0.022” for all three thread pitches, give or take a bit depending on the particular thread pitch. I machined the nipple threads to fit the female cylinder threads, noting the depth of cut as soon as the first one would screw into the cylinder and then machined the rest for that particular gun to the same depth.
The first operation is to machine the greatest diameter on the nipple, which is its head (where the wrench flats are cut), which on the three sizes of nipples were all 5/16” (0.3125”) in diameter. The next step is to machine the major thread diameter and exact length of the threaded body. For nipples, it is important that the thread have a relief cut all the way up against the underside of the head so that the nipple can screw all the way into the cylinder and make a gas-tight seal between the underside of the nipple head (the head is where the wrench flats are cut) and the bottom of the nipple well that is cut into the rear of the cylinder. The way I cut the relief was to simply disengage the carriage feed after the thread was finished and cut an annular groove at the same depth as the thread in the area between the last thread groove and the underside of the nipple head (the 0.3125” diameter part).
After the thread is cut, the next step is to drill part of the flash hole through the nipple. I used a #60 drill, which was about the same size that I found in the factory nipples. I used a small center drill to cut a very small center dimple so as not to drill a large recess into the end of nipple, and then drilled the hole to a depth of only 0.125” (1/8”). A #60 drill breaks REAL easy, so to help prevent breakage I didn't drill the hole any deeper than I had to because it doesn't need to be very deep. The flash hole is stepped, the diameter of the flash hole in the cap teat is 1/16” to take all the fire from the primer cap but steps down to #60 just before exiting the nipple to prevent a lot of high pressure gas from escaping back out.
After the #60 hole was drilled in about 0.125” or 0.130” deep, I cut the nipple off about 0.025” longer than its finished length, using a regular parting tool. The next step is to machine the teat that the cap fits on. But before that can be done, a special jig needs to be made to hold the nipple blanks since they are too short to chuck back up in the lathe and be on-center consistently. Using the remaining 3/8” bar stock I machined a female thread in one end that more or less matches the thread in the revolver cylinder. This thread needs to be fairly precise to keep the nipple blank held firmly on center to withstand making some 0.010” deep cuts in it. I ground an internal thread boring tool from a 1/8” square high speed steel tool bit, the threading tip being ground at about a 15° angle to the axis of the tool bit so the tool bit enters hole in the 3/8” bar stock at an angle, which gives clearance to the front side of the tool bit and keeps its from hitting the inside of the hole. If this isn't done, then a good part of the length down the front side of the tool bit has to be ground off to give the thread-cutting tip clearance to cut into the side of the hole, and grinding high speed steel on a bench grinder by hand is a very time-consuming job, even on a 1/8” square tool bit. Because it is at angle, though, the back side of the threading tool will run into the thread bore if it goes in too deep. If you have an insert-type miniature internal thread boring bar then you don't need to make your own. Once the female thread is machined into the 3/8” bar stock so the nipple you just made will screw into it without slop, cut that end of the bar stock off so that it is about 2.5” long and set aside. Finish making the rest of the nipple blanks you need, checking them before cutting off by screwing into the revolver cylinder as well the female thread in the 2.5” length of bar stock. When all the nipple blanks are finished and cut off, remove the remaining bar stock from the lathe and re-chuck up the 2.5” length with the female thread in it. Screw the nipple blanks into it one at a time to finish drilling the flash holes in them using a 1/16” drill bit. I used a small center drill to start the hole on center, and a lot of care needs to be taken to make sure that the center dimple isn't so large in diameter that it bells the end of the flash hole. If a large starting hole is cut, the priming compound in the cap won't have much of anything underneath it to buck-up against when the hammer hits it and it won't ignite reliably when struck. When drilling the 1/16” hole, if you have a good sense of feel you can tell when the drill bit runs into the smaller #60 hole. If you aren't sure of yourself, use the tailstock micrometer feed to drill the 1/16” hole in far enough to meet up with the #60 hole. After the 1/16” hole is finished, machine the cap teat to its finished profile and length. Get the dimensions from an original nipple, being sure to take the nipple length measurements so it includes the thickness of the head where the wrench flats are cut since the length from where the underside of the nipple head mates with the cylinder to its tip is its critical length. I cut the taper on the teat at a 5° included angle, so the compound feed is set at 2.5°. The major nipple diameter I used is 0.171” at the base of the cap teat, which fits a CCI #10 pistol cap.
When the cap teats are finished at a 5° included angle on all the nipples, the last machining operation is to machine the nipple wrench flats in a milling machine. The tang that the nipple wrench fits over is 0.177” wide, which leaves only 0.003” between the wrench flats and the side of the teat (0.177” minus 0.171” = 0.006”, 0.006”/2 = 0.003”). Using the 2.5” long bar with the female thread in its end, screw in a nipple and tighten it in with pliers or a hand-held drill chuck that will accept a 5/16” diameter. Mount the 2.5” bar horizontally in a milling machine vise and using the table X , Y, and Z feeds, position a 3/8” end mill to cut the flats so that it leaves a 0.025” thick flange between the wrench flat and where the threaded body joins the nipple head. Calculate the depth of cut so that it leaves a 0.177” wide tang between the wrench flats. Take the 5/16” diameter of the head and subtract 0.177” from it and then divide by two to obtain the depth of cut (0.3125” minus 0.177” = 0.1355”, 0.1355/2 = 0.06775”. Round off to 0.068” = depth of cut). Since nothing is ever perfect, make several partial cuts with the end mill to make sure that the tang ends up 0.177” wide. If you go too deep the end mill will cut into the side of the cap teat. After one wrench flat is cut, rotate the 2.5” bar stock 180° and cut the wrench flat on the other side. If everything goes according to calculations, the remaining tang will be 0.177” wide and the nipple wrench will fit it perfectly. When one nipple is done, leave the 2.5” bar in the vise, unscrew the finished nipple, replace it with an unfinished nipple, and make the first wrench flat cut on it. When rotating the 2.5” bar stock be sure to brush away all metal chips from the mill vise so everything clamps back up precisely. I have a set of C-5 collet holder blocks that are square and hexagonal and are used in conjunction with a mill vise to precisely cut square and hexagonal profiles in the milling machine, and they made this job quite easy since it is difficult to rotate something exactly 180° without a fixture like the collet blocks. One way to do the job without a collet holder block is to clamp the 2.5” bar in the vise or to the mill table and cut a flat down one side, making sure that the flat is not so wide that it will prevent chucking up the 2.5” bar in a three-jaw lathe chuck for later use in case you need it again to make more nipples in the future. The flat will locate the bar in the vise so that it can be rotated exactly 180°. The end play can be located precisely in the vise by butting up the end of the 2.5” bar against a straight edge held across the ends of the vise jaws before tightening up the vise. When cutting the wrench flats be sure that the cutting is done on the right-hand side of the vise so the end mill rotation bites into the nipple and screws it into the 2.5” bar like two gears meshing, it is a common problem for parts to rotate that are held in the milling machine by threads and aren't tight enough to resist the forces generated by the cutting tool. Because of that they make left-hand end mills and drills.
The last steps are to de-bur the nipples and heat-treat them.
rl632
I had to make up a new set of six nipples for one of my Italian-made replica 1858 .44 Remington cap and ball revolvers because they were so badly rusted they might blow out, plus make six more nipples for my brother-in-law's replica 1851 .36 Navy Colt because his little nephew dry-fired the revolver and mushroomed them over. The nipples that the local gun shop had in stock weren't the right thread size and they said nipples from Midway, Cabella's, Bass Pro, etc, were a special order that could take three months, plus they had had a lot of trouble in the past with getting the wrong size thread. While I was at it I removed all the nipples from all my replica revolvers to see what size threads they have, and no two guns used the same thread! They were all metric as well, which didn't surprise me since they are all Italian. While I was at it, I decided to make new nipples for all of my pistols to have on hand because of the problems with ordering new ones.
Metric thread pitch notation is not given the same way as in the English system, the metric sizes are given in the distance from one thread crest to the next measured in millimeters instead of how many turns per millimeter or centimeter, while English engineering it is the number of threads per inch, or tpi, which is the mathematical inverse used for metric engineering The thread sizes I found were the following, given in both metric and inches:
6mm x 0.75mm, 0.236” x 33.87 tpi
5.5mm x 0.95mm, 0.217” x 26.73 tpi
5.2mm x 0.9mm, 0.205” x 28.2 tpi (this thread is close to the U.S. #12-28 thread, but the body of the #12 thread is 0.216” and too big to fit)
I'm sure there are other thread diameters and pitches as well, so you will need a set of metric and inch-size thread gauges to determine exactly what you have.
When I machined the thread bodies, I made the diameters the exact metric measurements even though the original nipples were under-size, some by quite a bit. When I installed them, they all fit fine. My lathe has metric conversion gears plus eight different thread pitch switch gears that came with the lathe and go in the gear train from the headstock spindle to the carriage feed screw gear ratio selector box. Using the switch gears I was able to duplicate all three thread pitches even though the gear ratio box for the carriage feed screw supposedly couldn't do the 0.95 mm thread pitch. The 0.9 mm thread pitch is close enough to 28 tpi so that I just used that inch-size thread.
The important thing with making nipples is to be sure that the nipple length from its tip to where it tightens up against the cylinder body is not too short, if it is too short the pistol hammer will not strike the cap hard enough or won't strike it at all. If it is too long the hammer won't strike the cap squarely and possibly peen the end over at an angle and close up the flash hole.
I used a medium carbon steel (probably AISI 1045) that will harden up to somewhere around 40 Rockwell C so the nipples will resist mushrooming and have a long life. The bar of steel I used is a new 3/8” X 12” bridge spike that I tested for hardenability, it hardened up nicely so I used it as bar stock for the project. After all the machining was completed I heated up the nipples to bright cherry red with a propane torch and quenched them in plain water to harden them, then I tempered them to a dark straw yellow color so they won't fracture. Before tempering they need to be sanded a bit with fine sandpaper to remove the light coating of fire scale. I don't use sandpaper in my lathe so I turned the nipples with an electric drill motor for light sanding.
The metric thread profile is very similar to the United States thread profile. They both have 60° sides with truncated crests and roots, but I ignored the exact amount of truncation and simply machined my tool bit to a sharp 120° point, which for an application like this works okay. I followed standard thread-cutting procedure, setting the compound feed at 60° and used the compound feed to advance the cutting depth. The ultimate depth of cut, as measured on the compound feed dial, was somewhere around 0.022” for all three thread pitches, give or take a bit depending on the particular thread pitch. I machined the nipple threads to fit the female cylinder threads, noting the depth of cut as soon as the first one would screw into the cylinder and then machined the rest for that particular gun to the same depth.
The first operation is to machine the greatest diameter on the nipple, which is its head (where the wrench flats are cut), which on the three sizes of nipples were all 5/16” (0.3125”) in diameter. The next step is to machine the major thread diameter and exact length of the threaded body. For nipples, it is important that the thread have a relief cut all the way up against the underside of the head so that the nipple can screw all the way into the cylinder and make a gas-tight seal between the underside of the nipple head (the head is where the wrench flats are cut) and the bottom of the nipple well that is cut into the rear of the cylinder. The way I cut the relief was to simply disengage the carriage feed after the thread was finished and cut an annular groove at the same depth as the thread in the area between the last thread groove and the underside of the nipple head (the 0.3125” diameter part).
After the thread is cut, the next step is to drill part of the flash hole through the nipple. I used a #60 drill, which was about the same size that I found in the factory nipples. I used a small center drill to cut a very small center dimple so as not to drill a large recess into the end of nipple, and then drilled the hole to a depth of only 0.125” (1/8”). A #60 drill breaks REAL easy, so to help prevent breakage I didn't drill the hole any deeper than I had to because it doesn't need to be very deep. The flash hole is stepped, the diameter of the flash hole in the cap teat is 1/16” to take all the fire from the primer cap but steps down to #60 just before exiting the nipple to prevent a lot of high pressure gas from escaping back out.
After the #60 hole was drilled in about 0.125” or 0.130” deep, I cut the nipple off about 0.025” longer than its finished length, using a regular parting tool. The next step is to machine the teat that the cap fits on. But before that can be done, a special jig needs to be made to hold the nipple blanks since they are too short to chuck back up in the lathe and be on-center consistently. Using the remaining 3/8” bar stock I machined a female thread in one end that more or less matches the thread in the revolver cylinder. This thread needs to be fairly precise to keep the nipple blank held firmly on center to withstand making some 0.010” deep cuts in it. I ground an internal thread boring tool from a 1/8” square high speed steel tool bit, the threading tip being ground at about a 15° angle to the axis of the tool bit so the tool bit enters hole in the 3/8” bar stock at an angle, which gives clearance to the front side of the tool bit and keeps its from hitting the inside of the hole. If this isn't done, then a good part of the length down the front side of the tool bit has to be ground off to give the thread-cutting tip clearance to cut into the side of the hole, and grinding high speed steel on a bench grinder by hand is a very time-consuming job, even on a 1/8” square tool bit. Because it is at angle, though, the back side of the threading tool will run into the thread bore if it goes in too deep. If you have an insert-type miniature internal thread boring bar then you don't need to make your own. Once the female thread is machined into the 3/8” bar stock so the nipple you just made will screw into it without slop, cut that end of the bar stock off so that it is about 2.5” long and set aside. Finish making the rest of the nipple blanks you need, checking them before cutting off by screwing into the revolver cylinder as well the female thread in the 2.5” length of bar stock. When all the nipple blanks are finished and cut off, remove the remaining bar stock from the lathe and re-chuck up the 2.5” length with the female thread in it. Screw the nipple blanks into it one at a time to finish drilling the flash holes in them using a 1/16” drill bit. I used a small center drill to start the hole on center, and a lot of care needs to be taken to make sure that the center dimple isn't so large in diameter that it bells the end of the flash hole. If a large starting hole is cut, the priming compound in the cap won't have much of anything underneath it to buck-up against when the hammer hits it and it won't ignite reliably when struck. When drilling the 1/16” hole, if you have a good sense of feel you can tell when the drill bit runs into the smaller #60 hole. If you aren't sure of yourself, use the tailstock micrometer feed to drill the 1/16” hole in far enough to meet up with the #60 hole. After the 1/16” hole is finished, machine the cap teat to its finished profile and length. Get the dimensions from an original nipple, being sure to take the nipple length measurements so it includes the thickness of the head where the wrench flats are cut since the length from where the underside of the nipple head mates with the cylinder to its tip is its critical length. I cut the taper on the teat at a 5° included angle, so the compound feed is set at 2.5°. The major nipple diameter I used is 0.171” at the base of the cap teat, which fits a CCI #10 pistol cap.
When the cap teats are finished at a 5° included angle on all the nipples, the last machining operation is to machine the nipple wrench flats in a milling machine. The tang that the nipple wrench fits over is 0.177” wide, which leaves only 0.003” between the wrench flats and the side of the teat (0.177” minus 0.171” = 0.006”, 0.006”/2 = 0.003”). Using the 2.5” long bar with the female thread in its end, screw in a nipple and tighten it in with pliers or a hand-held drill chuck that will accept a 5/16” diameter. Mount the 2.5” bar horizontally in a milling machine vise and using the table X , Y, and Z feeds, position a 3/8” end mill to cut the flats so that it leaves a 0.025” thick flange between the wrench flat and where the threaded body joins the nipple head. Calculate the depth of cut so that it leaves a 0.177” wide tang between the wrench flats. Take the 5/16” diameter of the head and subtract 0.177” from it and then divide by two to obtain the depth of cut (0.3125” minus 0.177” = 0.1355”, 0.1355/2 = 0.06775”. Round off to 0.068” = depth of cut). Since nothing is ever perfect, make several partial cuts with the end mill to make sure that the tang ends up 0.177” wide. If you go too deep the end mill will cut into the side of the cap teat. After one wrench flat is cut, rotate the 2.5” bar stock 180° and cut the wrench flat on the other side. If everything goes according to calculations, the remaining tang will be 0.177” wide and the nipple wrench will fit it perfectly. When one nipple is done, leave the 2.5” bar in the vise, unscrew the finished nipple, replace it with an unfinished nipple, and make the first wrench flat cut on it. When rotating the 2.5” bar stock be sure to brush away all metal chips from the mill vise so everything clamps back up precisely. I have a set of C-5 collet holder blocks that are square and hexagonal and are used in conjunction with a mill vise to precisely cut square and hexagonal profiles in the milling machine, and they made this job quite easy since it is difficult to rotate something exactly 180° without a fixture like the collet blocks. One way to do the job without a collet holder block is to clamp the 2.5” bar in the vise or to the mill table and cut a flat down one side, making sure that the flat is not so wide that it will prevent chucking up the 2.5” bar in a three-jaw lathe chuck for later use in case you need it again to make more nipples in the future. The flat will locate the bar in the vise so that it can be rotated exactly 180°. The end play can be located precisely in the vise by butting up the end of the 2.5” bar against a straight edge held across the ends of the vise jaws before tightening up the vise. When cutting the wrench flats be sure that the cutting is done on the right-hand side of the vise so the end mill rotation bites into the nipple and screws it into the 2.5” bar like two gears meshing, it is a common problem for parts to rotate that are held in the milling machine by threads and aren't tight enough to resist the forces generated by the cutting tool. Because of that they make left-hand end mills and drills.
The last steps are to de-bur the nipples and heat-treat them.
rl632