How to Build a Rifling Machine….A to Z…[ The Hook Cutter ]
Brought to you by Seacoast Artillery Company
What we are about to describe is one method of Hook Cutter production. Since we do not have a tool and cutter grinder, the method described is not fast, however, it is accurate, and we choose accuracy over speed any day, especially when it comes to things which are expected to produce precise work.
All of these tools and methods described can be used on a variety of rifling configurations. Except for the .080” offset tool holder, made specially for grinding the peculiar Brooke rifling groove shape, all of the tools and methods described here may be used with any uniform style of rifling such as the Parrott or James System rifling.
After this segment is released, Mike and I will do our very best to answer any questions about any part of the rifling machine or method used to make it. So, don’t be shy; ask away!
Step#
68. Cut a .650” long piece of Fagersta WKE45 Swedish Tool Steel from a bar 5/16” x 7/16” x 4”, available from Manhattan Tool Supply. Don’t waste your time on any lesser quality steel. Buy this quality or an equal if you KNOW for sure that there is an equal. We wasted our time and money until we found this type, so you don’t have to. This type stays sharp a long time under normal conditions of use. The last two barrels we cut did not need ANY sharpening at all. Surprised? We certainly were!! Happy too!
69. We score all sides with a 1” dia. cut-off wheel on a Foredom Tool .150” deep. Then place firmly in a vise with just the part you want above the jaws. Hit sharply with a large plastic mallet. Your scored piece should pop off easily.
70. Rough grind a 27 deg. angle by hand on a regular silicon carbide grinding wheel after carefully marking on one of the 7/16” sides.
71. Rough grind waste from in front of the hook, .180” in from end opposite 27 deg. angle and grind from the top until only .210” is left of the height measured from the bottom surface. This leaves .030” over final dim. for final grinding.
72. Rough grind a 33 deg. angle on the front after marking on the same side as before. Do NOT shorten the rough ground hook at all. You have only .050” over, total on the bottom surface finished length of .600”.
73. Grind a .050” deep relief cut with a cut-off wheel at approximately 45 deg. to the bottom surface of the hook at the intersection of the hook face and the forward 33 deg angle.
74. Take a look at the marker board sketches of the capture and rake angles you will be grinding. Understanding of how they get to final shape is the purpose here.
75. Set up your rough ground hook as shown in the vise and precision protractor photos and clamp firmly.
76. Using a diamond plated drum grinding point, grind the 27 deg. angle in .0005” stages until your final grind intersects with the bottom surface. We use two passes for each .0005” with thread cutting oil continually applied.
77. You can inspect the angle you just ground to see if it measures it’s IN USE attitude which should be 30 deg. Take a .0262” gage pin and place it on a parallel bar or 1-2-3 block on the optical comparator stage. Place the hook on it exactly .500” from the front end. This is to get the bottom of the hook at a 3 deg. angle from the 1-2-3 block. Sine of 1 deg.at one inch is .01745”, so sine of 3 deg. at .500” is .01745” x 3 = .05235” / 2 = .026175” or .0262”, rounded off. We lucked out and had a pin right at .0262”. Take a look at the OP image; your 27 deg angle becomes a 30 deg angle as if it were sitting on the 3 deg wedge inside the rifling head.
78. Set up to final grind a 33 deg. angle on the front of the hook. Grind until your
final grind intersects with the bottom surface of the hook.
79. Inspect as previously described.
80. Set up for cutting the hook face at a 2 deg. Angle. Grind the height dim of .210” from the bottom only until clean-up. A little extra on the height from the final of .180” is not going to hurt anything. Save your grinding drum when ever possible. Grind back in minus -X- axis until the 2 deg. angle cleans up.
81. Inspect using the same method as before. The tolerance on these angles is +/-
.25 deg. If your initial grind does not work, carefully set up and regrind to minimum necessary to get the correct angle.
82. Now lets make the offset grinding fixture which will allow us to grind the very
important 13 deg. top relief angle, which is 16deg. as ground and 13 deg. in use.
Get a piece of .625” dia., O-1, drill rod, 4” long. Chuck in the lathe, face off and center drill to .200” dia. with a # 4 center drill. Swap ends and repeat.
83. Place in the mill vise, tighten moderately with 1/3 above the top of the vise zero the -Y- axis on the center of the rod.
84. Move vise and part minus .080” along the -Y- axis.
85. Zero the -X- Axis on the end of the rod; center drill and drill the rod .300” deep with a .250” dia. drill bit 1.00" from the end.
86. With a 1/4”, solid carbide end mill, mill a slot by plunge cutting, in .050” increments along the -X- axis, 1.00” long by .300” deep.
87. Re-zero the -Y- axis and widen the slot, taking equal amounts off each side until a width of .312” is reached.
88. Chuck in lathe with opposite end from the slot sticking out 1.5”. Knurl a cross-hatch pattern for one inch from the end of the rod.
89. Place in mill vise with 1/3 above the top, with the knurl to the right. Look at the slot; the thick side should be facing you. Rotate clockwise 90 deg. while looking at the knurled end. The slot should be facing away from you now, with it’s thick side upward.
90. Center drill and tap drill two holes for two 8-32 set screws which will hold the hook securely as the cutter relief is being ground. They should be centered on the length of the slot and .400” apart, .150” minus -Y- from the surface of the rod farthest from you.
91. With the rough ground top surface of the hook visible, the off set hook grinding fixture should look like the one in the first photo.
92. The next two photos show how we used to hold the grinding fixture. It worked just fine, but didn’t do the old v-blocks any good with all that swarf going down the sides of the “V”. We decided to build a very simple set of “centers” with hardened, 60 deg. centers and a spring loaded plunger to put moderate pressure on the grinding fixture to hold it without looseness, but to allow easy rotation with your fingers on the knurled section. The body is a piece of scrap aluminum and none of the dimensions are critical except the top should be parallel to the axis of the centers within .005".
93. Set up the centers so they hold the grinding fixture at a 16 deg. angle as shown in the first and second photos.
94. Because we used 3/4” drill rod, we had lots of fixture relief milling to do. You probably won’t have this to worry about, starting with 5/8” drill rod.
95. After tightening the set screws securely, move the diamond plated grinding
point into contact with the uppermost part of the rough ground hook. Grind in
.0005” steps as you did before, using plenty of thread cutting oil.
95. Grind until the particular radius of your tool is achieved. In our case it was .4295” .
96. Inspect visually to make sure all parts of the cutting edge are sharp. Remove
the wire edge here with gentle strokes of a hard Arkansas stone placed flat against the cutting face. Check the hook
relief angle on the OC. Plus or minus ½ deg.is the tolerance here.
96. Set up as previously described, the angle displayed should be 13 deg.
97. We use a “canned” routine on our OC to get inspect the radius. You can also use the radius lines on some charts supplied with a n OC or draw a 10X or 20X template to compare the desired radius to.
98. It’s time to grind the side relief angles. For right hand twist, you remove 6 deg. from the right side of the cutter as viewed from the muzzle when the cutter is in the 12 o’clock position. It’s just the opposite for left hand twist. The opposite side is normally ground to a 9 deg. relief angle, but, as you can see on this particular rifling form, the profile goes ABOVE where the land is before the side of the cutter is reached. Therefore, no relief angle is necessary here. The photo shows what the angle looks like when it is ground .060” down from the hook’s highest point and we also had to grind in from the side .025”, because of a .050” difference in the width of our cutter and the width of the stock available. The .025" side grind was not necessary on the opposite side for the same reason that no relief angle is necessary on this side.
99. You can see the corner radius or “hook” in the modified “slant hook” rifling groove which is unique to Brooke rifling. It is equal to the depth of this rifling which is .023”. Its form is not absolutely perfect under 20X magnification, but pretty good considering it is ground by hand using a small hand-held diamond stone. You must grind this radius all the way back to the end of the hook, not just the cutting face of the hook cutter.
100. The silicone-rubber, (dental impression material by Kerr Co.), molding is
of the Parrott rifling that we make for the 1/6 scale, 100 Pdr. Parrott
Rifle, Model 1861. It shows what “blind hole” rifling looks like. You can see
how the grooves are gradually deepened by adjusting the waterfall cut actuator
and reach full depth in approximately one-half inch.
101. Mike inspects the side relief as shop-cat looks on. He loves sitting on that
little computer box. Must be the fan-driven warm air.
102. The last two details to be made are the .125” deep X .500 long chip recess
seen in front of the hook. Also, Mike made one refinement which we did not
have in our shop sketch. He beveled the end of the top of the 30 deg plunger tip
with a shallow 15 deg bevel, .350 long, so that the chips do not have a 90 deg.
shoulder to get caught behind.
Well, that’s about it. Any questions? Ask away!! We will discuss how all the parts work in concert in a future posting.
Regards,
Mike and Tracy
Seacoast Artillery Company
-Uploaded by ZakaryX
