Sine-bar Rifling Machine Chassis and Upper Structure
Step 5 The chassis construction is pretty straight-forward. Check out the marker board sketch. All the important dimensions are there and all of the sizes shown are flexible. If you need more height, then make it higher than 6”, etc., etc. This structure is way over-built. We did that on purpose, but you could use three transoms if you wanted instead of six. The machine would still work just fine. We wanted the extra weight; you might not. That’s O.K. We used six ½”-13, grade five, bolts per transom. Four per would work just fine.
I think everyone understands by now that these photos and dimensioned sketches are mostly aimed at giving you new ideas or perhaps really old ideas with a new clarity. You must make your own mechanical drawing or series of sketches just as we did. On our dimensional sketch you can see that most of the upper structure is on the chassis centerline except for the artillery tube indexer, (lower left), the chain-drive hand-wheel and the sine-bar. The cross-over plates are full-width and various lengths specified on our sketch. They are ¼” thick. Remember you must change the length and position on these if you make a shorter or longer machine. They are dual-purpose plates, providing increased rigidity AND support for major machine components. These plates form what we call the “Deck” to differentiate it from the ½” thick, aluminum, Sine-bar Plate.
Step 6. After you get the Deck installed, its time to install the parallel Carriage Ways and their support pillars. We used Thompson ball bushing ways which are case-hardened steel rods, 1.500” dia. X 66” long. These are used a lot to make custom machines and are found at machine re-build shops. You can get them new from MSC Supply, a large supplier of machine shop tools and materials. We inspected them on our calibrated surface plate. They were straight within .0025” which is really good for 66”. The size was right on at 1.5002”. We placed them in the clamping pillar-block supports and placed them on the Deck before tightening the two clamp bolts at each end. The placement dimensions are not critical, just align with the edges of your chassis sides and lengthwise dims. are not critical either. Do you see all that space in front of and behind the sine-bar? From now on non-critical dims. will be designated with a NCD and the critical ones with a CRITICAL. The ways should be co-planer within .0015” and parallel within .0015”. This is CRITICAL. If you have a surface plate the first is easy, if you don’t, just build the carriage accurately out of good quality flat stock and be sure that the four “ way” bearings are all in the same plane within .0015”, CRITICAL, and use this structure as a gage to position the way supports up or down with precision steel shims or feeler gages until the carriage slides freely back and forth on the ways without binding or chattering. Buy slippery plastic bearings for the carriage supports and save a ton of money. Caged ball bearings of this size are VERY expensive. The parallelism of the set of ways can be measured with a good vernier or digital caliper, as our photo shows. We left about .125 of each end of each way outside the front and back surfaces of each pillar block to help align our four foot vernier caliper. Because the “cross-over plates which form the Deck are not perfectly flat and the U-channel flanges, upon which the Deck is mounted, are not perfectly straight, you must install the way pillars in the following precedence: First mount one way as parallel as you can to either the right or left side of the machine, which ever side seems to be most straight. Tighten your two ¼-20 bolts moderately tight with a small 6 or 8 inch wrench which will firmly secure each of the two way pillars to the ¼” thick deck. Second, mount the way and its pillars opposite the first, being sure to drill the ¼-20 clearance holes in the deck large enough to allow a bit of side to side adjustment. .030” over the .250” dia. bolt size should be enough. Tighten those last four bolts finger-tight only. Measure the distance between the outside of the ways at both ends. Make these numbers match within .001 if you can. The spec. for parallelism is .0015. This means .0015 or Less. Once you get to this point, tighten this set of bolts moderately tight. The methods for getting this assy. Into a “co-planar condition where all top dead center points on each of the two ways are all in the same imaginary “plane” have been previously discussed. The proof that all this has been done accurately is the fact that the close fitting plastic bearings in the carriage pillars must slide freely upon the ways allowing the carriage “chatter-free” movement as to goes from one end to the other. Several trials and some shimming may be necessary to achieve smooth carriage sliding. Crank down on the way pillar bolts as much as aluminum will allow when you are sure that free carriage movement has been achieved.
Step 7. The photo with Mike standing next to the completed chassis is used to show that we placed all the various loose components on the Deck to see if our sketches allowed for enough clearance here and there. This “reality check” can save you some heartburn later on!! We built the chain drive next which was pretty simple. We bought enough industrial “power transmission” roller chain to form a continuous loop around two 4” dia. sprockets with the proper tooth spacing to fit the chain’s link spacing. You will have to dismount the two cross-over plates which hold the sprockets so you can cut the slots or notches in them to allow clearance for the bottom of the sprockets. The 1” dia. sprocket axles are secured to the deck in four inexpensive Browning pillow blocks with grease fittings. The spacing is 115-48=67”. Buy ENOUGH CHAIN and three “connector links”, one spare, for attachment to the carriage attachment hardware. Make sure that you buy a long-enough 1” shaft upon which to mount your 12” dia. hand-wheel outboard of the machine’s side and bench edge if you support the machine as we did.
Step 8. Look in the MSC catalog for these items. If you are comparison shopping, be sure to check out the large McMaster-Carr catalog too. They have all this hardware in their “Power Transmission” section including roller chains and roller chain sprockets. Adjust the alignment of these components until the chain goes around and round smoothly. NCD here. You get about 3:1 mechanical advantage with this set-up, ignoring friction, of course. This is plenty of power to cut grooves of up to .350” width, even in pre-hardened, chrome-molly steel, 28-32 Rc as long as you limit your depth of cut to two tenths, .0002” or less. The next two photos are displayed to give a general sense of how the components are interrelated. If you look closely you can see that we used four heavy duty O-rings where the way ends intersect the way support pillars. These act as bumpers for the carriage which normally does not get near them. You can also see a small mistake. We did not account for chain droop by making the second, third, and fourth transoms an inch less in height. We cut chain clearance notches with a hacksaw and filed the waste out from each notch rather than take the whole chassis apart. That task was fun……..NOT!! You can see the T-shaped , chain-end to carriage connector hardware (2x) we milled and drilled. We use cycle chain lube on it before each job.
You can tell by now that we joined the first two
Sections of this explanation together and the Chassis
and Drive Mechanism Sections have been merged.
Step 9. Use the photos above as a general guide to build this Artillery Tube Indexer next. Again all these dimensions are NCD. You can see that the dimensions which you use must be suited to your tube O.D. We used a ¾” O.D. plunger with a taper on the end which fits nine 60 deg. countersinks which are machined in the indexing collar which is bored to a slip-fit with the still-cylindrical cascabel and attached to it by 5, ¼-20 set screws down in the bottom of five of the nine collar countersinks. If this indexing collar slips half way through the rifling job, you will be VERY UPSET and will be forced to toss the tube into the scrap bin or to ream to a larger size if you have a rifling head for that size. Tighten those set screws accordingly, but don’t strip the threads in the aluminum collar. We think five is a minimum number to have, because of the CRITICAL nature of this application. The taper-end plunger is about 6 inched long and has a reduced size journal inside the supporting block shown, for a coil-spring plunger extender. You must pull the exposed knob outward against the spring action to retract the tapered end of the plunger from the c’sink in the collar. Please note that we use a very sophisticated plunger knob retractor. It looks just like a small pry-bar, doesn’t it? CRITICAL…..Place the centerline of your plunger at the same height above the Deck as the axis of the pinion gear shaft.
Step 10. Build the breech-end, 90 deg., V-Block tube support next. Look at that scale for dimensions here. The are all NCD except the height at which your particular V-block holds your particular size of breech on your cannon. Simplest way to do this is to draw it out full size and build accordingly. We suggest you buy some 1/8th inch thk. solid carbide pads (4) to JB-Weld to the V-block surfaces. Your tube will rotate much easier if you do. A small dab of gun-grease is good for this application too. Size the thickness of your V-blocks to match the standard width of the carbide pads available. Usually the 1.50” wide pads that we used are available.
Step 11 Lets build the muzzle-end, 90 deg., V-block support and muzzle-stop now. Again, the height is whatever you need to get your tube axis up to and co-axial with the pinion gear shaft axis and should be coordinated with the breech end support to have the entire artillery tube axis co-axial with the shaft axis. Drill the Deck clearance holes a little large, about .280 dia., for a ¼-20 bolt to allow for some multi-directional adjustment. Make a muzzle clamping bar also. We used 3/4 x ¾” stock and two pieces of all-thread about 4” long and two ¼-20 flange nuts. Leave these blocks unaligned until you complete the carriage and pinion gear assy. At that time you can clamp a 4”x 4”x1/4” thick piece of flat stock to the end of the shaft nearest the V-Blocks and mount a Magnetic base with a test indicator on it. With the pinion gear shaft in its bearings FREE TO ROTATE without any follower contact with the sine-bar, sweep the contact surfaces of each V-Block at the front edge and the back. When the four readings are the same or within .002 or .003”of each other, then tighten the V-Block hold down bolts. Repeat this procedure on the other V-Block and fasten it to the Deck as well. The muzzle stop is a simple, steel block as tall as your situation needs it to be by 2.0" x 1.5”. Its length should provide clearance for the rifling head which passes over it. This stop is there to prevent the artillery tube from pulling out of the V-Blocks as you cut the grooves. We clamp a medium size angle plate to the deck at the breech end to prevent the tube from sliding out of the V's in the other direction. Build your V-blocks to handle the largest diameter tube you anticipate building. As one of our photos shows, you can bush a smaller tube to bring its axis up to be co-axial with the axis of the pinion gear shaft.
Step 12. The carriage consists of a 4142, pre-hardened, ground steel plate .50 inch thick and two 4142, ground steel bars to contain the rack. They are nice and flat with a smooth ground surface so all you need do is cut them to length and drill and tap them for the assembly screws. You will also have to mill a long groove under the rack, through the .50 in. carriage plate so the follower pin can reach the rack and move left and right as it tracks along the sine-bar. Remenber the length and position of this groove is based on your specific range of rifling twists and a careful sketch should be made before you cut the groove, which includes where your sine plate is placed and how much it diverges from the tube's axis.
The Four pillars which contain the linear bearings are attached to the bottom of the carriage plate at the corners. They should all be bored out to accept the bearings". The size will depend on what bearings you use; we used spit plastic bearings, because they were cheap and they work great. NOTE: this bored hole’s location is CRITICAL, the distance to the mounting surface with the .50 in. steel plate should be held as close as possible (.001in.) .
The rack is held in place by the two steel bars and the bars should be tall enough to also capture the teeth of the pinion gear. The rack should be stoned on the sides and bottom to remove burs. It should be a sliding fit in the assembly with very little to no play side to side. All this should be heavily greased.
The pinion gear is attached (should be a push fit with two set screws)to the tube/rod, called the pinion gear shaft, that supports the cutting head. This shaft is held parallel to the carriage plate by two ball bearing pillow blocks. These blocks are positioned so the pinion gear will engage the rack with minimum play yet allow smooth movement; use shim stock to achieve this condition.
A follower that tracks on the sine bar must be attached to the rack, it is usually attached at the end of the rack with the sine bar located on the backside of the machine. We positioned ours on the middle of the machine between the linear ways to save space. This can limit adjustment and ease of use to some degree. We bored a blind hole (.50 in.) in the bottom of the rack then fitted the follower pin in the hole with a tight sliding fit, very little play, because the follower needs to be able to be rotated in the rack. The other end of the follower is a square block with a wide central groove cut to match the sine bar width.
The sine bar should be wide enough to prevent flexing as the follower moves along it. If you are going to use straight, non-progressive rifling, then a wide bar ( one inch) is better. If you are thinking of using gain twist, progressive rifling, then the bar must be curved. Bending a one inch wide bar will take quite a bit of force; we used a .50 in. wide bar and held it to the sine-bar plate with three screws to prevent flexing.
To ensure that the hook cutter follows the same track every time, backlash in the gear and follower assemblies should be eliminated. We used a moderately wound clock-work spring, attached to the pinion gear shaft at the back of the carriage and to the chain/carriage connector hardware as well.
Step 13. Let’s build a sine-bar and install it. We used 4142 steel, pre-hardened to 28-32 Rc, precision ground flat stock, .500” wide x .750 high x (your twist no. goes here, one turn in ‘X’ inches) plus 6”. It’s nice to have an extra 3 inches on each end for sine-bar follower over travel. We will show how to calculate the gain twist for one turn in 36” first, then we will explain how to do it for a straight twist. The harder one first is explained thusly:
Take a look at this Sine-bar shape explanation marker board sketch and math. Basically there are 3 Critical dimensions that we used to produce, then set up, the two sine-bars.
They are these: 36” Our 1/6th scale Parrott Rifle has gain twist which means that it goes from zero twist at the start to one turn in 36”. The sketch shows what the two bars look like on the sine-bar support plate. Also we have distance the rack travels which equals the circumference of the pinion gear’s pitch diameter, 5.026” not the gear’s O.D. Finally, the very important radius of the circle, R 131.442”, which is tangent to the start point (T) of the rack’s follower travel along the curved sine-bar.
To make the curved or gain-twist sine-bar, we cut our .500 inch X .750 inch, 4142 pre-hardened flat stock to about two feet over the chord distance which is 36.349” or 5 feet.
Then we swung an arc with a tape measure having a pivot hole at 132.442 inches and a pencil hole right at 1.000 inch. We used a piece of butcher paper on a smooth board placed on the floor to take the arc. We bent the bar every .500” in our Kurt ang-lock vise by placing one inch steel pins cut from drill rod stock between the jaws, two at either end of the movable jaw and one centered on the fixed jaw supported by a thin parallel bar. Hold the bar between the pins, starting at about 9” from the end, with the .750 dim. up and down, crank down on the vice handle. Easy does it; use moderate pressure until you see how much bending is going on. It was bend and try, bend and try, over and over until all parts of one side of the bar were coincident with that 131.442 radius line. The bar shows no perceptible wear even though the follower has been over it almost 12,000 times!
The straight twist is simple. Pin your straight bar at the breech end and kick the other end over to the right by 5.026” at a distance of 36”. Clamp it down. Slip the follower over the end. Your done.
That’s about it. Hope the math agrees with your’s.
Tracy and Mike Seacoast Artillery Company
Step 14. From these photos, you can get a pretty good idea how to build the pinion gear shaft support. We used the structure show which is aluminum plate .75” thick and two bolted gussets of the same thickness. The oil-impregnated sintered bronze bearing we used was 1.00” O.D. and .7505” I.D. to fit a 4130 pre-hardened shaft, (tube actually), with a .7500 O.D. and and a .4375” dia. through hole. This 7/16th inch hole can really save your bacon if the rifling head ever gets stuck somewhere in a BLIND HOLE. You just throw the BACON SAVER ROD of 3/8th inch diameter steel down the tube until it disengages the bottom wedge and lets the hook cutter retract into the body of the rifling head. Viola! The head, she moves out of the cannon’s bore, and you can breathe once again!
Step 18 The CRITICAL dimension here is the distance from the Deck to the center of the pinion gear shaft/tube taken just ahead of the front edge of the carriage. Let’s say that you measure to the top of the shaft, take half the shaft dia. away and get 3.039 (ours). Well, just make sure you accurately indicate the center of that hole on your .75 aluminum plate where your shaft/tube bushing will go. If you are not dead-nuts with this one, you will probably have to shim it until the shaft will pass through without any chatter. We did this and also put a thin film of epoxy aluminum under the whole structure, then put 200 pounds of barbell weights on it to squeeze the goo out. After it sets up and hardens, tighten your ¼-20 bolts from under the Deck, three on the main plate and two each on the gussets. Be sure to oil those shims if you want to get them out of there after the goo sets up. Before you assemble this structure and glue and bolt it down, don’t forget to shape the top of the main plate so it doesn’t look like a left-over floor tile.
Now Mike and I can start working on the rifling head photos and explanation. It will be AT LEAST 5 days before you will see this last, and most anticipated section. We hope to provide some answers to those excellent questions as well on Tuesday or Wednesday.
Tracy and Mike Seacoast Artillery Company
P.S. Yes we know that the big radius in the marker board sketch of the sine-bar lay-out is 131.442 in one place and 131.443 in another. That's my fault, not Mike's. I forgot to round off the number, but .001" in almost 11 feet is not much to worry about. My fifth grade teacher would wrap my knuckes with that thick, solid maple ruler she always carried, if she saw me do that, but you can't. Yes, I forgot the upper arrowhead on the 7.9xxxxxxx angle too. If we had a nice autocad program and a top-notch instructor like Cat Whisperer to teach us, we would not have these little irritations to deal with.
