Cut rifling

Hi Guys, as you know I`m in to making cut rifle barrels on my lathe, but it`s not all beer and skittles. Having problems with the cutter leaving scratch marks in the bottom of the groves. The cutter tip is made of T/C and trying a back relief with a 90* degree cutting angle so it just scrapes the steel off, with a forward rake of 5* degrees it some times grabs into the steel cutting to deep. I'm getting this with 1045 and 4140 steel, but not to bad with 12L14 steel, and what's the best cutting oil to use, water soluble or straight oil. I see Kruger barrels are lapped after rifling and yes I`m doing that as well. Thanks for any ideas ,Homebrew.357.
, The cutter bits.

You should see the mess that pro reborers make when they try to rifle hammer forged barrels.The steel is just not suitable for the process.In my limited experience,a shearing cut produced by a cutter at 45deg across the bore centreline is much less prone to problems than a 90deg cutter.A lot harder to sharpen with a constant cutting geometry though.If I was going to do barrels now,I would invest in a button,and build a hydraulic machine .Even if your time is free,as in retired,there is still a limit as to how long a sane person can spend doing the hundreds of cuts required on a makeshift setup, like a lathe.Regards John.

Thanks for your reply John.K, You have helped with the 45* angle across the face of the cutter, a more shearing cut than scraping one. As I`m only doing this for a hobby button rifling is out and will not be doing any more unless someone wants to make their own black powder rifle, no one makes black powder barrels in NZ, have to import them, so will try to improve on my quality, and of cause it keeps me fit!.. Cheers, Homebrew.357.
, While there`s bullets in the air, there`s hope!.

Every now and again ,I get the urge to do something,but it soon passes.I have no excuses,well not many,as I have a complete machine shop sitting in containers or out in the weather.I had the urge to build a cannon,but on enquiring of someone with one at the range,it appears the cops have imposed arbitrary conditions that require about $250 in fees for someone[licensed by said cops]to proof said cannon.There are no proof laws in Oz,the cops have just dreamed this up.Enough of this,my main reason is to float the possibility of using diamond impregnated plastic as a rifling cutter.Simply a spring loaded spiral which cuts forward and back at almost any speed.I know these diamond grit plastic strips do cut fast,and they are dirt cheap.Regards John.

Plastic diamond grit strips!, sounds the perfect job to smooth out the bore, brand name?. I have a diamond grinding wheel and a fine slip file with nickel diamond on them, but have not heard of the plastic stuff. If you can give me a heads up on them will see if I can track then down, Thanks, great stuff, Homebrew.357.

Thanks for the most interesting thread I've seen in a while! I have also wanted to rifle cannon barrels or even just cannon barrel sleeves. I'm curious why is a single cutter called "cut rifling" when a broach is not? The broach also cuts.

For cannon barrels I've been thinking along the lines of making a special bench with hydraulics to push a broach, but not like rifle and pistol broaches, just one groove at a time.
Using a universal dividing head a helical groove could be milled in a minor diameter bar with tapped holes placed at certain distances along the bottom, to hold down the broach cutter (with multiple teeth), The around the periphery of the starting end a series of radial holes for guide pins for indexing from one groove to the next etc.
For a cannon I expect a depth of .020" per groove would be about right, which could not be gotten in a single pass, but shims under the cutters would be used to deepen each groove.

As stated it would be quite a learning curve, but this is something I've anted to do for a long time.

The old Pennsylvania rifle bores were (I believe) cut with a kind of saw type blade inset into the end of the bar, and it acted more like a file than a broach. But with tool grinding available each successive tooth could be made to cut an extra thousandth deeper than the last, or, twice as many cutting an extra half thousandth more.
parts

The one I saw was about the size of a credit card,and sold by the SSAA as a knife sharpener.For around $19.99 from memory.Someone gave me a knife sharpener from the shop with two crossed impregnated plastic rods.It really rips into khife edges.cost around $4.A friend of mine who did engines had special honing strips made up for Nickasil bores,but they were plated metal and cost a couple of hundred from some crowd in Melbourne.He also used to get the same crowd to diamond plate a large file,at a similar cost.Regards John.

partsproduction said:

Thanks for the most interesting thread I've seen in a while! I have also wanted to rifle cannon barrels or even just cannon barrel sleeves. I'm curious why is a single cutter called "cut rifling" when a broach is not? The broach also cuts.

For cannon barrels I've been thinking along the lines of making a special bench with hydraulics to push a broach, but not like rifle and pistol broaches, just one groove at a time.
Using a universal dividing head a helical groove could be milled in a minor diameter bar with tapped holes placed at certain distances along the bottom, to hold down the broach cutter (with multiple teeth), The around the periphery of the starting end a series of radial holes for guide pins for indexing from one groove to the next etc.
For a cannon I expect a depth of .020" per groove would be about right, which could not be gotten in a single pass, but shims under the cutters would be used to deepen each groove.

As stated it would be quite a learning curve, but this is something I've anted to do for a long time.

The old Pennsylvania rifle bores were (I believe) cut with a kind of saw type blade inset into the end of the bar, and it acted more like a file than a broach. But with tool grinding available each successive tooth could be made to cut an extra thousandth deeper than the last, or, twice as many cutting an extra half thousandth more.
parts

Click to expand...

I saw a demo. at Fort Roberdeau a few years ago. They used a rifling machine from the 1700s. It consisted of a bench that held the barrel stationary at both ends . A wooden rod passed through the bore, the rod had a small mortise cut into it at the same angle as the pitch of the rifling. Into this mortise sat the scraper which had 4 or 5 teeth,it put you in mind of a rack gear, neg. rake angle both directions. the wooden rod was attached to a wooden cylinder with 3/8" x 3/8" wooden strips screwed to it 60* apart in a spiral equal to the rifling pitch. this assembly fit into a metal ring with 6 3/8" square notches cut into it and was pulled and pushed by the operator. The spiral strips in the metal ring forced the wooden rod carrying the scraper to turn scraping the pattern in the bore.. They pushed/pulled it back and forth 10 times then indexed to the next groove.After all 6 grooves were cut the removed the scraper and put a .001" paper shim under it and repeated the process until the rifling was .004" deep. I asked a lot of questions and think they were glad to see me walk on, as they lost count of the strokes a time or two while I was quizzing them.

One old time gunsmith described producing cut rifling manually as"The best and most strenuous exercise for the shoulders and arms that can be had." Rifling a cannon by hand would take years.My idea was to make up a small cutter head using a carbide burr,needing only one pass per groove.The cops have come up with all kinds of crazy rules here ,and I have no desire to go any further.The $250 fee for proof was game over as far as Im concerned.You also have to be a member of a re-enactor group,and I have no wish to mix with crazies with red coats and mutton chop wiskers.Regards John.

Reinactors are a strange bunch,all right!!

As I mentioned,in Williamsburg,it takes 600 strokes to deeply rifle a WROUGHT IRON rifle barrel. Wrought iron is very gummy (at least the wrought iron they have access to is). I tried filing on OLD wrought iron,and it was not so gummy at all. In Williamsburg,they have to use whatever wrought iron they can find,and it might not be the best grade. They tear up old fences,use whatever they can as it's not made any more.

Wrought iron was made in several grades back when that was THE iron they had. The best was imported from Sweden,refined from nodules fished up from a lake bottom. The real secret to its superiority was that it was refined using charcoal. The British used coal,and sulfur got into the iron,making it "hot short" when trying to weld it. No one knew anything about chemistry till about 1830. They didn't understand what was really going on chemically. Only knew from empirical experience which could be very good,depending upon the personal skill and experience of the master.

The wrought iron is bad to pressure weld to the cutter,and they (In Williamsburg) aren't using a proper cutting oil as it wasn't authentic to use modern stuff. So,they suffer along,and still do! They use vegetable oils. Not containing sulfur like modern cutting oils. I think soapy water would be better. They used soapy water to drill holes in armor plate in the early days of iron clads in England,with carbon drills.

Speaking of old iron and steel, I watched two videos recently on youtube of reinactors replicating ancient iron smelting. One was African tribsmen who last made iron in 1960 when a French car smashed into a tree, why dig the ore out of the ground when you have the pure stuff right at your hand? But they had been smelting iron before that back to 150-300 BC! (Smelting Iron in Africa - YouTube) and the second one was a reinaction of medieval time iron production in Holland. (Medieval Iron Production in Holland Thijs van de Manakker - smelting ore - YouTube)
Both of them leave the first smelting apparently a goodly percentage slag that gets mostly beat out in the second operation, forging. All we do today started back then and up until Bessemer pure iron was a dream, at least from a commercial standpoint. Fascinating!
Also, I read a paper by a professor concerning original Damascus steel, it was not made by folding iron and steel over, hammer welding, (repeat, repeat) as they do now, it was done by forging "wootz" iron in form about the size of a pancake, which was a trade item from India. Today I found a video of what they discovered by analysis of ancient Damascus swords;
Wootz Ep 4: Making Wootz Steel - YouTube

Sorry about running off into the thicket there, the mention of old wrought iron got my mind revved up. It must have been difficult getting the fine results they did with what they had during the Pennsylvania rifle making times.

You are right about the softiron/steel used.I recently did a bit of machining on a rifle made in 1871,relatively modern.The metal was so soft it tore and balled up with a carbide boring bar,nearly had an expensive disaster.It requires a very sharp acute angled cutting edge to get a smooth finish,I cleaned up the torn surface with a toolpost grinder.Must have been very tricky to chamber ream without tearing.Regards John.

Homebrew.357. I just bought a cut rifling machine last week haven't had a chance to test it out yet. For the reason of designing cutter box and cutter it's self. In saying that the reason you getting chatter is probably due to lack of rigidity of the cutting tool in the cutter box allowing it to be pulled up into the barrel. And or the tolerance between your cutter box and bore can also be an issue.

You are probably right about that Mikhail, as an example when shaping a keyway in a bore of a steel hub I've discovered that 1/2 to 1 1/2 degrees is about all the hook angle the tool can have without it digging in. While it's true that 3 to 5 is better for smooth cutting in a rigid tool holder and machine when you add a wimpy holder into the equation a compromise has to be found, because a 3-5 degree hook will dig in. On the other side of that is a slight negative hook, which, I'm thinking, will chatter beside taking a long while to make headway.

I have run up to 12 degrees positive rake on rifling cutters and have not had problems with them "digging in". The problem with running high positive is that it becomes much more difficult to control the geometry of the cutting edge.

Generally if there are problems with deep cuts, or "digging in" it's caused by something else. You have to have enough room to contain the chip that is removed by cutting without the chip altering the cut by creating pressure on the body of the cutter. In your setup a thick chip would create pressure on the cutter body that would push the cutter out of the cut and it should self regulate. This is a good thing. In other rifling head and cutter designs a thick chip can create pressure on the cutter that causes the cut to get deeper and creates a snowball situation that can lead to broken tooling and a wrecked barrel. Make sure that the point where the wedge bears on the underside of the cutter is ahead of the cutting edge.

Inconsistent cutting depth is usually a problem with the wedge assembly. The wedge has to be precisely positioned, and cannot move from cut to cut or during the cut, until it is repositioned for the next cutting depth. I would start looking here for any problems with cutting depth.

If you are getting scratches in the groove there are several things to look at. First, they are usually caused by breakdown on the cutting edge in a carbide cutter. If you look at it under magnification, you will probably see little nicks in the cutting edge corresponding to the scratches in the groove. With carbide it is essential that you get your rake and relief angles correct or the edge will not be durable while cutting. Try different angles and monitor the finish with each one. Generally, when your finish is the best, it means that you will also have a durable cutter. When you hit the sweet spot, it's like magic. Also if you inspect the edge under magnification after sharpening and you see any chips at all, these will only get worse as you rifle the barrel. The cutting edge should fine enough that you can not see a visible edge under 40X magnification. Razor sharp in other words.

Also, with a carbide cutter, scrape cutting will not give you the best finish and it is detrimental to the life of the cutting edge. You want a full cut and the chip should come out of the barrel looking like a rolled up piece of fried bacon (stripey bacon for those of you outside the US). It should be fluffy and feel like very fine tissue paper when crushed between your fingers. If the chip is not the full width of the groove, it means there is a nick in the cutting edge, or your cut is not deep enough. When running properly a carbide cutter is capable of rifling 10-20 barrels before resharpening.

The best case for lubrication is to pump oil through the rifling rod and out through the cutter box. You cannot have too much oil, but you have to be careful that the oil pressure is not acting on the components in the cutter box. High oil pressure can push the wedge out from under the cutter amongst other things. Use a high sulfur, traditional cutting oil. Water soluble generally does not have enough lubricity. If you are just brushing oil on the cutter after every cut, it can work, but it is far from ideal.

The experience I was talking about is a single point cutter in a long bar making a keyseat. It has been my well established experience that very much hook while shaping causes digging in in that case. In a rifling cutter I assume the cutting edges are opposing cutting edges on the opposite side, not what I had shaping a keyway.

This is what I have for a 6.5 mm the cutter has through tool oil that comes out at the cutting edge, with the plunger I have a radius that matches the one end of the cutter to make a ball and socket joint. I was able to fine a good 50lb spring to hold good pressure against the negative angle on the cutter box to reduce chatter. Any thoughts on this design? I'm all ears and want feedback. Can't figure out how to add pictures to post.

Sorry I figured it out need desk top version not mobile.

Rifling a cannon by hand would take years.

Not so. These guys rifle 4150 barrels, though not full scale.