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View Full Version : Maybe this is a silly question - self-twisting broach rifling



Tokarev
05-02-2012, 12:17 PM
Is this going to work, if I took a round carbide insert and cut groves at the rifling angle on its outside surface, then pushed it thru a barrel? Would it be enough for it to spin itself and cut uniform rifling?

Did anybody try that method?

I know that 45LC rifling angle is 1.63 degree, and 308 angle is roughly 3 degrees. These might be too sharp to spin the broach properly.

B R Shooter
05-03-2012, 07:54 AM
From what I've seen on rifling machines, when the button or cutter is pulled, there is a mechanism in place the rotate the cutter or button at the same twist rate. Looking at the diameter of the pulling rods, I doubt seriously if that is actually doing the rotating of the cutter, rather it is merely keeping the pull rod from twisting off. Buttons and cutters are ground with the "pitch" in place. I always thought a bearing mounted on the pull rod would take care of it all, but I'm not a barrel maker....

There is only one maker that "pushes", and that is Hart from what I know.

felix
05-03-2012, 08:09 AM
Back in the 70s for BR work, the choice of barrel was either Shilen or Hart . The Shilen barrel was selected if it was accurate from the get-go. The Hart would not be selected until it was shot in within a 100 rounds or so. The wait was worth it because the latter barrels lasted longer for the same accuracy. It all depended on when the gun was put together in relation to the season. In reality, however, more than one barrel was used during the season. ... felix

Tokarev
05-03-2012, 08:43 AM
I want to try broach rifling with that method using precisely what BR Shooter suggested - a thrust ball bearing at the end of the rod to take care of spinning.

There are 3/8" and 1/2" round cutters widely available, but I am most interested in cutting .429" or .452" rifling in a 410 barrel. Does anybody know if those diameters are available? I can make them out of 1/2" using a toolpost grinder, just being lazy.

B R Shooter
05-04-2012, 07:07 AM
OK, to get a little more technical, I think you want to cut rifle the barrel, not broach. My understanding of broach rifling is the broach cuts all grooves at the same time, and is not used by many barrel makers. Cut rifling cuts one groove per pull, and only takes maybe .0001" per pass, so MANY passes are needed, per groove! Button rifling of course swages the steel, and is much harder to pull through, but it is a one pass process. Keep us up to date.

John Taylor
05-04-2012, 10:31 AM
I have not had much luck getting a smooth cut on shotgun barrels, probably me not having a good day. A button will not work on a barrel that has already been contoured, you would have good rifling where the barrel is thick and very little where the barrel is thin. A rifling broach is very expensive and can break easy.
I have installed a few liners on 410s for small calibers but I think the best way to make a rifle out of a 410 is to cut the barrel off and thread the mono block and screw a barrel in. Green Mountain has some barrel blanks under $100 that work very good for this.

MBTcustom
05-04-2012, 10:38 AM
This would work kinda/sorta. You would want a bore-riding tail on that cutter to keep it centered. The big problem with this idea is that you will end up with very rough rifling that has "rings" akin to chatter marks all the way down the barrel. Not that that is necessarily a bad thing but it wont be the most accurate thing by a long shot. For a shotgun, maybe you dont mind. If you want smooth rifling, and you dont have the help of hydraulics, you need to make a rifling bench. The broach method can be made to cut smoothly, but again, you will need a lot of rigid power to pull that sucker through in one smooth stroke.

Tokarev
05-04-2012, 01:45 PM
Another alternative I am researching is laser engraving.

MBTcustom
05-12-2012, 09:57 AM
Have you thought about electro-chemical etching?

Doc Highwall
05-12-2012, 11:09 AM
I do not believe it will work. The cutter will skid in places and twist in others, compound this with the length of the barrel.

When I worked at Dan Wesson in Monson MA. our barrels were broach cut and the machine had a head that was set up to rotate at the same twist rate as was ground into the broaches.

Tokarev
05-12-2012, 11:34 AM
Have you thought about electro-chemical etching?

Yes, I have! That would require a template with negative groves made of plastic that would seal the rest of the bore watertight, i.e. it needs to be radially soft but rigid against twisting.

Laser engraving would require a rod, spinning a 45 degree mirror around the barrel axis simultaneously moving along it from one end to another.

Interesting challenges!


I do not believe it will work. The cutter will skid in places and twist in others, compound this with the length of the barrel.

When I worked at Dan Wesson in Monson MA. our barrels were broach cut and the machine had a head that was set up to rotate at the same twist rate as was ground into the broaches.

Thank you for this info Doc!
What if I primed grove edges with narrow scratches first, then did a 2nd pass with hexagonal broach, and finally with the round broach?

MBTcustom
05-15-2012, 06:01 PM
Or, you could just build a rifling bench and do it the old fashioned way. Learning to grind the cutters is the hardest part of building a rifling bench I hear. You must have a way to drive whatever you use to cut the grooves, in the spiral that you are after. The nice thing about a rifling bench is that the ROT is easily variable by increasing the angle of the rack arm.
A question like this can be answered by observing what they used back in the old days. They had access to electricity and the chemicals needed to do electro etching, but they didn't do it that way. They used simple rifling benches all the way up until the 40s or 50s to make 99% of all rifled barrels. I would think that a home hobbyist could build something like that relatively easily.

Casting Timmy
05-19-2012, 07:34 AM
I think you can find Advance Gunsmithing by WF Vickery online as a pdf for free. His book gives a lot of info about how to rifle barrels using different methods.

Tells hwo to convert a lathe to a boring machine, use an old barrel to cut rifling into a new barrel, at least that's the two I can remember right now.