"rigid tap" CNC broaching of pistol barrel?

[spaceman_spiff]

sorry its a question not an answer!

Im wondering if it would be possible to make make a simple broach, and the install it in a CNC mill that has rigid tapping.

Or to be more specific, synchronized spindle rotation and Z axis.

And then create the riflings by many repeated passes with the same broach.

Since there could be many, many passes, perhaps the broach could be very simple and strong, something single tooth but with alot of material behind it.

Flood coolant could be injected into the barrel from the bottom, pushing the chip(s) up and out.

????

 

[dave2176]

It is not very likely that the rifling in a pistol barrel would complete one rotation. I think you would want all cutting points in contact at the same time so that pressure would be applied equally. Since the rifling is only a few thousandths deep I think you would cut it in one pass.
Dave

 

[dracozny]

Typical Rifling is anywhere from .002 to .006. Cut rifling can be done with a single cutter broach but the shaft is near the same Diameter as the bore you are cutting in. More common methods on the professional level for cut rifling uses a multipoint cutter that can cut all the rifling in one fell swoop yet to the untrained eye you would think it was a button rifling machine.

You could do single or multipoint on a mill, although many would prefer to do it on a lathe. On Rifle Barrels I recall seeing it done in multiple passes at .001" Intervals with a small button that pushes the cutter deeper with every pass.

 

[Karl_T]

Your theory is sound a but a CNC is built for a small amount a linear force and a lot of rotation. You need a lot of linear force and a very small accurate amount of rotation.

read this book http://riflingmachinemethods.com/

I'm all set up to gun drill on my CNC lathe and button rifle 9mm and commie 7.62. there's a guy selling rifling buttons for these two bores on eBay all the time.


In practice you can't beat buying barrel blanks from Green Mountain

 

[Jonesturf]

+1 for Green Mountain

Sent from my SAMSUNG-SGH-I317 using Tapatalk 2

 

[spaceman_spiff]

Your theory is sound a but a CNC is built for a small amount a linear force and a lot of rotation. You need a lot of linear force and a very small accurate amount of rotation.

read this book http://riflingmachinemethods.com/

I'm all set up to gun drill on my CNC lathe and button rifle 9mm and commie 7.62. there's a guy selling rifling buttons for these two bores on eBay all the time.


In practice you can't beat buying barrel blanks from Green Mountain

If we're talking about a 5 thou deep by say 30 thou wide groove in steel thats not asking alot as far as forces. Even a mini mill can drive several hundreds pounds through the Z axis. Remember this is for cutting not button forging.

A groove like that has a cross section of about 1/10th a mm2..using the specific cutting resistance of steel of 315 kg/mm2 that comes out to 70 lbs.

 

[spaceman_spiff]

I did a little experiment to see how much force is required to make a groove like that.

I happen to have an approximately 1/32" wide grooving tool.

I put a bar of 303 SS and turned it down to 1.2".

Then I moved the tool in until it just started to touch.

I then moved the tool away from the spindle until it was past the work and moved it in radially 5 thou.

Then I moved it back into the work (scratching the work).

I then put a fish scale on the chuck and pulled until the chuck rotated.

It did so at about 16 lbs.

That was at a radius of about 3.5 inches.

So 56 inch lbs of torque.

The workpiece dia was 1.2".

So the force at the tool was about 46lbs.

Multiply up or down as needed for whatever material the actual barrel would be made of.

So I think the hard part of doing the the single tooth broaching of a pistol rifling on a mill would be getting the required finish. The forces arent really an issue as far as the mill is concerned, even a hobby mill could put out this much force. But deflection of the broach, chip clearance, and finish would need some tuning.

Would be neat because you could CNC control the twist rate, and pretty much put as many riflings as you want exactly how you want without any additional work, once you figure out how to do one.

 

[merkelerk]

Years ago I was at Colonial Williamsburg and watched a craftsman rifling a flintlock barrel using only tools and methods available to late 18th century craftsmen.
Very cool.