Machining radius contour barrel flutes

Ardent

Ardent

CGN Ultra frequent flyer
Rating - 100%
818   0   2
Location
Northern BC, Coastal BC, or Africa. Depends on the
Here's a question; what would be the best way to go about maching barrel flutes with a radius contour? Ideally I'd like to machine some really wild flutes, very deep with a radius profle and deeper as you move towards the muzzle, in a full bull barrel. I'm still limited in machining experience, the way I've so far considered is to end mill the channel with a slight angle towards the bore as you move to the muzzle, and then run a round stone and oil down the channel at the same gradient going deeper each grind until i end up with my radii. Unfortunately, I'll go through a lot of stones and time, though the stones are cheap. I'm simply looking to dramatically lighten the barrel and exponentially increase its surface area while keeping it quite rigid for its weight. Ideas? :) I've never seen a shop cut radius flutes, what cutters are they using?
 
You may be getting into grenade manufacturing... I wouldn't shoot or stand close to a deeply fluted barrel... even more so when it is stainless.

It looks neat but it induces stresses, and reduces weight a little along with an accuracy loss, possibly not meaningful depending on the cartridge/rifle.

The last stainless barrel I saw deeply fluted, opened up beautifully and all the pieces stayed attached... luckily it was being shot from bags and no fingers were lost... that barrel maker no longer flutes deep... and he bought a bunch back that he had fluted deep..
 
Try using a ball nose endmill with desired radius and put barrel on angle in a vise so you can quickly and easily machine radiused slots.Thats how I'd do it
Kuulnor
 
Good to know about the depth... I wonder if even though the solid ring of meat around the bore barrel may remain well above "mountain/sporter" countour the differential load carrying that's experienced with the flutes somehow causes fractures eventually...

guntech said:
You may be getting into grenade manufacturing... I wouldn't shoot or stand close to a deeply fluted barrel... even more so when it is stainless.

It looks neat but it induces stresses, and reduces weight a little along with an accuracy loss, possibly not meaningful depending on the cartridge/rifle.

The last stainless barrel I saw deeply fluted, opened up beautifully and all the pieces stayed attached... luckily it was being shot from bags and no fingers were lost... that barrel maker no longer flutes deep... and he bought a bunch back that he had fluted deep..
Click to expand...
 
kuulnor said:
Try using a ball nose endmill with desired radius and put barrel on angle in a vise so you can quickly and easily machine radiused slots.Thats how I'd do it
Kuulnor
Click to expand...

And noted, I'd looked at ball nose cutters and hadn't found any to my satisfaction, many were very small radius, I'm sure there's larger available. It's now looking like shallow, wide radius flutes to up the surface area.
 
use a radius mill cutter on an arbor set up half way down the dia. of barrel, to widen raise and lower. besides worrying about grenadeing on firing what are you going to do about stress relieving after machining?
 
Ardent said:
The barrel's going to be cryo'd once machined and bead blasted.
Click to expand...


I'm assuming your machining an already rifled barrel? Take very, very light cuts, and rotated to the next flute every cut to balance the stresses going in. If you finish one side first then another, you may inadvertently construct a "round the corner" barrell to a greater or lesser extent.
 
For fluting I usually use a radius cutter 1/4 inch wide. I seldom cut more than 3/32" deep but one could go to 1/8 and look ok if the barrel is heavy enough.
As far as stresses are concerned, you won't induce stress unless the cutter is dull or forced. You will only remove stresses which existed in the metal you cut away. A properly stress relieved barrel will move very little.
I always set up with a support in the middle of the barrel. If you want to deepen your cuts toward the muzzle, just use your dial indicator to set the barrel up at the appropriate angle.So, if you want to cut flutes which are .093 deep at the breech end and .125 deep at the muzzle, you simply set up so that the muzzle sits .032" closer to the cutter than does the breech end. I'll cut .060 or so for the first cut (in your case this would be the muzzle depth), then cut to full depth on the second cut. I cut each all flutes at the first setting then go around again for the second. I'll sometimes make a final cut at about .002" if the finish isn't acceptable to me.
To give you an idea of my personal feelings on fluted barrels, I have built myself a bunch of target rifles over the years. I can do anything I want and I have never had a fluted barrel. Regards, Bill.
 
Consider CNC as well. That would allow you to use a ball mill to cut pretty much any radius that you desire that is larger than the diameter of the ball mill, to whatever depth or combination of depth/radius/etc... you like.

Eg:

flutedbarrel.jpg


Wireframe of a .30 cal barrel 1" dia, 26" long. The flute would be 0.25"r at the bore (from stock), tapering away to zero 7/8 the way up the barrel. Using a CNC machine, that cut could be made with lots of different cutters, many different sizes of ball mills. Although it could also be made pretty easily on a conventional machine with a half inch ball mill, a CNC would give you more options to do more radical cuts.

If you are worried about stresses, take steps to eliminate them. Mill symetrically with light cuts. Have your barrel normalized, re-treated, etc... after all the cutting is done.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom