Flute your Barrel?

[QVTom]

It seems to me a fiddly process and one that would require lots of patience.  Also, it has the potential to go bad very easily. Considering the required use of a ball mill that will create lots of pressure due the chip form on a long skinny part that will undoubtedly want to vibrate. 

I have these 0.63 dia LW barrels that are quite heavy, I do like the bull barrel look so I don't want to turn down their diameters which would give the most significant weight reduction, fluting would make for a nice compromise between weight and the "bull" Look.

Thoughts on the process?

[SciGuy]

Machining the barrel will cause a stress release which will affect the size of the bore.  It could make a killer barrel stink or a so-so barrel into a killer.  Roll the dice take your chance.

[dukemeister]

I agree, and could easily cause the barrel to warp.

[rsterne]

I would never need to make that decision, as it's beyond my ability to do successfully....

Bob

[sperho]

Shoot it, then flute it, if you decide it's too heavy.  That way you'll see if you changed anything...  and you know if you have something to regret or not.....  Personally, I like a little more weight in the front for damping my ever-so-present wobble...

[QVTom]

"Shoot it then flute it"  a real wordsmith Beat me to it, not fast enough on the post button   These things are really heavy. 


I guess to find the answer a test before and after is in order.  Worse case, the club becomes a conversation piece.   I would think that the blanks are normalized after boring, reaming and rifling.  I'll call the LW people tomorrow to see what they have to say.

Tom

[Hanabata808]

With a fluted barrel, you'd score lots of extra style points regardless 

[QVTom]

Q and A from LW

1)      Are the blanks supplied in a stress relieved condition?
No, they are reamed and buttoned and then straightened.   Airgun pellets do not require this.
 
If you need production done this way it can be done but the cost is higher.
 
2)      Are there any concerns with profiling or fluting  the 0.63 diameter blanks in terms of warping or distortion due to machining stress or relief?
      Airgun barrels can be machined as is for the normal purposes.   The quantity of metal removed is not going to require it.  Fluting can  be done but it can not be deep fluting.

I assume normal purposes is breech attachment and the like.

Tom

[sperho]

Sounds like it's doable. If you want your design language to be consistent throughout the gun, you might consider a cutter that makes the fluting with the same, but miniaturized and negative profile of you compression chamber's external profile... Knowwhatimean? (Verne?)

[QVTom]

Sounds like it's doable.

Funny, I took their response as DON'T. 

If you want your design language to be consistent throughout the gun, you might consider a cutter that makes the fluting with the same, but miniaturized and negative profile of you compression chamber's external profile... Knowwhatimean? (Verne?)

Too much work. It was the simplest solution for the compression tube, the barrel is another matter. Verne? Some pop culture reference?

Tom

[glassman98]

Tom, if you do it, I would use a 1/4" single lip split ball cutter, at hi RPM for a light chip load. Craig

[Motorhead]

It would seem to me fluting best cut on a mill with a horizontal indexing head, then using a radius face key way type cutter run down barrels length while barrel was supported in a full length Barrels O.D. cradle held within a dead center one end and indexing head / rotary table at other.

Your ability to maintain cuts parallel to bore, machine marks left behind being uniform, and chatter in general GREATLY minimized.

JMO,
Scott

[sperho]

Funny, I took their response as DON'T. 

I was taking the statement, "Fluting can  be done but it can not be deep fluting." at face value.  I guess it depends on what "deep" means.

Verne? Some pop culture reference?

Yes, from the 80s. 

[SeanMP]

Tom I would say your probably safe and the risks are fairly low. The first inch and the last inch are all important and your not fluting in that area. I've done some fairly heavy profiling on .630 LW barrels with no adverse effects and fluting is substantially better than profiling.

I would use a slot cutter over a ball nose. As you mentioned the tool pressure on a ball nose would be a workholding nightmare.

[Pete]

I take it you don't have a traveling head steady for the mill...
They are a pain in the _ _ _ as you need to reset them each cut... but they work..

I would use a tungsten 4 flute ball nose with multiple cuts...

just a thought.... A Inverlute gear cutter..something around module 5 or 6
could give a nice shape... round bottom with convex sides

[ncpackrat]

I have done flute work on PB . On them you need to flute before you shoot them as it will make a difference in the shooting,as if it shoots tight groups it may not if you flute after it is shot.Second flute work makes the barrel stiffer,cool quicker,which doesn't happen with the air guns,and makes it lighter.I do this with a rotary table and 1/4 to a 5/16 ball end mill.Only take a few thousands off at a time  to keep heat and warpage down. Also leave bout 2 inch on muzzle and 4 inches on chamber end.As I said only done this on the PB guns.Hope this will help I have done several like this,good luck.Ernie

[Bent]

If you have the machine for it. I think the best way is to rough out the flutes using a 6mm normal cutter.. And turn the millinghead in 45° so you are plungemilling most of the material away. Maybe leave 0,1 or 0,2mm for the finishcutter. A little more if you are going close to 3mm into the barrel
Then use a ballcutter 6mm to remove the last material in 2 passes.

I would use HSS cutters for less vibration, and I guess that ½hour more machining doesn't matter?? 

[willbird]

I fluted one PB barrel, I had the luxery of a 3 axis cnc mill I could use any time I wanted. I ran a small racetrack pattern so the cutter was climb cutting on only one side, maybe .03" or so on a 3/8 ball cutter. I also did all the maths first and made the pattern move down in the Z axis so that the "spines" on the tapered barrel stayed the same width.

Cutters and the work move in response to cutting force...if you can climb cut and only make a finish cut on one side of the cutter the end result looks a LOT nicer. For anybody that does not know, climb cutting is making the finish cut on the side of the cutter where the cutting force pulls the work into the work, or the work into the cutter, it can only be done and should only been done when you are sure it will work. it can break things and hurt you if you do it when it is ill advised :-).

We used to run a series of parts, cams, that had right and left hand versions of the same parts, the parts were mirror images....the programs had been written to climb cut around the part, the mirror part was made by running the program backwards more or less via a utility in the cnc control. The difference in size due to the cutter/work "pull" I speak of was .01" or more even with a very stiff 1/2" solid carbide endmill.

If you "bind up" the ball mill in a slot (my term for it) it will always pull one way....and often leave a nasty finish on the side it is pulling away from, the cutting force may be flexing the tool, the machine, or the part, or all of the above.

That does maybe explain why what I refer to as "woodruff" type cutters may work nicer overall as some suggest.



Bill

[willbird]

Sigh * quote does not equal modify hehe

[MultimediaMan]

My dad used a big SAIMP (~65" Table) Hydraulic Tracing mill to do the work with carbide woodruff cutters. It was all he used that mill for: He made several follower rest towers and pads for the opposing side of the barrel to minimize/eliminate flexing... and tracing patterns cut to match the barrel contour for the stylus to follow. I spent many an hour running that thing: we never took more than about 0.005" when starting a flute, and never more than 0.001" or 0.002" when the cutter was at the finished depth - when cutting radiused flutes it's important to remember that as you cut the flutes deeper, the cutter removes more material and you need to need to back off how much you cut on a manual machine...

Bill Wiseman of Wiseman Barrels and Ballistics would take it a step further: When fluting a barrel, he would cut one flute, then rotate the barrel 180 degrees and cut the opposing flute until the barrel was done. (American Rifleman,  June 1986: a Heavyweight Elk Rifle) Of course, if you had an odd-number of flutes, this plan would need to be modified.

I'll get some pictures of the setup.