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GregS
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Machining an octagon barrel
Apr 2nd, 2010 at 9:28pm
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I would like to machine flats on a straight 1.200 dia blank 28in long. The muzzel should be about .600 and the breech 1.060 across the flats. I have a bridgeport with a long table and an 8in horizontal indexing head with an adjustable center. I am sure there is a slick, easy gunsmith way to machine a tapered oct barrel, smiths have been making them for years. I am trying to avoid the learning curve on my first one and hopefully learn by somebody elses mistakes.
Thanks for helping
  
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whitey hanson
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Re: Machining an octagon barrel
Reply #1 - Apr 2nd, 2010 at 9:43pm
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Greg if you have to do it yourself. And you got a indexer and tail stock and enough travel. And know how to use them just do it. Just adjust your tail stock at the right height to give you your taper. Put a end mill in the mill and do it. Then draw file when done. And good luck.
  
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Reg
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Re: Machining an octagon barrel
Reply #2 - Apr 2nd, 2010 at 10:33pm
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Don't try to take it all in one cut, use that indexer, take .020 to .030 max on a side then rotate.  Use coolant and a sharp tool.  Think of a torqueing pattern.  All of this is to prevent warping.  Big thing is to keep tool pressure and heat down.
Watch your RPM.
If you try to cut it all in one long cut , then you might have to use a jack with a light clamp somewhere in the middle to prevent chatter or bowing.
Use a height gage and indicator to keep track of progress.  It will show you if warpage is starting to build.
A power feed to the table is worth its weight in gold here.
Finish up with draw filing and you will have a great barrel.
Its actually simpler than the description, just follow basic machining procedure.  Keep the tool razor sharp, use coolant and index.
Let us know how it works out.

Smiley
  
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westerner
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Re: Machining an octagon barrel
Reply #3 - Apr 2nd, 2010 at 11:15pm
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You'll need a angel plate or vice to hold it in the middle otherwise it wont be ridged enough.  I'll also bet your table isnt long enough to take one complete pass. The easiest thing to do is swing the head over to finish  a cut.

I cut a bunch of blanks on my mill when it was new.   

       Joe.
  

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westerner
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Re: Machining an octagon barrel
Reply #4 - Apr 2nd, 2010 at 11:21pm
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The numbers you give sound a bit off to me.  .600 at the muzzle and 1.060 at the breech?  Maybe I'm not reading you right? Sounds like way too much taper to me.   

         Joe.
  

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ssdave
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Re: Machining an octagon barrel
Reply #5 - Apr 2nd, 2010 at 11:33pm
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I've got an octagon cutting jig for my mill, but haven't run a machine in over 5 years.  The jig is ingenous, I didn't make it.    

It consists of a heavy flat plate with a bunch of holes tapped into it so that you can attach a tailstock and an indexing head at different distances.  In between the two centers, there is a series of holes tapped in a straight line.   

One center is adjustable for height, so that the taper can be adjusted.  The other is a collet held in an indexing head.   
   
You start by machining a round tenon at the breech end to go into the collet.  Mount the collet and tailstock at the length of the barrel, put the breech tenon in the collet, and put the tailstock center in the muzzle.  Snug the barrel in and adjust the center height for the taper you want.

Now, there are a series of spring loaded pistons that screw into the intermediate holes between the centers.  You let the springs firm the piston up against the barrel underneath it, and then lock them in place.  This supports the barrel rigidly every couple of inches.

In practice, I use a fly cutter and take fairly small cuts.  A large end mill would work as well.  I cut a few passes, then index the barrel over 180 degrees, and reset the spring piston supports.  Make an identical cut to the first.  Now, rotate 90 degrees, cut, rotate 180 degrees, then 45, then 180, etc.

When you have cut all 8 flats the first cut, repeat the process for a few more passes on each flat again.  Repeat until you have it cut to form.

The beauty of this jig is the support.  It keeps the barrel from being bowed under the cutter force.   

I wish I had someone I could permanently lend the jig to near me, with the condition that I could go use it on their mill. It weighs about 140 pounds, and is a pain to set up on my small machine, and I don't have enough travel to use it effectively.  Luckily, I can slide it on my table to cut most barrels in two passes. Draw filing cleans up the overlap.

dave
  
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texasmac
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Re: Machining an octagon barrel
Reply #6 - Apr 3rd, 2010 at 12:15am
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Dave,

Would it be possible for you to take a few photos of the Jig and post them here or email them?

Wayne
  

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38_Cal
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Re: Machining an octagon barrel
Reply #7 - Apr 3rd, 2010 at 9:44am
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Dave, that sounds similar to what I've sketched up, except that I plan on using the side of an end mill and supporting the barrel on the off side with angle plates.  That will let me cut a radius to round at the breech end.  My mill is a 10x54" Enco copy of a Bridgy, with about 38" of travel.  Takes time to get all the component parts together to build it!

David
  

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Re: Machining an octagon barrel
Reply #8 - Apr 3rd, 2010 at 11:56am
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Practice on a piece of round stock first.  Wink

Might find any glitches in your set-up that way.
  
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creedmoormatch
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Re: Machining an octagon barrel
Reply #9 - Apr 3rd, 2010 at 12:09pm
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   Good , no great, advice Ohio Sam !

   Bar stock is cheaper to replace than is a rifled barrel blank .

   Creedmoormatch
  
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GregS
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Re: Machining an octagon barrel
Reply #10 - Apr 3rd, 2010 at 11:37pm
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Dave, 
Wish you were closer, I was envisioning a long sine bar but didn't want to build a 100lb fixture for one barrel. If it wasn't so heavy you could rent yours like they rent chambering reamers with a big deposit. I will make up a bar with jack screws, thanks for the idea.
Greg
  
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John Taylor
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Re: Machining an octagon barrel
Reply #11 - Apr 4th, 2010 at 12:29am
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I use angle blocks in a horizontal mill to take the vibrations out and keep the barrel from pushing away from the cutter. You can do the same with clamps and blocks with an end mill. You will want a cutter about 2"-2.5" in diameter if you want the Sharps stile tulips. Most tapers for Winchester barrels are around .050" per side for the length of the barrel. A barrel with 1.060" across the flats at the chamber end should be close to .960" at the muzzle. You can give it more taper if you like the barrel light at the muzzle.
  

John Taylor   Machinist/gunsmith
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ssdave
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Re: Machining an octagon barrel
Reply #12 - Apr 4th, 2010 at 1:37pm
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Now John's got the setup to do this right!  And the right skills, I might add.  

Here's my jig, it graces the floor of my shop and I trip over it periodically.

The key feature to it is the spring loaded, locking stops to support the barrel, as shown in the closeups.   

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whitey hanson
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Re: Machining an octagon barrel
Reply #13 - Apr 4th, 2010 at 3:14pm
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Dave sure too bad postage is so high..Been wanting to see that ever since you told me about it sometime ago. Maybe one day I will have to go to S.Dak.  Whitey
  
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Re: Machining an octagon barrel
Reply #14 - Apr 4th, 2010 at 3:39pm
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the easiest way i know how to do it is buy it that way.
irish
  
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Re: Machining an octagon barrel
Reply #15 - Apr 4th, 2010 at 6:12pm
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Dave,

Thanks for taking the photos and posting them.  That certainly is a clever setup.

Wayne
  

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Re: Machining an octagon barrel
Reply #16 - Apr 4th, 2010 at 10:36pm
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Interesting tool, should work well. Done a couple. One with a shaper. One with a vertical mill using V-blocks, shims, and hold downs. A lot of drawfiling to clean up. Since those, I agree with Irish and buy them if I can.
Chuck
  
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GregS
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Re: Machining an octagon barrel
Reply #17 - Apr 4th, 2010 at 11:02pm
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John, I like the Sharps tulips in your pic. I was going to bring the flats right out to the frame, (not nice) Am putting a .22 WMR on a low-wall and I thought the .600 muzzle would look OK. I will leave about 2in round at the breech now and run the flats into the round. Am going to use a bridgeport with a long table and about a 3/4in end mill and use it as an end mill and not side mill it. Will use a vice in the middle like you do. Thanks for you help
Greg
  
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Re: Machining an octagon barrel
Reply #18 - Apr 5th, 2010 at 7:14am
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gregs,
guess you want to do a lot of filing. if you do not side mill it you will file it. clamp an angle plate on the opposing side and use a large end mill will water sol. and it will work fine.
irish
  
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Re: Machining an octagon barrel
Reply #19 - Apr 5th, 2010 at 4:18pm
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SSDave

Thanks for posting pics.   
I make a few oct bbls here in the shop, and have been thinking about building another fixture or improving my setup.  I like the “spring loaded, locking stop” idea.  But my concern/question is, how much movement do you get in the barrel when machining, since the barrel is only held in at two points?   

Thanks

Mike Hunter
Hunter Restorations
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Mike Hunter
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John Taylor
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Re: Machining an octagon barrel
Reply #20 - Apr 6th, 2010 at 9:19pm
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One of the things not showing in the first picture is the "V" clamp on the angle plates.The two flats opposite of each other are cut first to get measurements and taper. Adjustments are made and the two flats are cut again and checked before going to the rest of the flats. I cut every other flat , make the barrel almost square. Then I cut the remaining flats.  I usually don't try to take it all off in one pass on each flat. If it is a button rifled and not properly stress relieved it will come out crooked.
  

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Re: Machining an octagon barrel
Reply #21 - Apr 6th, 2010 at 10:19pm
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Mike,

I don't have a good answer for you, as I only cut one entire barrel on it before deciding I needed a better machine with more travel.  Sliding the jig on the table introduces enough error into the cut that it takes some draw filing to clean up the interface between the two cuts.

I used a fly cutter, and the side supports were used to keep the barrel from springing away from the direction of rotation, as well as the bottom ones keeping it from bowing down.  The interrupted cut of a fly cutter generates a lot of vibration, but the pegs stopped that pretty well.  Adding a clamp in the middle like John has would be an improvement.

I have used the jig also to octagon rolling block receivers.  It works well for that, as I have a mandrel I screw all the way through the receiver, mount one end in the collet and the other in the center.  I use a half inch carbide end mill for that operation.  I think it would also work relatively well for fluting barrels if a person was to get into the tacticool business.

I really should pass the jig on to someone else, as I will likely never buy a bigger mill and do any serious machining again.  I went back to working a regular job for a living, and have close to 15 years before I can retire from that, and no guaranteee that I'll be interested in machine work when I have time again.   

I have Paul Shuttleworth octagon barrels for me, or buy them that way.  Same as I have Montana or McGowen turn and polish round barrels for me.  I'd rather do that than clean up the lathe after I get sanding grit all over it.  I send them a cad drawing of the profile I want, they plug it into the CNC and $30 plus $15 postage later it comes back to me perfect.  Plus, I don't have my lathe set up at the moment anyway.  As long as there's great craftsman like John Taylor and John King that will do work in a reasonable time frame, I'm better off keeping my gunsmithing tools confined to a couple of screw drivers and a dremel tool.

dave
  
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Re: Machining an octagon barrel
Reply #22 - Jul 25th, 2019 at 8:52am
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I know this is an old thread, but I sure wish I had that jig to do a tapered Oct barrel project.  The mill table is plenty long enough as it is a big Brown and Sharpe #2 universal with 52 inch table.  Have a choice of using B'port head on the overarm supports or using the 50 taper horizontal milling capability.
  
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Re: Machining an octagon barrel
Reply #23 - Jul 25th, 2019 at 12:41pm
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Here is a more resent thread on octagon barrels:

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Frank
  

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