This is my second attempt at barrel turning. This tutorial sums up what I’ve learned so far and is meant for beginners like me with little or no experience with lath work. Most of this is probably old hat for the expirenced builders and I hope they will chime in with tips and advice. I got the blanks from my friend Runar. Please do not start a discussion on metallurgy. The topic is barrel turning. The picture below shows a finished barrel and a blank.
1. Truing up the blank.Put the blank in the chuck and square up both ends.
Scrub off rust and scale with a bastard mill file.
The lath I’m using does not have the equipment to turn between centers so I centered the bore in the blank by turning down one end of the barrel, reversing the blank and mounting this end in the chuck.
Then I turned down the whole length of the barrel to get the sides parallel with the bore.
2. Threading the breech.True up the breech end again.
Tap drill the breech end to a depth of 15mm . Some people recommend using a boring bar instead of a drill. The idea is that a drill gives a slanted shoulder while a boring bar gives a square shoulder. I tested this by threading two 1” sections of barrel blanks. When fitting with a plug there was no visible difference between the two methods. This is probably because the shoulder of the breech was so small and the boring bar leaves a rounded corner. The barrel bore is 0.50” and the plug 9/16” which give a shoulder width 1/32” wide.
Start threading the breech in the lath with a standard tapered tap. You can easily feel when this tap hits the shoulder in the breech.
Finish threading in a vice using a bottom tap with the front ground off so it cuts full threads all the way. Be careful using this tap. It can cut past the shoulder of the breech. I taped my first attempt 5mm to deep and had to start over again.
Relieve the first thread of the breech with a boring bar. This has to be done to get the breech plug to fit tight against the breech end.
3. Turning the sacrificial breech plug.Take a piece of round stock with a diameter that’s larger than the blank. The threaded portion is only 10mm long. This allows you to screw the plug tight against the breech end without any fitting.
Put the blank in the chuck and turn the plug sides parallel with the blank.
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4. Turning the barrel profile.Turn down the barrel profile in steps. I used a CAD program to construct a turning table.
Measured from the muzzle end:0mm to 252mm, diameter 26,2mm
0mm to 231mm, diameter 25,7mm
0mm to 210mm, diameter 25,1mm
0mm to 189mm, diameter 24,6mm
0mm to 168mm, diameter 24,0mm
0mm to 168mm, diameter 20,8mm
0mm to 150mm, diameter 20,2mm
0mm to 133mm, diameter 19,6mm
0mm to 92mm, diameter 18,4mm
0mm to 44mm, diameter 17,8mm
This produces an oversized barrel profile. The steps are removed and the blank reduced to the final dimensions in the lath with a bastard mill file.
5.Calculate the width of the flats of the octagonal part of the barrel.Measure the diameter at both ends of the octagonal part of the barrel and use the formula
Flat= 2(SIN 22.5 x radius) = 0,7653 x radius
My barrel is 26.4mm in diameter at the breech => radius 13.2mm
0.7653 x 13.2mm = 10.1mm. Calculated the same way the flat towards the muzzle is 8.9mm
6. Milling/filing the rear part of the barrel octagonal using the sacrificial butt plug.Mill the sacrificial butt plug square, but leave it a bit wider than the breech end of the barrel and keep the corners round.
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Use the square plug to mount the barrel in the mill vice with the octagonal part of the barrel level.
Mill the four sides square. This guaranties that side flats and top/bottom flats are square (90 degrees) in relation to each other. Mill the flats to their calculated widths. NB! Pays to be fussy here. It makes it a lot easier to file the remaining four flats.
Mill the slots for the sights and barrel tendons next. This puts the slots are the middle of the barrel and square to the axis of the barrel. Do not mount sights and tendons. They will be in the way when doing the rest of the file work on the barrel.
7. Filing the octagonal part of the barrel.Paint the rear part of the barrel with blue dykme.
Carefully draw file the four machined flats to get rid of milling marks and blue color. This does not give any measurable change of the flat widths.
Take a coarse metal rasp and file down one of the remaining four flats. Do the filing across the barrel and keep the blue lines on each side even. This removes metal quickly. At this stage it does not matter if the flats get slightly rounded. What’s important is to keep the blue lines an even thickness. I’d like to point out that the rounded corners on the square breech plug make it easy to clamp in the vice.
Keep filing with the rasp until the blue lines are reduced to pencil line thickness.
Draw file the “flats” flat and to their final width. This was easier than I expected. The rasp marks go across the barrel and the draw file marks lengthwise. Hold the draw file level so it starts cutting in the middle of flat and keep at it until all the rasp marks and blue lines are gone. It takes me about 45 minutes to rasp and draw file a flat. When done all the corners are crisp and the widths between all flats vary with less than 0.2mm (0.008”).
8. Filing wedding bands.Filing nice wedding bands was the hardest part of barrel making. I feel the ones I’ve made are acceptable, but something does not look quite right and I not sure why. I filed the wedding bands from the octagonal part of the barrel. This was done on the old barrels I’ve seen pictures of. The bands are only on the top five flats, the bottom three are left flat. I started by cutting out the two first bands with a jeweler saw, blade #0 and cut down to the depth of the blade 0,6mm (0.024”)
Next I parted out the middle band with a barrett needle file, keeping the sides of the small bands vertical and slanting the sides of the middle band.
Next I shaped the middle band using a barrett file and a three corner file. Then I even out and straighten out the thin small band.
Next I saw out and part the last small band, trying to get identical to the first small band.
Then I finish shaping and sanding the bands to 400 grit. Looking closely at the bands I noticed that the bottoms of the groves that part the small bands from the large band are slightly rounded. Should I go over them again with a barrett file to sharpen them? Also my rings “lay” on top of the round portion of the barrel. On the old barrels they look more sunken into the barrel.
Addeum:Jim Kibler and Dave Rase spotted whats wrong with the wedding bands. The step from the octangonal portion to the round section of the barrels is to high. I should have tapered the flats almost all the way down to the round section , before filing the wedding bands.
9. Making and fitting the breech plug.Take a piece of round stock, turn down and thread 16mm and mill down the sides’ flat.
Do not cut out the tang until the pug is fitted to the barrel. This gives you two options for cutting out the tang and can save you a bit of filing when fitting the plug to the barrel.
Best regards
Rolf
