Making a Rifled Barrel

[Bruce_in_Oz]

These machines are not for the faint-hearted.

In the event you get a deep-hole drill, (the Holy Grail being the dual-head model), it may be flogged to death, bearings and seals wise. Remember, most of the Pratt and Whitney machine still extant are WW2 survivors or even date back to WW1. Really old ones were originally driven by overhead belts and many were later converted to either hydraulic of electric motor drive. One major issue is that these machines were built for use with Carbon or alloy steel drill bits and attempting to use modern Carbide bits at the appropriate greater feed rate can be exciting, to say the least. One major problem is the matter of the seals for the high-pressure coolant.

The drill bits are attached to a long (and I mean LONG) piece of steel tube with a section like a pie with a quarter slice cut away (see also "Pacman"). In the drill head is a chamber that feeds coolant down this hollow tube and sprays it out via holes in the single-tooth cutting bit. The coolant is used not only to cool, but to flush the swarf back up the "V" groove in that long extension tube. Not enough pressure and the bit will overheat, soften the silver-solder joint and snap off somewhere in your blank. Too much pressure will blow the seals in the head and then the resulting loss of coolant returns you to the first option. Too high a feed rate will make swarf that jams in the bore and leads to all of the above.

If everything is working correctly, you should be able to bore a .30 cal. hole from end to end in a 30 inch bar and come out the muzzle end within a few thousandths of an inch of dead centre. Getting this right generates a lot of very robust tomato stakes.

Reaming to correct bore size for rifling is done on a similar machine, however, as there is now a continuous hole from end to end, the required coolant / flushing pressure is not quite as high. However, flushing is EXTREMELY important, as, if a sliver of swarf jams, even for a fraction of a second, the bore WILL be scored. The reamers are about 3 inches long (for .30 cal) and, these days, are mostly carbide.

Some barrel makers performing "buttoning" of their rifling, use a slightly undersized reamer for this stage and then drive an "ironing" button through to polish the surface and make the "grain" lean towards the muzzle. You will notice that the breech ends on all blanks from reputable makers are clearly marked.

Then it's off to the rifling machine.

Some barrel makers also do a steady trade drilling and reaming long bores in specialized hydraulic rams; same technology, different product.

Information

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[bigduke6]

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Some barrel makers also do a steady trade drilling and reaming long bores in specialized hydraulic rams; same technology, different product.

The machine I was offered was used for Aircraft hydraulics.

I Worked on an old archdale when I was an Apprentice, it was used for something similar, it was upgraded and converted over time, job at the time was overhauling the lube oil system when I was doing a stint in the Millwrights.