Making a Cannon Barrel is boring

by John

The bore in my 1779 naval cannon is 14mm diameter, 270mm deep.

I made a D bit from silver steel, as per the Jerry Howell plans.  I tried it without heat treating, but it blunted after  boring a couple of centimeters  so I heated it red hot and quenched it in water, then annealed it  and resharpened it. There were  no further issues with edge holding.

I then tried it without, then with, a preliminary drilled hole in some scrap.   I have decided that it is better to give it a starting hole of the correct diameter.

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This is the setup.  The 50mm brass rod is held in a 3 jaw chuck, and the tailstock end held in a centre while the chuck jaws are tightened.  The bore is then started with a drill which is accurately sharpened.    Then the D bit is fitted, and the deep boring job starts.  I used an accurate 3 jaw chuck in the tailstock to hold the D bit.  The headstock does not accept 50mm stock, but the 3 jaw chuck does, albeit with some stick out.  Once the D bit enters the workpiece, it acts to stabilise the workpiece.  The whole process was easier than I had anticipated.


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Each peck of the  bit advances 2-2.5mm.   The D bit is withdrawn and the chips are cleared.  Initially I used  a small brush, but as the hole deepened, the brush was replaced with a compressed air blast, delivered through a small bore copper pipe.

The 270mm bore took 2 hours to complete.  It was not a boring job.  I was anxious not to muck up the hefty lump of brass.

Next to drill the trunion holes in the barrel stock.  That will be straight through all layers of the barrel.  (retrospective note added later…  The trunnion holes were stopped short of the bore, and I was just very careful to keep the holes at 180 degrees and in line)

Then to turn the exterior of the barrel.  There will be a video if that is successful.

Then to silver solder the trunnions to the barrel in one piece.  Then to use the D bit to rebore the barrel, removing the trunnion rod which is obstructing the bore.  Some readers will not agree with this method, and it is not according to the Jerry Howell plans, but it does ensure that the trunnions are exactly in line with each other.  Silver solder, if properly used, is said to be as strong as the parent metal, so I believe that I will not be compromising the integrity of the barrel.   The main disadvantage is that the finished exterior of the barrel will need to be held in the 3 jaw chuck during that final D bit reboring.  I have not quite worked out how to do that, while avoiding marking the finished brass surface.