Drilling the bore

[Runner]

Just for the heck of it, I started to drill a small cannon barrel today. I have it drilled 4 inches deep, and now need a longer bit. I suspect that a gun drill is the way to go at this point. How to make a gun dril rig? Will air work as well as coolant? This one will only need about 8 inches, but who knows about the next! This one will end up about .62 bore if all goes well. If not, it may end up .74.

 

[musketman]

Brownell's sells gunsmithing tools...

http://www.brownells.com/aspx/ns/home/default.aspx

Other than that, could you weld an extension to the shorter bit, as long as you get it centered it should be OK...

 

[WRussell]

Silver solder will also work fine for sticking an extension on your drill. Cut the join at an angle if you want more surface for bond strength.

 

[Gary]

Bore in a bit, pull bit out, brush & oil, repeat as necessary. BTW, silver soldering it to a drill rod will give you the ability to drill to the desired depth. You may want to fit them like a joint to ensure that it doesn't come apart. That's what we did for our ramrod drill rod.

 

[Wedge]

Gudday Runner,
Great to hear that you're having a go at drilling out a barrel. It's not easy but the job can be made simpler. You can buy long series drills and even extra long series. This would be my first choice of tools. They long series cost a bit more but you don't have to mess around trying to get two parts exactly in line and properly stuck together. I have joined many a drill to drill deep holes. The longest was about 3 feet and only 3/8 dia. The most important points are, keep the drill sharp, keep the drill sharpened corectly to the proper geometry. This last point is the hardest of all but it can be done with practise. My bigest problem when sharpening drills by hand was I did too good a job. The drills would cut exact size and would jamb in the hole, a real pain when that happened. To help achieve a smooth finish on the surface of the bore, reshape the corners of the drill with a diamond hone. Hone them to a small radius, about .010" is good. Be sure to run the radius back along the outside edge so the corner can cut cleanly. A picture is worth a thousand words at this stage. When starting the next drill size to run in, get a boring bar set up in the toolpost and bore the hole to the same diameter of the drill. Bore it out as deep as you can. This keeps the front of the bore exactly true and ensures proper alignment for the drill. An 8" deep hole can also be finished to size by using a standard machine reamer. These can also be bought as a long series reamer. OK, they are a bit exy (exy = higher cost) but they are worth it. Compressed air is NO good for drilling deep holes in steel or bronze. It is only used for drilling cast iron. You MUST use a high quality liquid coolant that also lubricates the drill. This must be flooded into the hole. If you are not getting wet when drilling, there is not enough coolant being used. Drill only about 1/16" to 3/32" deep, slide the drill out and remove the chips. Don't try and drill deeper or the chips will clog and bind the drill. A brake cylinder hone can be used to polish the bore and remove the ridges left by the drill. Use kero or diesel fuel when honing the bore. Good luck on your first job.
Joe / Wedge