View Full Version : Boring Model Cannon Barrel

Bruce Griffing
01-17-2009, 04:17 PM
My nephew and I are working on a small model cannon. It has a ~1" bore. We are making from a piece of A36 rod. We are having trouble clearing the chips and getting a clean bore. I don't have a reamer or a gun drill - I am looking for a one-off cheap way to get this done. At present we are using a 0.75" boring bar with a HSS cutter. Our main problem is getting a good finish. Any suggestions?

01-17-2009, 04:40 PM
As a start, A 36 is not a mat'l that will give you a great finish. It's commonly used in structural applications, your typical "Red Iron."

How deep are you trying to bore?

What is your setup? Lathe?
For removing metal, a drill will take out a fair amount quickly...try using a drill then finish w/ boring bar.

Bruce Griffing
01-17-2009, 04:49 PM
We want a 3.5" deep bore, about 1" in diameter. We have already drilled/bored the hole on my 13" Standard Modern lathe. I just want to get as nice a finish as I can on the bore. The diameter is not critical at this point.

01-17-2009, 04:52 PM
A D-bit reamer will do a nice job, if you've got some 1" drill rod or similar.


- Bart

Alistair Hosie
01-17-2009, 05:04 PM
Are you sure your not rubbinng?? try ofset the cutter a little to make sure you gat a good clean cut?My 2 cents for what it's worth.Alistair

01-17-2009, 05:41 PM
We want a 3.5" deep bore, about 1" in diameter. We have already drilled/bored the hole on my 13" Standard Modern lathe. I just want to get as nice a finish as I can on the bore. The diameter is not critical at this point.


as the size of the bore is not super (or any other) critical but the finish is, there is a cheap (costs next to nothing) and easy (sounding better by the minute) method that works.

Do it this way:

drill almost to size - finish doesn't matter;

on the "final" drill, "break" the edges (where the 118* point meets the flute edges) and stone/hone a small (~1/64" > 1/16") radius on both sides, put in chuck or tail-stock taper (to suit), drill slowly, feed in fairly quickly using plenty of cutting oil (hydraulic oil will do if needs be). Finish should be better/good.

to "finish off" - if needed - get a bit of 3/8" round (anything that will fit in your drill chuck) - hack-saw a diametrical cut (straight across) and down its length - about 1/2" or so - deep. Get a bit of cloth-backed emery paper about 4" long x 1/2" (or so) wide, put one end into the hack-sawed cut in the rod, and wind the rest about the rod by putting the rod in a chuck in a drill (any - but pedestal drill is best) and start it up and the emery will wind-on. Make sure the abrasive/"emery" coating is facing outward.

you can put the cleaning/abrasive device either in the chuck (head-stock) or portable drill or pedestal drill and hold the canon/job. Now start the lathe or drill - medium speed - a bit of practice will soon show you - and run the abrasive back and forth in the bore.

This is like a single leaf "flap disk". Just tear off any worn abrasive.

This takes a little practice but will do the job. It can wind up like a honed or polished finish if you get is right.

I suggest a bit of practice on some scrap first.

There is a chance that it may "grab" but I usually hold the job by hand and just release my grip and all is OK. If I use a portable drill, I set the slipping clutch to just "hold on" and if it grabs the clutch will slip.

I suppose that it is an "internal" (boring?) version of what you might be doing for an external finish (turning?).

Kerosene (here) - Paraffin (US) - or turpentine (Painters type) are OK for a "wet and dry" abrasive. Don't try gasoline ("petrol" here) as if it "sparks" it can get "interesting".

Its surprising how well this method works on many things. It was very old when I was young - and that's long time ago. "Die-makers" and "Die-Sinkers" have been using similar methods for high polish with minimum metal removal since for-ever.

01-17-2009, 05:42 PM
Bore it the best you can and go at it with a brake hone. Should be able to slick it right up. Keep it oiled well while honing.

01-17-2009, 05:42 PM
ive only ever bored aluminum, so im probably not much help, but i have issues with getting a clean bore too. the aluminum swarf gets spun around inside the bore and then gets mashed back into the side and gives me a rough finish.

but be sure to post some pics of the cannon when youre done.

Heres a link to a thread from before christmas with pics of a civil war cannon i made my father for his birthday.

the bore was just drilled out with a 1/4" drill and its only an inch or two deep.

01-17-2009, 05:47 PM
i guess sandpaper is out of the question ,,perhaps starting with 120 and working oyur way to 1500 to 2000 once you get past 600 you might want to use oil on the sandpaper at say 1000 to 2000 rpm for all grit levels, any how just a sudjestion..

01-17-2009, 05:52 PM
I would follow oldtiffie's recommendation with one addition. When you are doing the final cut with the stoned drill bit, stop the machine when you get to the bottom of the bore and then withdraw the drill. Often a bore will be scored when withdrawing a drill while the work or drill is still rotating.