Reamer Made to Correct a Cannon Bore

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davec2

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I really need another project like I need another root canal......nonetheless, I have begun a refurbishment of the full size cannon I built 50 years ago when I was a junior in high school. Don't ask me why after 50 years I have to do this now, but there are some issues with the gun that have bothered me for 50 years and if I don't get to correcting them now....well.....I don't need to explain any of that to this crowd.

So, many of you have seen these pictures before, but here is the cannon again for those who may not have seen it.......







One of the things that has always bothered me was that there is a very slight step in the bore about half way down. Now the nominal bore is 2.75 inches and the step is about 0.005 inches on a radius which amounts to about 0.36% of the bore diameter. For a cannon, this isn't bad and since I use cannon balls that have about 0.050" windage, the step never really mattered. However, several years ago now, I went back to Pennsylvania to see Ray Rapine about purchasing his bullet mold business. (Another story). During the course of our conversations, Ray also had a full scale mountain howitzer with a 3 inch bore that he was selling. Hanging on the wall behind the gun was a target with several 3 inch holes cleanly punched in a 36 inch diameter black bulls eye painted on 1/4" plywood. He told me he had shot that target at 600 yards with the howitzer. I looked to see if it was rifled and it was not. I asked him how he could get that kind of accuracy with a smooth bore. Ray told me the bore in the gun was very good and that he had made a custom mold to cast zinc round ball that only had 0.003" windage on the diameter of the ball rather than the usual 0.050" or so. Then he said, "There wasn't much wind that day. Of course wind don't matter much to a 4 pound ball." Then he winked. Ever since I have wanted to get that slight step out of the bore of my cannon and then modify my ball mold to cast a much tighter ball. There are several other things I want to improve about the cannon (I know a lot more about how things should be now than I did when I was 17 in 1970), but I wanted to start with the bore.


So here is the 6 foot long reamer that I just finished to clean up the bore. I have to make a muzzle guide yet but when that's done, I should be able to clean up the full length of the bore.










More on the project as this progresses.....
 

Phil Coffins

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Good idea. I'll be interested to see how you guide that cutter, will there be a pilot to start it in the bore? Let us know how much effort it takes to turn that big fellow! Dandy project!
 

hawkeye2

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Keep us up to date and let's see a 600 yard group after you finish.

Do you have any idea what became of Rapine's mold business? He told me not long before he passed that he had sold it and that the new owner was going to have them on the market soon.
 

Dude

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This is fascinating! I'm interested in the build story - as well as how the reaming works out, plus any data on the Rapine story.
 

Dude

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Dang, that was quite the teenage undertaking. Well done. When I was 17 I was only interested in my girlfriend's parts and trying to get a 396 Chevrolet to run the 1/4 mile quicker 😅.
Same here - except with me it was the motorcycle and my girlfriend. Shop was for jocks.
 

davec2

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Good idea. I'll be interested to see how you guide that cutter, will there be a pilot to start it in the bore? Let us know how much effort it takes to turn that big fellow! Dandy project!
Phil,

The original plan was to have a pilot in front of the reamer. However, the bore for the fist 20 or so inches is line to line with the 2.750" shell reamer. As a consequence, the reamer will go that far down the bore without needing a forward pilot. But it does need the guide I am machining for the muzzle that will support the reamer shaft as I work the reamer down through the last portion of the bore. I have toyed with the idea of opening the bore to a full 3 inches in a similar manner. In that case I would need the forward end pilot to start.

However, in a moment of sanity, I realized that there is no true "need" for the gun to have a 3 inch bore vs a 2.75" bore.....and if I did take it out to 3 inches, it would cost even more per round for powder and shot (and it's fairly expensive as is. Even a light load is 1/3 pound of powder and about $12 worth of cannon ball) !!!!
 

jimairwin

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This is phenomenal!!! You built the cannon in High School?
wonders never cease 😮
So you need to remove 0.010 in diameter...gonna be major work to do so with the nice reamer pictured. Lots of horsepower required! And you will need some guide. or did you say your bore has two diameters? Is the larger bore at the front? How far back to the step? i.e. how much length of the smaller bore? If your reamer is same diameter as the larger bore and the larger bore will guide the whole length of the reamer, you MAY be in luck. You'll need a rigid base for the tube (barrel) and an accurately placed guide to keep the rod concentric to the bore axis. I assume your reamer is tapered, not merely step up in size. If not you'd be well advised to get it tapered. Will help guide it as you proceed.

Good luck!

Jim (aka "Cannonball") been making cannon since the mid-50's
 

davec2

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So you need to remove 0.010 in diameter...gonna be major work to do so with the nice reamer pictured. Lots of horsepower required! And you will need some guide. or did you say your bore has two diameters? Is the larger bore at the front? How far back to the step? i.e. how much length of the smaller bore? If your reamer is same diameter as the larger bore and the larger bore will guide the whole length of the reamer, you MAY be in luck. You'll need a rigid base for the tube (barrel) and an accurately placed guide to keep the rod concentric to the bore axis. I assume your reamer is tapered, not merely step up in size. If not you'd be well advised to get it tapered. Will help guide it as you proceed.

Good luck!

Jim (aka "Cannonball") been making cannon since the mid-50's
Jim,

You are correct....fair amount of work to get the bore cleaned up the whole way. And the horsepower at this point is me. We will see how this goes. The barrel is cast iron and cuts fairly easily. Luckily the step to a smaller diameter is about 20 inches down the bore. The reamer is very close to line to line at 2.750" diameter with the first 20 inches of the bore and goes in fairly easily, so I don't need a leading pilot. I will be making a muzzle guide that will keep the reamer shaft concentric with the bore as the reamer is advanced. The reamer is not tapered. I am assuming it will stay centered in the cut as it advances as there isn't any lateral force being applied that will push it to one side or the other. I'll see how this goes. If I get into trouble, I will be back in touch.

What kind of cannons do you make ? I would like to see pictures, links, etc. ! Thanks again for the advice. I may need all the help I can get.
 

Dude

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Is the end of the reamer sharpened like an end mill? Either that, or it seems like it should be tapered a little on the end.
 

davec2

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The reamer has a slight chamfer on the end and the chamfer cuts.
 
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davec2

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OK....I finally had the time to make the bore guide for the reamer. Here it is on the lathe in process. I neglected to take a picture of the finished guide but will as I set it up for the reaming operation.




 

davec2

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Had a chance to try hand reaming a 2.75 inch bore today :eek:

Here is the finished muzzle guide......



And installed in the cannon muzzle......



Reamer in place for the start of the first trial run......



First batch of chips pushing ahead of the reamer !!!!



It takes about 10 minutes of hard pushing and twisting to ream about 2 inches of linear bore length. I made a gage and I think I am taking out about 0.015 on a radius or 0.030 on the diameter, which is more metal than I thought I would have to remove. I made about 6 inches of progress down the bore in three, 10 minute runs before my arms gave out. I detached a bicep tendon in my right arm 2 years ago that could not be repaired, so my right arm is fairly weak. If I had pulled the barrel off the carriage and stood it vertically, I could have weighted the reamer shaft and just turned the handle. But the barrel weighs nearly 600 pounds, so getting it off the carriage and building a vertical cradle is another project in itself. I think I have a way to apply a spring around the reamer shaft to apply tool pressure while I just turn the handle. And if I don't do all of that, in short increments, I can finish by hand. At the current rate of advance down the bore, it would take me another hour and twenty minutes of pushing and turning, so....not bad.... if I do it in increments of 10 to 20 minutes a day. The cut appears smooth and even and the bore gage indicates a nice straight cut. So far so good :) ;)
 

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