Touch Hole

[winniewino]

I recently bought a small bronze cannon from the UK.  It came without the touch hole being drilled, mostly because of UK firearms licensing laws.  I need to get the touch hole drilled, and need a little advice about the proper diameter for it. 
 
The barrel is 16 inches long, with an 18mm bore (approximately .70 inches). The breech is about 2.5 inches.  In the UK they drill the touch hole to 3mm (approximately 1/8 inch) and use 2mm fuses.
 
I think I can get 1/8 inch fuses in the U.S. (I am new to this), but if I do, what would be the appropriate diameter for the touch hole?  Slightly larger I assume, but I am interested in what is commonly done.
 
By the way, the cannon is a 1/8 scale replica of a British 68 pounder from the mid 19th century.  This type would have been used in the Crimean War.

[Doc Brown.]

You will want to go just a hair over 1/8" and get your self one of these little do dads. Also elevate the back a bit so you go in on a slight angle. What I really like to do is use an 1/8" drill bit and check it with a 1/8" fuse. Most times that will be good but sometimes its tight so I go one size up.

[winniewino]

Cool doo dad.  That doesn't look like something Home Depot would carry.  Do one of the sponsors sell these?

[Zulu]

You will want to go just a hair over 1/8" and get your self one of these little do dads. Also elevate the back a bit so you go in on a slight angle. What I really like to do is use an 1/8" drill bit and check it with a 1/8" fuse. Most times that will be good but sometimes its tight so I go one size up.

What is that thing?
Zulu

[Frank46]

Used to find and locate the center of round stock. Place in drill press, the two lower legs straddle the round stock and when the upper arm is even with the mark on the cylindrical piece you can lock your round stock in a drill press vise and drill a properly centered hole for the fuse. At least that was what was explained to me. Thing Enco, MSC,or Travers Tool have them for sale. Frank

[Doc Brown.]

You will want to go just a hair over 1/8" and get your self one of these little do dads. Also elevate the back a bit so you go in on a slight angle. What I really like to do is use an 1/8" drill bit and check it with a 1/8" fuse. Most times that will be good but sometimes its tight so I go one size up.

What is that thing?
Zulu

I call that thing a handy dandy. Others may call it a center finder. Get it from Enco. Its not expensive and you can get one on ebay http://www.ebay.com/itm/CENTER-FINDER-NEW-03-14-12-/170911294237?pt=LH_DefaultDomain_0&hash=item27cb1b631d
 
Theres probably other ways to do this but this way will guarantee you go in dead center.

[Zulu]

winniewino,
If I were you, I would get one of those things.
Zulu

[dominick]

I use a steel straight edge to find the vent location centerline.  I use two, same size, blocks of steel under the trunnions to level the barrel from the front view. Then put a 1/16" or small diameter rod down the bore and bottom it out to find the back of the bore.  Mark the rod at the barrel front edge and use the rod on top of the barrel as a length standard to locate the back of the bore.  Place a mark on the top of the barrel, 1/4" in front of the back of the bore. If the back of the bore is a drill point or dished, you want to make sure the mark is in front of this so the drill bit will come through at the straight cylindrical part of the bore ahead of this transition, otherwise you could snap the bit when it comes through.  I use a black marker and mark the top of the barrel for the front to rear measurement.  Then I use a steel straight edge and eye sight it level with the trunnions  and scrape it back and forth to scratch a mark through the black marker line. This scratch mark will be top dead center and where it intersects the black mark is the vent location.   Photos below.



 

[winniewino]

Found the "Handy Dandy" center finder on the ebay string.  For $6 it seems definitely worth it.

[megawatts]

It’s a pleasure to see that another English Barrel’ is being used in the US!
I hope the following will assist winniewino
1.Vent (a) marking out & drilling ~~ the attached photo give an idea of how I marked and drilled my barrel.
The  photo shows 2 red felt tip marks the larger right hand one indicates the approx end of the bore ~~ in your case check that it is the end as several were made with ‘patent chambers[that’s another thread].The left hand mark represents where the vent is to be drilled, mark on the side of the barrel the centre line of the bore, from these reference points, the angle of the vent can be established ~ why they are angled I don’t know but I’m sure some one does] ~~ take care setting up in the vice to get the angle to be drilled and don’t rush, the bore centre line less a ‘bit’ will show you roughly when the drill is about to enter the bore ~~ a broken drill is difficult to get out of the gun metal.
Vent (b) Dia. Mine/most of the UK ones have been drilled 1/8” to suit 2 mm fuse ~~ it works well, but remember to carry 1/8” drill in a small had chuck to clean the hole periodically as metal polish and burn fuse blocks it occasionally.
2. Shooting. (a) Proofing ~~ I don’t know how the US system works ,I ahve a photo to show that mine has been proofed at the Birmingham Proof House for 100 grns of proof house powder [another story] & ball weight etc,colleagues have been proofed at 120/130 grns
(b) Powder load, it doesn’t matter much as they seem to shoot best with 50/60 grns
© Patch, we tend to shoot with patches, ie treat the cannon like a ML pistol, purist may not agree, but our range shoots slightly down hill & the patches stop the ball rolling out, gives a better bang etc. 
3. General info, have a look at www.ncagb.com you will see examples of your cannon in action, one of the downloads will show the ‘gun drilling‘lathe used to bore your barrel I can assure you it’s the finest bore you will find.  If you wish I can send you photos of the gun metal melted and your barrel being cast in the foundry.
I hope this is useful and of interest.

[Zulu]

When you drill a vent at an angle, how do you get it started?  Obviously, you tilt your barrel.  What keeps the drill bit from "wandering" down hill?
Zulu

[Artilleryman]

Use a center punch to put a indent for the drill point to catch on.

[winniewino]

Megawatts, that's my gun alright. Thanks for posting the pic because I haven't managed to master this highly techincal skill somehow yet.
 
If you have the foundry pics to post as well I would appreciate it.
 
My handy dandy tool arrived today so I am looking forward to putting it to good use.

[armorer77]

To drill at an angle or any round use a center drill to start the hole . It is a very short stiff drill . Ed

[flagman1776]

I also use a center drill...  at 90 degrees to make a dimple the size of the drill tip.  Then I readjust the work to the correct angle & put the drill tip in the dimple I created.
I believe 2mm fuse is smaller than standard 1/8" fuse...  1/8" = 3.1750 mm   2mm fuse will easily fit in a vent (touch hole) drilled for "1/8 inch green fuse" but not the reverse.  And a vent drilled for 1/8" fuse needs clearance as well.
I use 2mm fuse in model sized cannons & standardized on 1/8" fuse in large scale cannons.  I was once gifted some red waterpoof fuse bigger than 1/8" & I passed it on rather than enlarge my vents. 

[de_lok]

Why drill the vent at an angle? This make it very difficult to upgrade to  a lock devise for musket nipples, 209 primers, 22 blanks, or whatever choice you may have. I have a friend with a 18 inch long Parrott barrell with one inch bore with the vent drilled at approx 30 degree angle that has just begged me to install a lock. The only way to do it is drill oversize and machine an incert for the nipple cap, not exactly ideal for a firing cannon........................................ I am interested in you guys input on any possible advantage of drilling the vent at an angle...............
Dewayne

[Double D]

Yes drilling the vent at an angle has two purposes-both safety.

1. It sends the ejecta in a specific direction.

2. It sends the vent prick used to pierce the charge at an angle, forward into the charge instead of straight up in down which migh miss the charge if the charge is not fully seated or the bag is a hair too thick. 

A vent at a 30 degrees is a bit excessive.  I think with out going doing stairs and looking most vent are some where around 5 degrees.

So plug the old vent and drill a new one.

[flagman1776]

I have one tube with the vent (touch hole) at a noticeable angle.  I just measured it at about 20 degrees...  in use the practical angle is probably 25 degrees or so from horrizontal.  I didn't drill the tube or vent but I did clean up the chamber so studied the dimensions at length.  This tube is cast bronze.  It was drilled so the vent is in the cast in pad but needed the angle to (barely) reach the bore.  Drilling the bore any deeper would have reduced the metal surrounding the chamber to unsafe dimensions.  Something had to give, in this case the vent angle.  At least that's what I surmise.
Having the vent drilled at an angle directs the vent blast & debris up falling well behind the gun.  I've had it fall 25-30 feet behind.  This is an extra safety concern for the crew to watch.  Setting fire to spectators & sundry articles belonging to our host is generally frowned upon.
I'd prefer the vent at 90 degrees...  and my other tubes are...  with the tube at a slight upward angle, the debris would fall behind the gun but more within the safety zone.   
So I agree, plug this vent & drill a new one.  The cannon locks for 209 primers, with their flange...  have a wide open passage for the vent pick.  I've been messing with a case with 209 primers & am sold on this approach. 

[megawatts]

Re: winniewino & others comments
The photos that were taken of casting his and other barrels [including Golf Ball Mortars] are now included on the www.ncagb.com website. If winniewino would like additional information etc I can be contacted through Roger at Shooting Supplies in Bromsgrove UK. 
 
I’m not sure if he had a Bloomfield or Monk barrel, however pictures of both are in the photo & video gallery together with one showing a 2 mm fuse [supplied by wireless fireworks in the UK] in a 1/8” hole ~ it shows my cannon (20 mm bore] which I never seem to get round to finishing the polishing.
Other photos shows the vent working, the videos especially in slow motion create loads of laughs.
I admit they do need cleaning which is usually done by putting a suitably marked pricker in the vent to show the cannon is clear.
 
Interesting comments on why the vent is drilled at an angle, we figured it was to keep some ‘meat’ at the end of the bore. Ours are circa 20 deg off the vertical; ignore the red dots on the photos they were for illustrative purposes & they never got cleaned off !.
 
We did not consider that the cannon barrels we had cast were really suitable for anything else than fuse as the barrel and carriage are true to scale.
 
Fuse diameter. Some members use 1/8” fuse, they work, but a bit incongruous in this application.
 
FYI we had some aluminium carriage wheels cast that enabled the same barrel to be fitted on a carriage ~~ photos of these will be under the ¼ scale wheels thread.
 

[de_lok]

Thanks for the replies to my question of drilling the vent at an angle, especially DD. Your #2 reason makes absolutely the most practical sense and reason to drill at an angle as the vent does need to be at the rearmost part of the bore and piercing an aluminum wrapped charge at an angle insures a good puncture and positive ignition. And @ 5 degrees it will still ejected anything in the vent at as safe an angle as any. I will keep this in mind on future builds....................         
I will mention this to my friend (I don't see him much these days as he works nights at our local plice dept.) and see if he would like for me to redrill the vent. My only concern with this is the posibility of carbon buildup and pre-ignition if the plug wasn't perfectly sealed in the bore. I always lean toward safety in these matters................Thanks again
 
Skratch>, I have been building cannon locks for years, I have actually made several hundred of them (I have some really nice cnc stuff available nearby). I wasn't trying to re-invent the wheel, just make a compact simple lock for scale cannons. Every now and then I am pleasently suprised at some of the new designs (of an old idea). I really like your 209 lock, it is not only a good concept but the design is also very nice, especially the lanyard guide, nice touch . Keep up the good work!
 
Dewayne

[Zulu]

It appears that I have to drill this vent hole today.
Is there something I should know about drilling bronze?  Is it different than drilling steel?
The barrel is bronze.  Not brass.
Zulu

[armorer77]

Use a lube . Brass and bronze are "grabby" . Ed

[Zulu]

Use a lube . Brass and bronze are "grabby" . Ed

Read this too late.
Drilled it already.  Drilled it dry at 150 RPM with a 1/8" bit.  Cut like butter.
No problem at all.
Zulu

[armorer77]

I never argue with observed reality . Ed