dead space below charge?

[firebuckeye]

Heres my question.  I drilled my piece of bar first and then took approx .030 inches out of the diameter with a boring bar.  There is now a step of .015 inces wide at the bottom, basically there is no radius going from where the boring bar stopped down to were the drill point stopped.  If this makes sense? Well my question is when I put my foil wrapped charge in there will be a small area below it that.  Is that going to cause a problem?  Does that step really have to be rounded off?  Even if it was, is it a problem if the charge is not all the way at bottom?  I had someone bore it for me and they did not round it off so this is what I have to deal with.  Please advise.

[Cannonball]

That could be dangerous! I've heard that a really small space won't do anything(like the space around powder pellets in a .50cal) but cannons are much larger and I've always been warned to never fire a cannon unless the round is perfectly seated.

[firebuckeye]

the round, golf ball, would be seated.  The aluminum foil charge would be approx .25" above the bottom of barrel
                                                          l_ _l
                                                            U
Kind of like that but that is not to scale.  The steps are approx .015" and the "U" is approx .25"  the bore is 1.700"  the "U" is a drill of 1.5"

[Artilleryman]

I a mortar the chamber is large enough to hold the maximum charge for the maximum range.  Smaller charges are used to get shorter ranges.  There will be an air gap between the powder and the projectile when small charges are used.  The transition between the bore and the chamber is a curvature that matches the curvature of the projectile in coehorn mortars.

[GGaskill]

The foil powder bag you should be using to load the charge with is sufficiently flexible that it will conform to the irregularity when you ram it.  But it would be nice to go in and at least chamfer the edge with a flap wheel or cylinder hone so it doesn't catch the powder bag.

When ramming the charge, you need to seat the charge firmly but without pounding.  Mark your rammer staff with a line showing how far in it should be when the charge is fully seated.

With golf balls as shot, almost anything is safe because they weigh so little.  No so with heavy shot.

[das]

 How many of you actualy put your powder in a foil pouch when loading a golfball mortar? As small as this charge is I have never done that. We simply pour the powder straight into our measure and then drop it right down the barrel . Allowing for plenty of time between shots I've never had a problem.

[firebuckeye]

I will try to chamfer it some way.I had a small machine shop bore it for me and I think they got frustrated with how long it took and thats why the did not chamfer it while they had it.  Or they just didnt care or forgot.  I felt bad and really did not want to bug them any more.  Also the wick hole is approxamately .25" above the step are and a totall of about .5" inch upfrom bottom.  Hopefully this will be ok, right?

[Terry C.]

The foil packet should not be so tight in the bore that the slight restriction you mentioned would prevent it from fully seating.

When you create a foil packet, it should be sized to slide very easily down the bore. Give it some slack, the packets will not be perfect, it can't be done. They are going to be a little out-of-round, and possibly a little lumpy too.

Neither will they be so tightly packed that there will be absolutely no airspace inside the packet. You are not creating a solid pellet, nor should you be trying to.

The packet needs to give when the ball is rammed against it. This is good, the little bit of crumpling of the foil will allow the packet to conform to the shape of the chamber.

I pride myself on the appearance of my charges, but as neat as I make them they are still never perfectly round and smooth. And for this reason they are sized accordingly.

[firebuckeye]

would you make a charge for a 1.700"  bore by wrapping foil around a 1.5" inch cylinder then, or were you thinking more play than that?  Perhaps 1.25" to wrap the foil around.  Thank you everyone thus far.

[GGaskill]

I would wrap the foil around a 1.625" cylinder.

Having the vent 1/2" from the bottom of the bore means you need at least a 1/2" of powder in the chamber for the fuse to reach it.  That may be too much for a golf ball.

[Double D]

Pour loose powder in a mortar.  No foil cartridge.   

If the measurements you have given are accurate, you are going to have problems with this gun.  You only need 25 to 30 grs of Fg to launch a golf ball.  You have no chamber  so when you pour in the powder and drop in your golf ball the golf ball is going to hole is going to be under the fuse holel.   If you put in powder  1/2 inch deep x 1.7 diameter to fill up to the vent hole you are going to have a lot of powder.  Just fill to the vent give you  1.135 cubic inches of powder.  If what Accurate Mike posted elswhere is correct-I have no reason to doubt it- the your powder chamber is going hold  266 grains of Fg. 

To much powder for a golf ball mortar. It will launch the golf ball so fast that you will never see it go and you will not know where it lands.  Way not not safe.

I thinlk it's time for you stop what you are doing and start learning.  You need to learn a little more about basic design.  Instead getting in a big rush and building  a badly designed cannon or mortar  that doesn't work right or gives you problems and makes you frustrated, or is jsut plain unsafe, stop what you are doing and think about it. 

Plan out what you want.  Sketch it up first on piece of scratch paper  or take one of our plans from the Golf Ball mortar Contest and use that. Lets talks about planning design first before you remove any metal. Once metal is remove it doesn't grow back.

Lets also get you educated up here...wicks draw liquid up like molten wax in a candle or perfume in a room deoderizer.  Cannons have fuses and vent holes and transmit fire to powder!

EDIT: Down post you see George point out my math was faulty...he is right...Radius= 1/2 Diameter.  In my original post I failed to convert diameter to radius when I did the math.  My bad.  I have corrected the math above..the numbers in bold are now correct.  It also requred I do some additional editing of my comments, this are in italics.  DD

[firebuckeye]

Thats clear on the fuse,  i have been reading the few books you all recommended the terms just have not set in yet I guess.  I was planning on slowing down.  I just thought I would be able to get one basic one done for now, in the mean time.   I am having someone from the forums here build me a nice cannon and  one that will be done properly.  I dont have the equipment or knowledge to build a nice cannon, at least not at this time. I am learning a lot and I appreciate it all.   

[GGaskill]

DD, I think you need to review your volume calculation that gives 4.53 cu in; I get only 1.2 cu in, which equates to 282 grains of powder.  Probably OK for a blank load but way too much for golf balls.

I think you should have the vent tapped for a screw in plug and plug it with a screw that goes all the way through, then clean up the inside of the bore where the screw comes through.  Put some gasket sealer on the screw and in the hole to fill up the space between screw threads and hole.  Then redrill the vent in the proper place at the bottom of the bore.

Can you give us dimensions of the barrel as it stands?  Maybe you could drill a chamber in the bottom if the back is thick enough and fix these problems.

[Double D]

My math could be wrong...volume of a cylinder 1.7 diameter b y  1/2 inch deep.  Pie x R squared x height = volume?

Oh yeah....Radius is  1/2 diameter....duh!  I'll edit the error out so as to not confuse

[firebuckeye]

The overall dimension is 5.5" x 13"  1.700 bore 11"  deep.  Well the 1.7 only goes like 10.75" and then its a little deeper where the drill bit went first.  There is 2" behind the deepest part of the bore.  I was wondering if I could put some lead or something in the bottom?  Possible drill and tap and the redrill the vent would be a good idea.  What about drill the vent bigger with a taper and have it welded by a professional?  If I have to put this asside and forget about it no big deal, Im not out that much and  I learned a lot.  Besides i need to weld trunions and stuff, wich are beyond my capabilities right now, on it to make it look like a replica.  The rules are they have to be repicas to be legal right?

[GGaskill]

Based on your dimensions, you have a howitzer, which is OK.  You could put in a 1" dia x 1" deep chamber which would be pretty good for golf balls and make firing a lot easier.

[Double D]

All is not lost.

You could also make this into a neat little mortar.

Here's what i would do. First contact one of our sponsors and ask them for help!

Have them do the following

Plug the current vent hole like George says.  For cosmetics you can have the plugged hole now be on the bottom, the new vent would be drilled on the opposite side.

Next cut the tube from  13 inch to  6 inch. This will give you a 4 inch deep bore, close enough for the 2 caliber rule of thumb for Mortars.

Set the 7 inch piece aside for future project or trading stock.  Another mortar could be built from this piece with a screw in base plug. Eyeball with no math sees a pop can mortar, could be wrong.

Have the bottom of the bore angled slightly so it is not flat. This will make a ball seat.  I just walk may boring bar in using the compound whichis normally setr at 30 degrees.  This doesn't even need to be full diameter. 

Drill a 1/2 diameter hole in the bottom that is no deeper the  1/2 inch from end of the tube. The vent should come in just above the bottom of the chamber. 

If you leave the end flat you could just screw on a trunnion bar.  Or you could have the end turned round  and slightly groove the bottom for a trunion barrel and either screw it on or have Tig welded.  You could also have the out side profiled to look like a federal Coehorn.

Here is a plan drawn with P&P vers. 2.01 of only the critical numbers required to make this mortar.  All the other numbers are those that currently exist  or are adjusted to fit the critical number.   This is called Millwrighting and Gunsmithing, not engineering.

[Terry C.]

Hmmm... I should read more carefully before I post.

I never got the part about this being a mortar. I was basing my reply on a cannon barrel.

Chamber diameter same as the bore, larger volume of powder in realtion to projectile size.


Nevermind...

[firebuckeye]

I think you should have the vent tapped for a screw in plug and plug it with a screw that goes all the way through, then clean up the inside of the bore where the screw comes through.  Put some gasket sealer on the screw and in the hole to fill up the space between screw threads and hole.  Then redrill the vent in the proper place at the bottom of the bore.

Is it totally safe to drill and tapthe vent hole toinsert a plug?  No risk of it blowing out?  What size srew or bolt would you recommend?  What about a set scre with weld on top of it?

[Double D]

Is it totally safe to drill and tap the vent hole to insert a plug?  No risk of it blowing out?  What size srew or bolt would you recommend?  What about a set scre with weld on top of it?

We have three or four post running around here with discussion on vents.

1. You do not need a vent liner in a tube made from a solid piece of metal.  You only need a vent liner in a tube that has a liner.  If later  your vent  hole erodes you can drill it out then and put in a vent liner.

2.  Original vent liners were threaded.  The were that way so when the erode the could be removed and replaced. The only need screwed in place tightly to be retain.  Welding them in defeat their whole purpose.

3. The size of them is determined by the size of your gun and the method of ignition?

Did you order Switliks book yet?  A lot  of your questions are answered in the book.

[Terry C.]

DD, he's not talking about making a vent liner. He's referring to the suggestion of plugging the old vent.

[Double D]

Well duh, whatcha mean read what he wrote.  I forgot I told him the plug the hole and turn the tube over and put the new vent on the other side.

I would just make a solid vent liner, no hole down the center and screw it in tight. Use some red loctite on the threads.  It isn't going to get hot enough to melt the loctite.   It's not going to be in the chamber area, its going to be in the expansion chamber where the ball is. Pressure yes but not significant enough to worry. 

[Artilleryman]

Dahlgren placed in his naval guns two vents, each a short distance from, and on opposite sides of , the vertical plane passing through the axis os the piece.  One of them was filled with melted zinc; the other was used  until it became so much enlarged as to endanger the safety of the piece; it is then filled with zinc, and the first one is opened.  Taken from Ordnance and Gunnery by Benton.

If a zinc plug works on a big gun then using a threaded rod to close off the vent doesn't pose much of a problem.  Make sure that it is flush with the side of the bore so that it can be cleaned properly with a sponge.  Loctite it if you have a loose fitting thread, otherwise just go ahead and file it flush with the outside of the barrel.  Turn the barrel over if you don't want to look at the repair.

[firebuckeye]

Very good info!  You mentioned that it would not be in powder chamber and exposed to extreme pressures.  Would it be ok if it was in powder chamber? 

[Double D]

That's exactlly what Norm said it's okay if it was  in the powder chamber. That exactlly what he was describing with the  Dahlgren,