Planning a sodacan mortar seeking comments on my tube design

[Double D]

Making the Gomer chamber isn't that big a deal.  The angles could created bysimply feed the boring bare by hand with the compound set at the correct angle.

The problem area is the radius ball seat and chamber bottom.  Special tooling and technique required.  Even that could be minimized by extending the mouth of the gomer chamber to ball bore diameter. Then you only have the bottom of the chamber to be concerned with.  Still some special tooling needed.  Even then that you don't need a full radius in the bottom, just in the corner to aid cleaning.

[dan610324]

that you do with an standard drillbit that you slightly modify on the tip

[GGaskill]

The two radii are what I was talking about.  They can be done with stepping but are a major pain that way.

Using a form cutter on the end of a boring bar is asking for chatter.  If you were making a breech plug, the boring bar would be held much shorter which would lessen the chatter problem.

If you could afford custom tooling that had the whole chamber on a single tool, it would be a simpler process.

[Cannoneer]

I'm not going to bother asking you approx. what a custom tool that could shape the whole chamber and the top radius would cost, because I've got the feeling it would be a considerable amount.

"Using a form cutter on the end of a boring bar is asking for chatter.  If you were making a breech plug, the boring bar would be held much shorter which would lessen the chatter problem."

George, you mention the possible chatter; but do you think it's doable? Is using a hss twist drill to form the bottom of the chamber a feasible idea?
 

[Double D]

The way it was explained to me is the hole is drilled then a form bit is put on a spade drill body and it cleans up the bottom of the hole, nothing more. Little bit at a time. 

 

[Cannoneer]

DD,
It looks like its going to be the tried and true cylindrical chamber after all, but I'll see if GG answers that last Q., and I'll certainly check out what the eventual maker of the piece will have to say on the subject.

The next and last question is going to be about welding, a topic on which I'm definitely going to need some input.

[dan610324]

if we dont think about golfballs , but only fox balls

how much powder would it need to reach the 30 yard pole if you had a narrow cylindrical chamber and used ffffg powder ??

by narrow I mean somewhere between 1/4 and 3/8

[Cannoneer]

Dan,
I've been asking questions about a pop can sized bore, not a GB mortar; I was wondering why you were mentioning 3 & 4Fg powders (not that Dom's and Ed's can mortars couldn't withstand the pressures).

[Cannoneer]

The way it was explained to me is the hole is drilled then a form bit is put on a spade drill body and it cleans up the bottom of the hole, nothing more. Little bit at a time.

DD,
I just reread your post; so, are you saying that this form cutter would make both the shape of the cone and the round bottom of the conical chamber?

[dan610324]

Im just curious to try to find out the minimum amount of powder and the absolutely best shape of the chamber to launch a fox steel ball 30 yards for competition use only .

not interested in several hundred yards

I cant do any experimenting as only blank firing is legal here in sweden
I dont like to spend a few years behind bars 

if its possible I would like to find the load size, granulation and chamber shape that burn all the powder in the barrel so there will be no muzzle flash at all , just a white cloud and a small thump

as the barrels are so short I would guess that the only possibility to reach that would be to use fffg or ffffg powder

it seems like the cylindrical shape of the chamber would be the best to achive the distance with an as small charge as possible

two 22 cases launched a golfball 30 yard , so how much is then needed for a fox steel ball if you have an narrow cylindrical chamber ?? lets say 1/4"x1" or 3/8"x3/4"
I would guess that a 1/4"x1" chamber would hold approximately 2,5 - 3 22 cases of ffffg powder
that maybe would be enough if you had a small clearence between ball and bore
lets say 1/80 instead of 1/40
this idea is only for competition use so the bore will need carefull scrubbing between each shot

with a chamber that narrow you can easily have 4 times the chamber diameter in wall thickness so the strength wouldnt be any problem even if you use ffffg powder

I got the idea when I was reading about gonnes on that austrian guys website
dont know if its any of this so far only theoretical ideas you could use for your build , but at least I hope it can give you some ideas

do you plan to shoot concrete filled cans or spherical projectiles ??
for cans maybe its not any good idea as it could destroy the thin aluminum , but if you would shoot cast zink balls it could be something to think about .
maybe a 1/2"x2" chamber or something like that
dont know , just some ideas

[Double D]

The way it was explained to me is the hole is drilled then a form bit is put on a spade drill body and it cleans up the bottom of the hole, nothing more. Little bit at a time.

DD,
I just reread your post; so, are you saying that this form cutter would make both the shape of the cone and the round bottom of the conical chamber?

It's done in steps.

Drill hole
open hole
taper hole
shape bottom

Drill the hole as much as you can with a drill bit-twist or spade.  Open it up with a boring bar.  Make the angled-tapered sides with boring bar.

For the bottom if you really think you need  full round of bottom, it you need that much correct detail  then a form tool can be used.  Look back to the post Gary made on sabots and see the light weight form tool Mike made for him.  A heavy spade drill bit that is radiused is used. You can just radius the bottom corner or if you want the radius the full bottom. Full bottom you could also do some incremental machining to remove metal before using the form tool.

Each step mean extra dollars.   

I wonder if any of the original tools used in the manufacture of these guns is still around.  Perhaps a phone call to Watervliet would be worth while.

Personally if I were having a mortar made I would tell the machinist what I wanted and provide a drawing with the specifications and let him do the job.  There are more tricks in this trade than you can shake a stick at.   

I visited my my friend last week who use to make parts as a sub contractor for the aircraft industry.  He showed a bunch tooling that he made and used.  Some big end mills and lots deep hole stuff using modified commercial tooling.  Built up tooling with modified extensions for one time jobs- a  big Silver-Deming drill in a piece of long seamless tubing and  1/2 inch shaft in the other.   Not to drill a deep hole, but to drill a hole in bottom of a deep box. He told me you don't go hogging on this stuff you nibble. I saw similar odd one of tooling the Mill wrights shop I use to visit back in Redding. 

Dan, take a look at the golf ball contest drawings for ideas.  My chamber was just a 1/2 inch twist drill hole. OAL depth 1 1/8.  My design has a removable breech plug so I could make different shaped chambers.  Why the concern about fire coming out?   My load for 30 yard golf balls was around 24 grains of Fg.

Is this to much fire?



Switlik found that equal volumes Fg  and Cannon grade produce equal velocity despite a 40% increase in pressure in the Fg over Cannon.

I don't think reduced volumes of FFG or FFFG or FFFFg is going reduce fire and still get the velocity needed to loft  the Fox or golf ball 30 yards.  In the interest of science I am willing to try for you.

[GGaskill]

Dan, start with a 6 mm diameter chamber and enlarge as necessary to get the desired range.

[dan610324]

with a 6 mm chamber diameter even the powder manufacturer recomend fffg powder
from 3/8 actually

so in such a short barrel I believe you could go one step further and even use ffffg to be able to come as close as possible to a complete combustion inside the barrel

but remember that this is just an crazy swede who tries to do a little logical thinking

dont forget that  ALL  blackpowder have the same combustion speed

ok with that I mean all bp used for shooting
lets take goex for example, if its cannon grade or ffffg doesnt matter .
its actual speed of burning is the same

the difference is in the granulation 
a powder grain start burning on the outside ,
so a smaller grain should more likely have the time to burn out completely in such a short barrel as a mortar

[RocklockI]

if we dont think about golfballs , but only fox balls

how much powder would it need to reach the 30 yard pole if you had a narrow cylindrical chamber and used ffffg powder ??

by narrow I mean somewhere between 1/4 and 3/8

The chamber I put in my new mortar is 1/2"x1" it holds about 50 grains of 3f .  We drilled the 1/2 pilot drill to chamber depth then drilled and bored it short to leave it 1" deep .

We will come up with a tool for a fully radiused bore bottom . I suggested my spade type that i use for sabots . Proly not .

ETA to correct powder charge .

[MikeR C]

If you are making small chambers, do not forget the lowly "D" bit. I have a small mortar with a chamber that is 1/2" at the top, 3/8" at the bottom, with rounded bottom and I cut the whole thing with a "D" bit after drilling a pilot hole. The Bit was made from O1 steel, turned on a lathe to conture, sliced in half, and heat treated with a O/A torch. It cut two chambers with acceptable finish in 1144 stresspruf.

Just a thought,
Mike R C

[Cat Whisperer]

Good point Mike.
A LOT can be done with less than optimal tooling.
It takes more work, and may take much more care in getting good finishes.

I bored my first mortar in 1974/75, old beer-can caliber, with a 3/4" bit clamped in the tool holder.  Not fun, but it worked.  I guess I just didn't know better.  The powder chamber curved at the widest matching the bore and at the bottom 3/4".

Use the best tools you can.  Get 'er done.

[RocklockI]

Jebuss johnny I meant 50 grains not 25-30 .....

[RocklockI]

If you are making small chambers, do not forget the lowly "D" bit. I have a small mortar with a chamber that is 1/2" at the top, 3/8" at the bottom, with rounded bottom and I cut the whole thing with a "D" bit after drilling a pilot hole. The Bit was made from O1 steel, turned on a lathe to conture, sliced in half, and heat treated with a O/A torch. It cut two chambers with acceptable finish in 1144 stresspruf.

Just a thought,
Mike R C

Mike IIRC  That is also called a 'half bit' Mike of Seacoast has also suggested that to drill mortar bores .

O-1 radiused ,then milled in half a little relief , plus a hole in the cut out half for air to blow in and clear chips .

Harden and ....you're done

It should reduce the time needed to bore mortars and howies .

Gary 

[clumsum]

I know it has been a long time since this was discussed but I found the plans for this tube somewhere on the net years ago. Over the years I tried a few machine shops to see if they would build one for me, with no luck. Last year I found a young man with a shop that said He would be glad to build it. Had it built, then I built the bed out of laminated southern pine, made the thru bolts, nuts and washers. Forged the handles one turned a little wonky but thru out all of this I was having some medical issues. Got the beer cans filled with concrete ,those weighed in at near 2 1/4 pounds and I pored 2 half full, ,all of them had a wire loop in the top of the cans so I could tie 3 foot of surveyors tape to them. The shoot, got setup first shot was 1/2 chamber cannon grade powder and a full can, range about 100 feet. So then tried 1/2 chamber load with 1/2 can, range about 100 feet. Then the next shots were with full chamber and full can, range about 90 yards with a pattern of 15 to 20 feet. The last shot was full chamber and 1/2 can range 90 yards and it hit in the middle of the full cans. Oh yea the elevation was 50 degrees. Notes ,roll up the tape so it will stream out and it will turn the can around so it hits bottom first and if you pull the tape off to the side it wont burn but it will blow off. Have some 2FF might try some loads with it nex time.

[Double D]

Get rid of the tape, it isn't needed with a mortar.  It will act as a drag and slow the can down.  With reasonable loads I can see my cans out to 300 yards. 

Standard elevation is 45 degrees, but 50 won't hurt, although 45 may give you a shade more range, maybe a full 100 yards. 

What is the diameter and shape of  your powder chamber?

How about some pictures of what you built?

For a target.  Stand a Pallet up on its side.

[clumsum]

The tape was so you can find the beer cans in soft ground or tall grass, The chamber is 1.25" x 1" and I may bore it out a little, I will know more when I try some 2f powder , Sorry no pictures.

[Double D]

Why 2F?

That is a pretty small chamber for a pop can mortar.

Get a scale and weigh you charges and keep track of how much powder it takes for each range.

90 yard is a respectable range for a pop can mortar.

Get an old wooden pallet and stand it up on edge and aim at that for a target.

You will need to carefully weigh your charges and learn how to aim the gun to hit it.



 

[clumsum]

Thanks for the information.