minimum wall thickness

[john pike]

ive got a piece of 10 inch 1018, 2.75 diam.

playing with my new lathe, i made up a drill bitt extension and drilled a straight through bore at 3/4 inch,

whats the minimum thickness i can go at the front of the cannon,
where it tapers down and then up,

im leaving the rear full thickness.

thanks,
johnp

[GGaskill]

How thin a wall do you want?

[john pike]

How thin a wall do you want?

again sorry for my lack of "teminoligy" but im just wondering how thin i can run my taper towards the front of the barel befor the curve up at the end of the barrel,

im trying to make my own home grown signal cannon, with some fancy
work here and there,

johnp

[GGaskill]

Your terminology is all right.  You want to keep the wall thickness over the powder chamber (or area where the powder will be rammed) the same as the diameter of the chamber (or bore if you aren't using a reduced diameter chamber) so with a 3/4"bore, the wall thickness should be 3/4" for a total diameter of 3 times 3/4" or 2.25".  You are already in excess of that with a 2.75" overall diameter.  I would keep the 2.25" minimum for at least 5 calibers (5 times 3/4") and then the wall thickness could come down to 1/4" behind the muzzle swell.  

Are you going to have a cascable (the knob on the back)?

[Squire Robin]

Cannon pressure peaks in the first 3 ball diameters of barrel length then drops to not a lot, so presumably you can go thin after that.

Here's the link, scroll down to Fig. 16 which shows the pressure curves for both fine musket powder and chunky.

http://www.angelfire.com/ga4/guilmartin.com/Appendix2.html

[Cat Whisperer]

Note also that the very end of the barrel has supporting steel on only one side, hence is a weak point on the barrel.  That is why you will see reinforcing bands and muzzle swells there.  Not from the pressure of one shot, but from the repeated (light) hammering of many rounds; hence with modern US artillary the requirement to log each round fired and the need to inspect the muzzle when approaching the 4000 max-charge-equivalent rounds fired.

George's cyphering sounds reasonable.  Overbuilding is OK.

[john pike]

Your terminology is all right.  You want to keep the wall thickness over the powder chamber (or area where the powder will be rammed) the same as the diameter of the chamber (or bore if you aren't using a reduced diameter chamber) so with a 3/4"bore, the wall thickness should be 3/4" for a total diameter of 3 times 3/4" or 2.25".  You are already in excess of that with a 2.75" overall diameter.  I would keep the 2.25" minimum for at least 5 calibers (5 times 3/4") and then the wall thickness could come down to 1/4" behind the muzzle swell.  

Are you going to have a cascable (the knob on the back)?

Yes i am,  though i driled too deep, so ill probably  make it seperate and
shallow thread/locktight, it on,  leaving 3/4 behind the chamber,
Grrrrr,,, i have a total of 1.25 now, so ill just shallow drill my center hole and tap it for 1/4 20, make up the cascadable thread that, cut a bolt
and locktight it on,
(so much for pre-planning,) i got carried away with the lathe,,grin,,

thank you for the info, what i drew up , i went to 1/2 inch thickness around the area behind the muzzle swell,
i started my taper, at 3.5 times the caliber, so at 5 times, in length
i have3/4 inch wall, so im good,

im also doing the "horn" on the front inside, testing for a bigger bang?

i need to make up a mold and press up a bunch of bread-balls,

johnp