Group buy-group pour, bronze 24 PDR Coehorn golf ball mortar

[Zulu]

Does investment casting pour into a mould made with lost wax?  Is the mould reusable?
Zulu

[flagman1776]

If we flip the fraction to 1.723 / 5.82 we get 1 / 3.378 or "about 1/3 scale"

[GGaskill]

Is the mould reusable?

The wax patterns are typically made in silicone rubber moulds so many can be made with little effort.  This mould is reusable.

The waxes are coated with investment and the investment dried.  Then the wax is melted out to leave a cavity in the investment which becomes the mould for the metal.  This mould is destroyed either during the post-casting cooling phase or during the actual removal of the casting.

For relatively small pieces like this, a number of them will be made into a tree with a single sprue and feeder system and they will all be cast at the same time.


Regarding casting the bore/chamber, this might be possible considering how short the bore is but there is some risk of eccentricity and lack of roundness.  If casting hollow is the plan, I would suggest that it be undersize to minimize machining but allowing enough metal to get the bore centered and round.

[Zulu]

Is the mould reusable?

The wax patterns are typically made in silicon rubber moulds so many can be made with little effort.  This mould is reusable.

The waxes are coated with investment and the investment dried.  Then the wax is melted out to leave a cavity in the investment which becomes the mould for the metal.  This mould is destroyed either during the post-casting cooling phase or during the actual removal of the casting.

For relatively small pieces like this, a number of them will be made into a tree with a single sprue and feeder system and they will all be cast at the same time.


Regarding casting the bore/chamber, this might be possible considering how short the bore is but there is some risk of eccentricity and lack of roundness.  If casting hollow is the plan, I would suggest that it be undersize to minimize machining but allowing enough metal to get the bore centered and round.

George,
Is the silicone rubber mould made with the first wax pattern?
Zulu

[GGaskill]

The original pattern can be anything.  I have made them from wood and from aluminum since they were machined but they could be wax if they had a lot of hand details like royal crests and such.  They could even be hybrids with machined tubes and wax details added, for example.  Only requirement is sufficient strength to resist handling.

[gunsonwheels]

DD:
 

I have sent the wax carver dimensions.  I got the dimensions by dividing the original dimensions by golf ball dimensions.  (5.82/1.723= 3.378)

Like "flagman" says it's reversed for the scale... or... 1.723"/5.82"=.3 scale (rounded to two decimal places) or a little less than one third scale.  The multiplier is .296... so take any one of AOP's drawing dimensions and multiply it by the multiplier and you will have that particular finished dimension for the GB sized mortar.  The other is the scale of the full size in relationship to the GB'er or the FS is about three and a third times any of the GB sized dimensions.
 
I am curious if there are any other antique ordnance outfits investment casting bronze tubes... I've never heard of any so I hope this goes and does so beyond the GB'er.  "Gimme one of everything and two of all the good stuff"  .
 
Also can I pick mine up in person (about 20 minutes away from the ranch/range here  )?
 
GOW/George

[Double D]

...or you can divide them by a 3.378 and get the exact same numbers....

[RocklockI]

I am making the positive for the mold that will be made for this 'group buy' on the 24lber bronze golf ball mortar .
 
Here is the 1-1 scale print I drew from DD's supplied prints and charts .
 

 
There will be a need for the buyer to drill their own touch hole , or have it done for them.
 
The bore and chamber will be cast in place ,there should be no need to machine anything ,except the touch hole .
 
This is another pic of the print .

 
Along with a test piece of wax showing the ball nested safely in it's hemispherical chamber .
More later .
The drawings are correct ,but the photo has a bit of depth perception that makes the print look small .
Gary

[GGaskill]

This could be a fun side trip before or after the next CBC² III.  Like on a Tuesday if after to allow travel.

[Mike H.]

Still no rough order of magnitude price range?  Rounded to $100, are we looking at $100, $200, $300, or beyond?

[Double D]

We are not at the stage yet to determine a price point, we don't even know if this can be done. 

[Cat Whisperer]

Bore needs to be at LEAST 2 calibers long.  Golf balls shot from short tubes MIGHT make it off the poarch. 

Powder chamber bottom must not have sharp inside corner - should be rounded.

I see you're using P&P.02 - much better than DD's P&P.01 version.

 

[Double D]

That drawing is a direct scale down from the original Federal pattern drawing....AAA construction safety standards say barrel length should not exceed 2 times bore diameter...

I can assure you that my 1.5 to 1.75 caliber length barrels will toss a ball off the porch and well into the neighbor back forty...

[Mike_60]

...There will be a need for the buyer to drill their own touch hole , or have it done for them....
 

It would probably help if you were to put a small dimple in it as a drill point.

[gulfcoastblackpowder]

It would probably help if you were to put a small dimple in it as a drill point.

Excellent suggestion.  When I got my Hern, I was wishing they had done that for me.  I still would have checked the location before drilling, but a guide would be helpful.

[RocklockI]

Yes there will be a small center drill located at the vent .
 
To be accurate it will need to be drilled at an angle ,the angle will be indicated by the center drill ,BUT it will be up to who ever drills it to set up the piece for the drilling and drilling accuratly ,and drill bits that break are a real problem  . A real problem .
 
Personaly I like a vent dia. of @.082" ,the bigger you go it is less likely break , DD likes .177" thats big for my tastes on something small but , but it's up to the buyer .
 
I have nothing to do with pricing ,at this point I am the wax carving artist only .
 
Thanks for the interest . Gary

[Max Caliber]

Here is a shortened 1/3 scale GB Coehorn (casting mistake) with a bore of one caliber plus 3/16 inch in length and a tight 1.695 diameter. It will throw a ball a long, long way with a 2F charge in a foil cartridge.
 
 
 

[flagman1776]

self delete

[seacoastartillery]

Bore needs to be at LEAST 2 calibers long.  Golf balls shot from short tubes MIGHT make it off the poarch. 

     I think I figured out the problem, Tim.  Somehow we must find a way to convince you to buy real black powder, you know, the kind with niter, charcoal and sulfur.  The synthetic stuff just doesn't seem to work in mortars.  I think I know how difficult it is for you.  The temptation to pick up a bottle or two of that make believe powder is very strong when you are wandering around in that big Gander Mountain store up on 81, near Roanoke.  It's so easy and convenient, and after all the time you spent in that store looking at Prairie Dog lures, blinds, books on stalking them, personal water hydration systems and Dog Musk Oil (gotta have some of that!), you are in a big hurry and just don't have time to search for the real stuff in Roanoke.   

T&M

[Cat Whisperer]

Bore needs to be at LEAST 2 calibers long.  Golf balls shot from short tubes MIGHT make it off the poarch. 

     I think I figured out the problem, Tim.  Somehow we must find a way to convince you to buy real black powder, you know, the kind with niter, charcoal and sulfur.  The synthetic stuff just doesn't seem to work in mortars.  I think I know how difficult it is for you.  The temptation to pick up a bottle or two of that make believe powder is very strong when you are wandering around in that big Gander Mountain store up on 81, near Roanoke.  It's so easy and convenient, and after all the time you spent in that store looking at Prairie Dog lures, blinds, books on stalking them, personal water hydration systems and Dog Musk Oil (gotta have some of that!), you are in a big hurry and just don't have time to search for the real stuff in Roanoke.   

T&M

I was speaking from my experience with FFg and FFFg Goex.  The powder chamber looks disproportionately long for the amount of powder needed, which if shortened would allow for better velocity by simply deepening the bore a whisker or two.  Making the bore as long as drawn is marginal and could be made better.

But you're right, the real stuff is not to be found locally.  I haven't been the GM store but once in the last couple of years - too expensive and the gunsmith moved on.

[RocklockI]

Today I started machining the wax positive . It went well ,and here are some pics of the progress.
 
Here is the wax blank after being trued ,faced and bored. The chamber is in to .

 
This is the tool that made hemisphereical   ball seat . It worked very well .

 
Here is a somewhat blurred pic of the bore and ball seat and chamber .

 
Tomorrow ,I will cut the profile .
 
Gary
 
 
 
 

[flagman1776]

Thanks for the picts.

[KABAR2]

Is just the angle of the photo or is the chamber on the small side?

[Double D]

Bore needs to be at LEAST 2 calibers long.  Golf balls shot from short tubes MIGHT make it off the poarch. 

     I think I figured out the problem, Tim.  Somehow we must find a way to convince you to buy real black powder, you know, the kind with niter, charcoal and sulfur.  The synthetic stuff just doesn't seem to work in mortars.  I think I know how difficult it is for you.  The temptation to pick up a bottle or two of that make believe powder is very strong when you are wandering around in that big Gander Mountain store up on 81, near Roanoke.  It's so easy and convenient, and after all the time you spent in that store looking at Prairie Dog lures, blinds, books on stalking them, personal water hydration systems and Dog Musk Oil (gotta have some of that!), you are in a big hurry and just don't have time to search for the real stuff in Roanoke.   

T&M

I was speaking from my experience with FFg and FFFg Goex.  The powder chamber looks disproportionately long for the amount of powder needed, which if shortened would allow for better velocity by simply deepening the bore a whisker or two.  Making the bore as long as drawn is marginal and could be made better.

But you're right, the real stuff is not to be found locally.  I haven't been the GM store but once in the last couple of years - too expensive and the gunsmith moved on.

My turn to needle Tim... 235 miles to Fort Shenadoah and  Back Creek Gunshop.  95 miles to Park and Sons, in Advance  NC both major black powder distributorships...but then they do restrict purchase to no more that 50 lbs  per person.  I have to go further than 95 mile to get Wally world...  

My last four purchases of black powder were from  Back Creek, a little over 2000 miles one way-but I avoided the hazmat fee from having it shipped.


Gary that wax work is looking good.  You could make a similar cutter to make the gomer chamber instead of a straight cylinder.

[RocklockI]

Hey Gomer ,what do you mean gomer chamber ? If you are talking tapered insead of straight ,well then silly boy ........... I am already over budget on this project of your's Douglas  .
 
The chamber is straight and it is 1/2 inch in dia. and is .900" deep full .5 dia. then there is the tapered point . It will hold @45 grains 3F that will make a GB go into low earth orbit .
 
Not sure about a Fox ball but it ought to be fine .
Gary
 
Victor3 here you go .

[seacoastartillery]

     Hey Gary, I sure don't want you mad at me or anything, but as long as you still are working on the bore, I am putting my vote in for the goner chamber.  I want my Fox ball to be a 'goner' when I fire my bronze coehorn with a full chamber.  Just ask me or Mike about an authentic blade for that form tool if you want to.

     Gary is taking great care in the manufacture of this 1st prototype, 'Master Positive'.  I am certain it will be perfect when he gives it to the foundry.

Mike and Tracy

[Double D]

Hey Gomer ,what do you mean gomer chamber ? If you are talking tapered insead of straight ,well then silly boy ........... I am already over budget on this project of your's Douglas  .
 

Okay you drive a tough bargain,  I put another beer in your pile.....

[gunsonwheels]

M&T:
 

Just ask me or Mike about an authentic blade for that form tool if you want to.

If it were me I'd ask them... I too would like a larger/tapered chamber but ultimately it's up to RocklockI
 
GOW

[Victor3]

Victor3 here you go .

Ahhh yes, I remember the 'pit bull' mortar. 
 
Just a suggestion on the golf ball mortar since you're planning on an as-cast bore. It might be a good idea to turn a plug out of somethng (wood, plastic rod, PVC pipe, etc.) that will slip into the bore to make sure that your master stays good and round on the trip to the foundry.
 
That blue wax you're making it out of looks familiar. Is that the hard stuff designed for machining? We used to use it for proving out CNC programs before going to metal.

[GGaskill]

I too would like a larger/tapered chamber ...

It would be a relatively minor machine job to add a taper to the chamber after the fact.  Setup would be somewhat of a pain for only one or two but a whole bunch would warrant a special holding fixture which would make it easy.