How to make a round ball mold

[ratpatrol]

  I"ll start with the math first. Think back to high school trig  class --triangles--  The long leg  of a 45 deg  triangle is your bore size or C to find  short legs A or  B you look up sin or cos of 45 degres--0.707107 . B =C x sin . Bore size X 0.707107 1s the size you will set a mill boring bar -fly cutter. Next  on a Milling machine you set the tool 45 degres to the work on a rotary table. I use aluminum round stock  to make molds It's easier to center on rotter table. You need to be able to put two pieces together in perfect alignment with dowel pins or steps, face them in a lathe and leave a small male tit, this what you center to in the mill , Large balls you need to drill out center material, feed the fly cutter down,and turn the rotary table, whine the cutter leaves a spot on back of ball and cutter is at outer edge of mold, check depth and diameter, your half way done.   Machine a spruce  hole,  Make handles, I use a clamp to hold half's together, This maynot make a perfect round ball but it's fun and about free.

[Victor3]

 A picture would probably be helpful. I had the rotary and a flycutter on the shelf here, so I made a mockup to roughly show what you're talking about...

[cannonmn]

Maybe this is already well-known but if not, here you are:

I used to make some pretty accurate round lead balls in a kind of quickie way with no machinery.  If you can find a styrofoam balls the size you want at a craft store, you are halfway there.  These are so easy it'd almost pay you to make a cannon based on the size of styro ball you can find. 

Get some foundry sand or some proven substitute for it.  I used to use regular sand with barely enough moisture in it so it would stick together enough to retain a shape, make sure it has very little moisture in it, maybe use completely dry sand and add some "Pam" nonstick pan spray or other oil to it to give it a little body.

Take a box a good bit larger than the ball and fill it halfway with the sand.  Stick a pencil squarely into the styro ball, only into one side.  Stand the ball up on the sand and hold it while filling the box to cover the ball completely plus at least another full caliber or two of sand over the ball, with pencil sticking up.  Tamp and press the sand down very firmly so it will have no voids and will retain shape.  While pressing down on sand with one hand so it won't come up, carefully pull pencil out of ball and sand.

Put on face shield, long sleeved shirt etc. to protect skin in case any lead should be ejected, but that didn't happen to me, and I even tried slightly water-damp sand.  I seem to recall some smoke from the styro so you probably want to pour outside or in garage, I seem to remember having something thrown at me for doing this in the kitchen.  Melt enough lead to make ball plus sprue.  Pour molten lead in the hole at a constant rate, not too fast.  The lead vaporizes the styro and replaces it to form a perfect ball.  Let it cool for a few minutes at least.  Dump box contents and clean off ball, cut off sprue with hacksaw, bolt cutter, whatever. 

Load and shoot.

If you like this method, of course you may want to make a big box and put in many balls to pour at one melting.

The balls have the same grainy-feeling surface as styrofoam, but the ones I did were prefectly round and flew just liked a mirror-finish ball from a steel mold.

[Cat Whisperer]

Excellent having these two methods here together.

If you're doing the sand casting methods, allow a little more windage AND ensure that you gauge each cannon ball - they will be less spherical than those cast in metal moulds.  Which is to say that those cast in metal moulds will harden on the outside quickly, and draw in metal through the sprue (and riser if used) so keep plenty of resevour of metal there so you don't have voids internally.

[ratpatrol]

 victory3   That is the right idea, A bridge port mill has a tilting power head so you can use a rotary table flat on ways. I have a 3 jaw chuck mounted on rotary table, I also  have a old Gorton mill and It's Quill is like a drill pres, but have a index rotary table that tilts. some idea.The hard part is indexing  mold half  without a dro.  also  think in a mirror image whine machining second half.
  More tips, the bigger the ball the larger the spruce or the ball will not fill out also lead and mold has to-be hot,hot

[cannonmn]

Another use for a sabot is to adapt a smaller ball to a larger bore.  Your sabot needs to be relatively long in order to hold the ball in position reliably.  I've used two sabots made from 3/4 in. plywood, back to back, under a smaller ball to shoot it from a larger bore.  Make sure the sabot stack is long enough so the round can't possibly get cockeyed in the bore while loading or firing.  The sabots and ball are held together by a steel bolt that goes thru all sabots and into the ball.

[dan610324]

maybe Im stupid , but I cant understand why set the tool at 0,7 times the diameter of the bore .
when that tool rotate it must make an cavity with the radius of 0,7 times the bore
equal to an ball 1,4 times the bore

am I totaly wrong in my thinking ??

[GGaskill]

I can't understand why set the tool at 0,7 times the diameter of the bore.

I must be totally missing something here as I cannot see how this process can generate a hemispherical cavity without continually adjusting the radius of the cutter.

[dan610324]

no you adjust the radious directly to the finished dimension , then you feed it a bit and make an complete turn to the rotary table .
then you have an shallow cavity with the correct radius , but not deep enpogh for the half hemispher you want .
then just repeat this steps until you have your half mold .

up to this point I think I understand it .

but that part with 0,7  the bore diameter in radius , that I cant understand

[ratpatrol]

   Maybe this will help , It's the biggest square that will that will fit in a circle, now turn it at all angles and imagine the points are cutters,you now have a ball. The number  0.707107 is a trigonometry function for sin or cos for 45 degres.

[GGaskill]

As I said, I am missing something.  As far as I can imagine, assuming the setup as shown in Post #2, moving the rotating cutter down vertically only while rotating the work piece will make a conical cavity with a radius in the bottom if you go down far enough.

Please excuse my obtuseness but I am not getting this.

[dan610324]

no it shouldnt been moved downwards , you just center it in the aluminum piece and then you move the table slightly to the right and make an complete turn on the rotary table .
then move the  table again and turn the rotary table one turn .
repeat until you got the right depth in the half mold you are working on .

do you mean 0,7 x caliber from center of mill axle to tip of the cutting hss bar , or ??

but it still doesnt make sence to me , if you set it 0,7 x cal diameter the smallest circular thing you can do with it is 1,4 cal diameter .

I dont understand why you are talking about an square fitting in the bore , when you start rotating that tool you still must have 0,5 cal from center to tool tip to make that size cavity .

the 0,7 meassurement maybe is the correct dimension from flat to flat in an square fitting to an circular hole , but its still the outer point of the tool that decide what radius you get . not the flats .
when you rotate that square thing 0,7 from flat to flat its still the opposite corners at bore diameter distance that cuts the cavity .
so I cant for my life understand how you are calculating , but ok my math skills aint that advanced .
but so far I have never managed to do an 1/4 inch hole with an 1/2 inch drill bit   

as usual its just my opinion

[Double D]

This is one of those "don't sound right" things that you have to go set up in the mill and try to see if it works.  I can't quite get my mind around it but something says it does.

[cannonmn]

This place is one of many offering styro balls, their price on a pack of 100 one-inch balls is $15.  I didn't price shop, someone probably has 'em for $10.  Shipping won't be much.  They also offer 1.5, 2, 3, 4, 5, 6-inch balls but I've only tried casting using the smaller ones.  I did a 1.5 or 2-inch, can't remember which, and it came out fine.  I think I used a 3/8 in. wood dowel to make the sprue hole, I just used "pencil" above as an illustration.  I'd rather cut off a larger diameter sprue than risk having lead hit the side of the sprue hole and start to harden too soon.

http://www.hygloss.com/itempage-5101-434-508-2584.html

[dan610324]

yeah could be , but I hope someone with an sharper intellect then me would explain it to me .
because I cant understand how something that is 1,4 times the bore in diameter when its rotating can make an bore diameter cavity

[Victor3]

 I'm gonna give y'all a hint, free of charge 

 Note that ratpatrol said "This may not make a perfect round ball..."

 (because the resulting machining can't produce a perfectly accurate hemisphere in the mould)

[dan610324]

of course it wouldnt be perfecr, but good enough for an muzzle loading cannon .
probably within 1/1000 th of an inch
its all about how exact you are when you set the radius on the tool bar and how slow you rotate the rotary table .

[Cornbelt]

I know this is almost vulgar its so ugly, but it works. Find a steely a little smaller than the ball you want, heat it up red hot and smash it between two boards. Pour the lead in the cavity. I've got a diving head, but needed a ball within 15 minutes. It was only a .50 and not for a cannon, but got me something to eat.

[Cat Whisperer]

I know this is almost vulgar its so ugly, but it works. Find a steely a little smaller than the ball you want, heat it up red hot and smash it between two boards. Pour the lead in the cavity. I've got a diving head, but needed a ball within 15 minutes. It was only a .50 and not for a cannon, but got me something to eat.

There is a place in life where dirtball is OK! 

[ratpatrol]

  I will try again------the fly cutter is set to cut a  HOLE  .7 tens smaller than ball diameter that you want. yes  It will cut a hole fed straight down, whine you turn the table it cuts a ring,  I also said it has to be centered to mill axes at 45 deg.  The cutter doesn't cut full circle until  it is fed down to lower edge of work, that's whine  you see the half hemisphere. 
    Forget about 1.4 times diamameter rad   or what  ever,  also you do not move the table ,only the quill down           

[Double D]

After thinking about this a bit It starting to make sense.  Now I wish I had a mill to go try it.

[cannonmn]

also you do not move the table ,only the quill down           

So if the rotary table just stays non-rotating, you don't really need one, you could just use any 45-degree angle fixture to hold the work?

[Cat Whisperer]

also you do not move the table ,only the quill down           

So if the rotary table just stays non-rotating, you don't really need one, you could just use any 45-degree angle fixture to hold the work?

I think he's saying you don't move the mill table left-right, only the quill down while rotating the work.  If you don't rotate the work you'd be cutting a cylindrical hole; but since it is rotating (axis at 45 degrees to cutter axis) the net result is a hemispherical cavity.

[Victor3]

of course it wouldnt be perfecr, but good enough for an muzzle loading cannon .
probably within 1/1000 th of an inch
its all about how exact you are when you set the radius on the tool bar and how slow you rotate the rotary table .

 Not really. The reason for ratpatrol's calculation is because a cutter set at 45 degrees, when fed into the workpiece will form an elipse, not the radius that the flycutter is set to.

[cannonmn]

I recommend the first person who gets the RP method to work, post a new discussion with title something like "Ratpatrol Mold Method Demonstrated" and show pictures.  That way it'd be easier for machinist retards like me to unnershtan.  Meanwhile my head hurts and I'm goin' on to other things for now.

[sseib]

Lets see if I can help.

If you set the boringbar diameter to the ball diameter you have to feed in from the side thru the center of the ball.
Picture a globe, you are cutting the equator diameter while rotating.

If you use ratpatrol's method, you set the boringbar diameter to bore size X 0.707107 and feed from the top down.
Picture the globe again, you are cutting at the 45th parallel diameter while rotating.

Steve Seib

[kappullen]

This method works.

I've made many a mold this way.

Lenses are also made this way.

It is easier to set the Bridgeport head on 45 degrees, and the rotary table flat.

This way you merely crank the knee up between cuts.

What is a cut?

Once the fly cutter is fed in to the blank a bit,
the rotary table must be cranked 360 degrees
to form the pocket.

Then repeat the process until you are to finish depth.

It's a bit tough to find center between rotary and spindle.
One direction an edge finder can be used.

The other it's a matter of touch off with the cutter,
rotate the table and touch off again.

Then you adjust the tool between your marks.

Easy as pie!

Kap

[thelionspaw]

Here's what I did: I got a styrofoam ball of 2.5 and for other moulds, got rubber balls. Next I mixed dental cement (more durable than plaster of paris). Then put a small cork on the bottom of a small cardboard box. The cork creates a sprue hole. Have the narrow end of the cork up. Balance the ball on the cork. Pour the dental cement or plaster into the box. When it dried, I sliced it in half on the band saw and removed the ball. Why knock yourself out with machining?

rc

[GGaskill]

Then repeat the process until you are to finish depth.

How much do you raise the knee if you are making a 2" ball?

[hatchet]

ok, here is the BEST WAY.  and by saying best way, i know i'll issue a challenge to someone who'll tell me i'm wrong. 

you face the piece of stock alluminum with a fly cutter or wide enough cutter head that may take inserts or is tha big of a square end mill to get a fully "flat surface"

next take a full radius ball end mill bit and sink it to the radius of the ball you wish to create. 

here's a hint: if you sink the full radius bit just a bit too far and create two hemishperes w/ a straight side, you may re-face the surface with the fly cutter to take away the straight size, and actually make a smaller ball.  the raidus will be still be the nominal ball end mill size, and your mating faces will be the same as well.

you'll need to drill pin outs for locating the centers of the two hemispheres. i'd suggest one size drill bit for a press fit so the pins stay in one half of the mold and another size to allow about .003 over the pin size for alignment.

i was spoiled so i used a 3-axis cnc whene i did mine.  the balls were a bit big at first, but some wet sanding of the faces brought the balls down to just the right fit.  we use a c-clamp when casting rounds.  the gaiting allows for two rounds to be poured at the same time.  i used a smaller ball end mill to run the gaiting and yet another ball end mill bit for the pouring cup on the sprue.