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Making internal Hemispheres

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  • Making internal Hemispheres

    Friend wants molds made for cannonballs in the 3" range ,how would you cut the internal hemispheres?

  • #2
    No Idea but I will watch this thread with enthusiasm Alistair
    Please excuse my typing as I have a form of parkinsons disease

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    • #3
      Make in two halves. Use a radius attachments . Instead of turning a ball ,turn a internal radius in each . Easy.
      Every Mans Work Is A Portrait of Him Self
      http://sites.google.com/site/machinistsite/TWO-BUDDIES
      http://s178.photobucket.com/user/lan...?sort=3&page=1

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      • #4
        3 inch inside radius

        I went out to shop and made a guick little set up to cut an inside radius. I did not want to waste a piece of material so I just made a guick easy tool and tried it in a piece of wood. It worked great. The radius tool swings a 1.5 rad
        using a bolt as swing point. Just go a little deeper each pass. I think I would have to give the bottom plate more clearance to get to full 1.5 depth. But pic should give good idea of how tool works.
        Jim Sehr

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        • #5
          Using a 4-jaw chuck I think I'd true a 4.5" round stock, concave a face as described, flip the stock 180 and do the other face, then through-drill it for a couple alignment dowels then part it off. With the faces together, final drill and ream the alignment holes, put in the alignment dowels, then drill and countersink the sprue. Add some handles and pintle hinge on the mold halves. After the first pour the errors will reveal themselves and hopefully the mold can be touched up as needed.

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          • #6
            you should be able to scoop out that small amount of wood with a bowl gouge no fancy equipment needed .Even though I liked the design Alistair
            Please excuse my typing as I have a form of parkinsons disease

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            • #7
              radius tool

              Alistair
              It is true you could scoop out a piece of wood with a hand tool.
              But what I was showing was how to do it in metal and hold a few thousands
              dia on the radius. The only reason I used wood was I did not want to waste
              a piece of metal on a part I had no need for. And I did not spend a lot of time making the tool . If I was going to make the cannon balls then I would make a better tool and keep it , this was meant to be a throw away.
              Jim Sehr

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              • #8
                Radius

                The tool works fine for a shallow part but the fun starts when you try to go to the radius depth..

                JRW

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                • #9
                  I bought this for doing internal hemishperes, for lead down rigger(fishing) ball moulds ect.
                  One of these days i will make a bigger version for ball turning , hemispheres
                  ect as it is a bit differant from a normal ball turning set up.



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                  • #10
                    jimsehr yes I have seen this done as you did and it works fine in actuality if you want consistant results your method is the only way to go.In fact I am interested in the cutter as I want to make a spindle copying device for one of my woodlathes.Alistair
                    Please excuse my typing as I have a form of parkinsons disease

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                    • #11
                      Internal Hemisphere

                      Internal radius is one thing,an internal hemisphere is a little different,for an internal hemisphere the tool needs to be able to enter the work piece deeper so that the piviot point is lighned up with center point of the hemisphere. The tools shown are what I was thinking about,but I am working with limited materials and tooling in a new town with limited knowlege of where to get small amounts other than mild steel. Will mild steel be rigid enough to not cause chatter? I plan on using aluminum for the molds and may have to cast them to save on material costs.

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                      • #12
                        cutter travel

                        J. R. Williams
                        I think the tool as designed will cut about 1/2 inch deeper then 1.5 depth needed to get half of 3 inch radius. If I give the bottom of the tool clearance . And the nice thing is you can take rapid light cuts with little or no chatter.
                        Jim Sehr

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                        • #13
                          As a gunsmith I have made many a ball mold for the odd caliber of muzzle loading firearm. I suppose the same technique would work for a 3 inch diameter cannon ball as well. First step is to make what is called a "cherry". Looks a great deal like a ball ended rotary burr. You turn the ball on the end of a length of drill rod, leaving a wasp waist where it connects back to the drill rod shank. Just don’t turn it down so far that it is able to flex and break off.
                          Next you mill, file and turn the serrations on the surface of the ball to make it a rotary file/burr. These serrations need to project up the wasp waist and end at the full diameter drill rod shank. Now heat, quench and harden the ball and waist areas.
                          To use it you need two blocks of aluminum of a suitable size to contain the cavity for your cannon ball /muzzle loader ball. They need to have the same overall dimensions and a pair of faces that will meet perfectly flat. With the cherry rotating in the vertical mill, you close the two aluminum blocks in on it from opposite sides. The cherry will cut the ball cavity to an equal depth (hopefully!) if you have gotten it set up correctly in the mill's vice. When the two halves come together flush, the cutting is done. The small hole at the top of the blocks is the sprue hole. Enlarge it slightly with a counter sink to form a funnel shape down into the ball cavity. Fit the blocks with a pair of handles and a means of locking them closed, plus a sprue cutter at the top, and you are ready to cast some cannon balls.

                          Steve
                          Steve
                          NRA Life Member

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                          • #14
                            Radius

                            Jim
                            Excellent graphic. It appears you can make the diameter providing the long tool shank will be rigid enough. I would drill a large pilot hole to almost the required depth. Give it a try on your wood "try piece".

                            JRW

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                            • #15
                              You can do it on a rotary table on a vertical milling machine with the head tilted.
                              THAT OLD GANG 'O MINE

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