Making internal Hemispheres

[deltaenterprizes]

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

[Alistair Hosie]

No Idea but I will watch this thread with enthusiasm Alistair

[lane]

Make in two halves. Use a radius attachments . Instead of turning a ball ,turn a internal radius in each . Easy.

[jimsehr]

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

[dp]

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.

[Alistair Hosie]

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

[jimsehr]

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

[J. R. Williams]

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

JRW

[thistle]

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.

[Alistair Hosie]

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