Suggestions on how to hold spherical material.....

[angelboy]

Not exactly wood turning but I thought there might be some chucks or clamps or even specific techniques that might carry across to what I want to do.

I want to cut the bottom off stone/crystal eggs and cigar-shaped materials to make a level base. What's the best way to hold the eggs/cigars so that I do this (with a chop saw or angle grinder on a cut-off stand)? As each egg/cigar might be of varying sizes then I need something that can deal with that.

Any ideas?

 

[MikeG.]

I'd avoid the problem altogether. I'd use my hands to offer the pieces up to a linisher (belt-sander) or disc sander. The idea of such a curved shape being anywhere near a spinning saw blade fills me with dread.

 

[Rorschach]

A big V-block and some wedges to level it all up as you want it, then strap it down firmly. Do not use a chop saw as this is more likely to grab, use an angle grinder and take it gently. Mark your cut line and do a rough cut followed by a clean up. If you want it to sit nice and firmly you will want to dish out the centre of the base.

 

[Dalboy]

I would go with MikeG's idea. the only problem is that you would need to keep removing it from the disc/belt and keep it cool as stone and ceramic can produce heat checks which could spoil the item if it is to be left as is. The same if you use an angle grinder.

The ideal tool would be a slow running water-cooled diamond saw but again it is the holding of the piece that would be the risk factor.

There are some homemade jigs for turning which hold egg-shaped and sized items but they would need to be adapted again it would not be suitable for fast cutting blades like a chop saw

 

[Phil Pascoe]

How many? A good idea for a hundred may well not be worthwhile for a few.

 

[angelboy]

Because I'll have to remove a decent part of the material then grinding it would cost more than cutting I think.

I've been looking at lapidary and they have saws that are basically tile cutters but all the videos I've seen of people cutting other types of stones is done by holding the material. I think using a table saw has taught me to keep my hands well clear of the blades.

Having said that, when I retiled my kitchen I used a powered tile cutter using my hands to offer the tile up to the blade - but then tiles are flat so less chance to screw it up.

 

[marcros]

I have been watching "Outback Opal Hunters" on some obscure virgin channel. It seems to be similar to operations that they regularly do on there. Lapidary is probably the way forward. I dont know enough about it to say whether the methods that they use are safe, but they are hand holding the stones.

 

[AndyT]

Pete Maddex has posted a picture of a method he used for holding a bowling ball, to drill a hole in it as part of making a carving mallet. He uses a big hole in some plywood, about 3/4 the diameter of the ball, clamped down with hinges.

I've mentally filed it away as a method of holding anything round, adaptable for scale.

 

[Robbo3]

Commonly called a doughnut chuck. A baseplate, sometimes with a centering hole for the workpiece, & an outer ring joined by threaded rod, sandwich the work to allow access to the outer end. Often used to hold bowls or vases to finish off the base or to hold spheres.
This should give you the idea coutesy of Kevin Neelley
- http://www.turnedwood.com/tools&jigs.html

 

[Simon_M]

A home-made doughnut chuck would also be my suggestion. If using threaded rod, I like to use tee nuts that are flush with the outer surface. The rod can be locked with a nut/washer on the underside. It avoids having an exposed head e.g. away from knuckles or a cutting tool.

There is usually no need to shape the opening to match the workpiece e.g. cut at an angle because contact across one plane is sufficient. Three rods are a minimum, but four are often easier to tighten e.g. one pair first.

Attaching a support to the base e.g. a block cut at 30 degrees can make clamping/holding a workpiece easier. Time spent making a jig can make the eventual task much easier.

 

[angelboy]

I think I might be able to work on the doughnut jig idea. If I made the hole in square ply and put flat headed bolts to the cutting side, then I could either slide the jig towards the blade or clamp down the jig and make the cut with an angle grinder in a holder. I could make a few sizes to cross over the different egg/cigar sizes.

Brilliant !

Thanks for all the advice everyone!

 

[Racers]

Pete Maddex has posted a picture of a method he used for holding a bowling ball, to drill a hole in it as part of making a carving mallet. He uses a big hole in some plywood, about 3/4 the diameter of the ball, clamped down with hinges.

I've mentally filed it away as a method of holding anything round, adaptable for scale.

Yes the Ball-o-Matic 2000.

Ball-o-matic 2000 by pete maddex, on Flickr

Two holes some loose screws a block with a cut out and a clamp.

Pete