Hollowing Out Solid Metal

Would you consider burning the metal away with a long oxy acetylene nozzle?

If you just want to remove weight, why not drill additional holes [say 20mm dia] and install similar plugs?

the extra holes idea is a good one

thanks

"What I want to know is there a tool that can hollow the shot puts out - i wish to make a rough hollow sphere about 60mm in diameter at the centre."

Yes, it is called a lathe and holds the sphere so that it can be rotated about the access hole. A heavy bent bar with a cutting tip can then be inserted and cut out the interior to almost any required inside diameter, cylindrical or spherical.

I gotta go with Stan on this one. As best I know, the most cost effective way to hollow out a sphere is on a lathe, although it can be done on a mill as well, with a less satisfactory result.

A set of soft jaws and a bit of patience and ...voila! A hollow chunk of metal.

Actually there a few ways to secure the workpiece but my knee jerk response is machinable soft jaws. concentricity can be achieved by inserting a rod into the existing hole and indicating it in, both circular and linear. I can offer a slightly more detail descrip if needed.

Happy hollowing,

Charles

If you have the lathe and want to spend the time, cool. But if you have to pay a machine shop to hollow them, prepare to spend a small fortune, and unless you pay a bigger fortune you just may wind up with spheres that are enough out of balance that they are impossible to throw properly. My opinion... Get a small foundry that does onezie/twozie work to cast some new ones for you out of your metal of choice. Or, just buy hollow ones if they are available.

thanks guest - i will look into it

I gree with 'Guest', look at the problem first, if you want adjustable weights you may be easier to cast them your self out of resin and a silicon mould, that way you could make them any weight you want. Moulding kits are available from handicraft shops or art shops.

I like the idea of casting in resin.

Here are a couple of ideas for how to make balls of different weights (note - I just came up with them and have no idea how practical they really are):

• Mix into the resin a quantity of iron filings (or other particulate metal - needs to be able to be evenly distributed throughout the resin without sinking while the resin is still wet). By varying the amount of metal you can create balls of different weight.
• Embed a metal sphere in the center of the cast ball (difficult to get it centered, but no impossible). By selecting the size of the sphere you can select the weight of the final ball.

"I like the idea of casting in resin."

Hey: They are "Shot Puts" 115 mm dia. spheres of C.I. Also available in various weights and materials. Resin might be OK if loaded or mixed with metal granules.

To alter existing parts I'd still make the alterations on/with manual machine tools.

uh hum...#14.

Anything is possible with the right machine tool, these are made by turning on a 6 axis CNC machine.

I have been involved on similar projects. Begin with 52lb billet of Aluminium and end with 6 lb $12,000 masterpiece.

Order one from the manufacturer of the shot putt.

That would be the best idea but there are no manufacturers in my country most are from India or China.

thanks everybody

To the doubters. if i needed a well balanced, inexpensive shot hollowed out, I would go to an inexpensive manual machine shop.

Much luck.

Hey mate, are you sure you're not trying to make some sort of exploding cannon ball?

http://www.madsci.org/posts/archives/nov99/943902992.Sh.r.html

To the Paddy O'Flannigan, who asked if he was trying to make a cannonball, well, yes. That is where the term "shot" comes from, as these balls were readily available a few hundred years ago, being "cannon shot" and many soldiers and sailors could keep fit exercising with the nearest heavy objects and could improvise games and contests with them. I don't KNOW the history of the sport, but as a betting man, I would say it probably had a military origin, as did the javelin throw (really just a type of spear!), and the Marathon (where a soldier ran back with news of a battle, then collapsed dead!), wrestling, boxing, fencing, and karate (all of which would be types of hand-to-hand combat), including of course, archery and rifle and pistol shooting (which have hunting origins as well as military. English Yeomen used their hunting long-bows in service of the King, fighting the French for hundreds of years) Perhaps strong-armed cannoneers were called upon to quickly transport shot from a central storage area to positions closer to their gun emplacements? Or else it just started as barracks braggadocio (I can put a 16-pound shot further than you can! Oh, yeah? Let's go over to the battery and see!)

To "aussiethrower":

Not sure what the plug is for. Can these balls also be used for the Hammer throw by replacing the plug with one attached to a wire and handle? I believe the ball in both is 16 pounds.

Back to your original question: Yes, a competent machine shop can hollow out your ball, however it would be very difficult, if not impossible to achieve a spherical cavity much larger than the hole you already have, without destroying the threads where the plug goes. If that hole is only about 15mm, you could probably get a boring bar that is about half that or less, say about 7mm with a 7mm cutter attached. This would allow you to bore out, at most, about Ø 29-30mm, or roughly twice the size it is now. Of course twice the size in diameter or radius of a cylinder means 4 times the volume, since the radius is squared. Changing from a cylinder to a sphere complicates this a little, since you are going from a squared term (r²) to a cubed term (r³). You would also want to make the hole deeper.

But first, try drilling the 15mm hole deeper, to a total depth, measured at the drill point because you do not want to break through, of about 100mm. This will actually make your ball better balanced than it is now, with only a reduction of about 1% in weight, since the 60mm deep hole barely passes center and you are only plugging it with a 15mm long plug (presumably of the same material). You could even do this at home if you are very careful, with a small drill press, by lining up the hole in the ball with the drill, and rotate slowly by hand until the ball is centered, then clamp it in place.

This might satisfy your requirements, allowing you to adjust the weight and balance with the right combination of heavy and light, slightly less than Ø15mm, shims. This could be even perhaps a stack of steel and plastic washers held onto a hex-head bolt with a simple nut that slips inside and is secured by the original plug.

If that won't work for you, a competent machinist can cut a nearly spherical inside radius of about 15mm (30m diameter) using a succession of fixed boring bars and cutter angles, or even truer using a CNC lathe and indexable inserts on a hydraulically control fine-boring tool. If you want more metal removed and don't mind the slight out-of-balance of a larger cylindrical cavity (remember, you started with an off-center, out-of-balance cylindrical cavity anyway!), then the entire depth, from 15mm (just past the plug) to 100mm could be bored out to Ø30mm, taking care not to have too thin of a wall thickness at the bottom. This would give you about 7.5% weight reduction from the original. The spherical cavity of the same diameter would be somewhat less reduction.

Of course, if you are willing to have a larger plug made, you can bore out the threads, increase the cavity diameter (spherical or cylindrical) and re-tap the hole for a larger plug. Depending on what thread form your original plug uses, you may even be able to find a threaded insert that will allow you to re-use the original plug.

Good luck!

thanks so much for your very detailed reply.

i think im going to get the plug ( yes its can be replaced with a swivel plug for hammer throw) removed and make the diameter a bit wider. I will also go for a cylinder rather then a sphere on the inside.

thanks

The simplest, cheapest, most balanced and versatile solution would be to drill and tap (20mm thread, if that is what is there now) all the way through in a perpendicular "3 axis" pattern (front to back, side to side and top to bottom). This would remove a considerable amount of material to lighten the weight. It would also allow you to adjust weight evenly by adding set screws in the holes beneath the 6 plugs (which would probably also be set screws, or perhaps a short hexagon socket flat countersunk head screw - maybe c'sink to leave the head slightly proud of the surface and grind to blend with the spherical contour). Just keep a hex key and a few spare set screws in your gym bag, and your shot will be field-serviceable!

Do you need to put a plug back in the hole for a smooth outer surface?

Also, will you be permanently lightening the ball, or do you want to be able to vary the weight? If you want to vary the weight, use my previous suggestion, or the one proposed by Munky, although Multiple holes may be a bit of a chore, I do like the idea of using setscrews of various lengths for the weights (one at the bottom and one at the top of the hole). These could be preset in matched pairs. Use the type with a nylon patch to give slight interference for anti-slip and still be removable.

If you want to permanently lighten the ball, and you need a smoother outer surface, have a machine shop make you a part that will be a press fit into the top of the hole, including the same spherical radius to mach the outside of the ball.

To be sure the pressed plug goes no deeper than the surface, machine a counterbore (step) of the same depth that the plug is long. Also, this plug should be the same length as the remaining wall thickness at the bottom of your hole for a good balance.

You should probably make a dimensioned sketch of what you want for the machine shop or have them make one for your approval before cutting any metal. Remember the old maxim: Measure twice, cut once! Alternative is: Measure, cut shorter, measure again, cut a little more, measure again, etc. If you cut to much you are hosed! Also, if you cut a flat bottom in your hole with a milling cutter, remember that since the outside is curved, you may have a good thick wall at the center of your hole, but it might break out or be too thin at the edge, so check the geometry by drawing a full scale sketch of the center cross-section, including a circle with the same diameter of your ball and a rectangle with the dimensions of your hole. If your hole is drilled only, remember to include the drill point geometry.

One additional note before starting all this: You might find an off the shelf solution which is cheaper. If not, and what you are trying to do is in demand, you may have just discovered a niche product you could sell to others like yourself for a nice profit!

Since cost was not an issue in the original question: Perhaps we can melt down our dental work and make balls of gold and silver.

I hope I am worth more alive than dead! Except for the "Silver Amalgams" I got as a child, my last dental work, including a few caps and fillings was mostly a polymer/ceramic mix, although the substrate for the caps was probably some kind of stainless alloy.

No gold in my middle class mouth!