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Questions about sphere making

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Author Topic: Questions about sphere making  (Read 544 times)
madsalts
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« on: March 16, 2015, 06:54:39 pm »

I don't know where to post, so here goes.  I'm interested in making spheres with a machine, and have two questions.

1.  Is it better to use a water and grit slurry or pads on the grinding cups?  I can see pads being less messy (by far) but using pads rather than slurry means having to have several different sets of cups.

2.  How many stages of grit, from coarse to fine, should be used?  Should I go 80, 100, 160, 220, 300, 400, 600, 800, 1000, 1200 or something like this, or something different?  I'll be working with stones with hardness such as marble, nothing real hard like granite.

thanks.
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jakesrocks
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« Reply #1 on: March 16, 2015, 07:35:57 pm »

Madsalts, if you have math skills and a good understanding of metal work, there's no reason why you can't build your own sphere machine at a fraction of the cost of a commercially built machine. Here's a pic of one that I'm in the finishing stages of building. Total cost around $500.00.


While diamond cups are nice, as you said, you need a set of each grit. That and a set of cups is only good for about 2 or 3 different sizes of spheres. Again for a fraction of the cost of diamond cups, you can buy a whole bunch of common black iron plumbers bell reducers. 2 or 3 different sizes sets will cut almost any size of sphere that you want.

I'll be using silicon carbide grits, again because of cost. Yes, it can be messy. Not the type of work you'll want to do on the kitchen table. It should be done outdoors, or in a shop where a little mess won't matter.

For grits, 60/90, 220, 360 & 600, followed with cerium oxide on leather or felt.

For final polish I soak leather or felt overnight in water, form it over my cutting heads and wire it in place. While the leather is drying, put you sphere back in the machine. It will form the bowl shape in your leather or felt polish pads.

Here's a small 2 head machine that I picked up at an estate sale for $25.00 . It'll make spheres up to about 1-1/2" diameter.



After polishing your sphere, let the pads dry on the machine. Then cut the wires and remove them. Store them in a big zip lock baggie to prevent contamination.
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madsalts
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« Reply #2 on: March 16, 2015, 08:22:16 pm »

Thanks for the fast and detailed reply.  I think I will build a machine.  The leather/felt seems like a good way to go.  I'm not sure that I follow regarding the leather/felt.  I understand that I want to wet the leather and stretch it over the cup, then place the cup on the machine (if it isn't on already) and then put the sphere inside so that the leather dries to shape.  At this point, I'm guessing that I would use grit, and perhaps just leather for a final polish.  Why would I want the leather to dry on the cup?  wouldn't I be using water with the leather, or am I using it dry?  Either way, how do I get grit onto the leather/felt, with wax?  or just rub it in to the leather/felt when it's wet?

What's the purpose of using water at all?  For cooling, or so that the grit moves a bit better?

Also, how big should the cups be relative to the size of the sphere?  I'm guessing as large as possible without touching each other.  Is this correct?

Thanks.
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jakesrocks
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« Reply #3 on: March 16, 2015, 09:13:46 pm »

If you use 2 or 3 heads, the leather or felt must be used on all of the cups. By allowing the leather or felt to dry while all of the cups are pressing against your sphere, they will take a semi permanent shape. After your polishing pads are dry, remove the sphere. spray each pad with a little water and add a paste of your preferred polishing compound to each pad. Replace the sphere in the cups and turn on your machine. A squirt of water on each cup when they appear to be drying out is a must. Never let it run dry.

For all stages of grinding and polishing, the cups must be run wet. This is true of both diamond & conventional cups. It serves 2 purposes. #1, it creates a sort of paste of the slurry & grit to coat the sphere. #2, it acts as a coolant & lubricant.

Another thing that should be mentioned. Completely clean your sphere and cutter cups between grit changes. Even a grain or 2 of say 60/90 grit carried over into the 220 grit stage will leave scratches in your sphere. The same holds true each time you change to a finer grit.

These machines really aren't as messy as you may think. Something as simple as an aluminum pie pan under the cutters will catch most of the drips. You can use a cheap paint brush to reapply the dripped slurry & grit to the sphere. This will save a bunch on the cost of grit.

The machines also use gear head motors that turn at 100 RPM's or less. Mine turn at about 87 RPM's, so they don't throw the water & mud like a lapidary machine running a 1725 RPM's would.

There's a trick usind a continuous link chain to distribute grit, slurry & water to your cutters, so you don't have to sit for hours watching your machine. I'll see if I can find the video, and post a link in the morning.
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« Reply #4 on: March 17, 2015, 02:44:04 pm »

Madsalts, on another forum a bunch of us were building sphere machines. You might find the info in the discussion thread interesting. Here's the link. http://andy321.proboards.com/thread/48288/sphere-machine?page=1
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« Reply #5 on: March 17, 2015, 05:55:40 pm »

I built this sphere machine based on one in an old lapidary journal article in 1980. I used it for quite awhile and then it went to deep storage. About two years ago I started restoring very old hand made German marbles the were made from 1850 up to about 1920. The motors had been used enough that I found that I needed to replace them, let me tell you I was shocked at how much they had increased in price but what has not.

If you notice the base is just made from exterior plywood with slots cut into it with a jig saw. The metal is brass plate (I would use steel or aluminum now). You can find all kinds of information on sphere machines on youtube and I think that anyone wanting one should just build their own and save big bucks.

In the second image I spent some time playing around trying to perfect a two head machine, never could get it to work properly and just quit wasting my time. Notice on this machine how small the motors are on the gear reduction units. I found these motors on a surplus web site and they were very inexpensive. These motors are 24 volt DC and they are super strong, strong enough that you cannot stop them with your hand.

I also show in my oopinion the best way to feed the slurry onto your heads, its just a chain cut to length and joined. Also I show my grinding heads, I use PVC pipe fittings and PVC pipe for reusable inserts. By using the PVC inserts all you have to do is change out the inserts when you want to use a new grit.

Hope this gives you all some ideas.


* sphere.jpg (297.35 KB, 1002x1983 - viewed 39 times.)

* sphere2.jpg (158 KB, 1001x1207 - viewed 13 times.)
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jakesrocks
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« Reply #6 on: March 17, 2015, 06:55:45 pm »

Lopacki, can you show a good pic of your chain slurry feed ? There used to be a video of one in use, but I can't find it. Must have been taken down.
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madsalts
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« Reply #7 on: March 18, 2015, 09:59:28 am »

I'll check out the link.  I've been looking around at cups, and have a question.  Is it necessary that the cups wear at the same rate?  If I have a three-head machine and want to replace a cup, should ALL of the cups be replaced at the same time, or doesn't it matter if I have one that's unworn with two that are somewhat worn?

thanks.
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« Reply #8 on: March 18, 2015, 10:20:31 am »

Depends on the type of cups you're using. Either diamond or conventional cups should all wear at the same rate. I've never used the diamond cups, (Too damned expensive), but I suspect that if one cup wears out before the others, you'd have to change all of them. If you changed only one diamond cup, the one you changed would cut much more aggressively. It may effect the roundness of your sphere. Of course I'm just guessing here. Maybe someone with diamond cup experience will weigh in on this.
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« Reply #9 on: March 18, 2015, 11:41:33 am »

Jake,
I just went to the hardware store and purchased some small open link chain. I measured it so it hung into the grit bowl when suspended over the cup. The links were closed so I just snipped one spread it and then closed this link once the chain was closed.

All my best ..... Danny
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jakesrocks
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« Reply #10 on: March 18, 2015, 12:35:49 pm »

Danny, I was hoping to find a link to a video showing the chain thing so madsalts could see how it's done. There was a good video a while back, but I can't seem to find it now.
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« Reply #11 on: March 18, 2015, 02:10:13 pm »

Jake,
Here is a link for a person that is restoring marbles. It has the chain feed on his machine. He says to mix the grit with oil but I say no to this I just use water and it works like a charm.


All my best ... Danny
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jakesrocks
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« Reply #12 on: March 18, 2015, 02:27:48 pm »

Not the same video that I've seen, but the same general idea. It will show madsalts how the chain carries the grit up to the sphere. Thanks for posting that link.

Don - - - (Jake is my dog)  lol
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« Reply #13 on: March 18, 2015, 05:29:49 pm »

Don,
I will make sure that if I want to talk to your dog I will start with Jake ...... Sorry about that.

All my best ....... Danny
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madsalts
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« Reply #14 on: March 19, 2015, 03:42:30 pm »

Great links and great replies.  I think that the only question I have at this point is how big the cutter cups should be relative to desired sphere size.  As the number of cutter cups is added, I understand that fewer will fit on the sphere.  I'm guessing that cups should be larger rather than smaller, and small enough so that they don't touch each other.  Is this right?  Thanks.
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« Reply #15 on: March 19, 2015, 06:57:27 pm »

Great links and great replies.  I think that the only question I have at this point is how big the cutter cups should be relative to desired sphere size.  As the number of cutter cups is added, I understand that fewer will fit on the sphere.  I'm guessing that cups should be larger rather than smaller, and small enough so that they don't touch each other.  Is this right?  Thanks.


I don't know if it has ever been narrowed down to an exact science, But I'd use 2/3 to 3/4 the diameter of the sphere you want to make. You want your rough sphere to sit deep enough into your cups to prevent it from popping out of them. As you go through the different grit stages, your sphere will get  a little smaller, and will sit deeper into the cup. Too large of a cup and you run the chance of the sphere sticking inside of one of them.
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madsalts
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« Reply #16 on: March 19, 2015, 07:24:00 pm »

thanks
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« Reply #17 on: April 16, 2015, 10:56:21 am »

Any reason you can't charge the iron or brass cups with diamond powder?

The Chinese are offering it for peanuts these days, and the old-school faceters charge their own laps, surprised I haven't heard about it.

Diamond brazing rods seem like a nifty solution too, if you've got the welding equipment.
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« Reply #18 on: April 16, 2015, 01:29:57 pm »

Any reason you can't charge the iron or brass cups with diamond powder?

The Chinese are offering it for peanuts these days, and the old-school faceters charge their own laps, surprised I haven't heard about it.

Diamond brazing rods seem like a nifty solution too, if you've got the welding equipment.


Iron & brass cups would probably be too hard to take a charge & hold it. If a person had lathe skills, and access to a metal lathe, cups could probably be turned out of copper or tin which would both hold a charge. But you'd need a set of cups for each grit stage. with iron or brass cups, you just clean them & go straight into the next grit.
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« Reply #19 on: May 24, 2015, 09:10:57 am »

Heh, heh, heh.

A good tip, thanks for it. I just happen to know a master machinist with a metal lathe and time to kill.

Now, copper cups, hrm.

Maybe I should finish my metal casting furnace and cast them myself... or can you buy copper cups?
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« Reply #20 on: May 24, 2015, 10:54:26 am »

I've never seen copper cups offered for sale. If you have the casting equipment, you could certainly cast your own in several sizes, and get your machinist friend to true them up & put a finish on them. He could also cut the internal threads for your shaft adapters. Just remember that you're going to need a set of cups for each diamond grit size, plus a set of polishing cups.
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