Post by jm on Nov 1, 2016 1:10:51 GMT -5
A while ago I ran across a website that showed one way that stone spheres were made back in the days before electricity.
www.sheldonbrown.com/rinard/ball.htm
Since I don't have access to any running streams on my property, I started wondering if it was possible to do the same thing on a smaller scale. After I dug around online a bit I discovered the existence of marble mills that work on the same same principle. They have a rotating disc and a stationary disc and the rocks roll around in grooves cut in the discs. I looked at those and thought 'I bet I could make something like that'.
So, following my usual routine of A.) Trying to build something just for the fun of building, and B.) not spending any more money than necessary, I looked around through my garage to see what I could find.
Here's what I came up.
The main ingredients are:
- a drill press
- a 7" masonry grinding wheel
- an ice cream bucket
- some boards and plywood
- a piece of 5/8" steel rod
First, I cut a disc out of a 1x8 that just fit into the bottom of the ice cream bucket. I chucked it up on the lathe and cut three grooves in it, about 3/8" deep. Then I put it in the ice cream bucket (with a little bit of caulking under it) and used a couple screws through the center of the disc to fasten it to a piece of plywood. The one in this picture has already been used, so the grooves are worn deeper than when it was new.
Then I cut some threads on the end of the 5/8 shaft so I could thread the masonry grinding wheel on it. The grinding wheel came from Home Depot. I made sure to get the one that was made with silicon carbide, not the aluminum oxide type.
For the stones, I cut some cubes of granite on a little tile saw I have. I used a jig to cut all the corners off. It's somewhat time consuming, since each cube requires 20 cuts to knock all the edges and corners off. After I figured out a system, though, would only take me a minute or two to round off each one.
Once I had the stones somewhat rounded, I put them in the bucket. For reference, the stones are a little under 3/4" across.
Then I clamped the plywood the the drill press table, aligned everything, and turned it on. I had the speed set as low as it would go, about 200 rpm.
This picture shows one of the partially used grinding discs.
To keep a constant pressure between the grinding wheel and the rocks I hung some old scuba diving weights off the handle of the drill press. It's pretty low tech, but it lets me easily adjust how much pressure the grinding wheel is putting on the rocks. When first starting out I use less weight, since all the rough edges tend to bounce the grinding wheel up and down somewhat. Once the corners get worn off and it's running smoother, I put some more weight on to try to help it cut a little faster.
I found out the hard way that when the stones still have rough corners on them, the grinding wheel vibrates enough to splash some of the slurry out of the bucket. I solved that by putting a lid on the bucket. It doesn't show in the picture, but I cut a slit in the lid from the edge to the center so I could get it on and off without having to unchuck the grinding wheel. The electrical tape around the bottom of the bucket is just in case the wheel gets misaligned and chews through the side of the bucket. There will an extra layer there to keep the slurry from immediately pouring out. I know it wouldn't hold up very long, but I did have once instance where that happened and the tape saved me from having to clean up a big mess. I'm more careful about alignment now, but I still put the tape on just for the extra insurance.
When the grinding wheels do finally wear out, so far they've all separated right where the metal hub attaches. The hub will continue to spin, but it's fairly easy to tell when this happens because the sound changes drastically.
Here's what the rocks look like throughout the process.
The process isn't fast, but I like the fact that once I get the stones roughed out I can put them in the mill and I only have to check them once in a while.
The board in the bottom of the bucket does wear out after a batch or two, but I've got lots of lumber laying around so it's easy to replace. The pine boards wore pretty quickly, so I'm trying some harder types of wood to see if that makes a difference.
So far I've done two batches of granite marbles and one of obsidian. In that time I wore out one grinding wheel ($5.50 at Home Depot) and partially wore out two others. The rest of the stuff came from my garage, so costwise I think I'm doing pretty good.
On the current batch I mostly filled it up, so there's not much free space between the rocks. I was curious to see what kind of difference that would make from the last batch, where I kept it about 3/4 full. So far the full batch seems to be grinding down a fair amount slower than the 3/4 full batch. Now I know.
Once I have the next batch done I should have enough for a tumbler load. I'm anxious to see what they look like when they're all polished up.
I know this setup is ugly and probably inefficient, but I've had fun making and using it and to me that's what it's all about.
Anyway, that's what's been keeping me busy in the evenings for the last little while.
Questions/comments?
www.sheldonbrown.com/rinard/ball.htm
Since I don't have access to any running streams on my property, I started wondering if it was possible to do the same thing on a smaller scale. After I dug around online a bit I discovered the existence of marble mills that work on the same same principle. They have a rotating disc and a stationary disc and the rocks roll around in grooves cut in the discs. I looked at those and thought 'I bet I could make something like that'.
So, following my usual routine of A.) Trying to build something just for the fun of building, and B.) not spending any more money than necessary, I looked around through my garage to see what I could find.
Here's what I came up.
The main ingredients are:
- a drill press
- a 7" masonry grinding wheel
- an ice cream bucket
- some boards and plywood
- a piece of 5/8" steel rod
First, I cut a disc out of a 1x8 that just fit into the bottom of the ice cream bucket. I chucked it up on the lathe and cut three grooves in it, about 3/8" deep. Then I put it in the ice cream bucket (with a little bit of caulking under it) and used a couple screws through the center of the disc to fasten it to a piece of plywood. The one in this picture has already been used, so the grooves are worn deeper than when it was new.
Then I cut some threads on the end of the 5/8 shaft so I could thread the masonry grinding wheel on it. The grinding wheel came from Home Depot. I made sure to get the one that was made with silicon carbide, not the aluminum oxide type.
For the stones, I cut some cubes of granite on a little tile saw I have. I used a jig to cut all the corners off. It's somewhat time consuming, since each cube requires 20 cuts to knock all the edges and corners off. After I figured out a system, though, would only take me a minute or two to round off each one.
Once I had the stones somewhat rounded, I put them in the bucket. For reference, the stones are a little under 3/4" across.
Then I clamped the plywood the the drill press table, aligned everything, and turned it on. I had the speed set as low as it would go, about 200 rpm.
This picture shows one of the partially used grinding discs.
To keep a constant pressure between the grinding wheel and the rocks I hung some old scuba diving weights off the handle of the drill press. It's pretty low tech, but it lets me easily adjust how much pressure the grinding wheel is putting on the rocks. When first starting out I use less weight, since all the rough edges tend to bounce the grinding wheel up and down somewhat. Once the corners get worn off and it's running smoother, I put some more weight on to try to help it cut a little faster.
I found out the hard way that when the stones still have rough corners on them, the grinding wheel vibrates enough to splash some of the slurry out of the bucket. I solved that by putting a lid on the bucket. It doesn't show in the picture, but I cut a slit in the lid from the edge to the center so I could get it on and off without having to unchuck the grinding wheel. The electrical tape around the bottom of the bucket is just in case the wheel gets misaligned and chews through the side of the bucket. There will an extra layer there to keep the slurry from immediately pouring out. I know it wouldn't hold up very long, but I did have once instance where that happened and the tape saved me from having to clean up a big mess. I'm more careful about alignment now, but I still put the tape on just for the extra insurance.
When the grinding wheels do finally wear out, so far they've all separated right where the metal hub attaches. The hub will continue to spin, but it's fairly easy to tell when this happens because the sound changes drastically.
Here's what the rocks look like throughout the process.
The process isn't fast, but I like the fact that once I get the stones roughed out I can put them in the mill and I only have to check them once in a while.
The board in the bottom of the bucket does wear out after a batch or two, but I've got lots of lumber laying around so it's easy to replace. The pine boards wore pretty quickly, so I'm trying some harder types of wood to see if that makes a difference.
So far I've done two batches of granite marbles and one of obsidian. In that time I wore out one grinding wheel ($5.50 at Home Depot) and partially wore out two others. The rest of the stuff came from my garage, so costwise I think I'm doing pretty good.
On the current batch I mostly filled it up, so there's not much free space between the rocks. I was curious to see what kind of difference that would make from the last batch, where I kept it about 3/4 full. So far the full batch seems to be grinding down a fair amount slower than the 3/4 full batch. Now I know.
Once I have the next batch done I should have enough for a tumbler load. I'm anxious to see what they look like when they're all polished up.
I know this setup is ugly and probably inefficient, but I've had fun making and using it and to me that's what it's all about.
Anyway, that's what's been keeping me busy in the evenings for the last little while.
Questions/comments?
