3D printed grinding and polishing cups
Jan 10, 2022 23:17:26 GMT -5
catskillrocks, NDK, and 26 more like this
Post by jm on Jan 10, 2022 23:17:26 GMT -5
I've been making spheres for a few years now and I was never very satisfied with the grinding and polishing cups I had. I made several dozen spheres with them and most of them turned out pretty good, but there was room for improvement.
My old grinding cups were made from plumbing pipe caps with diamond segments brazed on. They worked ok, but I was never able to get the segments brazed on in a very good circle. This tended to introduce a lot of wobble into the sphere machine when running them.
For polishing I was using diamond polishing pads with foam backing disks. I cut a cone out of the middle and slit the polishing pads partway through from the inside so the spheres would fit into them better. It worked ok, but on rocks that had softer spots in them this setup tends to undercut a lot and make the spheres out of round.
I wanted to make something that worked better and that would be easier and/or cheaper to make. After giving it a lot of thought I decided to try making some 3D printed cups with interchangeable grinding segments. Here's what I came up with.
The hole in the middle has 3d printed threads in it for screwing in a mandrel. The holes around the rim are not threaded and are set in pairs of two so that the grinding segments are interchangeable. You can see from the wear patterns on the diamond segments that they are in a decent circle.
The diamond segments have flat head machine screws brazed onto the back of them so they can be bolted onto the grinding cups. I made a jig to hold the screws and diamond segments while I brazed them so they would all be uniform. They turned out fairly good, once I got the hang of brazing the smaller screws onto the larger diamond segments. It takes a lot more heat on the larger piece to get it up to the correct temperature. The loose screws in the picture are the wrong size, I didn't have any of the right size handy when I was taking pictures.
I've only made the one set of grinding cups so far but they seem to work very well. I'm planning on printing some bigger cups for making larger spheres. It should be much cheaper than making them out of metal.
At first I was a little concerned that the machine screws would break out the side of the grinding cup, but so far I haven't seen any sign of them cracking. If they do break I'll just reprint them with thicker walls.
For polishing I decided to go with 3D printed cups with velcro epoxied onto them so I can swap different polishing pads onto them. They work much better than the foam backer pads I was using before. I've been using 4" diamond polishing pads that I cut up into different sizes for different size polishing cups. I sized the cups to fit the different circles I cut out of the pads.
Both the grinding cups and polishing cups seem to work really well. I'm sure I'll come up with some improvements for them, but they're not bad for version 1.0.
My old grinding cups were made from plumbing pipe caps with diamond segments brazed on. They worked ok, but I was never able to get the segments brazed on in a very good circle. This tended to introduce a lot of wobble into the sphere machine when running them.
For polishing I was using diamond polishing pads with foam backing disks. I cut a cone out of the middle and slit the polishing pads partway through from the inside so the spheres would fit into them better. It worked ok, but on rocks that had softer spots in them this setup tends to undercut a lot and make the spheres out of round.
I wanted to make something that worked better and that would be easier and/or cheaper to make. After giving it a lot of thought I decided to try making some 3D printed cups with interchangeable grinding segments. Here's what I came up with.
The hole in the middle has 3d printed threads in it for screwing in a mandrel. The holes around the rim are not threaded and are set in pairs of two so that the grinding segments are interchangeable. You can see from the wear patterns on the diamond segments that they are in a decent circle.
The diamond segments have flat head machine screws brazed onto the back of them so they can be bolted onto the grinding cups. I made a jig to hold the screws and diamond segments while I brazed them so they would all be uniform. They turned out fairly good, once I got the hang of brazing the smaller screws onto the larger diamond segments. It takes a lot more heat on the larger piece to get it up to the correct temperature. The loose screws in the picture are the wrong size, I didn't have any of the right size handy when I was taking pictures.
I've only made the one set of grinding cups so far but they seem to work very well. I'm planning on printing some bigger cups for making larger spheres. It should be much cheaper than making them out of metal.
At first I was a little concerned that the machine screws would break out the side of the grinding cup, but so far I haven't seen any sign of them cracking. If they do break I'll just reprint them with thicker walls.
For polishing I decided to go with 3D printed cups with velcro epoxied onto them so I can swap different polishing pads onto them. They work much better than the foam backer pads I was using before. I've been using 4" diamond polishing pads that I cut up into different sizes for different size polishing cups. I sized the cups to fit the different circles I cut out of the pads.
Both the grinding cups and polishing cups seem to work really well. I'm sure I'll come up with some improvements for them, but they're not bad for version 1.0.
