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lathe
06-21-2014, 03:23 PM
I thought that making a ring wouldn't be too hard for a beginner. However I have become stumped about how one would finish making the ring once the piece has been parted off. For instance I can see how you could make a chamfer or such on the front side but then to do it on the reverse side it seems you have to part it off and turn it around in the 3 jaw chuck.
Here lies the problem in that the 3 jaw chuck does not seem real good at holding small length objects such as a ring or a coin. Is there an attachment for holding smaller things such as rings or coins? For instance how could you drill a hole in a coin on the lathe?

daveo
06-21-2014, 03:36 PM
Make a spider or back it up with a short length of pipe?

gzig5
06-21-2014, 03:40 PM
After it has been profiled and parted off, mount the ring on an expanding mandrel in the lathe. The mandrel can be turned to size just before mounting the ring if you are really worried about concentricity.

darryl
06-21-2014, 04:43 PM
I use scraps of mdf for things like that. Mount a piece on a faceplate, then turn a recess that you can press-fit the ring into. At this point you have to be careful to take light cuts so you don't overcome the holding power of the press-fit, but that's kind of understood anyway.

One thing this method gives you besides a way to hold a part is concentricity. Whether you're turning a recess to press a part into, or a stub to press it onto, you can also use wood screws into pilot holes directly adjacent to either the inside or the outside of the part to help hold it in place. You can put washers under the heads of the screws if that suits, and you can also arrange a live center in the tailstock and a suitable disc or whatever to pressure the part against the mdf for the holding power.

I've been using this method for years, and now have a few different types of mounting for the mdf pieces. One of them is simply a piece of shafting welded to the center of a steel disc, which was then faced to true it up- a series of holes drilled in the disc gives a way to mount the mdf piece with screws. This mount I just put in the chuck. Another started life as an end bell from a motor- this one already had a series of holes drilled around the mounting surface, and I added a hub that's threaded to fit my spindle. It's about the size of a faceplate, and the benefit is two-fold- the mounting screws for the mdf are all around the outside, which means that you wouldn't normally get interference from the screws when you are creating a recess to mount some workpiece into- plus it's basically hollow between the mdf and the mount, so you can bore right through without cutting into the mount.

I have some other custom mounts I've used also, though these two are the most commonly used ones. A couple of times now I've taken some mdf scraps and cut them up to suitable sizes for mounting on these things. I've about used up the scraps now, so I need to cut some more. The last batch lasted me about two years. I usually cut them as squares, then knock the corners off to leave an octagon shape. Sometimes if the corners are going to interfere with the process, I'll turn them round before turning the recess or whatever I'm needing to mount a part. If I need the full diameter that my lathe is capable of, then I'll knock off all the corners on the octagon, leaving 16 corners- then I might even carve them closer to round on the table saw.

Bob Fisher
06-21-2014, 11:53 PM
Darryl has the answer, it's an old clockmakers trick to hold what they call wheels in order to true the bore to the teeth.It guarantees concentricity as long as you do not remove it from the lathe. Bob.

boslab
06-22-2014, 12:58 AM
Also found this little project a while ago while thinking about the same
http://www.cartertools.com/mandrel2.html
Looks quite handy for rings
Mark

Old Hat
06-22-2014, 01:08 AM
Before parting completely thru, do your back O.D. chamfer then part thru.

justanengineer
06-22-2014, 02:03 AM
The jewelers I know use a mandrel, Ive used them successfully for smaller parts like this as well. The real advantage is that you can mount the ring/part away from the faceplate or chuck far enough to easily work on both sides. Barring this, I'd just make a custom set of internal soft jaws for the chuck.

If you get in the habit of making your own fixtures the order of operations somewhat becomes irrelevent. You could finish the outside of the ring first and make the internal chamfers or other features after the fact simply by cutting into the arbor/jaws as necessary.

mars-red
06-22-2014, 09:28 AM
Makeshift expanding arbors aren't too hard to make, and can be a neat little project on their own. When I was making the tapered discs shown in this picture:
https://lh3.googleusercontent.com/-BkDU1DK07QA/UYZmRtVy0MI/AAAAAAAABo4/Rf9acyMd0K0/s912/roller%2520pins%2520and%2520body.jpg

I needed a way to reverse them for finishing, so I made this to hold them:
https://lh6.googleusercontent.com/-MGNjBHwTSkk/UYhXDnlfS1I/AAAAAAAABpo/DaW7tRQjGL8/s912/tiny%2520expanding%2520arbor%25201.jpg
https://lh4.googleusercontent.com/-JU6gZX1jkWU/UYhXEBZf_hI/AAAAAAAABpw/HiXSIcO6ne8/s1024/tiny%2520expanding%2520arbor%25202.jpg

I make a different split collar for it for each use - with only one slit like that it needs to be a really exact fit within the bore of the part you're holding.

dave5605
06-22-2014, 01:12 PM
I've used 5c emergency or pot(think that's what they are called) collets that you can machine them to whatever diameter you want to hold. Fairly inexpensive and probably come as big as about 4" in diameter. I have several used ones off of eBay that still have useful life.

You can buy an inexpensive collet holder that you then stick in your lathe chuck.

browne92
06-25-2014, 09:56 AM
Sorry it took so long to respond to this, but I don't get out to the shop every night.

I made a set of arbors in (almost) all sizes. They work well and were easy to make.

http://i1305.photobucket.com/albums/s551/browne92/DSC01088_zps39c2940d.jpg (http://s1305.photobucket.com/user/browne92/media/DSC01088_zps39c2940d.jpg.html)

Edit: After looking at the pic, I figured it needed more explanation. Turn to size, drill and tap, two slots with the band saw, and the bolt spreads it out to grip the ring.