Think prop spinner for a model airplane (is this sounding familiar?)
Assuming that I'm not turning from solid (oh, it sure is!), how hard is this going to be on a Smithy-sized lathe (7" swing over the ways, cheap Chinese construction). I'm thinking that I'd use soft aluminum, no thicker than 50 mil and probably more like 30 or 40.
I've never spun metal before, but I've seen videos so I know I'll be able to do it with hand-made tools, like a pro, the very first time.
While we're on the subject -- how do you spin a piece that's rounded on the end? Make a dimple in your sheet, then spin down from there? You've got to have some surface area on the tail stock, don't you?
You're gonna have to first turn the spud that supports your piece to the inside shape. Then hold the piece to to the spud with a hardwood pusher. Push on this pusher with a live center of course. Once the pusher is spinning cut away enough of it to get enough clearance for your spinning tools. BTW, pieces that are long in relation to their diameter are hard to spin. You will probably need to anneal the piece a couple times. Good Luck. Eric
Full disclosure: I've never done this, but I've watched.
A piece like that likely would be much easier to spin if you start with a tube, and work it down over a steel mandrel. Use a lot of pressure on the tool (you may need a wheel-type) to shrink it down uniformly as you progress toward the point.
That would work unless you wanted a closed end, like a prop spinner. The first time I tried to make a long narrow piece it started to wrinkle and I was unable to get the wrinkled edge shrunk back down enough so I ended up cutting the piece short. So instead of a silver cup about 1 inch dia at the bottom, 1 1/4 at the top, 1 3/4 long, it ended up about 1 1/4 long. Still made a nice shot cup, just holds a little less tequila. Eric
Years ago I watched a metal spinner making teardrop headlight shells for high quality reproduction pedal cars. It was formed almost completely in one setup. Now I wasn't close enough to see any real detail, but I did see a small dimple in the shell when he was done, the pressure pad and form being shaped to form this dimple when the disk was clamped. The clamping pad was fairly well relieved to allow tool access. He spent what seemed like a long time getting the metal started forming, then all of a sudden, he zipped along and got 80+% of the shaping done in seconds! Some back and forth work to smooth out the ridges, then the pressure pad was pulled back. At this point, there was sufficient friction between the shell and the form to hold it, and he finished off the shaping in the region near the end that he couldn't really reach at the beginning. The owner of the shop explained the dimple was pressed out in secondary operation.
Be careful about going too thin on material, it often tends to thin out as you form it.
Another trick I just recalled, he used the main roller tool and a back tool to form a small and shallow upturned edge on the blanks as a first step after clamping. Upturned being away from the spindle, toward the tailstock. What this does is strengthen the rim and helps prevent the edge of the disk from buckling.
I have no idea if the disks were annealed or not. But I suspect getting it done as fast as possible helps avoid work hardening the material.
How many are you planning on making? It seems to me that you could make a die set fairly easily to form them. I have no experience with aluminum, but just used hardwood to make a die set for copper. For aluminum I expect you would have to use steel.
We build spinning machines for all sorts of applications. What you are attempting will take lots of trail and error for sure. Here is a link of a spinning machine we retrofitted.
How big is the part?. What you're proposing is quite doable and if you're willing to have a go can be learned without too much trouble. When I taught myself to spin, about 1997, there was not that much information on the internet but quite a bit more now. I started with a prop spinner shaped part, I wouldn't now as there are much easier forms to start with, but I persevered after destroying my initial couple of blanks and managed to get a complete part by number 6. The main thing with a part with a small initial clamping area is to get the metal laid down properly to support the blank or it'll fatigue and break near the clamping piece. The laying down of the material onto the spinning chuck is done on the pass back towards the tailstock. A couple of pieces I've done of this nature are here
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. The aluminium one is easy as that was 1050 and doesn't really seem to work harden, the brass one was probably 10% spinning and 90% annealing between spinning.
Jim, Thank you for posting. I have no idea how to help you, but I really enjoyed watching videos on metal spinning this morning. Never saw that before.
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