double headed coin

Where that kind of setup tends to fall short is in holding items when production machining and you rely on fixed register points (the step in a collet, or step chuck, for example).. Mind you, I'm not suggesting that they don't work well----far from it. It's just that there are times when a thou makes a huge difference, and collets generally won't register close enough to hold the tolerance. I'm not speaking of concentricity, but holding lengths. Soft jaws are repeatedly reliable for that operation. I've run countless production jobs by both methods and have resorted to a fixed stop in the spindle of a machine in lieu of relying on a collet with a step, or collet stop, when collets were better adapted to the job at hand. Small parts run at high spindle speed is a good example. Do keep in mind I use a Hardinge-Sjogren collet chuck. A lathe equipped with a lever closer is more likely to repeat, but only when each item is held to a close holding diameter, wavering no more than a thou.
Harold
Reply to
Harold and Susan Vordos
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Remember this is a one- or two-off project though.
But you are of course 100% correct. Even good lever closers won't hold even a halfway decent length tolerance plain collets. Story:
Say one had an elderly parent who spent a *lot* of time in a hospital this summer. Further consider that said hospital wanted to ding the relatives two bucks each time they exited the parking lot. But they had a token system so the relatives didn't have to plug in two bucks of quarters at the exit gate.
Further imagine that the tokens were nothing more than brass slugs with some fancy stamped designe and a raised rim. And that a trial effort at reproducing one worked splendidly.
Then consider that one might just possibly have a hardinge turret lathe at one's disposal.
The problem one finds is that the only way to accurately get the thickness of the part under control is:
a) barfeed the stock to a stop in the turret,
b) perform a facing operation to set the extension of the stock from the collet, within a thou, and
c) parting off the slug from the stock with the cutoff tool.
Because the stock draws back into the spindle a large (over 15 thou) and non-repeatable (+/- five thou or so) one *has* to waste material and another operation to get the thickness tolerance inside a thousanth.
All, hypothetically speaking of course.
Jim
Reply to
jim rozen
I am certain that the original poster is not interested in doing production machining of double headed coins. That IS the subject of this thread. This was the original post:
"I was wondering if anyone would know where I could have a double headed coin made. I have both coins and would like to know if theres such a place or person that I could hire to have that done. thanks."
As you can see, he just wanted ONE double headed coin made.
My lathe is equipped with a lever closer See
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and as far as I know nickels are within a couple thousands of each other. Nickels being the only coins I have made double headers out of.
Abrasha
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Reply to
Abrasha
So you're suggesting that learning something that he may not have previously known is bad?
If not, and you're trying to extol the virtues of collets to someone that has used them for a lifetime, you're wasting your time. I've yet to find a collet that will duplicate the performance of soft jaws-----the sole exception being when the parts are small and *not* short. You can include step chucks in my comments, of which I own several, including the closers. I also have internal collets. Machining wasn't a hobby for me, it was my livelihood, one I took very seriously. I'm not exactly short on experience.
You seem to misunderstand that I'm not bad mouthing your setup-----which I'm sure worked adequately for your purpose. Assuming one has a lathe and a three jaw chuck that accommodates soft jaws, do you really think they'd benefit by buying the collet setup to machine these coins when it can be done by simply machining existing soft jaws? I'd have the job run before you'd returned from town with the collet.
Be certain to read Jim's post. There are times when collets simply fall right on their collective asses. That was, and is, my point.
Harold
Reply to
Harold and Susan Vordos
No, at least not intentionally
I did not take it as such.
It did indeed.
You're probably right.
Abrasha
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Reply to
Abrasha
I am not trying to say that you don't know the best way to do this. But as a hobbiest without a lathe with collets or a chuck that accomodates soft jaws, I think I would try chucking a bit of stock in the lathe, turning the diameter to the diameter of a Nickle, recessing the center slightly so the nickle seats on the rim and then glueing a nickle to the stock using the tailstock to hold it while the adhesive sets. After machining then heating to soften the adhesive. Hot melt adhesive might work for this as long as one took light cuts.
Dan
Reply to
dcaster
A standard Jewelry apprentice task was to take a dime (they were almost pure silver when I did this) and cut it in half .. the thin way .. using a jeweler's saw. Actually, you had to do two dimes that way. Then you soldered the two heads back to back. It took me many years to accomplish the task and unfortunately, I long ago lost both the two-headed and the two-tailed dimes. That's the right way to do the trick. One can cheat and file the one side off the two dimes and then solder them together. Not all that difficult to do with soft solders. With silver solder is it much, much, harder to do.
Boris
Reply to
Boris Beizer
The (inexpensive) Taig 3 jaw chuck uses soft aluminum top jaws that are machinable just like the big guys. they are not repeatable once removed and replaced though...
Reply to
Felice Luftschein and Nicholas
Interesting. Even *good* chucks with soft jaws don't repeat that well when swapping between sets. We used to have to true up soft jaws after a few go-rounds because the teeth would wear a bit, and the aluminum would get beat up over time.
And here I'm talking about a five thousand dollar chuck.
Jim
Reply to
jim rozen
I use super glue for things like this. A little heat and they slide right off. It is best to cut some rings in the end of the rod to improve the bond.
Reply to
Chuck Sherwood
and
I've never been able to put soft jaws back where they came from and have them run true. There's simply too many places for error to accrue-----particularly when one expects them to run within .0005", and I do. Yes, mine are numbered, too.
The method I use for machining them provides for skim cuts to have them run true once again--so reinstalling them endlessly causes almost zero loss. I use an adjustable "spider" to preload the jaws, setting them such that only a few thou need be removed to get them running true, and to size. I also have a weird habit of holding parts to a uniform size, so they can be run in soft jaws successfully. It's a way of life with me.
Harold
Reply to
Harold and Susan Vordos
According to jim rozen :
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How expensive a chuck do you think that you need? I got a very nice Bison 6-1/4" 3-jaw with two-piece jaws, which is all that you need to allow you to use soft jaws. You can then either purchase the soft jaws (fairly expensive), or machine your own, if you have a mill. A horizontal mill would be excellent for making batches of soft jaws of whatever material suited your needs -- mild steel, aluminum, brass? (I've never seen brass top jaws, but other than the slightly greater expense of the metal, does anyone know why it would not serve?
Enjoy, DoN.
Reply to
DoN. Nichols
I've never seen them, either, but I can't see any reason they wouldn't work. Expense is likely the chief reason they aren't common. Considering even steel jaws don't mark the work, there's no real advantage in using them.
One of the points that I failed to mention about soft jaws in lieu of step chucks or soft collets. Once you've opened up a step chuck or collet, it's often worthless for smaller diameters (depends on the depth). In essence, they're somewhat perishable. Soft jaws, on the other hand, can be re-machined to fit pretty much any contour or size, so they're not rendered useless, or relegated to specific use *unless so desired*. Further, once you've used them up, it's easy to weld in new metal so the process can be started all over again. No need to make new jaws. For that reason, it's nice to use steel in place of aluminum. Aluminum, once welded, would have to be solution annealed and once again artificially aged in order to get back to a desirable hardness.
I strongly advise anyone to purchase only chucks with master jaws (two piece jaws) when buying, if at all possible. Even if you think you'll never run production work. They're more than adequate for one off work, often the best possible solution for holding parts. Soft jaws free you up like no other device when it comes to holding objects in your lathe, or even your mill when needed.
Harold
Reply to
Harold and Susan Vordos
The okuma lathes I worked on used hydraulic chucks, and they were expensive - but one could re-install the jaws carefully, cleaning the teeth with a brush - and they would repeat better than a thou, days later.
Mostly it was wear on the jaws that required them to be trued up.
Those chucks were scary. We ran ten inch diameter chunks of nylon, a foot long in them, roughing at 3K rpm. For that we turned up the hydraulic pressure. They would set the jaws up so that they only clamped in a tenth or an inch or so - so that there was no chance of getting a finger between the part and the jaw when hitting the foot pedal.
Ouch.
Jim
Reply to
jim rozen
The list price on the Taig chuck is $60.40 (beats $5K!) and spare sets of jaws are $7.60 and $7.72 for full circle jaws. They also make a 4 jaw chuck with soft jaws for slightly more. Of course it is only a 3.25" dia chuck and is a direct scroll rather than a pinion chuck. I do sell a few to people who use an arbor for mounting the chuck in a 5C collet.
What's funny is how many people are confused by the Taig 3 jaw, if only because most beginners machining texts make no mention of the idea of soft jaws.
I have a section of pics about truing the Taig jaws here:
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I also have a Bison 5" chuck that has 2 part jaws, I think it was around $300.00 and is really well made. I have yet to get around to using soft jaws on it though. I guess I should fire up the CNC or as others suggested tool up the horizontal mill...
Reply to
Felice Luftschein and Nicholas
That's actually pretty decent. The chuck that came with my Graziano would repeat consistently within a half thou, but almost never if the jaws were removed and re-installed.
That's the chief reason I like steel jaws, although I use both aluminum and steel. The only reason I'd ever re-machine the jaws while running a production run is if I managed to clamp on a chip-----which was rare. (I use air, but well placed).
I can well imagine! Ever get pinched?
I've never operated such a chuck-----ever. I've always been on manual machines, even when running production, of which I've done more than my share. On one job, where I was holding 3/4" hex stainless stock, making hundreds of aircraft parts, I managed to pull a hernia from exerting on the Hardinge-Sjogren collet chuck I use. One of those hydraulic chucks would have looked pretty good!
Harold
Reply to
Harold and Susan Vordos
No, but we did have some part ripouts. A few of them knocked the steel doors of the machine. We ran them with the door interlocks defeated - but it was suicide to leave the doors open on the large jobs. My rule was to never hit that green button until the door was *all* the way closed.
Jim
Reply to
jim rozen
Yeow!~
That really puckers your butt.
I recall running some fairly large chrome moly forgings on the LeBlond sliding gap bed (a 48" machine) at Sperry. The forgings, which we fully machined, were a part of the axle assembly for the missile launchers. In roughing, one of the operations was to face off approximately 1/2" off the length, which we normally did with just one pass. I'd been running the parts for a couple days and finally had my confidence up that they wouldn't pull off the chuck. They were held only by a short distance, from the inside, with the standard external jaws in a 3 jaw chuck. The part was roughly 12" long, maybe 9" diameter, with a flange that was much larger on the end we chucked. The bore was fairly large, but the wall was more than adequate for serious chucking. Well into the day, I started the facing cut on one of them, only to have it come out of the chuck. It all happened so fast I didn't really have time to react properly, but instinct made me step backwards, at which time the forging hit the ground where I had been standing. Damned things weighed maybe 25 pounds. That sucker would have driven me like a nail. sigh!
I really miss those days! Best job I ever had.
Harold
Reply to
Harold and Susan Vordos

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