New kid on the block here. Intro: I'm a woodworker for the most part but have gotten interested in doing some metal work as well. Got a
12x36 engine lathe recently to make some parts/tools for my metal spinning interests. Specifically a beading tool.
This tool, for those who may not be familiar is basically a smallish pully like wheel on the end of a forked handle that's used to roll over the bead on the outter rim of a spun vessel, bowl and the like.
I bought a short length of 2 1/4"dia cold rolled steel bar from which I thought I'd fabricate this roller. Being basically a wood turner, as I said, I had it in my mind that once I machined or faced off the end of the bar then turned the groove around the radius I could part it off on the lathe. Looking at this big round bar of steel it occurs to me that this would be a rather daunting task to try running a parting tool that far into the material to cut it off the parent stock.
If, on the other hand I were to saw it off with a power hacksaw, how would one go about mounting it back up in the lathe to face off the cut end nice and square with the radius?
I think I'd turn my "pulley" about 2" back from the end. Then I'd turn a hub on that 2" to a diameter I was comfortable with - say 3/4". Then cut the pulley w/hub off with bandsaw, hacksaw etc. Chuck into lathe with rough-cut out. Face to length, finish pulley, bore center etc. Part off the 3/4" hub.
Given the machine in question, it *should* be able to part off a piece that diameter, if a reasonably rigid setup is done. It takes a bit of fiddling to get the speeds and feeds right, and I would suggest some good cutting oil as well.
Basically with a pot chuck. One face of the part is good, so you bore a recess in a piece of aluminum or brass to just fit the part. You could use a setscrew to hold it in, or slot the perimeter of the pot chuck and clamp down on it in you lathes three jaw chuck to grip the part.
OK, Jim, bandsaw it is then. Now the question is how does one go about mounting the newly severed piece that will be in the neighborhood of
1/2" thick by about 2" in diameter in the lathe to clean up the sawed off face? Can you put something that thin in a three jaw chuck? Given that my "band saw" is a PortaBand and not a proper metal cutting bandsaw, there's every possibility (assured) that the end will be quite a bit less than square.
A quick answer to that is to measure the steps on the chuck jaws. You presumably either have two-piece jaws (the stepped part is mounted onto master jaws which remain in the chuck, and they can be unbolted and reversed), or you have a replacement set of chuck jaws, which step with the longest step at the outside of the chuck.
Mount the workpiece in the reversed jaws, set up the tool and toolholder carefully so you won't hit the jaws as you face, and start facing. (Make sure that you clean all chips from between the jaws and the workpiece.)
I would suggest, if you want to radius the edge of the roller, that you leave it cylindrical until you have it faced off, and then mount it on an arbor and take gentle cuts to do the rounding -- perhaps even using a file to do that part. Beware of sleeves encountering either the chuck jaws or the lathe dog which is driving the arbor while filing.
Also -- I *think* that you may want to case harden it once it is fabricated, to reduce wear on the rolling surface.
Agreed. Cut it too thick, and then face it down to the desired thickness. You can probably measure the thickness between the jaws with a micrometer or perhaps even a caliper (vernier, dial, or digital, depending on what you have.)
If your jaw steps are a bit bigger than 1/2" -- can you get away with making the roller thicker?
If not -- and if you have the two-piece jaws on the chuck -- it is perhaps time to consider getting some soft jaws, which bolt on in place of the hardened top jaws. You bolt them on, set the chuck to a comfortable setting while closing part of the jaws onto a piece of round stock, and bore the jaws until they are a close fit for your workpiece diameter, and just slightly less than 1/2". Then loosen the chuck, remove the round stock and put the workpiece into the just made custom set of jaws. You can even face the workpiece a bit thinner if you need to, as the jaws are fully machinable.
If you expect to make more of these pieces, I would suggest that you stamp jaw numbers into the side of the soft jaws to match the jaw numbers on the master jaws, so you can reassemble it in the same position, to make subsequent use more accurate. Otherwise, you can re-machine the jaws to hold a larger workpiece in the future, until there is not enough of them left to do any good.
I'm really leary of turning/parting off stuff close to this monster three jaw chuck, though. I work fairly close to the fourjaw scroll chuck on my wood lathe but it's a whole different ball game on this engine lathe. Guess it's a matter of getting use to it. Lots more control with the tooling on the metal lathe
Your best bet at this point is to make a fixture to face the other end. Basically a large 'pot chuck' if you cannot affort a *real* pot chuck.
Those things look like collets, but they're designed specifically to hold large diameter, thin items for facing or boring.
So the idea would be to put a slightly large piece of aluminum or brass stock in the chuck, and bore a recess in it that is a teeny bit bigger than your workpiece. Then figure some way to fix the part in the fixture so you can face it.
Some ideas:
1) thin out the OD of the fixture behind the part, and then slot it with a hacksaw so that the chuck jaws will compress it down on your part.
2) setscrews around the perimeter of the fixture, bearing on the OD of your workpiece.
3) superglue
4) soft solder
5) compination of screws into the *face* of the fixture, both through the center, and around the perimeter of the part. Use the center screw when facing the outer edge of the part, and then put the outer ones in when you need to face in to the center.
Just remember that the part is not being held very securely, so go easy on the depth of cut. You don't want a part rip-out.
OK - this is what we call a "jam chuck" in wood turning. The forces at play here in machine work are, I found out tonight, considerably larger than turning a piece of soft wood!
I think the slotted sides on the pot chuck sound like the easiest thing for me at this point.
This evening I spent some time getting a piece of 2 5/16 dia bar stock turned down to diameter, hacked off a piece about 2" long and rechucked it using the faced off end against the inside of my three jaw. Perhaps naively I'm assuming the inside of the chuck is an adequate reference surface for mounting a workpiece in the chuck but it was long enough that the chuck jaws helped true it up and it seemed to run fairly true. Obviously we're not talking NASA grade macnine work here! (grin).
Unfortunately in trying to clean up the woefully out of square end I managed to get a rather horrific catch destroying my cutter in the process.
In facing off something that's really out of square would it be best to start from center and work out to the perimeter?
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