I'm considering purchasing a 5C collet chuck for my lathe. I'm currently using 3 & 4 jaw chucks and want the added accuracy of 5C collets. Having no experience with 5C collets, can someone tell me if they will hold my work: I work a lot with bar stock in the range of
0.7" to 1" diameter, in pre-cut lengths of 0.120" to 0.5". I need to bore these pre-drilled pieces to ID's ranging from 0.5" to 0.8". This is not production work - I can't build a specialized fixture or modify a collet for each piece.
I plan to have 5C collets in 1/64" sizes for my OD range. Will standard 5C collets hold my work for boring? What I mean is, I don't want to bore a step in the collets (I'm not doing production work) to hold the piece a fixed depth in the collet. I'd like to have some sort of internal collet stop that still allows the 3/8" boring bar to pass through the center. Any help is appreciated.
Greetings Ed, Collets will work in your application. Not only are adjustable stops available but also spirin loaded stops. So these push the part out when the collet is released. If the collet mounted stops won't work because the part is too long then a stop which mounts in the spindle tube or collet closer draw tube will work. If you are going to get one of the closers that uses a key (like the Bison Brand) to close the collet and the part is long then a stop that fits into the spindle through hole will be the best option. Some are available in catalogs but making one is simple. You can turn a piece of aluminum (or most any metal you have lying about) to the size that fits your spindle hole, at the rear, about .004" under, saw it in half at about 45 degrees, mill the sawn faces smooth, tap one of the halves and drill the other. Then, screw a piece of all-thread through this piece so that the end of the all-thread is where you want the part to bear with the wedge shaped piece at the rear of the lathe. Slide the piece without threads on the all-thread and use a nut to tighten the wedge shaped pieces together. This will fix the stop in your lathe. On the business end of the all thread you screw any shaped piece on you want that will allow your tool to go completely through the part. An advantage with this type of stop is that it is a "dead length" stop. So as part diameter changes the part will always be stopped in the same place. With a collet mounted stop as the diameter varies and the clamping pressure varies the part length varies. This is because the collet is drwan back into a taper to cause the collet to collapse against the part being held. With a smaller part, or with higher clamping pressure, the collet is drawn back farther into the taper. There are closers that move the taper and the collet is stationary but these are expensive. More convienient, but more expensive that the Bison type closers that use a key are the lever actuated closers. Cheers, Eric R Snow, E T Precision Machine
Sure will. Probably better than a regular three-jaw chuck. Certainly as good. I've yet to have work come out (if I tightened the collet, that is.)
The collets will be much better than the chucks for that application. You're doing stuff that approaches thin walls -- a regular three-jaw chuck will certainly distort something with 1/16" walls. Collets won't do that.
Sure. If you look at the collets you'll see that the gap is slightly bigger for the 1/8 increments, smaller for the 1/32, etc. At least with my collets they are. The 1/8 multiples have about a 1/16 1/8" diameter range. But of course, you don't get as good a holding all around as with the closest fit to your work.
Most modern 5C collets are threaded internally for an adjustable stop. The stop however, would also block the boring bar. I've never seen the kind of stop you're talking about. But it isn't that big a deal to make a tubular stop that would allow the boring bar through -- however, if you think about it, the stop's wall thickness would have to be no bigger than your boring bar. How about just using a regular adjustable stop and putting in a piece of thin wall tubing to act as the spacer and still leave room for boring bar to clear?
If you're thinkingin terms of one of the Bison 5C, spend the extra bucks for the "adjust-throug" versions. The added accuracy and run-out reduction is well worth the cost.
If I understand your question, the solution is to buy a standard Hardinge style collet stop (screws into back of collet) and make your own stop rods which are hollow for boring bar clearance. Hardinge uses 1/2-20 threaded stop rods so you'll need ones with a bigger head on the "stop" end. Over the years I've had the same situation you're in and accumulated a whole bunch of home-made stops of various end diameters.
Here's a hint to same some machining...buy those cheapo adaptors used to mount grinding wheels on motor shafts. Most have a 1/2-20 thread with a hollow big end to slip over the motor shaft. A couple bucks or so. Machine the big end to suit your job.
You'll get better concentricity with a drawbar through the spindle, if your late is big enough. To use a drawbar for 5C collets, you need at least a 1-3/8" bore through the spindle. Then you need a closer nosepiece to fit your internal spindle taper. Once you have that, and good quality collets, your concentricity is limited by:
1) The exiting taper in the spindle.
2) The accuracy of the closer nosepiece (Royal makes some very nice ones.)
3) The accuracy of the actual collet.
You will also probably prefer the lever style closer mechanism (often found on turret lathes), instead of the handwheel on the outboard end of the spindle.
If you don't have the 1-3/8" spindle bore, you will have to use something like the Bison collet chuck, which while good quality, is not as convenient for quick part changes. You'll be stuck with having to use a key like that for the 3-jaw chuck to tighten and loosen the collets -- and to change collets.
If concentricity is important, with the collet chuck, you really should spend the extra for the "adjust-tru" feature, which lets you tune the centering of the collet chuck after mounting it on the spindle.
The length to diameter ratio makes things a bit more difficult, especially with some less than 1/8" in length, and perhaps 1" in diameter. You could (as others have suggested) make special stops which are tubular section to clear the boring bar and hold the workpiece in the collet.
Note -- that if these workpieces were not already cut to length, you would be better to work with bar stock through the collet (you can pass up to 1" bar through the spindle and the collet and drawbar). then you turn to diameter (if necessary), drill and bore, and part off just outside the collet, then you loosen the collet and advance the bar far enough so you can produce the next piece. For this kind of operation, the lever style closer is particularly nice. But -- you haven't yet said whether the lathe is big enough to allow this.
Aside from making a special tubular depth stop as others have suggested, which is still some special work for each size of stock you want to work with since you can't buy them, the alternative (also mentioned by some) is the collets designed to be bored to the size you need -- and this could include a step to hold the depth, and keep the thin workpiece square to the axis of the lathe. These are not of a hardened steel (like normal collets), but rather a mild steel -- or even brass -- with three pins to hold the pre-slit jaws opened to normal spacing while you're boring to size for the workpiece (and boring clearance behind the stop to accommodate the boring bar). Once you have it to shape, you remove the pins, and the collet will close down on your workpiece as you draw it in. Your diameter range is 0.700: through
1.000" -- but in what size steps? If just a few, it would be worth while to bore several collets to size for each project. Alternatives would be to bore a series of steps so the collet can hold more than one size (size steps not too close together), and use a second one for the intermediate sizes.
Note that to hold a collet nosepiece, the spindle taper will probably need to be a MT-4 or larger. Mine (a 12x24" Clausing) is MT 4-1/2. If you have the 1-3/8" spindle bore, you probably also have a spindle taper large enough to accept the nosepiece. And if you have a Hardinge lathe, it probably has a spindle designed to accept 5C collets
*without* an adaptor nosepiece.
A companion to the nosepiece is a spindle thread or taper protector which is also used to remove the nosepiece. *Don't* put the nosepiece in without the protector in place, or you may have to do things which would damage the nosepiece or the spindle nose itself to remove it.
I was wondering when someone would get around to that. Get some brass or steel emergency collets and machine to what you need. You can relieve what you need for thru tools and you can take them out & put in later and have everything as near perfect as you will need. Fiddling around with a bunch of stops is bullshit, a PITA. Using emergency collets for the sizes you are doing, you'll be able to change to a different diameter piece in the time it takes to remove and replace the collet. Unless of course, you want to fiddle around with different stops that often are tuff to get a part to be in squarely. Do yourself a favor, make it easy to make good parts. Cheaping out on tooling and Mickey-Mousing are a waste of time. And I don't necessarily mean dollar cost.
There are indeed a variety of ways to skin this cat.
A brass or nylon emergency collet can be bored to size, they also make soft steel ones.
But I've got a large number of regular hardinge collets that a tooling shop transformed into pot collets, by boring them out, presumably with carbide tooling. These were with very short (1/8 deep) recesses, but they could have been done deeper.
For larger diameter sizes there are step chucks made with the pins, which are also bored to size. Those are typically semi-steel.
If the original poster has a lathe smaller than 5C, I would mention that I also have a large number of very small diameter 3C collets, that the same manufacturer had used as the starting point for some 3C pot collets.
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