I am in the process of purchasing a new chuck for my 12" x 30" Craftsmas Lathe. I currently have the original 5" 3 jaw, and the 8" 4 jaw that came with it. They are pretty old and a bit worn out.
I have been trying to figure out what the holding capacity is for the different size chucks. I can not seem to find this information anywhere. For example, my 5" chuck will only hold around a 3 1/2" peice of round stock.
I am working on some 4 and 5" alluminum rims that I am making from some 3/4" thick plate. I need a chuck to handle these diameters. My 8" independent chuck would work, but it is not very accurate (worn out). I also would like a self centering 3 jaw chuck for this operation.
Is there any table that shows an approximation of what holding capacites the different size chucks have? When they state inside and outside jaws, does the inside holding refer to chucking to the inside of a pipe? And can the steps seen in most of the jaws be used for holding larger items on the outside diameter?
Any links or information to help me better understand the terminology and how these different chucks are used would be greatly appreciated. I have been searching the net and browsing many catalogs, so I have a pretty good idea of what is out there, just not sure what I need.
I put an 8" Phase-II chuck on my Craftsman 12" lathe and it worked fine. You can't crank the jaws all the way out and still get the carriage all the way to the left - the extended jaws will hit it.
But, you get reversible jaws with just about any chuck you buy new. You can't get large work all the way against the chuck body, but you can hold it nested in the steps of the jaws. With the jaws reversed, you can hold work within an inch or so of the chuck's size.
So I have seen chucks come with one set of 2 peice reversable jaws, or 2 sets of jaws, for internal and external holding. So I guess if I purchased a 6" chuck with 2 piece reversible jaws, I should be able to chuck up a 5" diameter piece in the steps of the jaws (if I were to reverse them).
I have my eye on a Bison 6 1/4" chuck from Enco which is on sale right now. Any comments:
Yes -- by reversing the top-jaws with the two-piece jaws, *or* by installing the second set of jaws with the two sets. Either should get the same range of sizes.
I consider the two-piece jaws to be better for my purposes, because that means that you can also use soft jaws. These are jaws which are full height from inside end to outside end -- but are made to be bored in the lathe to hold a specific workpiece. One advantage of this is that the bored soft jaws will hold a more accurate concentricity, if they are bored for the specific size of the workpiece. And --they will be less likely to mar the finish of the workpiece.
Soft jaws are made both in mild steel and in aluminum, depending on the nature of your workpiece.
This is a nice chuck. I got this one -- with two-piece jaws (from New England Brass and Tool) for my 12" Clausing, and it is a good solid chuck. I like Bison chucks -- very nice chucks, and very nice price.
You have mine above. I have not visited the emco web page, as I already know the chuck. (Though perhaps I should ask whether this is a direct-mount chuck threaded for your spindle, or one which requires a separate backplate which you need to fit to your machine.)
I will be bringing a number of chucks, including Bison and Buck to the Visalia show. Many are two part jaws.
I also have quite a number of D1-3 Chucks and drive plates, etc that will be for sale, Buck, Bison, Atlas, etc etc
Plus some NEW Buck Adjust-tru clones...8"
"In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann
I've looked into buying a threaded back plate, they are $50.00 for the 6" chuck. This would save me $50.00 overall, but I would have to do some additional machining on the backplate. I am not quite sure how to line up and drill the mounting holes to get perfect concentricity. I imagine I would first install the backplate and make sure it is perfectly round by removing material if necessary. But am not sure what the easiest and most accurate way would be to mark the holes on the plate.
One method I was thinking of was to measure the chuck mounting hole locations. Then I could mount the backing plate onto my x-y cross slide milling table, find the exact center of the plate, and then going the appropriate x-y coordinates for each mounting hole using the center as my 0,
There are a number of ways to locate the holes. In the end, though, it doesn't really matter.
It is not the location of the holes that determine the concentricity of the chuck - it's the step that you turn on the backplate. The screws are there to hold the chuck on - nothing more. The screw holes are a bit oversize anyway.
They make "transfer screws" which you could thread into the chuck's tapped holes. They have points which stick up. You'd screw them in so the points are just proud of the surface and then set the backplate in place and whack it over the hole locations.
There's some on this page, if it doesen't come up just search for "transfer":
That type is nice because they come packed in multiples a holder/wrench and can be backed out of blind holes easily.
I've heard you can do about as well with plain old cup point setscrews threaded in upside down. They'll leave little circular marks you can easily locate the center of by eye with a centerpunch. But if the holes are blind, think first about how you'll remove them if they get stuck.
I just used a transfer punch to locate the screw holes. The important thing is the fit between the shoulder that you turn in the backplate and the mating recess in the chuck body (and of course the concentricity of that shoulder with respect to the spindle axis).
The biggest problem I had was the confusion in selecting the proper backplate for the chuck I had bought (Bison 8" 4-jaw independent). I could find no catalog listing for a 2 1/4"-8 threaded backplate specifically for that chuck, except for a rough cast one which seemed to require too much machining for my abilities at the time (boring and internal threading). I opted to buy a Bison threaded backplate for "Self-centering scroll chucks - Plain back" because it came pre- threaded for my spindle. The problem was that the backplate's diameter was not specified in the catalog. The backplates were only listed for "size of chuck". I had no way of knowing if a backplate for an 8" scroll chuck could be adapted to an 8" 4-jaw independent chuck. I finally had to go ahead and purchase both the chuck and a backplate to determine if they could be used together.
It turned out that the diameter of the backplate required for my chuck was considerably smaller than the chuck itself, so the backplate I had ordered ("for an 8" chuck") was way oversized. Rather than sending it back I decided to turn it down myself. It all worked out in the end, but if I had it to do again I would've bought the chuck first and taken a measurement of the shoulder diameter to determine what size backplate I'd need.
What has always worked for me is to turn the backing plate to a push fit in the recess in the chuck. After getting a satisfactory fit, chalk the backing plate up(or the recess, either has worked for me). I've got a lifetime supply of chalk balls for chalk lines, but colored blackboard chalk works as well. Orange or blue seems to work well. Anyway, chalk it up, insert the plate and give the backing plate a good whack with a heavy rawhide mallet. The chalk transfers except for the bolt holes, leaving the holes outlined on the backing plate. The old machinist's book I got this out of had the machinist use various calipers and dividers to find the center of the hole, then centerpunch it, for really big chucks, like 50" or so. I just eyeball it, center punch them and use a center drill in the drill press to start the holes. You want a free fit between mounting bolt and hole, so you don't really need .001" accuracy here, although it's nice. I've made a number of backing plates from solid hot-rolled plate this way, they've all turned out good enough.
I think a have a pretty good understanding now. I also found a website which describes the process in detail. I imagine others have seen this before, but here it is again just in case:
One question I have after reading this article is which surface between the backplate and chuck should I have touching. The outer surface or the inner surface of the chuck. According to the article, the surface that does not touch should have a .025" clearence.
How important is it to have a bar running between centers on the lathe to elimate any spindle movement while machining the backplate? Do most people do this.
I think I will go ahead and order the plain back chuck and attempt to machine my own backplate, or at least the pre-threaded one designed for the Bison chuck.
two years ago. I made the backplate from a piece of CRS that cost about $12 (the price of steel has gone up since then). It consistently will mount with less than .0015" TIR. I have compared it with a Bison of the same size (it is actually a 160mm in diameter like the Bison) and is compares favorably. I like Bison stuff and own serveral items by them, but I thought I would mention this chuck since it has served me well.
Just be sure that you know the thread used in the chuck. It is almost certainly a metric thread in a Bison chuck.
Left-hand drill bits drilling into the cup?
Another trick which you can use (and I have used) is (if you have one of the import drill presses with a circular table), to remove the table, turn up a stub which fits the hole that the circular table fits into, with a bit of a shoulder, and clamp the 3-jaw chuck jaws onto the other end of the stub. The, with the backplate off, offset the table support arm on the column enough so you can rotate one of the holes under the chuck, and align with a stub in the drill chuck turned like a lathe center. Once you have the chuck positioned correctly, clamp everything firmly, and replace the center with a center drill, and place the backplate on the chuck. You will be properly positioned to drill the first hole. Center drill it, and follow with a drill bit which is just barely clearance for the screw. Then test the fit of the screw though the back plate into the chuck. Once you are sure that fits, remove the screw and rotate the backplate so the screw lines up with the next hole (being sure not to rotate the chuck while you're about it) and center-drill for the next backplate hole. Repeat by moving the existing screw and hole to the next position on the chuck, until you have all the remaining positions center drilled. (This does assume that the holes in the chuck are properly indexed around the chuck, which should be the case with a Bison, but should be checked for cheaper brands. To check without disturbing the setup, just make sure that you drill each hole after center-drilling so you can test fit another bolt while the first is in its own hole.
If the holes are not regularly spaced, you will have to mark the first hole and the corresponding position on the chuck, remove the backplate, loosen the table clamp, and rotate the chuck to position the next hole under the drill -- making sure that you don't have to side-shift the chuck again, as you will, if the distance from the center of the chuck varies.
After all of this is done, you may wish to drill the holes up in size, and perhaps to counterbore so the heads of the screws don't project as much from the back of the chuck assembly.
The outer surface is what should be in firm contact. The projection of the inner part is just to insure concentricity.
I have never done it (nor heard of it before now). I think that it may depend on the type of bearings used in the machine -- and perhaps on the size as well. My machine has opposed tapered roller bearings, and there is no end-play when it is properly set up.
A lathe with babbit bearings, or other sleeve bearings may not have that much control of end-float.
And a really big lathe, even with tapered roller bearings, may have sufficient differential expansion over the large distance between the two bearings so there may be some end-float at some temperatures.
This is common - using a pre-threaded backplate. However be sure you understand the 'register diameter' issue for threaded chuck mounting. There's a specific sequence of operations that's best for doing this, and often a pre-threaded backplate will not mate properly to the spindle even though the threads are correct.
But -- if you mount it backwards, and hold it spaced out with a spacer ring made for the purpose, you can have access to the register area to tune it to the proper size (presuming that it is undersized). If it is too large, enlarge it a bit more, and make a ring to fit via thermal differential (heat the plate or chill the ring), and then turn the ID of the ring to the proper register diameter.
And that is easier to fix than a pre-threaded *chuck* which has the register diameter wrong. :-)