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
Sorry I accidentially hit the send button.
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
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.
I have my eye on a Bison 6 1/4" chuck from Enco which is on sale right now.
I buy Chinese chucks from Enco and then convert them ... in shop ... to
Bison is a very good chuck.
I wouldn't go with anything less than 6-1/4" (3-jaw) or 8" (8-jaw) on your 12"
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
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
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,
0. Don't know how accurate it would be. Should be close though. Any other
There are a number of ways to locate the holes. In the end, though, it doesn't
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
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
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
Thanks for all the advice.
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.
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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.
That makes sense.
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
The price is very good on this chuck. I would need a pre-threaded backplate
to machine. Would the standard Bison style backplate work? Here is a link
of the backplate I'm talking about:
It does state that it fits Bison chucks only. Not sure what the difference
is and why this is the case. Not sure if I should try this on one of the
cheaper import chucks. Any comments.
Here is an ENCO brand chuck that is probably exactly the same as the import
one you mentioned on ebay:
It states that it has .003" TIR. Where as the Bison has Raidal: .0012" and
Axial .0008" TIR. Since the Bison is on sale right now, the price
difference is around $50.00.
about two years ago. I made the backplate from a piece of CRS that
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. :-)