SteveM wrote:I have one, but I need the 4-jaw to do offset work,
For one or two items, yeah, a four jaw. However, if there's a volume of parts and they are identical, soft jaws work just fine for offset work, too. You can also use a two jaw. all depends on the nature of the work being held.
The deal with a four jaw is that you can hold pretty much any configuration. It's just slow business.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Harold_V wrote:For one or two items, yeah, a four jaw. However, if there's a volume of parts and they are identical, soft jaws work just fine for offset work, too. You can also use a two jaw. all depends on the nature of the work being held.
How do you machine the jaws for offset work?
I can see milling them off the chuck, but then you lose that magic concentricity with the spindle that you get from boring then in place.
A parallel OD adapter with your tailstock taper inside, the applications are endless. I know many lathes have the same taper in the spindle but not having to remove the chuck can really speed things up.
For repetitive offset work on round stock I use an MT2 collet chuck (originally bought for the tailstock) fitted in a parallel OD adapter held in a 4 Jaw or in the 3 Jaw with a shim on one jaw - dial the work in once and then get some work done,
I actually can't recall if this was mentioned yet or not. And today few would even consider the method. Long before 3 jaw self centering chucks were invented, and even before the independent 4 jaws were invented, everything was done either between centers or on a faceplate. With the proper accessories and hold downs, a good face plate can hold anything a 3 jaw, 4 jaw, collet, or anything else can hold. Plus as a bonus it can have a counter balance weight bolted down to it when turning off set work. Note I said it could hold it. I didn't say it was even close to being as fast as other more modern methods.
I've got a older book that was first written in the 1920's. In it they show master gauges used for checking the day to day factory floor gauges used in a typewriter manufacturers being machined and then ground to way under 1/10,000ths of an inch for size and location. This was all done by hand tapping the gauge, or possibly using temporarily mounted fine thread screws into each location on a lathes faceplate using nothing more than shop made hardened and ground tool makers buttons, and a shop made dial test indicator that was designed to highly magnify the readings. I can't even imagine the patience, experience, and skill it must have taken to get each location into position using what today would be considered very primitive equipment. Obviously only precision lapped and plain bearing lathes, and the same for the tool post grinders would allow those accuracy's at that time period. And today any work at that level would be considered strictly for jig boring and jig grinding at the bare minimum. At that time I don't think the jig borers or grinders were even thought of. But it does show what can be possible with a faceplate.
Even if I had a lathe that was capable of being accurate enough. And I do have one indicator that could measure it, I very much doubt I could locate any part even close to those tolerances with a set of tool makers buttons. I bet there might be a few here that could though.
Harold_V wrote:For one or two items, yeah, a four jaw. However, if there's a volume of parts and they are identical, soft jaws work just fine for offset work, too. You can also use a two jaw. all depends on the nature of the work being held.
How do you machine the jaws for offset work?
The jaws are machined in situ, but on a mill. Depending on the configuration, a rotab may be required, or a CNC can be employed, creating a virtually perfect image of the part(s) to be held. A less than convenient way to go about machining the jaws, but a serious time saver when there's a quantity of parts to machine.
I can see milling them off the chuck, but then you lose that magic concentricity with the spindle that you get from boring then in place.
The real concern in machining them off the chuck is that there is no compensation for anomalies in the chuck slides, which are often distorted. Further, it would be difficult (but not impossible) to address depths, which, on properly machined soft jaws, is a critical feature.
Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
I say my Mitutoyo long probe Dial Indicator as an attachment I use most effectively besides
my trusty Adjust-Tru* 6 Jaw Buck chuck.
The major flaw that many of old lathes, such as Le Blond I have is that it has no caliper
on the Z direction. No, not the vertical direction Z as for milling machines but side to side
direction as you're standing in front of the lathe. If you have a DRO or even a TravaDial,
that would be good. I can turn a step on a bar piece or face it within .001 - .002 accuracy with
just this indicator with a common magnetic stand held on the front wall of the lathe's carriage
(Photo).
To use it:
0. Eyeball to make the indicator probe rod parallel to the lathe bed edge via the mag's stand rod
adjustments. Eyeball the probe from two views - top and horizontal. It doesn't have to be super
parallel. We're turning short rods
1. Insert work bar in head stock chuck (or collet) and close the jaws lightly
2. Touch tool on the right end of work by loosening the jaws and slide work out to hit the tool. You don't
want to bang the tool against work that is held tightly in the jaws!!!
3. Tighten the jaws
4. Set the indicator to zero
5. Start facing work to desired amount for length or back off tool and move over tool to the left
at desired step or grooving location using the dial indicator
You can clamp a stop on the lathe bed rail. But I don't like that. It'll mar that precisely ground rail besides
you need to figure out precisely where to place the stop block along the rail. And, I won't like to hit that
caliper if there is one on the block with that massive carriage.
Also, another weakness on my old American lathe is that the tail stock quill extension function is inaccurate.
There is no caliper at the tail stock's handle either. We must rely on the coarse engraved vertical marks on
the quill in 1/16" increments. So, here is my solution:
Use the same indicator mounted on the stationary tail stock's flat top using a magnet block
(Mighty Mag brand) and place another magnetic block (such as the base of the magnetic stand with the V)
onto the quill itself. This 2nd block becomes a stop for the indicator's probe. We can now drill or ream to
desired depth accurately (sorry, no photo for this). Don't forget to tighten the tail stock base before use.
On the magnetic stand, a long rod can be attached with a flat end to act as a stop for the probe to give
extra reach.
Come to think of this making hole business, I did use the tool post to bore with this dial indicator
arrangement. The depth of the hole can be accurately made. Of course, it is more easier to use
the tail stock for drilling and reaming.
School's way of reducing work length is to face it accurately using the compound caliper at 90 degrees.
Furthermore, to make the compound caliper use super accurate is to use the hypotenuse triangle principle.
CAUTION:
=======
Always remove or swing the probe away after use. I've almost damaged the indicator a couple of times
until I got used to move it away.
_________
*I can adjust this chuck to less than .0002 concentrically. I use 6 jaws instead of 3 jaws for better
distribution of force so that when I turn a thin tube piece for cutting multiple loco's driver tyres, the
tube won't distort as much. After making those contoured rings (flanged and 3 deg tapered tyre profile),
I can press fit the rings onto spoked driver centers. I can also accurately make the tyre width scaled
5.5 inch each consistently using the Dial Indicator scheme
Toolpost Grinder, almost any high speed spindle you can mount can do some useful things including engraving graduations on handwheels.
Cross-Slide milling attachment- mill slots for bayonet action mechanisms; slot cams; deep, fast helices for height adjusting and locking rings and gib strip retaining slots on round columns; gears and so on.
