Chucking round stock? 4-jaw how do you???

reading through the "chucking round stock" thread, I see the wisdom of learning to master the 4-jaw. I've leaned too hard on the 3-jaw for too long.

So... how in the heck do you "dial in" a piece of stock in under 2 min? I'm sure lots of practice is involved, and I will practice, but I'd be happy if I could get to that 1/2 mil in under 5 min.

I start with the jaws lined up on the concentric circles on the face of the chuck. Set the stock in and snug each jaw equally. I put a dial indicator on top, and then loosen the low side, tighten the high side. Repeat... sometimes for 15 or 20 minutes chasing the last mil or so. Frustration.

So how do you do it?

Practice, practice and practice again plus a little bit of feeling, you can impose colossal pressure with a 4 jaw so don't go too mad,........ nearly there? don't loosen a jaw, tighten it's opposite a bit more.

Take care. Sami.

What indicater are you using to do this, when I get down to .002 in. I go to a 1/10 of a thousand incicater. Thats .0001
Is time a real problem as in having to get it done in 2 min.
after I dial it in for round, I go the length and get stright as I need it.
nothing wrong with speed unless I loose accuracy.

Well if you're starting with a nice round part its easier. When you're trying to dial in material that is .200" out of round and bumpy, trying to make sure it'll all clean up then it takes a bit longer.

First thing I do personally is line up the jaws using a ruler, 6" or 12" depending on chuck size.
You don't want to grab a 100lbs piece of material, swing it on there to find out the jaws are a little too close and it won't fit. So I get 2 jaws where I think they need to be, and leave 2 a bit looser which I tighten first as soon as the part goes in.

If you properly line up the jaws you can get within .030" easily enough right from the start. Closer on smaller parts.
Then I set the dial, find the high spot, tighten it a bit, go opposite and loosen by about half the difference depending on the spring of the chuck. Check 90 from that while spinning around to see what it needs and adjust. Usually a few turns gets it within a .001 if the part is round and not springing all over the place. Sometimes it can take a while to properly dial something in.

If doing many parts I like to mark 2 jaws with black marker. They're the ones I loosen to take parts in and out. Also helps me keep track as I dial things in. Thats just me, I'm sure others do it differently.

Also, on long pieces I sometimes use very thin shims, or paper on a jaw tip or 2 to get the end of the material to kick back in the proper direction. Theres all kinds of little tricks.

Your on the right track. Myself I would rather usa A 4 jaw anyday, but for some it takes along time to master. Try moving the needle 1/3 of the distance that you have been, concentrate on jaw number 1 and 2 or 3 and 4. Indicate the two first then go to the other two. At that point just go slow and easy then some practice next thing your great and all your coworkers are coming over saying how the hell you do that.

Make sure that you understand exactly which jaw you need to move before you move the chuck key to another jaw, I other words think it through very carefully before taking any action. It's easy to get frustrated and in a hurry. If you think it out it WILL come to you. Good advise from Sami too, sometimes if they are all pretty tight you cam bump the low side a wee bit looser too.

Good luck.

Don't get lost in meeting some arbitrary time. A full time lathe apprentice living under the gun with a 21 year old's eyesight, reflexes, and coordination will attain that two minute mark in a couple of weeks.

If you're older it will take a little longer particularly if you're a HSM and don't get an 8/5 exposure. Often I catch learners spinning the chuck for several revolutions. This can be a big time waster. You soon get locked into a daze staring at the indicator. Work the jaws in opposing pairs, turning the spindle more than a half rev at a time. Look for waste motion and try to cut it out of your routine. Practice no more than 1 hour per session. Let the subconscious mind do its job.

The mistake many make early in the game is that they try to swallow he work that is grip too long a length. If your stock is cut just a bit longer than finish length you should grip only about 1/2" or so. Then you can dial in close to the chuck and bump the overhanging end around then back and forth a time ot two untill the work is on the money. Then you can drill a center hole, skim a steady rest journal and face off the end.

Swallowing to work may acutally prevent you from bumping in the overhanging end. Even a new chuck will allow the jaws to splay a trifle unevenly enough to complicate dialing in swallowed work. If the grip is short you can move the work in the jaws.

Give yourself a chance. You'll get quicker if you allow yourself time to improve. It won't happen overnight.

I wrote a series of article in Home Shop Machinist covering basics of machine shop practice especially for the HSM newbie. My "New Hand" article in Nov/Dec 2004 issue dealt with 4 jaw chucks in considerable detail with photos and illustrations. If you can round up that issue perhaps some questions can be answered.

First, use the concentric circles on the chuck to get the jaws close to the same spacing. You can use any corner or edge, as long as you get the jaws concentric. Next, run your indicator up close. If you have an indicator with small travel, as mine is, you need to get pretty close before reading the dial or you'll crash the DI.

As stated above, work opposing jaws. The secret is to half the distance of the farthest jaw by moving it inward (unless chucking for boring or inside work, in which case you move outward). Once you have it within a range that will not mangle the indicator, turn one ful revolution, noting the high point and low point. Say high is 12 and low is 4.... go halfway to about 8. Check to see where the high point is now. Half that. you'll be within a few thou in two turns. Keep going and you'll have it within .0005 in well under two minutes.

Practice helps, but procedure along with practice is even faster.

Mike has a great point about watching the indicator move as you tweak the screw and shooting for half of the range rather than blindly guessing at a "move".

The other trick I've used is to bring something stationary up near the work but not touching it. This could be a tool mounted in the compound, the indicator tip that doesn't touch the work. Use your eyeball to "gauge" the gap between workpiece and stationary object, again working opposite jaws, when "roughing in" the work.

Ideal is when the indicator (now touching) is not wildly spinning as you rotate the work, this makes quick math and a sense of "where to go next" much more rapid.

The main advantage of the 4 jaw as I see it, is instead of saying "I can only get within .00X inches" you *decide* up front what's an acceptable runout number and then make it happen.

The brilliant machinist who taught me how to indicate work in a 4-jaw pretty much taught me to do the same process Forrest, limy sami, and Mike C. talk about. It is awsome, how much faster it is than using the clapped-out old bellmouthed 3 jaw I used to use, where I had to rotate the work all over the place to get it to spin round.

I have found when trying to indicate in rough work, that putting a band of tape, like thick masking tape around the stock in order to get a more average reading. you can also get an "elephant's foot" tip for your indicator that will help, but I like the tape in addition. just make sure the tape is only 1 layer thick and doesn't overlap creating a thick spot to confuse things.

also, the type of indicator used and the distance that it can indicate in 1 revolution can be very important. an indicator that only indicates +/- .025 per revolution is harder to read in this situation than one that does say +/- .050" per rev. you don't have to keep track of where your null point is AND count revolutions at the same time.

the most difficult thing i have found is trying to indicate in work that is on the small end of what the chuck can grab. larger work just seems easier.

practice, practice,

jon

Alluded to, but not stated, in other posts, is that is is better IMHO, to place the indicator horizontally so you can reach both opposing screws at the same time. By doing it this way, instead of on top, you should be able to get it real close in just a couple of revs. This assumes the lathe is not too big to reach the rear screws.

Charlie

it may that you are over compensating. to much backing off the low side and the high side being tweeked past center. i did this many 2 many times i found myself trying to lock down my stock way to soon. i turn 5" od 7 " long. the od finish will be no less than 4.95 thats only .050 for a very rusted and not completely round peice. also i have id to deal with not much there ether. i used to run a 3 jaw adjust a buck. you could center anything in 3 jaws but the next set up would be like chasing mating squirrels around a tree. 4 jaw will grab and hold way more. but wait till your you only have a thou to go before you start lock down sequence thats my 2 pennys over and out

Use 2 chuck keys to shift the workpiece.
Read the indicator on 1 and 3 while those jaws are horizontal.
Adjust with the keys to split the difference. Note the number.
Now bring 2 and 4 horizontal. Adjust them to that number.
Rotate 1 turn and tighten the two high jaws to split the remaining few thou. difference using one key.

Done. 1 min 30 sec.

My Nardini 1440 at work always wears the 8" Bison 4 jaw. Keeps wanna be engineers off my lathe.

And when I rework a machine part, .003 is NoT good enough.
.0005 is good for me. That is why I use a 4 jaw.

--Doozer

Start by getting the jaws as concentric as possible using the rings markings/grooves on the chuck. Then, using an indicator find the high point and mark with chalk or something easily removed later and note the T.I.R..
Then find the low spot opposite the high and undo the low jaw. Having done that revolve the chuck back to the high spot and tighten to about half your T.I.R..
Then clean your markings and repeat the process as required - this will no doubt involve adjusting the other pair of jaws as required until you achieve your required T.I.R.
Keep at it and you'll soon become very adept. Trust me, my old apprentice training foreman made us practice for at least an hour a day until he was happy with our accuracy and speed!
Regads
Mike

A suggestion:

Start without using an indicator.

Learn to rough center just by eye. This is how:

Put a pointer of sorts in the toolpost. I often
use a cutoff blade but that can dig in, so I
would suggest you start with the back end of a
toolbit.

Put a white card or piece of paper under the
workpiece, so you can easily see the gap between
your pointer and the workpiece. Illuminate the
card with a lamp and de-emphasise any lighting
that tends to illuminate the workpiece surface
itself.

The first thing you must set in your mind is
the notion that you are going to center the
work up in stages. At each stage, the tension
between the opposing jaws will be tighter and
tighter as you go along.

So to start you want to keep the tension on
the jaws pretty light.

Put your workpiece in and center it as well as
you can. Typically this means: have the jaws
positioned into the chuck body about the
same distance. If the chuck is small and the
part large, have the jaws protruding from the
body about the same distance.

Now turn the spindle and find the spot where
the distance becomes the closest to your
pointer. Bring the pointer in, using teh cross
slide, so it almost touches the workpiece. But
not quite, leave a bit of a gap visible as you
sight through to the card underneath. The
card is there to help make that gap visible,
remember.

Now turn the spindle 180 degrees, and you will
see the gap grow to just about its largest size.

Turn the spindle so adjusting screw closest to the
rear of the machine, is right at the rear. If
two screws are equidistant (ie, they were at
45 degree angles) then simply pick one at random
and put it towards the rear.

The gap got smaller just then.

Now gently slack the screw pointing towards
the front, and tighten the screw at the rear,
there by reducing the gap somewhat. The goal
here is to make it such that when you flip the
spindle 180 degrees, the gap stays the same.
So you need to guess about how much to move the
part by adjusting the pair of screws.

Important things to remember now:

1) the two axis of the part in the chuck adjust
independently, so for now only touch one pair
of screws.

2) for now keep the overall tension between
the opposed adjusting screws pretty light.

So after making your adjustment, flip the
part 180 and see if that gap is the same. If
not that make a trim adjustment so it is closer.

The gap will still be large, and you may be
tempted to move the pointer closer, but not yet.

Now turn the chuck 90 degrees and go to work
on the other axis. There will be one screw
where the gap is large, and one where it is small.
Do the same drill, if the gap is large then
you want to slack the front screw and snug the
rear one. Do this repetitively till you have
made the gap showing be nearly the same if the
spindle is turned 180 degrees.

Now is the time to bring the pointer in because
you can do so without digging it in to the
workpiece.

Repeat the adjustment process again, this time
you are working with a smaller gap and the
adjustments will be a good deal finer. At the
same time you can begin to increase the pressure
that the opposing screws extert on each other
through the workpiece.

Typically within three iterations you can
have the jaws tight and the part centered within
your error band. The last adjustments are
often done to make the part more snug, so you
don't slack one screw and tighten the other,
you simply tighten one.

Other important bits:

You want to have the centering process proceed
in a gradual fashion where the overall tension
in the screws increases as you go along.

The two axis of the chuck are to first order
independent. You do first one axis and then
the other. Then step up to a higher overall
tension level and a higher accuracy.

Dial gages tend to confuse the novice at first.
It is altogether too easy to watch the clock and
forget what is really happening to the part.
Visualizing the position of the workpiece with
respect to a fixed pointer is a way of gaining
skills at a basic level. Sort of like saying
'if you get the spares the strikes come by
themselves' in bowling.

The human eye is incredibly sensitive, using
only a white card and a pointer, it is easy to
center a part up to within five thousanths TIR
with a bit of practice.

Once the part is this close the dial gage can
be employed and brought in the rest of the way,
as close as one wishes.

Jim

Thanks all - I think my biggest problem has been too tight too soon. I get within a couple or three mils pretty quickly, but that's when I'd have it tightened, then started working opposing screws, mostly tightening to push the part half way to the middle of high and low indications and loosening when I couldn't push it any further.

Will also try without indicator, as Jim suggests... see if I can develop a feel for it. (Yeah, I still have to think a little more than I should about up/down and which way the needle turns.)

Having a couple of small chuck wrenches with knobs and an inicator that clamps on toolpost are handy.

After centering by eye put indicator on work.

Rotate work until indicator needle changes direction and set indicator to zero.

Rotate chuck more until the indicator needle changes direction again.

Note reading on indicator and turn in or out on the cross slide until you have halfed the amount on indicator.

Bring up a set of jaws horizontally and by using the two small chuck wrenches turn one in while turning the other out to get indicator on zero.

Repeat on next pair of jaws.

This should get you close to centered.
Use the regurlar wrench to tighten jaws more trying to get about the same amount of tightening on each jaw.



Indicator mount for quick change tool post can be made so it can be swiveled and used for indicating face as well.



gary

Gary, does that lathe work or do you just eat off of it. I don't recognize it but I'm still having lathe envy.

Unless you already have a hole drilled in the end of the work, you can also use this nifty little trick a guy showed me once:
Blue the end of the workpiece and scribe two centerlines with a height guage or calipers. Then line the intersection point up with a center in your tailstock. This assumes, of course, that your tailstock center is coaxial with your spindle axis ( another of those sources of error Forrest was talking about) but it really doesn't matter all that much since it's only meant to get you close anyway. Saved me alot of headache starting out.