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Quickly Aligning A Four Jaw Lathe Chuck

randyc

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#1
Many new hobbyists seem to have little use for this type of work holder, preferring devices that tend to self-align, like a three jaw chuck or some form of collet system.

A typical 4-jaw alignment experience might go like this:

  • Work is installed in chuck and the jaws tightened loosely while visually centering the work
  • Chuck is rotated by hand, checking work eccentricity with DTI and adjusting as required
  • Repeat , over and over and over and …

Does that seem about right ? OK, that procedure will get shorter and shorter with practice but it can be improved considerably with just one simple change:
  • Make another chuck key.
I didn’t take any photos when I made the small chuck key shown at lower right but making the tool is a simple process. The exterior features are not critical but the same square interface dimensions as the original chuck key are obviously required. The part is blued using my normal hillbilly process: position the parts over the gas burners on the kitchen stove and dunk ‘em in used motor oil when the correct color has been reached.

P1040996_zpsmk3xbcvt.jpg

For initial alignment in a four jaw chuck, I prefer a travel indicator rather than a DTI. This is because the run-out of the work piece is likely to be excessive, at least initially, and would probably exceed the travel limits of a typical DTI.

This one is permanently mounted to a magnetic stand and is parked on the back of the lathe taper attachment when not required.

P1050009_zpspnatvjgr.jpg

At this point, for safety sake, disengage the drive system of the machine by loosening the belt drive or placing the spindle drive in neutral. In this old Sheldon, lifting the lever loosens the belt as can be seen in the photo.

P1050003_zps6ys0gxnp.jpg

Rotate the chuck (and work piece, of course) so that one of the jaws is aligned with the travel indicator. With the spindle of the travel indicator touching the center line of the work piece, note the reading (or zero the reading). Rotate the chuck 180 degrees and note the reading.

2015-04-12_zpspylagy8k.jpg

Insert the two chuck keys in the near and far side adjustment screws. NOTE: This is a posed photo with the lathe drive train disconnected. NEVER leave a chuck key in a lathe chuck. If the key is in the chuck it needs to have a hand attached to it !

P1050004_zpshjczpyri.jpg

Using the two chuck keys, one to loosen and one to tighten, watch the indicator while gently adjusting the chuck keys until the work is moved ONE-HALF of the error previously noted.

Rotate the chuck ¼ of a turn so that the other two jaws are now aligned with the indicator axis. Note the indicator reading then rotate the chuck 180 degrees and determine the difference between the highest indicator and the lowest one.

Using both chuck keys, tightening and loosening simultaneously, move the work one-half of the error distance.

Repeat this one or two more times until the run-out is about .001 or .002. At this point, we need to do some tightening to secure the work in the chuck. Continue the process of rotating the chuck, checking the run-out and then rotating 180 degrees and correcting by one-half of the small error.

You might try using only one chuck key to “push” the work away from the high point of the run-out. Do this a couple of times and the result should be a tightly secured work piece with minimal run-out.

OK, so the work is centered at the location of the indicator, near the chuck, but it’s highly unlikely to be centered along the entire length. Typically the next step is to move the indicator near the end of the work. Rotate the work until the high point is found.

P1050006_zpsu3kvrs2a.jpg

Move the indicator off of the work then lightly tap the high point of the work piece with a soft-faced hammer. Check the run-out and repeat the process as required.

P1050007_zpsdx0nprhr.jpg

When the run-out is within desired limits, carefully drill a center hole and then use the tailstock center to keep the work properly aligned with minimum run-out.

P1050008_zpsg5dtrtno.jpg

If for some reason it’s not practical to center drill the end of the part, a steady rest can provide the support required to keep the work aligned.

This simple process can reduce the time required to align a 4-jaw chuck from minutes to seconds. When I aligned the test bar for the above photos, I timed the alignment process. It took less than one minute to align the bar to within .001 !
 

kd4gij

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#2
I have been using 2 keys on my lathe at home for about 10 years. The 4 jaw I use at work every day is 20"dia. My arms arn't long enough to reach around it and the work.:D
 

randyc

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#3
I have been using 2 keys on my lathe at home for about 10 years. The 4 jaw I use at work every day is 20"dia. My arms arn't long enough to reach around it and the work.:D
I don't recall when I started using two chuck keys, it's been a few years but definitely not 10 years ... maybe we read the same suggestion on another forum ?

Fortunately, most of us won't experience your problem of reaching around a 20 inch chuck since this is a hobby machinist forum, right ? (My shop slab couldn't possibly even support a lathe of that size, LOL !)
 

darkzero

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#4
The 4 jaw I use at work every day is 20"dia. My arms arn't long enough to reach around it and the work.:D
20" chuck, well shoot, then the lathe should be large enough that you could just lay on the bed, after all it is a "bed", then you could use 2 keys. And by laying on the bed, you could also get close up to the workpiece, close one eye & eyeball that sucker to get dead nuts. ;) I would love to see the look on you're boss' face if he caught you doing that! :big grin:


Rotate the chuck (and work piece, of course) so that one of the jaws is aligned with the travel indicator.
When I first started using the 4-jaw I use to chase that sucker around for days cause I was chasing the absolute highs & lows. And if it was round stock that wasn't very concentric it would be weeks. Well I didn't know any better then & I had no one around to teach me. Then one day it dawned on me, just tighten the highs at each jaw, moving half the difference of what the opposing jaw indicated. I was no longer afraid to use the 4-jaw anymore & like using it. I still only use one key though.

I prefer to use just a dial indicator for indicating the 4-jaw too. If I get down to 1/2 thou or less it's good enough for me. I haven't needed to dial something with accuracy better than that so I never use a DTI for that.
 

Bill C.

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#5
The 20" diameter sounds like the 36" vertical one I ran sometimes as a operator after high-school. That old Bullard model might fit in the average size garage. For its size I recall it spin pretty easily when in neutral position.
 

randyc

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#6
The 20" diameter sounds like the 36" vertical one I ran sometimes as a operator after high-school. That old Bullard model might fit in the average size garage. For its size I recall it spin pretty easily when in neutral position.
That brings back some memories ! Those Bullards are very cool (unfortunately I never even got to touch the controls on one) ! When I worked at Westinghouse, there was a line of those "small" Bullards in one building and that line of machines must have been 100 yards long !
 

Bill C.

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#8
That brings back some memories ! Those Bullards are very cool (unfortunately I never even got to touch the controls on one) ! When I worked at Westinghouse, there was a line of those "small" Bullards in one building and that line of machines must have been 100 yards long !
I should say I only used it for one project. The shop had the job of making forging dies for the old International Harvester plant in Louisville. They assigned me the job of roughing the forged blanks of steel into useful mold sections for the lathe machinist. The shop had a hydraulic controlled tracing lathe that he used. I remember breaking many cemented carbide tool bites. I could never talk and run a machine without problems back then. I was in my teens. That was the only time. That old machine wasn't used much to begin with but I did like it. Those were the days.
 

smoa

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#9
I honestly never even thought about two chuck wrenches, and I've dialed in thousands of parts. One important note, Never take your hand off the chuck wrench when in use. I know this was probably just done for the picture, but I think a note should be added. I've seen some nasty gouges in ways due to the chuck wrench being left in, not to mention some stiches in side of one lucky apprentices head (lucky it wasn't worse).
Bryan
 

David S

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#10
For anything over 13 mm diameter, I only have a 4 jaw independent, and have always used two keys. But for most stuff I don't use an indicator but rather just place my tool holder loose in the QCTP rotate the chuck backwards and ease the tool in to the close spot then proceed to rotate and split the difference. I can get pretty close quickly for most stuff that I start turning from scratch.

David
 

Bill C.

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#11
I honestly never even thought about two chuck wrenches, and I've dialed in thousands of parts. One important note, Never take your hand off the chuck wrench when in use. I know this was probably just done for the picture, but I think a note should be added. I've seen some nasty gouges in ways due to the chuck wrench being left in, not to mention some stiches in side of one lucky apprentices head (lucky it wasn't worse).
Bryan

Bryan,

I never, knew anyone I worked with that, used two wrenches. Also noticed the stock hanging out further than I was taught.
 

darkzero

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#12
No need to police this one guys. If you have seen Randy's other informational threads you will know he is not a rookie. :)

The reason the stock is hanging out so far is he is showing how to dial in a part that would need to be supported with a center. After dialing in the stock at the chuck side & tailstock side you can then carefully center drill it even though stock may be hanging out much further than it's supposed to for that. If the stock is not stout enough and/or the situation does not allow, as Randy mentioned, a steady rest can be used for support to center drill. Sure there's other ways of doing this but this method is not uncommon.
 

Andre

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#13
For average 4 jaw work I'll get it centered by eye then bring the cutter up to the work, maybe .010' from the high spot. When you see the work get close to the cutter you know the high spot. Can get it dialed in within maybe 3 thou that way.
 

randyc

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#14
...One important note, Never take your hand off the chuck wrench when in use. I know this was probably just done for the picture, but I think a note should be added...
Bryan, take another look at the post, I even italicized the cautionary note for emphasis :)

...Insert the two chuck keys in the near and far side adjustment screws. NOTE: This is a posed photo with the lathe drive train disconnected. NEVER leave a chuck key in a lathe chuck. If the key is in the chuck it needs to have a hand attached to it !
 

schor

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#15
I've used the 2 key method, but I like abom79's method. You need to do it 1000 times and you don't need 2 keys. I think I've done it 20, so I have a ways to go yet.
 

randyc

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#16
I've used the 2 key method, but I like abom79's method. You need to do it 1000 times and you don't need 2 keys. I think I've done it 20, so I have a ways to go yet.
I always like learning new methods ! My eyes aren't as good as they once were ... I can't locate a post from abom79. Can you point me in the right direction :)
 

randyc

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#19
I think I saw an article (maybe in Home Shop Machinist) where the author made a couple of chuck keys with round handles for centering in a 4-jaw.
GREAT idea - would speed things up even more !
 

JimDawson

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#20
Thanks Jim. I was expecting to learn something new but I think that post describes the method most of us have always used.
That's pretty much the way I have always done it for about the last 50 years or so. :)
 

darkzero

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#21
In regards to Abom79. There's no special technique that he uses. It's just the fact he's so good at it that makes him so quick at doing it in front of your eyes. Adam is one of the Youtube machining guys. You won't find posts here about it, although he happens to be a member here but really doesn't come here much. You have to watch his channel to know what he's about.
 

mksj

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#22
Also use the twin key method for adjusting a Bison 4 jaw combination chuck (Scroll + Independent). Made two keys for the independent jaws with magnets in the end. The magnets keep the keys in place when turning/adjusting and checking the run out. The combination chuck is a bit quicker to set up then a independent, I set all 4 jaws to a fixed stop/position, then scroll down onto the piece. Check run-out with a dial indicator, and tweak the centering using both keys at once on opposite jaws. Scroll feature of the combination allows doing repeat pieces quickly, and with very little variance (but I still recheck). I am pretty compulsive of not leaving the keys in the chuck at any time other than when I have my hands on the chuck to adjust it, even if it is to get something else, I remove the key(s).

The combination chuck also works great for square/rectangular stock. Really liking this chuck the more I use it.


Bison 4 Jaw combination chuck.jpg
 

randyc

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#23
The magnets are a very clever idea but I'm not envisioning where they are located and how they are secured. Any chance of posting a photo with a brief "how to" description ? Thanks and that's a very pretty chuck !
 

mksj

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#24
I bored a 6mm x 1.5mm deep hole in the end of the key with an end mill. Used a bit of metal bonding epoxy to secure a 6mm x 1.5mm Neodymium magnet in the end. Picture of the new keys with magnets and original key. Much easier to setup with the dual keys, and I do not have problems with the keys falling out when I turn the chuck to check the alignment. The keys are not that heavy and the Neodymium magnets can be quite strong when in direct contact with ferrous metals. The applied hand torque is similar and more even/balanced than the original key, it is also possible to torque the new keys evenly using the square end of each key (fits a 5/8" 12 point socket).

Like the designing "Vacuum Tube Amplifiers"... Have lots of tubes and run some Cary 805AE amps with modified Quad electrostatic speakers, too chicken to build anything running a 1000+volts.

Bison combination chuck keys with magnets.jpg
 

randyc

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#25
Many thanks, it's very clear and again a very clever idea which I intend to steal :)

Glad that you liked my book; I designed all of my high-voltage supplies and they are limited to 450 volts. At one of my previous employers, we used a HUGE vacuum tube amplifier to drive a 500 pound vibration table up to 20g acceleration. The amplifier made the lights dim when the plate supply was enabled and the 400 SF room would heat up about 10 degrees F in the fifteen minutes or so required to make a vibration run. I often wondered about the courageous tech that serviced that amplifier.

At the other extreme is this little dual triode that I intend to use as a preamplifier for the piezoelectric transducer shown beside it. This will be used on an old Gibson J-55 guitar. The preamplifier will be built into the guitar cable as a small module very near the guitar jack to minimize high-frequency attenuation from cable length. Note that the vacuum tube is smaller than the guitar jack.

P1040401_zpsdd1bc2a7.jpg
 
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randyc

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#26
...Much easier to setup with the dual keys, and I do not have problems with the keys falling out when I turn the chuck to check the alignment. The keys are not that heavy and the Neodymium magnets can be quite strong when in direct contact with ferrous metals...[/ATTACH]
A final question: is the body of your chuck keys non-magnetic (i.e. titanium alloy) ?
 

taycat

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#27
cheers for that.
put my 4 jaw on this morning just to try it. although had to cut bit of plate to use as only one key.
what a difference.
now ordered spare key.
 

mksj

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#28
The keys are aluminum alloy and stainless T bar held in with a set screw, just what I had on hand. But could also use steel. I can use much shorter keys because the independent jaw adjustments move with the scroll, an independent only chuck would need longer keys. Once set, the repeatability with the combination chuck is quite good, but I still verify TIR as small variances in jaw pressure or material size can change the center. Yet, one can zero the piece very quickly with the dual keys.:D
 

BoliverShagnasti

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#29
I started with the 3 jaw chuck and it was about .005 off from the beginning. Not bad for most of what I was doing, but for precise work, every time you re chuck you add the concentric errors.
I would mark the work to fit it to the chuck for return cuts and use the indicator to get it back. But the part held in the chuck is centered different than the part of the work I just cut.
You can also use a homemade lathe center with dog and cut it each time you use it.

Once I started using the 4 jaw, I will never go back to the three jaw. The 3 jaw is more work to maintain concentric parts.
It seems like it would be less work; but if you want precision, you have to work around the reality of this design.

When doing production parts, you can turn two of the jaws out the same number of turns (or half turn or whatever is required), to release the part.
Then put the next part in and turn them down the same number of turns, then dial it in fast.

I have one key now and have been looking for a second.

Just some thoughts.
 
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Chrisvn

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#30
I have made this tool to make the alignment quicker, especially on non-round material, but it also works well on round stock. The hardened tip is spring-loaded to compensate for the change in length as you get closer to the center. The tail is made from 6mm mild steel and is about 250mm long and the square portion is 12mm key steel. The tail allows for quite a lot of flex to swing with the material out of center. The tail is just clamped in a chuck in the tailstock with the spring-loaded tip put in a punch pop mark in the material. This mark can be in the center or out of center if you want to turn eccentric. The square head allows for a nice flat surface to locate the DTI on. Works like a charm. Initially, you do not even need a DTI to get it close, you can just eyeball it.

center_tool.jpeg
 
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