Centring in a 4-Jaw Chuck

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Gordon

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Gordon, You don't have to wind the indicator back each time, just put the indicator on the tool post and move it. It's easier to move the carriage. Then rock the chuck to find the low spot, or rock the chuck to indicate off the corners.
I have an indicator which I can mount in my tool post but when I move the carriage I have to move the plunger back by hand in order to get it back into position. Being a clumsy oaf I end up moving something during this process.
 

goldstar31

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So what happens when the raw piece of metal is not a regular plane figure- in other words literally a lump where a centre has to be picked up? I've a couple of spring loaded 'wobblers' in my tool kit for such eventualities. Again made to the George Thomas designs . I never quite fancied the old 'Sticky Pin' method with the use of a child's modelling clay.
Ah Yes!


Norm
 

Cogsy

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So what happens when the raw piece of metal is not a regular plane figure- in other words literally a lump where a centre has to be picked up?
I use math for instances like this. Measure to determine the point that need centering relative to the surface of the material and determine the offset required, then indicate as normal but instead of aiming for a 'zero' reading between the two sides I'm looking for the correct offset (hopefully in the correct direction if I've been paying attention). Then I check it visually with a dead centre in the tailstock simply to confirm my process/math. I know my eyes can't tell if it's a couple of thou out but I figure if I've made a math or directional error it's going to result in a large, visible error.
 

goldstar31

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I confess to being lazy so with a wobbler of sufficient length, the error is greatly magnified.

As it's a time for confessions, I never thought of doing it by maths- so thank you

Regards

Norm
 

Noel Gordon

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Hi All,, It would seem that ALL pro machinist abhor the thought of using 2 keys but hobby machinists think it a good idea.. Just a thought for you all,just think what it would do to you if you forgot the back key what would happen when you hit the start button on a lathe with a 10 feet dia chuck !!! think about REAL carefully I have personally seen the results of a dumbo doing this and its NOT nice to have to clean up the resulting mess.. Just a final comment from me..it dosent matter if it 10' or 4 inch it will still hurt like all hell if the key catches you..
 

ALEX1952

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In reply to Cogsy you are quoting two different opinions mine is the one in bold type the other is from Noel Gordon, however I completely agree with his comment regarding chuck safety, even for a small machine it is bad practice which will eventually become normal. The potential for serious injury is unthinkable, if you do it in your own shop you will probably get away with it as the key nearest to you will invariably go up and over the back the rearmost will go down and probably stall the machine. Why do you think some manufacturers of lathes, chucks etc put a spring on their keys yes it is a safe guard which most people remove because its a pain but but mainly it is because they recognize the danger and do this to avoid a law suit. Also don't work over a chuck and if you must, isolate the machine, you may not turn it on but somebody else might, some machines are operated from the saddle by a lever which can easily be nudged the one that springs to mind is Colchester Student which will be found in many a hobbyists shop.
 

Andy Munns

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School metal shops teachers will growl at students for parking keys in chucks. Students and apprentices are taught never to do this and that the chuck key must always be held, or rested in the chip tray. There have been many case examples of broken or injured hands, etc. plus broken windows, holes in ceilings, etc. My navy mate describes in detail the serious punishment he received when as an apprentice artificer/stoker he parked a chuck key in the chuck.
 

kuhncw

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Hi All,, It would seem that ALL pro machinist abhor the thought of using 2 keys but hobby machinists think it a good idea.. Just a thought for you all,just think what it would do to you if you forgot the back key what would happen when you hit the start button on a lathe with a 10 feet dia chuck !!! think about REAL carefully I have personally seen the results of a dumbo doing this and its NOT nice to have to clean up the resulting mess.. Just a final comment from me..it dosent matter if it 10' or 4 inch it will still hurt like all hell if the key catches you..
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Noel, when I use two keys (or one key), the key comes with my hand when I pull my hand away. I certainly agree that a key left in a chuck is dangerous.

I also understand why using two keys in a chuck large enough such that you cannot not hold both keys at the same time would be extremely dangerous.

Regards,

Chuck
 

Cogsy

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I don't see the issue here at all - as I said clearly, and Chuck is also saying, is that we never let go of a chuck key when it's in the chuck. This method means you will never have a chuck key ejected from the chuck if it's accidentally overlooked. It seems the pro machinists are in the habit of taking their hands off a chuck key while it's still in place. I caught Joe Pie doing this in one of his early videos - several people mentioned it in several videos and he issued the challenge to point to a time stamp where the chuck key was visibly in the chuck with no hand on it. When I pointed out such a time stamp he responded with something like "a bit harsh, it was only for a couple of seconds and my hand was never more than 6 inches away". You can decide if it was harsh or not. I notice in his later videos the chuck key is usually not visible at all (I think Joe is great by the way). It seems that old adage is true - familiarity breeds contempt. We hobbyists who don't spend 40+ hours a week, every week, in front of our machines are more rigorous about chuck key safety than the 'pros'.

Also, I never work 'over' a chuck. As my dial indicator is mounted on the cross slide, it reads the top surface of the workpiece. So the keys are used top and bottom of the chuck, I'm certainly not straddling it. My lathes are also not the type with a clutch where the lathe can be kicked into gear by a lever unexpectedly, they require a button push from the operator. So again, I don't see the problem (unless you're a pro who leaves chuck keys in place without a hand on them ;)).
 
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School metal shops teachers will growl at students for parking keys in chucks. Students and apprentices are taught never to do this and that the chuck key must always be held, or rested in the chip tray. There have been many case examples of broken or injured hands, etc. plus broken windows, holes in ceilings, etc. My navy mate describes in detail the serious punishment he received when as an apprentice artificer/stoker he parked a chuck key in the chuck.
8th grade metal shop...we were going to work on the lathe! One kid had been bragging all week how good he would do, because his dad was a patternmaker. Not sure why he felt that would impart any special powers to him...but...

He, of course, was the one that started the lathe with the key still in the chuck. It slammed the key into the bed and stopped. In a panic he reached for the stop button and hit...reverse! Slam! in the other direction.

Fortunately, it never left the chuck.
 

tornitore45

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Hi All,, It would seem that ALL pro machinist abhor the thought of using 2 keys
Yap, I have seen several Video of professional that I respect but can beat them with my two keys method. Turn slack, turn tight, too much, turn slack, turn tight, almost there, turn slack, turn tight and so on.

As for the key in the chuck. I leave it all the times. Is not that is parked there for an extended time, but in the same operating frame of centering or swapping out a part is no big deal. Way would I start the lathe if centering and tightening the part was not completed. My lathe can not be started accidentally. Even that argument has limitations. If it is possible to "bump" a lever and start the lathe then it can happen while the key is in your hand and inside the chuck.
Rather than worry about being absent minded (I am not) I would worry about a lathe that can be started accidentally moving a lever.
When I was in 8th grade I worked on a Grazioli-Fortuna. The motor was always running and you started the chuck with a lever at your left.
 

110samec

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Of course the chuck key left in the chuck predicament can be solved with one of those chuck keys with the spring on them, making it impossible for them to be left in the chuck
 

nealeb

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First thing I've always done on getting a chuck with one of those "safe" keys is take the d****d spring off it! And that's before I've tried using it to centre work in a 4-jaw...
 

110samec

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First thing I've always done on getting a chuck with one of those "safe" keys is take the d****d spring off it! And that's before I've tried using it to centre work in a 4-jaw...
They are annoying, however you will never leave one in a chuck even accidentally
 

goldstar31

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Today is a time of litigation. I'm not sitting in judgement one way or another but if a spring is removed from a chuck key and there is an accident, who is responsible? The employer has in goof faith and care for his employees tried to ensure their safety. The onus, it seems will fall upon whoever took the matter into their own hands. It suggests that a claim can be made and if proven, the perpetrator will feel the 'Majesty of the Law'

Again, the person who sets an apprentice to clean floors instead of learning a trade is denying the apprentice his agreed opportunities for a rightful living.

I'm in a midst of something 'interesting' and wittingly or unwittingly, my affairs are a matter for the police i the first instance.

There you are- your homework for the weekend:D

Norm
 

Dubi

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Today is a time of litigation. I'm not sitting in judgement one way or another but if a spring is removed from a chuck key and there is an accident, who is responsible? The employer has in goof faith and care for his employees tried to ensure their safety. The onus, it seems will fall upon whoever took the matter into their own hands. It suggests that a claim can be made and if proven, the perpetrator will feel the 'Majesty of the Law'

Again, the person who sets an apprentice to clean floors instead of learning a trade is denying the apprentice his agreed opportunities for a rightful living.

I'm in a midst of something 'interesting' and wittingly or unwittingly, my affairs are a matter for the police i the first instance.

There you are- your homework for the weekend:D

Norm
In my shop if you leave a key in the chuck you are fired. Very simple and plain to understand.
 

nealeb

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Today is a time of litigation. I'm not sitting in judgement one way or another but if a spring is removed from a chuck key and there is an accident, who is responsible? The employer has in goof faith and care for his employees tried to ensure their safety. The onus, it seems will fall upon whoever took the matter into their own hands. It suggests that a claim can be made and if proven, the perpetrator will feel the 'Majesty of the Law'
In my single-user home workshop, no-one to sue but myself! Have to agree that things are different otherwise. However, I first took a spring off a chuck key when I found the spring so strong that I seriously risked eventually rounding the key or the key "hole" as it was so difficult to keep it engaged when tightening. Would have made fine control of the key for centring difficult as well - although the spring didn't last long enough for me to find out! Still, I'm a "single-key and hold it in my hand" user, and while two keys in a 4-jaw might make centring quicker, I doubt if it would make that much difference. Like, for example, when aligning a machine vice using DTI and soft hammer, you get a feel for how big a correction you need to allow for retightening the other side. I do like the idea of rubber-banding four slips to the faces of a rectangular piece of work, though. That one goes in the "remember for the future" category.
 

KellisRJ

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On chuck keys. I read about this on a forum, and knowing my own limitations, made one too. A key hook with a proximity switch. If the key isn't in the hook, the lathe won't run.
 

Gordon

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On chuck keys. I read about this on a forum, and knowing my own limitations, made one too. A key hook with a proximity switch. If the key isn't in the hook, the lathe won't run.
The problem with that is that I have several chucks. 4" , 8", three jaw, four jaw, collect etc and each one has a different size chuck wrench.
 
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