Tightening jacobs chucks

[Sam Longley 1Participant @samlongley1]

I challenged an experienced engineer on a youtube video as to why, when tightening a Jacobs pattern chuck he placed the key in all 3 holes to tighten as in theory it was not necessary.

He replied that he could give no reason & tended to agree with me but did it out of habit

I recently challenged another engineer & he claimed that it was very necessary as each hole tightened the chuck a little more

Now bearing in mind that they would all be working in professional machine shops & using good quality chucks I feel it is a waste of time

What is the opinion of the forum – do they do it & is there a technical reason to support the habit

[Sam Longley 1Participant @samlongley1]

[Simon CollierParticipant @simoncollier74340]

I do it. Can't hurt, might help. I do the first with little more than a nip, then successively tighter on the next two. I can't justify it and I am not an engineer, but it feels right.

[Michael GilliganParticipant @michaelgilligan61133]

Sam,

There are different 'profiles' on each jaw [clearly illustrated in the repair guide], so there must be some miniscule variations in the 'action'.

… Best I can think of, so far.

MichaelG.

.

http://www.jacobschuck.com/keyed-drill-chuck-repair-guide

Edited By Michael Gilligan on 22/01/2017 09:03:33

[RobboParticipant @robbo]

Sam

Always do it, taught to do it, and it does make a difference. Same thing for the S/C 3-jaw chuck.

[Jon GibbsParticipant @jongibbs59756]

Please forgive this stupid question but…

I can see how this is practically achieved in a pillar-drill or mill, where the chuck can be easily reoriented, but what about when the chuck/arbor is rammed and locked into the lathe tailstock taper?

Do you still tighten in every position then too?

Many thanks

Jon

[Alan Waddington 2Participant @alanwaddington2]

I do it because that is how I was taught as an apprentice, back then it was best not to question "why" too much, you just accepted that those telling you to do something we're doing so for a good reason.

Maybe it comes from days gone by, when chucks were not quite as precisely made as later offerings ? Or as a method of double checking you had actually tightened it at all.

I doubt that in my 50's I'll be breaking the habit any time soon.

[John HaineParticipant @johnhaine32865]

I normally use keyless chucks but when I do use Jacobs type I find that if you "fully tighten" it on one hole you can get a bit more on the next, and on the third. I read somewhere that you should tighten on all 3 to get best concentricity.

[Neil WyattModerator @neilwyatt]

The chucks only have thee holes so one is always in a convenient place. As the force is transmitted through the same ring, surely it's just like giving a nut a couple of extra 'nips'?

So possibly the most effective way to slightly over-stress the chuck each time you use it

Neil

[Jon GibbsParticipant @jongibbs59756]

Another thought is whether the number of teeth on the bevel gear of the chuck is divisible by 3.

If it isn't divisible by 3 then there will be a slight mechanical advantage difference between the 3 holes with the same rough key orientation?

Just a thought but perhaps over-thinking it?

Jon

[Dave HalfordParticipant @davehalford22513]

My father did this and he was a war time trained engineer

[Neil WyattModerator @neilwyatt]

I wonder if anyone, anywhere has EVER made an experiment of this rather than just 'assuming' what is best?

I do imagine, though, that when applied to an apprentice it's a good way of making sure they remember to tighten the chuck properly.

[gerry maddenParticipant @gerrymadden53711]

It does make a difference ! I pondered this for a long time and then proved it 'on the job' so to speak. My standard technique is to use just one hole. But when drilling masonry where often the bit starts to slip, I would release and re-tighten up using the three holes. After this the bit would never slip again . Of course I was careful to maintain the same tightening torque on the key. But actually Its also obvious when doing this that the chuck collar does move a little further and therefore the grip in the bit must be increasing. I guess its a little bit like expecting say an end cover on a bearing housing which has three screws in it to nip-up correctly by tightening only one screw. It will just cock over due to clearances and tend to lock-up in its bore.

[gerry maddenParticipant @gerrymadden53711]

…the effectiveness of three hole tightening may also be a function of how worn out the chuck is.

[Nick HulmeParticipant @nickhulme30114]

If the ring is close fitting and clean, lubed and free moving then there might not be much advantage, if there is slack, drag, wear and dirt then using all three holes could give you a tighter hold than just one.

– Nick

[EmgeeParticipant @emgee]

All above seem valid for a drill chuck on a driling machine either fixed or hand held, especially those that have seen a lot of use.

On my lathe 3j SC I always use the same number jaw point to tighten which has proven to be the one that gives best concentricity. The T/S chuck is keyless and gets a good twist by hand to tighten before use.

Emgee

 

edited typo

Edited By Emgee on 22/01/2017 17:29:26

[oldveloParticipant @oldvelo]

Hi

An old mentor of mine insisted that we tighten a three jaw chuck using all four holes.

Try it!

Eric

[vintagengineerParticipant @vintagengineer]

Where is the fourth hole?

Posted by oldvelo on 22/01/2017 19:06:04:

Hi

An old mentor of mine insisted that we tighten a three jaw chuck using all four holes.

Try it!

Eric

[Harry WilkesParticipant @harrywilkes58467]

Posted by Robbo on 22/01/2017 09:26:42:

Sam

Always do it, taught to do it, and it does make a difference. Same thing for the S/C 3-jaw chuck.

Me too and still do it, it's become a habit !

H

[Enough!Participant @enough]

Posted by Jon Gibbs on 22/01/2017 09:34:56:

I can see how this is practically achieved in a pillar-drill or mill, where the chuck can be easily reoriented, but what about when the chuck/arbor is rammed and locked into the lathe tailstock taper?

You install it with one key-hole uppermost. The other two are then at ±120° and reasonably easy to reach. It becomes habit after a while.

(That said, I'm a bit agnostic about the "each hole" practice. I've never heard, and can't come up with convincing justification …. but it can't hurt).

[Sam Longley 1Participant @samlongley1]

deleted

Edited By Sam Longley 1 on 23/01/2017 08:37:53

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, my father taught me how it should be done, he did his apprenticeship with a reputable roller bearing manufacturer with a kinda split personality. The first thing he was told, is that they don't put three holes in the chuck for you to choose a favourite one. The way to tighten is to first nip the drill bit by hand and then starting with one of the holes, use progressive force on all three holes. In other words slightly tighten with the first hole followed by a bit more force on the next hole, which is in the direction the tightening ring revolves, and then apply the final tightening force on the third hole round. The idea being that the tightening ring has a small clearance between itself and the rest of the chuck components and the action of tightening on each hole pushes the ring slightly out of concentricity and distorts the ring very slightly, but the use of three holes in the correct manner will bring the ring to the best concentricity possible with minimum distortion. This procedure also helps prevent long term permanent distortion of the ring over many operations and puts a much more even load on each jaw. I have always used this method and if fact go round twice most times and I never get drill slip on non-abused chucks.

Regards Nick.

Edited By Nicholas Farr on 23/01/2017 08:35:22

[Ian S CParticipant @iansc]

To test the theory you would have to tighten the chuck using a torque wrench, then use a similar device to test the torque required to move the piece in the chuck, the test would require to be done a number of times in each mode(1 hole, and 3 hole), then the average for each taken.

Ian S C

Edited By Ian S C on 23/01/2017 08:43:12

[MWParticipant @mw27036]

Posted by Neil Wyatt on 22/01/2017 14:18:05:

I wonder if anyone, anywhere has EVER made an experiment of this rather than just 'assuming' what is best?

I do imagine, though, that when applied to an apprentice it's a good way of making sure they remember to tighten the chuck properly.

I do agree, this reminds me of the great hammerite debate, nobody so far has taken an old tin of hammerite and a new one and painted the same piece of metal to compare them.

You quite rightly point out that having 3 or 4 holes around a chuck is not an invitation to tighten all of them at every position. It is simply done to ensure that you can have nearby access for the key at any point of it's circumference, or perhaps to overcome an obstruction to your hand.

The purpose of a drill chuck is to simply clutch a drill with a reasonable amount of strength over a variable range of sizes. The rack form on the scroll only needs to be tightened once with the chuck key, tightening it beyond that will offer no benefit. And like you said earlier, probably induce unnecessary stress on the chuck.

This is almost as logical as saying that because a hexagon nut has 6 flats that you must tighten on all 6 faces with a spanner.

Michael W

 

Edited By Michael-w on 23/01/2017 09:07:29

[Neil LickfoldParticipant @neillickfold44316]

In my experience, a new or a chuck in good condition, only requires tightening on any one position. Older chucks that are near f—ed need to be done up on the other hole settings as the ring just flops around and does not tighten properly. I have seen on old chucks where you use 2 keys at the same time gives great repeat ability. In reality, if the chuck is like that, throw it away and buy a new one. Some people like wasting time and think they are saving money in the process.

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