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Tightening jacobs chucks

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Sam Longley 122/01/2017 08:10:34
918 forum posts
34 photos

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

Simon Collier22/01/2017 08:56:18
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448 forum posts
63 photos

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 Gilligan22/01/2017 09:03:01
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19601 forum posts
997 photos

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

Robbo22/01/2017 09:26:42
1504 forum posts
142 photos

Sam

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

Jon Gibbs22/01/2017 09:34:56
739 forum posts

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 222/01/2017 09:36:43
523 forum posts
87 photos

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 Haine22/01/2017 09:36:48
4428 forum posts
264 photos

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 Wyatt22/01/2017 09:40:30
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Moderator
18899 forum posts
734 photos
80 articles

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 Gibbs22/01/2017 09:58:54
739 forum posts

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 Halford22/01/2017 12:23:02
1890 forum posts
22 photos

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

Neil Wyatt22/01/2017 14:18:05
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18899 forum posts
734 photos
80 articles

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 madden22/01/2017 14:51:17
227 forum posts
119 photos

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 madden22/01/2017 15:03:46
227 forum posts
119 photos

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

Nick Hulme22/01/2017 15:25:20
750 forum posts
37 photos

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

Emgee22/01/2017 17:28:14
2315 forum posts
277 photos

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

oldvelo22/01/2017 19:06:04
280 forum posts
54 photos

Hi

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

Try it!

Eric

vintagengineer22/01/2017 20:56:17
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468 forum posts
6 photos

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 Wilkes22/01/2017 21:21:35
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1265 forum posts
64 photos

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!23/01/2017 01:05:31
1719 forum posts
1 photos
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 123/01/2017 08:30:35
918 forum posts
34 photos

deleted

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

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