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Old 03-05-2010, 03:20 PM   #1
A_Pmech
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Default How To: Remove a Jacobs chuck arbor

I recently bought a Jacobs #18N 3/4" chuck with a #4 Morse Taper arbor. For my application I'll need to use the chuck with both the existing #4 Morse Taper arbor and a 3/4" straight shank arbor.

Here's the chuck when I bought it with a #4 Morse Taper arbor installed. The smaller chuck to the right is a 1/2" Jacobs with a #2 Morse Taper arbor installed:



To give an idea of scale, here it is next to a standard 1/2" Jacobs economy drill chuck:



What is a Jacobs Taper?

Before I get into removing the shank, I'll start by explaining just what a Jacobs taper is.

Basically, there are two standards for fixing drill chucks to the drilling machine. The first type of chuck is called a "threaded back" chuck. These are often used on hand drills and small import drill presses. The back of the chuck is threaded, usually 3/8 - 24 or 1/2 - 20 although other standards exist. The chuck screws onto the driving shaft and seats against a shoulder. As the drill spins, the chuck is tightened further onto the shoulder.

Here's an example of a 1/4" Jacobs chuck partially unscrewed from a shop-made arbor:



The threaded back chuck has two drawbacks:

1) The thread does not accurately locate the chuck concentric to the axis of the driving shaft.

2) A threaded chuck cannot operate in reverse, the chuck would simply screw off the shaft.

These drawbacks are solved by the Jacobs Taper. Like the Morse Taper, the Jacobs Taper is a type of self-holding machine taper. Although similar in dimensions to the Morse stub taper, the Jacobs Taper is proprietary to the Jacobs company. Due to geometric advantages, self-holding machine tapers accurately center themselves into their mating socket. They resist torque and disassembly by elastically deforming the socket when assembled, causing the female socket to tightly grip the male taper. Friction alone holds the two together in semi-permanent assembly. Axial thrust only increases their holding power.

Unfortunately, what makes them accurate can also make them hard to disassemble!

The usual method for removing a Jacobs chuck from it's arbor, a drill motor or drill press quill is the Jacobs Removal Wedge. Two wedges are placed between the arbor and the chuck and driven together with a hammer or a bench vise. However, this particular arbor and chuck combination does not lend to this approach as there is very little shoulder on the Morse Taper for the wedges to bear on. Even with a sufficient shoulder, the wedges can be difficult to use in the best of times.

This Jacobs company illustration shows how they are used:

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Quote:
Originally Posted by Sir Stanley Hooker
One stroke to produce power and three strokes to wear it out.

Last edited by A_Pmech; 03-05-2010 at 03:51 PM.
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Old 03-05-2010, 03:34 PM   #2
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Default Re: How To: Remove a Jacobs chuck arbor

i have no answer for you but thats the biggest chuck i've ever seen! totally awesome. what are you using it for?
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Old 03-05-2010, 03:45 PM   #3
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Default Re: How To: Remove a Jacobs chuck arbor

Good explanation. This is the kind of stuff I really need to know. Please continue!
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Old 03-05-2010, 03:47 PM   #4
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Default Re: How To: Remove a Jacobs chuck arbor

For this chuck, I decided to use another method Jacobs suggests, drilling the chuck body and pressing the arbor out.

Drilling the Body

I began by chucking the drill up in the lathe, using brass stock to protect the ring from damage. Then, using a 29/64 drill I drilled though the back of the chuck and into the arbor space:



You can see the leading edge of the Jacobs taper through the hole in the back of the chuck body:



With access to the leading edge of the Jacobs taper, I drilled it 1.5" deep with a 3/8" drill. This may release some of the holding force of the taper, but it also places the pressing force at the back of the arbor rather than the front.

When compressive forces are applied to an object, it tends to enlarge in the unconstrained directions. Whereas, when a tensile force is placed on an object, it tends to cause the object to "neck". The 3/8" hole places the pressing force near the end of the taper, "pulling" the leading edge of the taper out and causing it to "neck" slightly. This can aid removal:



Here you can see the hole in the arbor:



Pressing out the #4 Morse Taper arbor

I located a piece of pipe slightly larger than the OD of the #4 Morse Taper arbor and a couple inches longer. I placed it over the arbor so that it would bear on the chuck body.

Then, I took a 3/8" bolt and ran it down though the chuck body and through the 3/8" hole drilled in the arbor. I gently closed the chuck jaws on the bolt and placed the whole assembly in the press:



After a few pumps with the handle, the arbor and chuck separated with a BANG! I'll try to upload the video later.

The separated chuck and arbor:



Assembling With the New 3/4" Straight Shank Arbor

After cleaning the mating taper surfaces I retracted the chuck jaws and placed the chuck body on a piece of scrap aluminum on the concrete floor. Then, I placed the new arbor in the chuck and gave it a couple sharp blows with a soft faced hammer.

It is important that the taper be seated firmly, otherwise it could spin and gall the mating surfaces. Per Jacobs' instructions, DO NOT press the two together in any kind of a press as it will permanently lock the taper and may distort the chuck body:



Here's the result!



There's been some discussion about removing chucks here on GJ and I thought my experience would prove useful to others.

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Quote:
Originally Posted by Sir Stanley Hooker
One stroke to produce power and three strokes to wear it out.

Last edited by A_Pmech; 03-05-2010 at 03:55 PM.
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Old 03-05-2010, 04:02 PM   #5
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Default Re: How To: Remove a Jacobs chuck arbor

If you are taking requests, I'd like to know how to disassemble a Jacobs chuck. I have one of my grandfather's I'd like to rehabilitate and use in my mill, but it "sticks." Thought it just pressed apart but no luck so far.
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Old 03-05-2010, 04:05 PM   #6
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Default Re: How To: Remove a Jacobs chuck arbor

A Pmech,

Can you reuse the #4 arbor after it has been drilled? If so, will it be much more difficult to press it out the second time around?

Thank you for the excellent tutorial.
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Old 03-05-2010, 04:07 PM   #7
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Default Re: How To: Remove a Jacobs chuck arbor

If you google "jacobs chuck" disassembly or "jacobs chuck disassembly" you'll get multiple sites with instructions. There are also removal sites. Don't personally know if any of them are worth anything.
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Old 03-05-2010, 04:18 PM   #8
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Default Re: How To: Remove a Jacobs chuck arbor

Quote:
Originally Posted by emeraldcoupe
i have no answer for you but thats the biggest chuck i've ever seen! totally awesome. what are you using it for?
It's a good size, that's for sure. It will replace the small 1/2" chuck that was used to drill it out. The straight shank arbor allows me to use it on the carriage and the #4 Morse Taper arbor allows me to use it in the tailstock of the lathe.

Eventually, I'll buy another 18N and then I can avoid swapping arbors all the time.

Quote:
Originally Posted by Bolster View Post
If you are taking requests, I'd like to know how to disassemble a Jacobs chuck. I have one of my grandfather's I'd like to rehabilitate and use in my mill, but it "sticks." Thought it just pressed apart but no luck so far.
Hi Bolster,

Have a look here for Jacobs chuck servicing instructions:

http://www.jacobschuck.com/pdf/s2.pdf

If I come across a chuck in need of repair, I'll be happy to post up when I do the repair. However, the 18N I just worked on is essentially brand new so I'm in no hurry to take it all apart just yet.

Quote:
Originally Posted by balrog
A Pmech,

Can you reuse the #4 arbor after it has been drilled? If so, will it be much more difficult to press it out the second time around?

Thank you for the excellent tutorial.
Certainly. It should come out just as easily the second time, so long as it is seated only with a hammer. Easily being relative, of course. I would say it took in the neighborhood of 5-10 tons to force the arbor out.

You're welcome!

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Quote:
Originally Posted by Sir Stanley Hooker
One stroke to produce power and three strokes to wear it out.
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Old 03-05-2010, 05:05 PM   #9
Charles (in GA)
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Default Re: How To: Remove a Jacobs chuck arbor

I bought a nice used 18N on a #3 morse taper arbor to replace the smaller (about 5/8" chuck and arbor) in my Grainger/Dayton drill press. The chuck did not run true (typical drill bit had 3 to 4 thousand wobble in it) and I was not able to separate it, finally gave up before I got stupid and damaged it.

Took it to work and gave it to the foreman of the machine shop and it was handed back to me in two hours, running true within a half a thousandth.

They dipped the arbor end in liquid nitrogen which caused it to rapidly shrink and the chuck came right off. They then cleaned the tapers, checked the arbor alone in their equipment and found it dead on, and reinstalled the chuck squarely.

Most drill presses with a Morse taper in the quill have a slot for a drill press "drill drift"

http://www.grainger.com/Grainger/items/4H102?Pid=search

http://www.grainger.com/Grainger/items/4H100?Pid=search



and this is how you remove the chuck and arbor as a unit (or the arbor alone) from the quill of the drill press. Arbors are inexpensive, chucks are not really that bad, keep one for every purpose, already set up and checked for trueness.

Charles
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Old 03-06-2010, 10:02 AM   #10
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Default Re: How To: Remove a Jacobs chuck arbor

Charles,

I tried liquid nitrogen alone and it wouldn't budge! I figured if I ran out of tonnage on the press I'd bathe the arbor in liquid nitrogen and try again. Fortunately, it wasn't THAT stuck.

Now that I have the chuck drilled it shouldn't take more than a couple minutes to swap arbors when the occasion arises but a 20N and a few more 14N's are planned.

In my experience, the usual cause of a self-holding taper running out is a burr in the socket or on the male taper and/or swarf between the two. Needless to say, it's important to religiously clean the two before mating!

Good addition on the drill drifts, I forgot to discuss those!





Video

As promised, here's the video of the press operation. Unfortunately, I made the mistake of taking the video "sideways" to capture the whole thing from close-in.

So, turn your head sideways and watch it here:

http://www.youtube.com/watch?v=Ws9SpERvFj8
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Quote:
Originally Posted by Sir Stanley Hooker
One stroke to produce power and three strokes to wear it out.
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Old 03-06-2010, 11:21 AM   #11
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Default Re: How To: Remove a Jacobs chuck arbor

very nice info..... this is one of those things that i've often wondered while working on some things, but never remembered to do any research. Now i may have to take a second look at some of those chucks that i have boxed up.
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Old 03-06-2010, 11:36 AM   #12
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Default Re: How To: Remove a Jacobs chuck arbor

Quote:
Hi Bolster,

Have a look here for Jacobs chuck servicing instructions:

http://www.jacobschuck.com/pdf/s2.pdf
LOL, those are the exact instructions I tried to use a month ago, when I failed. My only explanation is that I was using an arbor press with insufficient "grunt." Does it take a large amount of pressure, or just a little? Thanks.

Quote:
Needless to say, it's important to religiously clean the two before mating!
Good advice for a whole range of human endeavors!
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Old 03-06-2010, 12:02 PM   #13
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Default Re: How To: Remove a Jacobs chuck arbor

That was really interesting. Thanks.
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Old 03-06-2010, 02:12 PM   #14
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Default Re: How To: Remove a Jacobs chuck arbor

interesting!
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Old 03-06-2010, 02:26 PM   #15
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Default Re: How To: Remove a Jacobs chuck arbor

This is one big ass chuck .. what's the capacity?
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Old 03-06-2010, 02:29 PM   #16
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Default Re: How To: Remove a Jacobs chuck arbor

Quote:
Originally Posted by Bolster View Post
LOL, those are the exact instructions I tried to use a month ago, when I failed. My only explanation is that I was using an arbor press with insufficient "grunt." Does it take a large amount of pressure, or just a little? Thanks.



Good advice for a whole range of human endeavors!
Hi Bolster,

I have never disassembled a Super Chuck, so I can't comment on the tonnage required. If the arbor press didn't work and you were following the instructions properly as I'm sure you were, I'd say more grunt was required.

Very true!
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Quote:
Originally Posted by Sir Stanley Hooker
One stroke to produce power and three strokes to wear it out.
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Old 03-06-2010, 02:31 PM   #17
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Default Re: How To: Remove a Jacobs chuck arbor

Quote:
Originally Posted by ImportTuner View Post
This is one big ass chuck .. what's the capacity?
1/8" to 3/4" is the rated capacity.

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Quote:
Originally Posted by Sir Stanley Hooker
One stroke to produce power and three strokes to wear it out.
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Old 03-06-2010, 02:33 PM   #18
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Default Re: How To: Remove a Jacobs chuck arbor

I was cringing looking at the pics of you drilling out the chuck..

Why don't Jacobs drill them out from new, knowing that the hole can be required for arbor removal?

Quote:
Originally Posted by ImportTuner View Post
This is one big ass chuck .. what's the capacity?
*giggles*
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Old 03-06-2010, 03:12 PM   #19
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Default Re: How To: Remove a Jacobs chuck arbor

Great post! I always was interested in this operation. You continue to impress me dude.....

Instead of being a cocky arrogant ass wipe, like some of the people who are good at this stuff around here are, you are informative, thorough, and professional.....you'd make a great teacher! Very impressive for a young guy!

Keep up the great posts!
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Old 03-06-2010, 03:38 PM   #20
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Default Re: How To: Remove a Jacobs chuck arbor

You neglected to factor in the retaining screw that goes into the chuck and threads into the threaded arbor to properly hold the chuck on, which in many cases these are left hand threaded screws, thus providing the retention needed for reversing a drill.

I have mucho experience when it comes to drilling, having designed and built multi spindle CNC drilling machines and having managed very large tool and die shops (150+ employees) I've worked with more than a few hundred chucks myself.

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