How to attach a quality drill chuck to a Morse Taper 2 arbor?

[Neil WyattModerator @neilwyatt]

My theory is simple:

Jacobs and Morse tapers were just made to match factory standards tapers with no great or clever 'plan' in mind, and the standards determined retrospectively by measurement.

This is different to, say, Jarno, which was designed with simple measurements making it easy to reproduce without reference to a standard taper.

Neil

[Howard LewisParticipant @howardlewis46836]

Sorry to disagree with Neil's earlier statement, but Jarno tapers all have a common angle;

Google brings it up, as a 1 in 20 taper, in Inches, 0.6 inches per Foot, or 2.864 degrees..

Personally. I think that it is pity that the angle of Morse tapers all vary slightly as the number changes.

But as long as they do what is required, does it matter?

In contrast, the INT tapers used on Milling Machines are intended for location, and are easy to detach, the drive being provided by the dogs on the spindle engaging in the slots in the arbor.

Anyone interested in the various tapers, Morse, Brown and Sharp, International, R8, various makes of Split Collets, Clarkson screwed End Mills, and the Myford Series 7 Mandrel, should study Tubal Cain's "The Model Engineers Handbook", Third Edition, Section 3.

On Google, Little Machine Shop has charts of Morse,Jacobs, Brown and Sharp, and Jarno tapers.

Howard

[Neil WyattModerator @neilwyatt]

Posted by richardandtracy on 02/06/2017 08:07:14:

Just to add a little to this:

Whether a taper is self releasing is determined by the co-efficient of friction and taper angle. If theta is half the angle of the taper between one side & the other tapered side, then if tan(theta) is greater than the co-efficient of friction it will be self releasing (eg ER collets). If less, it will be self locking (eg Jacobs tapers) if roughly the same (such as with a Morse Taper) you may need a drawbar to hold it in and occasionally a wedge to get it out.

Regards,

Richard.

While I agree with the co-efficient of friction relationship, the idea that Jacobs tapers are more secure than Morse tapers is BUNKUM!

Instead of just repeating the myth, I have actually looked up the figures and many Jacobs tapers are steeper than morse tapers (which are all about 1.5 dgrees) and so are actually LESS secure.

In fact, if we ignore MT1 and JT4, every single Jacobs taper is STEEPER than Morse tapers.

I hate to let the facts get in the way of a good tale, but here they are:

Morse Tapers

0 1.4908

1 1.4287

2 1.4307

3 1.4377

4 1.4876

4-1/2 1.4894

5 1.5073

6 1.4933

7 1.4894

Jacobs Tapers

0 1.4117

1 2.2074

2 2.3350

2 Short 2.3350

3 1.5251

4 1.5009

5 1.4801

6 1.4868

33 1.8184

Neil

[Neil WyattModerator @neilwyatt]

Posted by Howard Lewis on 02/06/2017 10:53:28:

Sorry to disagree with Neil's earlier statement, but Jarno tapers all have a common angle;

Google brings it up, as a 1 in 20 taper, in Inches, 0.6 inches per Foot, or 2.864 degrees..

Sorry, yes Jarno is 1:20 not 1:24, Browne and Sharpe are close to 1:24 but vary a bit.

Neil

[richardandtracyParticipant @richardandtracy]

Neil, I'm well & truly caught out for not checking my facts first. Despite doing a CNC toolpath generation program for most of these tapers recently. Somewhat niggled with myself.

Also explains why all my Jacobs chucks have a little LH thread screw in them to keep them in.

[Mutter, mutter, grumble]

Regards,

Richard.

[Michael GilliganParticipant @michaelgilligan61133]

Neil,

Sorry to come back into this so soon, but I must just mention that your figures do broadly support my previous [but still unsubstantiated] assertion that, on a typical drill-chuck arbor, the JT was intended to release more easily than the Morse.

I will try to remain silent for a little longer this time.

MichaelG.

[SillyOldDufferModerator @sillyoldduffer]

Yet again my world of half-understandings has been rocked on it's foundations.

Most of the explanations I've found so far on the web about how tapers work are unconvincing. Some accounts favour a relationship between the coefficient of friction and the surface area of the joint – but somehow it doesn't apply to bearings. Van der Waals forces are a quite popular explanation, but I think they are too weak to explain taper grips. More convincing are theories that relate the coefficient of friction and the tangent of the taper angle: at least they recognise that the angle is important.

I'm most comfortable with the explanation that locking depends on plastic deformation. It suggests that as a taper is pushed into the socket it tries to force the socket open whilst the taper is simultaneously squeezed. Within it's elastic limit, the metal of both taper and socket acts as a powerful spring and clamps the male and female together. The harder the two are pushed together, the stronger the grip. Also, the flatter the taper, the harder the union is to break. When pulled apart, the clamping effect collapses, but the clamp is fully maintained if the joint only tries to rotate. The notion that tapers are a kind of reversible force-fit makes sense to me.

The taper angles adopted in the past are a strange and illogical mix. My guess is that the various makers adopted unusual angles as a way of protecting their rights, not for an engineering reason. It would be hard for a competitor to claim in court that he had coincidently made a 1.4377° taper that just happened to fit Mr Morse's Patent No 3 Socket, especially if the 'coincidence' was repeated across all the peculiar taper angles in the Morse range.

Dave

Edited By SillyOldDuffer on 02/06/2017 13:22:41

[choochoo_balooParticipant @choochoo_baloo]

Related to my OP, I actually want to remove the original arbor on my Jacobs No 34 chuck. I decided it's needless to buy a new chuck when this British Jacobs is likely much better.

As a learning exercise more than anything, I wish to replace the arbor with a new tang style one from Arc Euro.

I have attached a couple of photos; can someone please direct me to, or upload a Jacobs Taper chart, since after having a quick look on Jacob's website doesn't help me identify what mine will be; to then buy with MT 2 other end from Arc.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by choochoo_baloo on 02/06/2017 16:23:35:

… can someone please direct me to, or upload a Jacobs Taper chart

.

Try this page: **LINK**

https://www.amachinetool.com/blogs/news/16397981-machine-tool-taper-explanation

… It has the dimensions, and lots more.

MichaelG.

.

According to this ebay listing, yours should have the No.6 JT

http://www.ebay.co.uk/itm/JACOBS-No-34-3-JAW-CHUCK-AND-KEY-0-13mm-2102-/222507765123

Edited By Michael Gilligan on 02/06/2017 16:41:10

[HasBeanParticipant @hasbean]

Just to add a little to this:

Whether a taper is self releasing is determined by the co-efficient of friction and taper angle. If theta is half the angle of the taper between one side & the other tapered side, then if tan(theta) is greater than the co-efficient of friction it will be self releasing (eg ER collets). If less, it will be self locking (eg Jacobs tapers) if roughly the same (such as with a Morse Taper) you may need a drawbar to hold it in and occasionally a wedge to get it out.

Regards,

Richard

+ 1

Can't remember where I read it from but something to do with the correlation between the tangent of the included angle and the coefficient of friction of the material(s)

Paul

[MikeParticipant @mike89748]

I've always used this method to get a chuck off a Jacobs taper: Before first fitting the chuck, drill and tap a central hole in the back of the chuck, any convenient thread, and, to remove, open the jaws wide and screw in a long Allen screw. If the metal is thin at the back of the chuck, drill a clearance hole for any convenient thread. To remove, clamp a nut firmly in the jaws, and screw in a long bold. Might not be the "proper" way of doing the job, but it does work. This works best, and may prevent undue strain on a precision chuck, if you make a very deep nut out of a bit of mild steel hex.

[Howard LewisParticipant @howardlewis46836]

A drill chuck with a Pozidrive or Phillips screw visible at the bottom is probably not on a taper; and likely to be on a Pistol Drill. It is more likely to be on a 1/2 x 24 Unified thread, with the LEFT HAND THREADED screw used to prevent the chuck unscrewing if the drill is run in reverse.

In this case chuck removal entails:

Open Jaws fully: Remove L H threaded screw: Place chuck key in one of the holes and strike with a mallet so that the chuck unscrews.

I suspect that the angles quoted previously are in fact half angles (That to which the Top Slide should be set over when machining one)

2MT is almost 2 degrees 52 minutes (1.4307 x 2 = 2.8614 – 2.'51.684".which is double the figure quoted..

Howard

Edited By Howard Lewis on 02/06/2017 18:05:47

[HopperParticipant @hopper]

I wonder how much of the adhesion between two tapered surfaces is due to the type of molecular attraction that causes Jo' blocks (gauge blocks) to stick together when "wrung" together? ISTR vaguely from trade school it was to do with the sharing of electrons between molecules on each adjoining surface.

Apparently the same kind of molecular attraction is what allows gekko lizards and the like to climb up vertical windows and across the ceiling. Their little toes are not suction cups, as they appear to be, but tiny pads that conform closely to the wall or window surface and share electrons between molecules, providing the necessary "attraction".

[SillyOldDufferModerator @sillyoldduffer]

Posted by choochoo_baloo on 02/06/2017 16:23:35:

Related to my OP, I actually want to remove the original arbor on my Jacobs No 34 chuck. I decided it's needless to buy a new chuck when this British Jacobs is likely much better.

Have you got the original arbour off yet? Once that's done it will be easy to identify by measuring it.

I've had disasters taking stuff apart when I didn't know how it was fixed together. Modern Jacobs No34 Chucks are available to fit various arbours and are helpfully stamped to identify which one it is. Your British No34 doesn't seem to have that information. Can you see evidence of a taper where the arbour enters the chuck? If not I'd start by assuming it was a thread (tapping to dismantle as described by Howard) rather than using wedges.

Hope you get it sorted.

Dave

[Roderick JenkinsParticipant @roderickjenkins93242]

Posted by SillyOldDuffer on 03/06/2017 10:23:40:

Modern Jacobs No34 Chucks are available to fit various arbours and are helpfully stamped to identify which one it is. Your British No34 doesn't seem to have that information. Can you see evidence of a taper where the arbour enters the chuck? If not I'd start by assuming it was a thread (tapping to dismantle as described by Howard) rather than using wedges.

I have similar thoughts. Can you show us a picture of the back of the chuck, where the arbor enters?

Rod

[Howard LewisParticipant @howardlewis46836]

If you are REALLY desperate, you could try cutting off the arbor, close to the chuck, and then clamping the No 34 to a piece of round bar in the Lathe chuck and see if if it is possible to drill / bore away the remains. If the arbor can be cut with a hacksaw or parting tool, then it can be bored out until it is weakened sufficiently to allow removal.

But obviously, if it is a taper (measuring immediately behind the chuck may give a clue as to which Jacobs taper it is) you do not want to exceed the major diameter of the taper.. But by now, it should have lost a lot of its grip on the chuck.

If the chuck is on a taper, although boring out will weaken the grip of the arbor, the forces involved in boring are likely to have screwed it further in. That's the bad news, but the heat may and torque may have dislodged it enough to be able to remove it. If it a screw fitting, without a central Phillips/Pozidrive screw, the thread is likely to be 3/8 UNF. With a central Left Hand screw, the thread will be 1/2 x 24, which should give an indication of the root diameter of the thread, and theredfore, maximum size for the bore. Once this has been reached, it ought to be possible to pick out the remains of the thread with a scriber.

HTH

Howard

[Nick HulmeParticipant @nickhulme30114]

Posted by Michael Gilligan on 02/06/2017 11:54:08:

Neil,

Sorry to come back into this so soon, but I must just mention that your figures do broadly support my previous [but still unsubstantiated] assertion that, on a typical drill-chuck arbor, the JT was intended to release more easily than the Morse.

I will try to remain silent for a little longer this time.

MichaelG.

But to what end, since you are not supposed to pull a chuck off an arbour whilst it's in a machine and the MT has standard provisions for removal on most machines. For machines with no draw bar, wedge slot or auto-eject for the MT a chuck which held it's taper better than the arbour might be a boon as it would reduce the risk of being left with an arbour stuck in the machine 😀

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nick Hulme on 04/06/2017 12:32:40:

.

… might be a boon as it would reduce the risk of being left with an arbour stuck in the machine 😀

.

Properly designed machine spindles/quills incorporate extractors, and/or slots for wedges.

MichaelG.

[John ReeseParticipant @johnreese12848]

Choo Choo did not say whether the chuck was keyed or keyless. If keyless be sure not to seat the taper using a press. That can expand the body of the chuck enough to lock it up. Don't ask how I know.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by choochoo_baloo on 02/06/2017 16:23:35:

Related to my OP, I actually want to remove the original arbor on my Jacobs No 34 chuck. I decided it's needless to buy a new chuck when this British Jacobs is likely much better.

As a learning exercise more than anything, I wish to replace the arbor with a new tang style one from Arc Euro.

I have attached a couple of photos; can someone please direct me to, or upload a Jacobs Taper chart, since after having a quick look on Jacob's website doesn't help me identify what mine will be; to then buy with MT 2 other end from Arc.

.

John … for info ^^^

[you do make a good point though]

MichaelG.

[ZebethyalParticipant @zebethyal]

Morse taper originally was thought of as 5/8 inch per foot (0.625). As precision improved, it was realized that the existing patterns did not quite conform to this ideal. Rather than orphan equipment already in use, the slightly-off specifications have continued to be used

The above is quoted in several places as a reason why Morse tapers are not all exactly the same angle.

[Andrew TinsleyParticipant @andrewtinsley63637]

I am totally amazed at the length of this topic. I never think twice about putting an MT2 taper into my Rohm chucks. Just push the chuck taper into the chuck and the MT2 taper into the tailstock and go drill something! What is so difficult about this? Or am I really missing something?

Andrew

Edited By Andrew Tinsley on 05/06/2017 11:10:31

[Nick HulmeParticipant @nickhulme30114]

Posted by Michael Gilligan on 04/06/2017 12:41:45:

Properly designed machine spindles/quills incorporate extractors, and/or slots for wedges.

MichaelG.

Yes, I hoped you might have noticed I stated that before observing that the only advantage of your being right would be for machines which do not, the ML7 tail stock is the only instance of absence which comes to mind

😀

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Nick Hulme on 05/06/2017 20:07:38:

Posted by Michael Gilligan on 04/06/2017 12:41:45:

Properly designed machine spindles/quills incorporate extractors, and/or slots for wedges.

MichaelG.

Yes, I hoped you might have noticed I stated that

.

Nick,

I did notice what you wrote … but I felt the need to include the phrase "properly designed"

I have nothing more to say on the matter, unless and until I find supporting evidence for for my hypothesis.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Choo Choo if you read my post of 02/06.2017 timed at 10:53:28 you will be directed to Google "Little Machine Shop".

If you then click on "Reference", you can view a series of charts giving dimensions of Tapers, including Jacobs.

Howard

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