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releasing tapers

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Michael Gilligan11/02/2019 11:04:51
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Posted by Hopper on 11/02/2019 10:43:05:

NDIY raises a good point indeed. Why a tang captive in a slot and unable to rotate if purpose, as has traditionally been claimed, is merely ejection? A round hump would indeed do the same job for ejection purposes.

[ ... ]

Can't find any specific reference in Machinery's Handbook or others either way. Would be interesting to learn where the traditional wisdom originated.

.

The best I can find in Machinery's is under 'Twist Drills'

Tang: The flattened end of a taper shank, intended to fit into a driving slot in the socket.

Tang Drive: Two opposite parallel driving flats on the end of a straight shank.

.

I'm sure NDIY can take that as some endorsement

MichaelG.

ega11/02/2019 11:31:09
1116 forum posts
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Posted by Nicholas Farr on 11/02/2019 07:27:50:

Hi, both Chris and Hopper are correct, the tang is for ejection purpose only. see page 19 of this **LINK**. The driving force on a taper drill should only be transmitted by the friction between the drill taper and the machine socket, therefore these should always be kept in good condition. Many times in industry, the unworthy have used the closest taper drill they could lay their hands on, to use as a hammer on the drift to knock out the drill that is still in the machine, which puts small dents in the taper and stops them from fitting correctly, thus when used next time often twists the tang and with heavy cuts, will rip it off completely.

Regards Nick.

Paragraph 4 on your linked page also makes the case for a draw bar - not, of course, possible with a normal MT shank drill. Interesting point, too, about the size of pilot holes.

I once saw a suggestion on an American site for the incorporation of an off centre cross pin in the lathe barrel positioned so as to engage with the tang.

As to the shape of the tang, this has to be such as to allow the taper drift inserted from the side through the slot in the quill to engage with it.

Peter G. Shaw11/02/2019 11:47:27
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My lathe, a Warco 220/Mashstroy C210T has a self-ejecting MT2 tailstock. Originally I used a drill chuck with a MT1 taper on the end which I fitted into a MT1-MT2 adaptor. In this mode it worked satisfactorily, but suffered from a large tailstock travel loss. Eventually I replaced the MT1 taper with the correct adaptor for the chuck and gained some, but not all of the missing travel. I then removed the tang, rounded the end, and found that I had removed too much! Ok mea culpa, but tool removal became difficult so I had to add a bit of metal back on to the end of the MT2 taper - a thick washer araldited in place.

Same thing happed with my running centre. (You would think I had learned from the drill chuck attempt, but actually I did them both at the same time.)

So, the point I am making is that in my case, there is a sweet spot for tang reduction to enable full travel of the tailstock, along with correct self-ejection. I think it may have been the late John Stevenson who, correctly I believe, said that this looks like poor tailstock design. However, bodging like this is possibly the best way forward for my lathe.

In respect of using them on other lathes etc, it will not happen here - I only have the one lathe. What happens when I have finished with this lathe is very unlikely to concern me - the lathe itself is not the best in the world and will only go for a low price. In anycase, if it is sold, it will probably be sold as a job lot, ie lathe & accessories. In any case, the adaptors are reasonably cheap and can be easily replaced if necessary.

Peter G. Shaw

SillyOldDuffer11/02/2019 12:28:34
3997 forum posts
810 photos
Posted by Michael Gilligan on 11/02/2019 11:04:51:
Posted by Hopper on 11/02/2019 10:43:05:

NDIY raises a good point indeed. Why a tang captive in a slot and unable to rotate if purpose, as has traditionally been claimed, is merely ejection? A round hump would indeed do the same job for ejection purposes.

[ ... ]

Can't find any specific reference in Machinery's Handbook or others either way. Would be interesting to learn where the traditional wisdom originated.

.

The best I can find in Machinery's is under 'Twist Drills'

Tang: The flattened end of a taper shank, intended to fit into a driving slot in the socket.

Tang Drive: Two opposite parallel driving flats on the end of a straight shank.

.

I'm sure NDIY can take that as some endorsement

MichaelG.

Tapers are puzzling in other ways too - like the strange choice of angles! The reason some shanks are fitted with a tang may be lost in the mists of time, so here's my theory.

The quality of a taper's grip depends on the male and female being well matched in every respect. It's important for both to have a good finish. Carelessness, dirt, wear and dings all reduce the effectiveness of the joint, and it's not unknown for them to slip.

Allowing a taper shank to spin in its socket damages both rather badly. Galling, tears, scratches and loss of circularity. Once damaged, slipping and even more damage becomes ever more likely. Although shanks are cheap and easily replaced, the socket is part of the machine and fixing it less straightforward. In a world where machines not busy cutting metal are nothing but a waste of money it pays to protect the machine from outages due to accidental damage.

My guess is the tang is only there to stop an accidentally loose taper spinning in the socket and damaging the machine. Tangs might be less popular today, at least on automatics. I suspect many modern machines can detect when a tool isn't cutting properly and reject it automatically, or stop and alert the operator. Perhaps a CNC expert will tell me I'm dreaming again?

Dave

Howard Lewis11/02/2019 14:03:13
1819 forum posts
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With regard to using the taper in the mandrel, I do.

Useful to maintain concentricity of a part that is going to be turned, milled or gearcut in the lathe and then the Mill/Drill.

If, for instance, I am turning a blank for a gear, the small chuck with a 2 MT shank is sleeved up to that of the Lathe mandrel.

In that way the diameters turned in the lathe should remain concentric when the 2 MT chuck is moved to the HV6 Rotary Table for cutting the tooth spaces.

Without using this method, there would be a need to clock and centre in a four jaw chuck.

Must all depend on the purposes for which the machines are used.

Howard

Clive Foster11/02/2019 14:04:06
1639 forum posts
45 photos

I suspect that vibrational effects are much more important in taper release (and initial gripping) than is generally recognised.

I recall the flywheel extractor for the engine on an Acto rotary mower we had maybe 40 years ago. A simple round steel bar, maybe 6 or 8 inches long and 3/4 - 1" ish diameter, screwed on the end of the crankshaft after the flywheel nut was removed. With an assistant applying upwards force by holding the flywheel on opposite sides a sharp rap with an ordinary hammer on the top end made the bar go "Riiing" and the flywheel jump off its taper just like that. No levers involved. Simply held up by hand. As the holder when we first tried youthful Clive was very surprised. So was Dad. So much that we put the thing back on. Verified that it was still totally immobile by conventional means including big pullers, large levers et al and tried again with identical ease. At the time I wondered if there was some magic length and frequency involved but these days I think pretty much any adequately high frequency of vibration would have done. Being a nut welded on a piece of bar the thing was hardly sophisticated!

Getting back to machine tapers I'm probably not the only guy to notice that a dead-blow hammer needs a lot more walloping to shift a taper than an ordinary steel one. Hardly surprising if vibration is involved as dead-blow hammers are all about creating a solid push to shift things with minimal vibration. These days I strangle a club hammer and hit the drawbar on my Bridgeport with a sharp twist of the wrist to release things. Surprised the heck out of a sometime toolmaker friend who was borrowing the machine when my way shifted a stuck R8 with a single rap when a couple of minutes of his efforts with my big dead blow had failed.

My take on the tang issue is that with decent tapers in the spindle and on the drill only a modest push is needed to hold things well enough to start drilling. With the tang stopping rotation any vibration during drilling will act to push the drill harder into the taper. Sufficiently so that it will stay put if cutting conditions cause it to try to pull out. Without the tang the drill will be free to rotate if vibration or pull-out loosens the taper. Once rotation starts its pretty much impossible to stop. I have actually seen this happen with a moderate size drill whose tang had been removed. Said drill had been seriously walloped into place with a hammer and copper block but to no avail.

It usually seems to me when removing a taper drill that its in a lot tighter than initial insertion force plus drilling force. Vibration working things tighter could be why.

Clive.

Andrew Johnston11/02/2019 14:49:43
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4498 forum posts
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Posted by SillyOldDuffer on 11/02/2019 12:28:34:

My guess is the tang is only there to stop an accidentally loose taper spinning in the socket and damaging the machine. Tangs might be less popular today, at least on automatics. I suspect many modern machines can detect when a tool isn't cutting properly and reject it automatically, or stop and alert the operator. Perhaps a CNC expert will tell me I'm dreaming again?

Well, I'm not an expert, but I can't offhand think of a commercial CNC mill that uses Morse tapers. They all use autochangers so the holders have pullstuds rather than tangs. Most holders are variations on the International series of tapers.

Simliarly I can't think of automatics or CNC lathes that use tangs. The old capstan lathes used parallel holders, and you could get Morse taper holders with an ejector slot for the tang. Most modern CNC lathes use a generic standard like VDI or one proprietry to the manufacturer. I suspect Morse taper drills are not used on CNC lathes; better to use those based in inserts for better repeatability

Andrew

larry phelan 111/02/2019 16:16:08
394 forum posts
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Dave [S-O-D ]

I saw that hint about the timber cover for the lathe bed in Sparey,s book many moons ago,and it was the first thing I made for the lathe. It,s a lot cheaper than trying to repair a damaged bed if a chuck slips at the wrong moment.

As an aside,I often wondered about those tangs too,I thought at one time that they were there to provide the drive.

And yes,some MT centers are shorter than others and can get stuck in the tailstock.

How do I know???? ASK ME !!sad

JasonB11/02/2019 16:32:39
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Looking at my reprint of Chas A Strelinger & Co's catalogue of 1895 they show the "Pratt Improved" drill chuck which will hold round or tapered drills and uses a plate with rectangular hole to fit over the tang to provide drive, the two opposed jaws are there to ctr the bit and stop it dropping more than to provide drive.

If using taper shank drills a split sleeve is used to convert the bit to parallel shank.

Michael Gilligan11/02/2019 18:26:52
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Posted by SillyOldDuffer on 11/02/2019 12:28:34:

Allowing a taper shank to spin in its socket damages both rather badly. Galling, tears, scratches and loss of circularity. Once damaged, slipping and even more damage becomes ever more likely. Although shanks are cheap and easily replaced, the socket is part of the machine and fixing it less straightforward. In a world where machines not busy cutting metal are nothing but a waste of money it pays to protect the machine from outages due to accidental damage.

My guess is the tang is only there to stop an accidentally loose taper spinning in the socket and damaging the machine.

.

I think that ^^^ explains it very nicely, Dave ... not least because I have the same ingrained as a 'folk memory' [which probably means my Dad told me].

If the taper slips, the tang abruptly stops it rotating far ... ergo, the shank is more likely to drop out than to be friction-welded into the socket.

MichaelG.

[still searching for Colt's patent]

not done it yet11/02/2019 19:24:55
2720 forum posts
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MG,

I think that is what I alluded to about a page ago?

Michael Gilligan11/02/2019 19:45:58
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Posted by not done it yet on 11/02/2019 19:24:55:

MG,

I think that is what I alluded to about a page ago?

.

It may well be ... but allusion and elaboration are rather different things.

MichaelG.

.

P.S. ... I hope you have also noticed that my posts on this topic have been generally supportive of you.

___________________________________

Edit: Perhaps your posing of a direct request might explain why people felt it appropriate to discuss the matter further.

[quote]

Look guys, I know the drive should be friction between the tapers, but answer me this:

[/quote]

Edited By Michael Gilligan on 11/02/2019 19:57:11

Michael Gilligan11/02/2019 20:18:47
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12784 forum posts
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Some fascinating images of Colt's machine-tools here: **LINK**

https://books.google.co.uk/books?id=T9e37mYzuNIC&pg=PA175&lpg=PA175

MichaelG.

Kiwi Bloke 112/02/2019 09:56:44
127 forum posts
1 photos

Clive Foster's Atco experience is fascinating - I must try to remember it for future use.

I've been thinking about releasing things stuck in tapers. I hate whacking the things free - it must do the bearings a power of no good. Self-ejecting arrangements, captive draw-bars, folding wedges and threaded collars at the nose end are so much gentler.

The trouble with thinking is that the more I think, the confuseder I get. When a bullet is fired, the back of the bullet starts moving before its nose. A compression wave spreads out through the bullet at the speed of sound (ie the speed of sound in whatever the bullet's made from). This causes the bullet to be plastically deformed - if it can 'go' anywhere - increasing in diameter, and contributes to the bullet being forced into the rifling grooves, and stops gas leakage. (Impressive and somewhat hair-raising experiments were done in the early 1900s by F W Mann, which involved the recovery of fired bullets without their suffering significant damage after they left the gun.)

Something similar (although elastic) presumably happens when the tang or small end of a tool in a taper socket is whacked. I would suggest that the whack will cause a transient increase in the radial forces between the tool and taper. Perhaps, if the whack is smart enough (not from a dead-blow hammer), the compression wave is followed by a 'tension' wave, which helps release. It would be better, (wouldn't it...?), if the blow could be applied at the large diameter end, so that there was only a wave of tension. Perhaps a slide-hammer puller, applied to the outboard end of the tool, or whacking a rod lying in a deep axial hole, bored from the small end, the end of the hole being beyond the wide end of the socket.

If this sounds crazy, just think about how you'd get a long rubber plug deep into a tube with an ID smaller than the plug's OD. You'd easily pull it in, but pushing would be impossible. I believe this is how the trailer 'Indespension' units were assembled (are they still going?).

This isn't meant to be a serious practical suggestion, just thought-provoking. Perhaps I should have gone to bed before now...

Hopper12/02/2019 10:06:22
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Methinks pressure waves in soft lead bullets under the power of explosive gunpowder may be a different kettle of fish from a tap with a tapered drift on a tough tool steel taper shank. Hard to imagine similar amounts of deformation going on. Maybe to a certain extent? Maybe. But more likely you just tap the thing and its pushed out.

Edited By Hopper on 12/02/2019 10:06:48

Chris Trice12/02/2019 11:26:16
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Agreed. Given the amount of energy imparted into the taper with a whack, I can't see any appreciable deformation occurring in such a large solid mass since most of the deformation would occur in the tang (or at least very locally to the point of impact) as the rest of the material directly behind it absorbs the energy. Anyone who has tried to whack the threaded part of a steering rack ball joint to get it to release will be familiar with the thread getting deformed. Certainly the thrust forward is going to massively overcome any increase in friction from whatever negligible expansion occurs.

Reg Rossiter12/02/2019 12:02:16
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RePosted by not done it yet on 11/02/2019 08:26:08:

Look guys, I know the drive should be friction between the tapers, but answer me this: Why was a tang fitted, when a dome (or even flat surface) would have sufficed as a point of action for the wedge? Why was the drill only able to be inserted in that orientaion.

In other words, was the tang a poor design or was it there as a back up tell-tale sign (that all was not well) before the taper surfaces were totally screwed up?

I’m not a mechanical engineer, so please give me a good design reason why the tang was developed in that shape, ‘cos those guys that designed it had a good reason for that shape. If it would have been better just flat topped, that is how they would have done it - simpler and faster not to have to locate the tang in the spindle slot, for instance.

The reason a tang is preferable to a domed or flat surface is down to maintaining the strength of the spindle. In order to use a taper drift you have to put a slot right through the spindle which weakens it. If you were going for the domed or flat ended option you would have to continue the round, tapered bore up into the ejector slot. Therefore at this point in the spindle you would have a round bore and a slot reducing the cross sectional area of the spindle and therefore the strength. Using a tang means that the tapered bore stops as the tang slot starts and leaves the spindle stronger.

Reg

John McNamara12/02/2019 12:12:21
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1285 forum posts
113 photos

Hi

A very handy site that covers Machine tapers is this one.

If you have an old taper you are trying to identify chances are it will be listed.

**LINK**

Regards
John

not done it yet12/02/2019 14:24:03
2720 forum posts
11 photos

Reg,

I can understand that might be true, but the dome would not actually need to be much more than a button - the wedge should only act vertically downwards at the centre line of the spindle. Therefore the wedge slot could be much further down the spindle than it actually is? Likely a simpler manufacturing process for the spindl, too.

Seems to me that maybe the driving taper came after the adoption of a tang drive, as more powerful machines entered the market?

HOWARDT12/02/2019 16:55:55
389 forum posts
14 photos

For what it is worth. Locking tapers e.g. morse, create a friction lock by virtue of there shallow angle. An included angle of less than 14 degrees will provide a friction lock when tapped into place. But this lock will remain in place so long as the major force is along the centre of the taper. If vibration or/and side loads occur then the taper may release. The Morse taper or Brown and Sharpe taper are both available by design with a tang which is designed to allow disassembly of the inserted taper in a spindle by applying an angled drift. The tang has a clearance in the spindle slot of 0.010" nominal, with this in mind any rotational force will act as a point load initially on the tang. It is not uncommon on worn drill presses to find a number of drills with twisted tangs, Twisting seems to get worse as the taper size increases. probably due to the blacksmith element of the larger drilling machines. So using a locking taper with any vibrational tooling, such as milling cutter will require a draw bar. The drive tang gives a long contact face with the drift, a domed pin will give a line contact so deformation of the either the pin or the drift will occur at each release.

CNC and conventional metal cutting machines use a non locking taper with the drive being made by a couple of face keys. Retention being made by a draw bar through the spindle is locked either manually or by hydraulics and spring packs.

i'll stick with convention and accept that standards are there for a reason even if that reason has been lost in time. I am sure some one will find an original document showing why soon.

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