WHY THE TANG?

I have just bought a 3MT morse taper adapter for the tailstock of my lathe and I notice that the tang is shorter than the other adapters that I have. My question is what is the function of the tang? I thought that the taper itself was there to stop a drill etc rotating and the tang was simply there for extracting the adapter by loosening the adapter in the tailstock. My usual practice is to enter the adapter into the tailstock and push and twist the taper to lock it. The tang will then rest fairly solidly against the internal mechanism of the tailstock. If I follow this procedure with my latest adapter, the overly short tang will ride up on the internal mechanism and release the taper.

Are there any agreed standard dimensions for tangs? Can longer tangs be purchased anywhere (the tang on my new adapter is a screw-in affair)? Is my understanding of the function of a tang correct?

Chas

Hi Chas

Plenty of choice here of MT dimensions including the tang,

**LINK**

I experience a similar problem on a denford lathe, without the tang or an insert the tool doesn't eject from the tailstock.

Emgee

Edited By Emgee on 15/09/2020 11:23:07

Sounds to me like the morse tapers aren't true - the tapers should lock themselves without the tang.

In theory the taper delivers the drive. In practice, bits of grit or burrs etc on the taper can can cause it to slip, or the drill bit can dig into the job such as when drilling brass and pull the taper out of the socket a tiny bit, or it can just be not firmly seated by the operator. The tang then offers a temporary second line of defence until the taper regains its grip. Same as many motorbike engine sprockets that are seated on a taper but also have a woodruff key as extra insurance in case of a sudden shock loading etc.

Best way to seat your taper in the tailstock is to slam it straight in by hand then tap the end of the drill bit or whatever with a brass hammer etc to seat the taper home. Twisting will not necessarily seat the taper.

That siad, it's amazing how much drive those tapers have. My old Drummond's tailstock with MT1 taper and no tang will drive a 1" drill bit through steel.

Edited By Hopper on 15/09/2020 11:55:01

Thanks Hopper, as usual a very concise and practical answer

I have resorted to banging the taper home with a plastic hammer in the past but I did so with a bad conscience, thinking I was being brutal.

The taper holding capability of my lathe ( a 15-year old Herless) has never been anywhere near your old Drummond so it is time I got the blue out and did some checking.

Thanks also to Emgee and Speedy Builder5, I will search for longer tangs just in case I can't get passable results from my tailstock.

Chas

I think that's completely correct.

A tailstock ejector or a flat, tapered drift tapped through a quill slot should be required to eject it.

Of course, in industry where time is money, people often fail to ensure the mating surfaces are clean, and if the machine is powerful and the feed forceful you can end up with a twisted tang. I don't think I've ever seen a workshop where there haven't been a few - except my own, but then I ain't doin' it for pay.

Sometimes you don't get a tang at all - I have a tailstock revolving centre that doesn't have one. I improvised by tapping the tail of the taper M4 and putting in a capscrew.

Can't find the stupid picture, but I've got a drawing of a pillar drill showing the tang is needed to eject the taper, I think from the patent. A lever operates on the tang through a slot in the spindle. From this I got the impression the tang isn't to stop rotation, it fits into a shaped recess only to make sure it's aligned with the ejector slot on machines that have them. My lathe tailstock ejects by pushing out the tang with the screw, and doesn't need a slot. It has no tang shaped socket.

Guessing again. Machines vary. Although the purpose of tapers is quick tool-changing, not all machines provide a built-in mechanism. My cheapo pillar drill needs wedges to release the taper.

I don't think tangs have any function when the taper is held by a drawbar. Those supplied for milling machines tend not to have them.

Dave

Tangs are not intended to provide a drive. The taper does that. Tangs are needed to eject the tool from the quill of a vertical mill. A tapered drift is inserted through a slot in the quill, and a mallet drives the tapered drift through, pushing the tool, to break the taper.

In a self ejecting Tailstock, the tang contacts the the internals of the barrel and this breaks the taper releasing the tool.

Without some form of tang, might prove impossible to remove tapered tooling from the Tailstock or quill.

Tooling without a tang can be tapped (If it is not already ) so a screw in tang can be inserted, or an extension screwed in so that it can be ejected. Screw in Tangs can be bought.

Howard

I agree, the tang is purely for extraction purposes.

That doesn't really explain it for me, Howard. If that's all the tang does, why not leave off the tang, extend the taper (or relocate the drift slot) and use the drift against the end of the tapered section?

When 1 st starting work as an apprentice sheet metal worker i was given the job of drilling lots of holes in flat bar. The machine was a huge thing. The morse taper drills , when inserted had to be rotated until they latched into a slot. When ejecting a tapered bar was inserted into the slot & tapped with a hammer.

Steve.

Bandersnatch,

Extending the taper would merely increase the gripping area, making removal more difficult, not to mention exceeding the long agreed / accepted standard dimensions for Morse tapers.

Moving the slot could be likely to reduce the gripping area.

With tolerances on both male and female tapers the position of the end of a taper will vary. Max size Male in Min size Female will push the tool forward. Min size Male in Max size Female will move the tool inwards.

With an included angle of nearly 3 degrees, (Differs from one MT size to another ) a thou or two on diameter can make quite a difference in position. TAN 3 = 0.0524, so a 0.001" difference in diameters would shift the point by 0.0.019" either way., so that you could differ by 0.038" , so the drift and slot sizes would need to be controlled more precisely..

Steviegtr has reinforced what I said, and explained just why the tang is there.Thousands of Engineers have used the tang for the purpose for which it is intended. If it's wrong, it has been wrong for a very long time!

(I do not follow the logic of a slightly different angle for each size of Morse Taper; preferring the constant taper for all sizes of the Jarno. But that is way that everyone accepted things, so we live with it, in the same way everyone decided to use right hand threads, rather than left, so we are unlikely to change it now )

If you don't believe me BANG a Morse taper without a tang in to a female taper where there is no access from the rear, and let us know how you got it out! An open ended sleeve with an extractor thread is cheating!

But unless you are very lucky, it will not be easy!

It can be done

Howard

Does the tang help in the manufacture of the male end of a drill, reamer etc. Have you ever seen a centre with a trang on it ?

Hmm

My tailstocks are the extractor type, and easily deal with centres with undersize extended ends.

Never tried it in the RF25, but given the very small diameter behind the 3 MT, would probably have to resort to a rod 3/8" diameter or smaller between the mallet and the centre, since a drift would be unlikely to contact it.

Howard

There will always be a centre in the tang used when the item was manufactured. Ihave taken advantage of this when machining the tapers of larger drills parallel, as we can only manage MT2. MT 2-3 reverse adaptors use up a lot of length.

I always use the same method as Hopper when fitting Morse tapers.

Edited By old mart on 15/09/2020 18:52:54

On my milling machine I have to rotate my Morse Taper drill chucks until the tang engages. If I don’t place it in one of two positions then it won’t go in fully. There is no accessible slot to remove the chuck. It has to be ejected by the drawbar. On my mill at least (VMC) I think the tang possibly would or could drive the chuck. I’m guessing in normal use though drive is provided by the taper but as the tang is well hidden inside the quill who’s to say it doesn’t play a part? I’d actually like to know what the inside of the quill on my machine looks like and how they make them.

I have seen a few tangs that are seriously twisted, that suggests to me they are not up to job of driving a drill. The taper of a drill should be treated with respect and and damage should be cleaned up, cleaning the socket and the shank should be done with care every time they are mated. The Barson drift was built around a brass hammer to give the drill a final tap to seat it firmly and the spring loaded drift for easy removal. I keep a small copper faced mallet to just give a drill a light tap. I find that drilling in the lathe seems to pull the drill out of the taper more than on my pillar drill even though the tapers and sockets are in very good condition.

Mike

Despite the tang being primarily for edjecting the tooling I think a tang slot machined into the quill of a lathe tailstock is also intended to help stop tooling such as a drill bit slipping and spinning. The nature of work on a lathe often means that there isn't as much load on a drill to force the tapers firmly together as there is on a drilling machine. There is nothing wrong in using the tang for this purpose in a tailstock, and it certainly works.

Lathe tailstocks that have a tang slot often still have a self edjecting facility, where the feedscrew pushes on the end of the tang when the quill is retracted, such as my Smart & Brown Modal A toolroom lathe. The last thing you would really want to do is bash in a wedge in the side of the precisely positioned tailstock and risk knocking it out of line. Some tailstock quills have the tang slot machined only from one side, so you can't really pass a wedge through them to edject the tooling, they self edject instead.

We do have a large old lathe at work though that has a tailstock quill with a tang slot, but the rear of the quill is solid with a thread machined on the outside diameter and projects out the rear end of the casting. A captive handwheel meshes with the external thread to drive the quill. So on this tailstock a wedge has to be used to edject tooling, but the tailstock is a very hefty casting with a very large diameter quill that is out of proportion to its 4 Morse taper, so a bit of a whack just won't do any harm.

Sorry but I don't buy the idea that the tang is purely for ejecting the tool.

The slot it engages in a drilling-machine spindle certainly does give that facility, but whilst my professional engineering text-books do not say so outright, their tables of standard specifications point to the tang also being a drive-dog.

If standard industrial practice was to rely solely on the taper for grip, drills would not have tangs machined to standard, accurate, detail dimensions, and spindle interiors would not be machined to match, beyond the taper itself. The drill would need end only in a short cylindrical stub faced to a shallow cone, able to enter a through-slot sufficiently for the drift to bear on it.

Nor do I. If that were the case, it could be done (without extending the taper) by growing a simple cylinder on the end of the taper - turned at the same time as the rest of it - rather than the awkwardly shaped tang that needs a subsequent machining operation. Why would anyone dream that up in the first place? Doesn't make sense to me.

But if the tang is (or was) intended for driving ....

Edited By Bandersnatch on 16/09/2020 01:17:45