WHY THE TANG?

[Michael GilliganParticipant @michaelgilligan61133]

Time for a little review, I think

Shout if you think I have this wrong:

• The circular-section taper was a logical development from the square-section that was commonly used on drills in braces.
• It was devised to improve runout
• We have no clear indication of what degree of taper was originally used; and this may indeed be ‘various’…
• Screw threads and tangs were proposed as means of retention/drive/extraction
• Morse’s optimisation of a  self-holding taper was invented later

Therefore, there might well be no clear answer to the opening question … The use of tangs on Morse tapers being a matter of evolution

I personally will be much happier if I can see Samuel Colt’s patent

MichaelG.

Edited By Michael Gilligan on 20/09/2020 15:08:40

[HOWARDTParticipant @howardt]

When you consider the amount of tools and holders that are fitted directly to tapers with no other anti-rotation device, then why would a drill tang be considered an anti-rotation device as against a removal device. Drills can be had in all morse taper sizes and each size covers a standard drill range with some overlaps. When considering small drill diameters on a 1MT the drill will break long before the tang twists. I think the tang was an evolution created by some one in the past to overcome the problem of removing a taper that caused less damage then driving a wedge between the tool and the end of the spindle.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by HOWARDT on 20/09/2020 16:20:09:

When you consider the amount of tools and holders that are fitted directly to tapers with no other anti-rotation device, then why would a drill tang be considered an anti-rotation device as against a removal device. […]

.

Third, fourth and fifth bullet-points in my list above … plus the text quoted from patent 924,388

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

[for what it’s worth]

It appears that this machine is the subject of Colt’s patent: **LINK**

See also: **LINK**

https://parkplanning.nps.gov/showFile.cfm?projectID=14231&MIMEType=application%252Fpdf&filename=Chapter%202b%20Historical%20Overview%2Epdf&sfid=71403

… so the tang and taper arrangement may be a relatively minor component

The search continues

MichaelG.

.

Ref. **LINK**

https://archive.org/stream/patentsforinven04offigoog/patentsforinven04offigoog_djvu.txt

A.D. 1854, April 12.— N«861. 

COLT, Samuel. — " Improved machinery for cutting or shaping 
" metals." Shaping locks and parts of fire-arms. 

The Specification and drawings, which should be referred to, 
describe milling tools and screw-cutting machinery for shaping the 
various parts of gunlocks, &c. 

[Graham MeekParticipant @grahammeek88282]

The Tang issue has been raised in the following thread, rather than give my interpretation there I thought it would be more appropriate here.

Mysterious Morse Tapers

As regards the Tang being a driving member. I am with Bosun in that it’s function is not for this purpose.

The waters are muddied somewhat in “Machinery’s Handbook 15th Edition”, page 1416, Table 2. In that it mentions “Tang Drive With Shank held by Friction” (See Table 7). There are further entries in that table, but the one that interests me is the “Tang Drive With Shank held in by Key” (see Table 8).

This latter example will be familiar to anyone who has operated one of the larger lathes which has Two Slots in the Tailstock Barrel. Where there is the normal Drift Ejection slot and one which is nearer to the end of the Tailstock Barrel, towards the Lathe chuck. This latter slot is for a Short Key to be drifted into the slot to retain the Morse Taper Shank, and to stop it rotating. It is an arrangement favoured by some locomotive builders for retaining the Piston Rod to the Crosshead.

This arrangement therefore makes the “Tang Drive” on the end of this particular Morse Taper Shank superfluous.

From this I deduce the “Tang Drive” relates to it merely being a means in which to “Drive” the Shank from the socket.

In my edition of “Mechanical & Metal Trades Handbook” on page 311. Under the heading of “Tool Holding Fixtures” the Metric Taper (ME) and the Morse Taper (MK) table. Lists the “Torque transmission” as being “Force Fit over the Taper Surface”. DIN 228-1 & 228-2 are cited as the Specification covering this.

The diagram accompanying the Table shows the Taper shank complete with Tang fitted into a plain tapered socket with no tang slot provision.

The Hardinge HLV, Emco Maximat Super 11, Myford Range, Compact 5 and numerous others do not provide a slot to “Drive” the Tang.

The Tang as a means of driving is really a non starter. For one thing it is at the smallest end. A position which makes it the least effective position to resist Torque.

Then there is the “Fit” between the Tang and the slot. In all sizes there is clearance present on each side of the Tang. If the Tang is rotated slightly until it makes contact with the Slot. Then the only drive being imparted is along the edge of the Tang or “Line Contact”. Hardly a good situation for transmitting torque.

A couple of other points I would like the reader to mull over is the situation where a 1″ Blacksmiths Drill is being held by its 1/2″ shank in a drill chuck, (shown earlier on in this post). The Drill chuck is retained to the arbour by the Jacobs, Jarno or DIN taper. The arbour of the drill chuck is held by the No2 Morse Taper. A 1″ drill should really be on a No 3 Morse Taper. (Certain drill sizes are allotted to certain Morse Taper shanks. The larger the drill the greater the resistance required to stop it rotating).

There is no Drive Tang on the small Jacobs, Jarno, or DIN taper holding the chuck to the arbour. Yet the system works. Why it works is obvious to anyone who has tried to remove a Drill chuck from its arbour.

Lastly consider the parts of a replacement Hip Joint, held together by a Morse Taper.

I hope you have found my ramblings interesting. I am not out to try and change the “died in the wool” opinions held by the devotees. Merely to make the little grey cells consider the other side of the coin.

Regards

Gray,

 

 

 

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I guess this argument could go on forever, in the Presto Counsellor booklet, it says “The tang is for ejection purposes only. Allowing torque to be taken by the tang will result in breakage” paragraph 4 page 22. However, below is a scan from my INTAL information booklet, (The International Twist Drill Co. Ltd.), which might be a compromise, to this saga.

Regards Nick.

[Howard LewisParticipant @howardlewis46836]

Anyone who has tried to remove a Morse Taper fitting, without a tang, from a Morse Taper socket will know just how EXTREMELY difficult it is.

For lathes with self ejecting Tailstocks, the tang is pushed, by the tailstock barrel, until the taper breaks.

A non self ejecting Tailstock is hollow so that a bar can be inserted to drive the tool out, by breaking the taper.

In a Milling Machine, or Drill, the tang engages in a slot in the spindle.. After use, a tapered drift is inserted into a transverse slot in the spindle (Already shown in one of the previous posts) and used to break the taper.

It does so by bearing on the tang, or if the Morse taper tool is tapped, an extension piece (of studding perhaps, in place of a screw in tang) to break the taper.

The tang is for extraction. The Morse Taper, by virue of its gripping power provides the drive.

(If the tang were intended to drive the tool, using the Morse taper purely for location, why do so many become twisted?) Possibly a dirty/ damaged taper, or not driven home, probably.

At least that is my view after nearly 70 years in production Engineering

Howard

 

[Robert Atkinson 2Participant @robertatkinson2]

Something that I’ve not seen mentioned on this thread is that tangs are found almost exclusively on drills and chucks and drills often “snatch” or jam. I’m strongly in the camp that while they may aid rotational drive, whatever the reason for their initial introduction* the reason they persisted, and possibly were developed, is to prevent rotation of the tool damaging the female taper. The female taper typically being in an expensive part of the machine.
The cases of twisted off tangs may be evidence of worn tapers or poor matching of taper size to drill size / machine torque.

As has been said by others, if the tang was only for ejection there is no need for it to be flat and have a matching slot in the female. A simple reduced diameter parallel section at the end of the taper would be just as good. The reduced diameter is required to stop mushrooming of the end jamming the taper.

*I think original intent in the time of Colt et all was for drive. Perhaps because they did not fully appreciate the capability of the taper to resist torque, did not have the ability to make or had not developed suitable tapers.

Robert.

[PeteParticipant @pete41194]

Morse taper dimensions including the tang length and width are supposed to conform to recognized and agreed to standards. ISO 296, DIN 228, ANSI/ASME B5.10 to mention just 3. https://www.cgtk.co.uk/metalwork/data/morse for dimensions in metric.

Scroll part way down on this Australian website and they point out the tang is only used for ejection which is another source that supports Gray’s, Nickolas’s and Howard’s analyis.https://aimsindustrial.com.au/blogs/product-guides/morse-taper-guide I’ve also read about the use of those short keys on large and heavy industrial machines, but have never seen one. I’d also agree with Gray’s point and due to the clearance that you still have only a line contact.

Morse taper drills and tool shanks might be used by the purchaser on everything from a drill press, lathe head and tail stock tapers, milling spindles etc. So in my opinion and if it doesn’t require a draw bar, the tang is still there even when there might be other methods of extraction such as with most lathe tail stocks since that allows use on a variety of machines. The Narex MT 3 tool shank I have came with a 3/8″ x 16 tpi threaded and cross pinned tang allowing it to be used and extracted from a standard Morse taper socket with a tapered drift, or the cross pin driven out and the tang removed so it can be used with a standard draw bar. It’s the first and only time I’ve seen that design on any MT tool shank. Although I would guess there could be other manufacturers that may have done the same as well.

I’ve also seen a few MT tool shanks at a mostly off shore tool supplier, and even visually the tang was too short. Mentioning that and being told all I would have to do is drill and tap for a bolt to extend it didn’t get a sale. So there might be at least some MT tool shanks that aren’t being produced to the correct standards as they should be.

In theory and if its true that the tang isn’t meant to help resist the torque loads. It’s only my own guessing and might be worthless, possibly some manufacturers decided to still add a slotted recess for the tang as a selling feature? Those machine tool manufacturers know far more than I ever will, but none of my lathes have had or seem to need it.

In comparison, the Morse tool shank and socket tapers have a very large surface area contact compared to a tool taper like the R8. Used within the limits of that taper, an R8 which is considered as a (semi) self releasing taper and will still hold with the correct draw bar torque. A Google search seems to indicate although I happen to think its questionable. Without step drilling, the R8 should be capable with up to 1″ /25 mm drills, and MT 3 to 1-1/8″ / 31 mm. But MT 4 seems to start with anything above 1-1/16″. From my perspective and with enough torque to twist the tang off, that still isn’t going to do anything to protect the tool socket or tool taper from damage. And would be one of the more difficult and expensive areas to properly restore. G. Thomas went into some detail about how close MT sockets and tool shanks have to fit together and the tight tolerances for taper angle, size and surface finish to resist the torque and prevent spinning the tool shank inside the taper.

[Robert Atkinson 2Participant @robertatkinson2]

Can someone in the “ejection only” camp explain why the ejection extension is flat and has a matching slot in the female? A round extension and no slot is much easier to make and will work just as well for ejection but have no anti-rotation capability. It does not matter if the extraction wedge acts along or across the tang.

My view is that rightly or wrongly it was originally for drive and extraction and has been keep on the male for compatibility with older machines. The only reason for keeping the slot, as opposed to a round hole, in the female is protection against spinning.

This is just my opinion but all the stuff on blogs is just someone’s opinion as well unless supported by references. It’s easy to find a post that supports a particular view.

Robert.

[Graham MeekParticipant @grahammeek88282]

As I said earlier I am not out to try and convert the “died in the Wool” devotees.

The slot in the Spindle, or Tailstock Barrel, and a Flat Tang requires less material to be removed and is therefore a stronger design.

The presence of the Extraction Slot provides the space for the Tang without sacrificing strength.

Having a slot across the diameter is never a good idea when transmitting power. Reducing the amount of material in this region still further to accommodate a Circular Tang would not be a good idea from a Designers point of view.

 

Regards

Gray,

 

 

[duncan webster 1Participant @duncanwebster1]

A round extension and no slot won’t work for a machine where you use a taper wedge in the slot to get the drill out.

[Bo’sunParticipant @bosun58570]

A Jacobs taper doesn’t have a tang, and I’ve not had one slip yet, so I (personally) have to conclude that the tang on a MT is not their for driving.  Especially when the Jacobs taper is generally a little larger and clearly not as long.

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