WHY THE TANG?

I beg to differ Nigel, the thread title says Why the Tang?, as in why is it there. If it's there because of manufacture in the first instant but adds utility in use both are relevant would you not say.?

I repeat I have no proof of this but it would explain anomalies like why is it not sufficiently strong as a driver of drills, and why do something complicated like a tang just for ejection. I feel my conjecture must stand as a candidate for the primary reason of it's existance and form and is worth further investigation.

regards Martin

.

Do please let us know if you find anything definitive, Martin

MichaelG.

If a MT is used with a self extracting device, like some lathe tailstocks, then the tang is nothing but a liability. I cut the tang off the chuck for my mini 7 x 12 tailstock, drilled a hole into the end after facing it off which was slightly bigger than the leadscrew size and put a thin brass plug down the hole for a bearing. I have gained 3/4" travel before the self extraction takes affect, which is a lot on a small machine. We will also be doing a similar mod to the 12 X 24 Atlas lathe to increase its travel also.

It may not get us much further in the debate, but I’ve just found : **LINK**

https://worldwide.espacenet.com/patent/search?q=pn%3DUS924388A

There is a clear statement on lines 12-16

... and his patent claims an improvement upon that ‘customary manner’

MichaelG.

.

Edit: pardon the digression, but I must also share this delightful drilling machine:

https://worldwide.espacenet.com/patent/search?q=pn%3DUS1224A

Edited By Michael Gilligan on 20/09/2020 09:17:31

I think you can write more-or-less what you like in a patent application, so long as it's not libellous or otherwise actionable.

It doesn't have to be true.

It looks as if their hardening processes were a bit different back then. Since the '70s, I've seen lots of twiste tangs, and a few broken with clear signs of twisting deformation before failure, but the drawing suggests it broke abruptly without deformation, as if hardened completely.

Edited By Mick B1 on 20/09/2020 10:41:35

.

I was only referencing the observation in lines 12-16 as being relevant here, Mick

... are you suggesting that he lied about what was the then ‘customary manner’ ?

MichaelG.

.

Edited By Michael Gilligan on 20/09/2020 11:10:46

On Googling "Why do large drills have tangs" I came across a reference which stated that on larger machines, if the drill taper slipped, and quill feed continued, damage could be done to the machine. Having a tang prevented the taper from slipping. As we all know?? Its the taper that does the work, but if the taper were compromised by trapped swarm, burrs etc, then the taper comes into play.

I could live with that explanation.

Bob

I still think my earlier thought is more logical.
If you sat down and decided that a taper was a good way of holding a twist drill then after drawing the bit and the socket your next thought would be how would the bit be extracted? Drilling machines of the day had long drive shafts in which it would not have been practical to drill a hole. The obvious thought then is to drill a cross hole at the top of the drive socket. A simple hole though would not suffice, it needs to be a slot? Once you have this slot you then need to consider the design of the end of the drill bit. It can be any shape provided a drift can act upon it to remove the bit. At some point you would realise that the tang shape we see today would not only provide a means of removing the bit but also prevent rotation.

Modern milling machines don’t have the same limitations as drilling machines but the habit has persisted because it works perfectly well.

Lied? Far be it from me to suggest such a thing!

I'd say he (perhaps inadvertently) overstated the importance of a partial auxiliary factor in order to emphasise the value of his invention.

I think the fact that the engineering industry has proceeded for over a century without conspicuous takeup of this invention largely bears this out.

IMO Speedy Builder 5's find is as good as it needs to be.

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

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.

.

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

MichaelG.

[for what it’s worth]

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

https://www.flickr.com/photos/ctarchives/6076144009/in/photostream/

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.