Morse taper spec.

I have just turned my first morse tapers; some plugs for the centre of a rotary table. In the process, I refered to the Model Engineers handbook to see what sort of angle I was looking for. I found that there was no reference to degrees, but taper per inch on diameter. Fair enough, but why are they all different tapers? I could understand if the taper increased (or decreased) with an increase in diameter, but they don’t, and the diference is sometimes as small as five, one hundred thousandths of an inch! Can somebody explain the thinking behind these specifications please?

If there was any deep thought about it - which looking at the numbers I too doubt - I reckon it's lost in the mists of time.

The tan of the angle is close to the coefficient of friction for steel on steel. It's possible different sizes were made and tested on different days, with different levels of oil contamination on the different days, so the test house determining the angles found fractionally different ones each time. That sort of design by testing went on at the company I work for when I joined it 30 years ago, and led to similarly bizzare results. All changed now, I may add.

Regards

Richard.

ARC euro trade catalogue has the tapers listed "for reference". Set your top slide with a sine bar and you are good to go.

Morse Tapers vary from one size to the next *WHY did we not use nthe Jarno which is constant for all sizes?)

The only angle that I can recall is 2 degrees 52 minutes for 2MT.

Given the taper per inch, some simple trigonometry should allow the angle to be calculated.

Although I wouldn't fancy my chances of setting the Topslide over one degree 26 minutes!

Using another MT of the same size as a setting master, or Sine Bar and Slips would be my choice.

Howard

My question was not really about how to set the correct angle, it was really about why each size seems to vary erratically by tiny amounts from one size to the next. It seems to make no sense!

Maurice

If I need an MT for something I set up the MT between centers and adjust the top slide with a Dti parallel to the taper.

It works for me.

Why does the sun come up in the morning? Are the stars just pin holes in the curtain of night?

Like all other random engineering stuff it was decided before there was anyone to indulge in debating the reasons on the internet leaving us with the choice to deal with it or use something else :D

I believe Morse tapers originated before accurate means of measuring the angles were commonly available. They were made to match master gauges for each taper. The master gauges were intended to be 5/8" per foot taper on the diameter. They did not get the taper exactly right on the masters.

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I can't find the details, but I'm pretty sure I have seen the discrepancy explained as a 'rounding error' in the method used to set the angles when the Masters were created.

This is worth a look: **LINK**

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3779551/pdf/264_2013_Article_1927.pdf

MichaelG.

Sparey remarked in his day about the Jarno system,which made more sense,but never came into common use.

Why ? Good question,but no answers ! Could be like some of the decisions arrived at by Co Counsels, in that there is no logic to it,and you are not supposed to understand it,just accept it.

I was looking into this recently.

Found this note interesting.

A question often asked within the clinical community is, “what specifically is a Morse taper and can it provide a stable connection between components?” A Morse taper is defined by the angle that the taper surfaces make relative to the longitudinal axis of the component and by the mismatch angle between the male and female part. The original Morse taper angle defined by Stephen Morse for tools was a relatively small angle of 2° 50′, with the mathematical relation that tang 2° 50 = 5 %.

Neil

The question has come up before and no-one seems to know.

As the tapers are precision made I'm confident that the odd angles are deliberate, not an accidental by-product of the way they were machined or calculated.

My guess is that Morse deliberately used a variety of slightly strange angles as a way of detecting patent infringements. At the time quick change tools were an important innovation and the Morse company would want to protect their idea for as long as possible. A Morse taper cannot be independently reinvented; anything to those specs not made by Morse must be a copy, and I think it would be easy to convince a court that the patent was infringed.

Accidental by-products do occur in measurements. Careful analysis of the dimensions of the Pyramids seem to prove conclusively that the Ancient Egyptians must have calculated an accurate value for π, 3.14159... This is a serious shocker, because it means their mathematical methods must have been far more advanced than other evidence suggests. Actually π emerges from the data because the Egyptians often measured distances with a device like a surveyors road wheel. And wheels naturally come with π, it's not a design requirement. π in Ancient Egypt is coincidence, not genius.

Dave

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Me too, Neil ... Which is why I wrote that the paper was 'worth a look' rather than being 'authoritative'

MichaelG.

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I suppose this is the most important statement in it:

... Morse created the taper shank series. Two sets of master gages were made up; one, sent to the Bureau of Standards in Washington, D.C., was accepted as a National Standard. The other remains with the Morse Company.

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International Orthopaedics (SICOT) (2013) 37:2081–2088

Edited By Michael Gilligan on 26/05/2018 09:51:51

There is an article in #26 MEW Nov / Dec 94, " Self Holding Taper Sockets" by Alan Jeeves.

Ian S C

Though interesting, I'm not sure that it's very significant. If they were "rational", it wouldn't be any easier to make them would it?

It would only need one setup on the machine for different tapers, though. Many machines have different tapers at the head and tailstock, and need to make bits for both. It would make it easier to use the same setup.

Regards,

Richard.

I read somewhere, a long time ago and I can't remember where, that the angles were purposely made different so that male and female tapers of different sizes couldn't be wedged together with resulting difficulties in separating them.

George

Magnus Pyke, in one of his wonderful radio talks, said that Charles Piazzi Smyth, the eminent Victorian astronomer, made a series of detailed measurements of the pyramids, and concluded that the builders had used the God-given inch as their unit of length, not the atheistic French metre.

George

This is correct. I can't find the reference for when I made some MT2 and MT4 tapers recently, but the spec was given as a diameter at one end, and a diameter at the other end, and the length of the distance apart of these 2 dimensions. The part that I found was interesting was the tolerance specified on the taper. The outside part could be made to the same taper, with the small end, could be made smaller by 0.0001 inches. The inside taper on the small end could be made bigger by 0.0001 inches. This difference would make then jam/wedge tight together. There was also mention to the reason for the sleeve extension outside of the sleeve, as an area to yield when the smaller sleeve is inserted and drifted to position.

Neil

I've yet to hear and tales of woe of anyone getting Jarno tapers wedged in such a fashion, and they are all made the same angle of taper.