OT: At What Angle Does a Machine Taper Become Self Holding

Spyderedge · Mar 26, 2016

At what angle does a machine taper become self holding/locking?

R8, B&S, MT, and similar tapers have to be pounded out of their sockets, while the 2A collets from my lathe, and C series collets just pop free when the draw tube is loosened.

Let's say for this question both collet and socket will be machined to a standard tolerance and very lightly oiled (like would be in a shop scenario)

R8 collets have a ~17* included angle, and 5C 20* included. So the difference between self holding and not must be between those two....

TDegenhart · Mar 26, 2016

The locking angle is about 7 degrees per side.

Tom

johnoder · Mar 26, 2016

NMTB 30-40-50 are not self holding and are 3.5" taper per foot on dia. - about 16.6 degrees included

CalG · Mar 26, 2016

It's a Trig function of the friction coefficient of the two elements. I don't recall the details, The description may be in Machinery's Handbook.

JohnMartin · Mar 27, 2016

johnoder said:
NMTB 30-40-50 are not self holding and are 3.5" taper per foot on dia. - about 16.6 degrees included

I know they're not SUPPOSED to be, but my horizontal mill usually takes a couple of good hits with a lead hammer on the drawbar to get it to release. NMTB 40. Spindle taper and toolholders/arbors are in very good shape.

dian · Mar 27, 2016

what does "self holding" mean? that you have to tap them out? that they work without keys? that you dont need a draw bar? chuck tapers are self holding for sure.

gustafson · Mar 27, 2016

dian said:
what does "self holding" mean? that you have to tap them out? that they work without keys? that you dont need a draw bar? chuck tapers are self holding for sure.

Pull a hub off of an axle and you will know what 'self holding' means.

When you can toss it on and it sticks all by itself, that is self holding

Shallow enough and heat and mechanical advantage are needed

Ringleboy26 · Mar 27, 2016

TDegenhart said:
The locking angle is about 7 degrees per side.

Tom

In college we were taught anything less than or equal to 7 degrees.

Peter from Holland · Mar 27, 2016

Not a single taper is selfholding when sideforces are applied

Peter from Holland

johnoder · Mar 27, 2016

peterve said:
Not a single taper is selfholding when sideforces are applied

Peter from Holland

None the less, these functioned or they would not have been for sale for years and years. Being milling cutters, they were side loaded.

IronReb · Mar 27, 2016

JohnMartin said:
I know they're not SUPPOSED to be, but my horizontal mill usually takes a couple of good hits with a lead hammer on the drawbar to get it to release. NMTB 40. Spindle taper and toolholders/arbors are in very good shape.

Every machine that I have ran in my life with those tapers has to be wacked lose when changing out.
But none have ever stuck in by hand, they only seat once pressure is applied with a draw bar.

I am thinking these tapers were meant to be none self holding like a morse taper is due to the difference in there functions.
I cant recall any morse taper tools used for anything other than drilling/tapping etc.

Peter from Holland · Mar 27, 2016

johnoder said:
None the less, these functioned or they would not have been for sale for years and years. Being milling cutters, they were side loaded.

The taper is for positioning not holding The drawbar holds it
Perhaps a good way to seperate a drillchuck from its taper is by using it with milling

Peter from holland

johnoder · Mar 27, 2016

In case not noticed in the scan, there is no provision for draw bar

peterve said:
The taper is for positioning not holding The drawbar holds it
Perhaps a good way to seperate a drillchuck from its taper is by using it with milling

Peter from holland

hanermo · Mar 27, 2016

The morse taper tools are self locking.
The most built, most iconic, first common good mill, Bridgeport (M head) has an MT2 (some B&S#7 iirc).

MT2/MT3 is still common on many small manual mills (asian imports).
And I think many milling machines/jig borers used MT2, 30-40 year back.

MT (and R8) are power limited.
MT2 == 1 hp/1kW.
MT3 == 2 hp/2kW.
R8 == 3HP/3 kW.
Ie max power you might see with those tapers is approx 2-3 kW on an industrial tool (ie real output power).

ISO30 seems to be 10 kW-15 kW, iirc (might be wrong).

A Haas DT1 has a 40Hp=25 kW vector drive inside.
(At least our demo machine had.)
Its settings limited to the 11 kW (Very Good Idea, btw. Cheaper to make lots of big VFDs, and a bigger VFD, lightly used, lasts forever).
Its sold as an 11.kW machine BT30 (ISO30 taper).

My Bp M head circa 1940, has original Bp 3-phase motor.
Its 1/2 Hp, and I drive it with a Hitachi 2.2 kW VFD, 220 V, single phase (euro power).
I just set the VFD to the right amps, ie 3 or so.
The motor and head are nearly noiseless at low revs (200 rpm or less).
MT2. Imperial (yuck).

IronReb said:
I cant recall any morse taper tools used for anything other than drilling/tapping etc.

bryan_machine · Mar 27, 2016

Deckel milling machines before sometime in the '60s are MT4, but with a drawbar peculiar to them. This yields a tool which is held in by drawbar to support milling, which needs a collar on the drawbar to eject the tool.
So MT4 is both locking (e.g. hard to eject) and in-need-of-drawbar to support milling power, on those machines.

(Apparently HBMs used morse taper for a long time as well, something I don't quite understand, since what we now call "40 taper" and "50 taper" seem to have been standardized well before WWII....)

Peter from Holland · Mar 27, 2016

johnoder said:
In case not noticed in the scan, there is no provision for draw bar

Thats probably why they are obsolete
Can you still buy these???? And if so are they being sold
The ones i ever saw in real life all have a threaded end for a drawbar
Also on the cheap chinese machines there is a drawbar
On the big boring machines with MT they used a locking key in a slot in both the tool and spindle

Peter from Holland

abarnsley · Mar 27, 2016

B s Brown and Sharpe No 7 End Mill 1 Inch | eBay

Plenty of new old stock, tanged, taper end mills out there...

Peter from Holland · Mar 27, 2016

abarnsley said:
B s Brown and Sharpe No 7 End Mill 1 Inch | eBay

Plenty of new old stock, tanged, taper end mills out there...

You say it New old stock

Peter from Holland

vanguard machine · Mar 27, 2016

yup, my nmtb30 mill spindle never releases without a few gentle raps with the side of a wrench, the socket and all tooling tapers are in excellent shape

Clive603 · Mar 27, 2016

Getting back to the OP's question the science book answer is :-

The angle with the centreline must be small enough that its tangent is less than the coefficient of friction between the materials from which the mating parts are made.

Naturally in a practical world we need a bit of leeway especially as the scientific answer assumes the surfaces to be smooth which in this context is close to that allowing parts to wring together like a gauge block should the male and female forms be sufficiently similar.

In a practical world the coefficient of friction between un-oiled steel surfaces can be taken as 0.1490. Tan 10° is 0.1763 so 10° and greater is considered a safe boundary for self releasing whilst 7°, tan 0.1227, is similarily safe for self holding.

Morse tapers are around 1.5° so they are very much self holding.

R8 is an interesting one because the taper angle is near enough 8.5° whose tangent is 0.1495 i.e barely self releasing in theory. In practice most of mine are lightly self holding if pushed firmly into place. Much much tighter when the drawbar is done up. Obviously designed that way because self holding tapers should give more repeatable alignment than non self holding. However true self holding makes it hard to get things out and seriously interferes with the gripping ability of a collet due to the inherently high friction between spindle and collet. Hence nearly self holding is a good compromise between accuracy and grip. ER collet angles are similar.

Morse taper collets are an engineering abomination.

Clive

OT: At What Angle Does a Machine Taper Become Self Holding

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