"Flash" wrote in message
...
Ed, I admire your ability to describe this with clarity and precision. A
very thorough and concise job.

I would like to add one application of taper pins which is not so common -
in fixing the wing-spars of some aircraft, a taper pin is used, with some
kind of keeper. Usually, the small end is threaeded, and a nut with washer
keeps it in place, thus allowing no slop or flex. There is an element of
shear involved here.

Flash

Thanks, Flash. Those tapered fasteners with the threaded small end are an
interesting case. Someone mentioned tie-rod ends, or some other suspension
part, that's tapered and held tight that same way. Once you put a screw on
the end you have something that's functionally a little different, but which
does have that property of generating a tight fit along the whole cone -- in
this case, with a preload that can be adjusted with the screw.

The refinement of tapered locating pins came along a little over a century
ago, when the art and science of precision toolmaking and gage making went
through a rapid period of development. It happens that I had to study that
work and that period to help write the 100th Anniversary Issue of _American
Machinist_, back in 1977, and since then it's been one of the most
interesting parts of the machine trades to me. There were a lot of brilliant
people who perfected the art, and then turned the whole thing into a
combination of art and science. There are few people I can talk to about
things like diamond pins, toolmaker's buttons, and toolmaker's faceplate
work. They don't believe that people could work to tenths, or even better,
in 1900. Or, they think I'm nuts to care about it. d8-)

--
Ed Huntress



"Ed Huntress" wrote in message
...

"Bob Engelhardt" wrote in message
...
A taper pin is so much more work to use - is it that much better than a
split pin (aka spring pin)? Or, putting it another way, in what
circumstances would a split/spring pin be inadequate and a taper pin be
required?

Thanks,
Bob

Roll pins (spring pins) are made to keep things from falling apart. Taper
pins are made for precisely locating parts relative to each other.

For example, a roll pin might be used to hold a flexible joint onto a
shaft. A taper pin (or pairs of them, actually) might be used to locate
the sections of a multi-part stamping die on a common die plate.

There has been some inappropriate use of taper pins in the past. Today,
there is some inappropriate use of roll pins. Roll pins flex and have
limited ability to locate. But their shear strength is adequate for many
jobs that formerly depended upon straight pins.

To get the big picture, you have to consider four kinds of pins. Straight
pins are used like roll pins, only they're capable of handling much
greater shear loads. They might be used to hold a drill chuck onto a
spindle, in a light-duty application. To keep the pin from falling out
and to prevent backlash, the pin might be a press fit into its hole.

A roll pin is a cheaper way to accomplish the same thing, with much less
shear strength but with an easier press fit. They've replaced straight
pins in many production applications.

A taper pin should not be used to hold things together, without some kind
of clamping or other locating to hold them in place. A screw tapped
alongside of the head of the taper pin, with the screw head overlapping
the edge of the pin, is one way to accomplish this. In much tool work,
the pins are not subject to strong shear loads so they may hold without a
clamp. But they can slip out of their holes without a clamp.

The fourth kind of pin is just a further illustration of what the taper
pin is about. It's a tapered diamond pin. It only contacts the work along
two lines, rather than a long the sides of a cone. It's used only for
super-precision locating in gage work, and in making master tooling
that's used only to qualify the production tooling. The idea is that you
can't get perfect contact on each of any pair of tapered pins, but you
can locate one tapered pin perfectly and then restrain motion relative to
that pin by locking the part along two lines that lie on the radius of an
arc from the tapered pin.

I know, following that in words -- or my words -- can give you a
headache. g If it's important, I'll try again. But the point is that
there are two ends of the scale in terms of locating precision, and roll
pins are at the low end. But roll pins stay in place and do the job well
when all that's required is to keep parts from slipping apart.

--
Ed Huntress