"Steve Lusardi" wrote in message
...
Ed,
That's a good explanation of the use of tapered pins, but as a user of
tapered pins over many years I have to disagree with them ever falling
out. In point of fact, once they are set, they can be very difficult to
remove. Also, another really big advantage they have over other types of
pins is that they do not remove as much shaft strength, as other types
often cause shaft failure at the drilled hole.
Steve

Yeah, the "falling out" is more theoretical than real. If you press a steel
pin into a steel hole with any force, even if it's tapered, it can stick
there like it's welded.

But, technically, even a locking taper can't take certain kinds of cyclic
forces without coming loose. Anyone with a B&S-taper milling machine, or
even a Morse or other "self-locking" taper, probably has had a tool drop out
at some time in their lives. Hopefully, it's been a rare experience for
those who have had it happen (I have).

I never did any real-world toolmaking but I studied the hell out of it
decades ago, when I covered tooling for magazines and then when I sold EDMs.
Once upon a time I knew more about tapered pins, much of which I've
forgotten. But the basic principles are there.

In any case, their purpose really is locating rather than retaining.
Straight pins and roll pins are for retaining.

--
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