Subject: Interference Fit

From: [email-masked] (The Rifleman)
Date: 1 Oct 1994 03:30:15 GMT

Consider a metal block about an inch thick with a .140" hole bored in it.
A .139" steel dowel pin moves with about an ounze of pressure through the
hole.  What diameter pin would be required for an interference fit which
requires some, but not excessive, hammering using a punch to knock the pin
in?

Should a .142" (.002" over) pin induce the proper interference fit?

Should a .144" (.004" over) pin instead be used for the proper fit?

A pin could be readily obtained in the second size (a wire gauge size), but
a lathe would have to be used to cut it down to .142".

---

From: PAUL <[email-masked]>
Date: Sat, 1 Oct 94 08:06:31 -0500

>Should a .144" (.004" over) pin instead be used for the proper fit?
 
The Interference you have listed will be somewhere between a tight press fit,
and impossible! On the diameter listed, .139" you should be looking for a
MAXIMUM of.0002" interference. (.1392") Ideally if you want to "push" this into
the holeby han
d, without the use of a hammer, you will need to have a size - to -size fit, or
possibly .0001 clearance between the two. It depends on the quality of your
surface finish. The +.004 pin you have listed either will not go in this hole,
or will shear the h
ole on its way in, depending upon how much force is used.
Your options seem limited to:
	1. Find a pin to fit the hole with the fit you are looking for.
		(You need to measure this hole more accuratly!)
	2. Lap the existing hole out to the size of an obrainable pin.
		(MSC sells very inexpensive "Midget Laps" for this very
ds)
			^(sorry, "obtainable pin"))^
E mail back if you have more questions. [email-masked]. Good Luck!