Pin punches and polymer...

**JohnKSa** · December 28, 2014, 11:26 PM

Be sure you properly maintain your pin punches, especially if you are using them with polymer parts.

With hard use, the end of a pin punch can flatten and a sharp lip can develop around the edges. That's not good even for use in metal parts, but it's especially bad if you're using the punch with polymer parts.

The lip increases the diameter of the punch and that, plus the fact that the lip tends to be sharp, means it can easily ream out the holes in the part to a larger diameter, creating a loose fit when the pins are reinstalled.

It's a good idea to occasionally check the ends of your pin punches. If the ends start to flatten and develop a lip, carefully remove the lip with a file, a whetstone or even a piece of sandpaper.

I go a step further with punches I use on polymer parts. They get a slight chamfer on the end. Not much, just enough to insure that the edges of the end of the punch are slightly rounded. That insures that even if I get a little sloppy or careless with the punch, it's unlikely that I'll shave the soft polymer material from the inside of the hole.

CowTowner · December 29, 2014, 07:58 AM

I recall being taught this lesson in 7th grade wood shop (1971?). The instructor had an example of a mushroomed tip punch he showed every student. Then he would take each of us and show us how to use the stand grinder to correct the issue with other "practice" punches. Killed two birds with one rock. Punch safety and grinder safety/use.

**4V50 Gary** · January 3, 2015, 12:28 PM

Good tips guys. We didn't get enough of tool maintenance at school. The program can easily be made into a three or four year program if they included more hand tools and their maintenance (as well as the artistic element and CNC operations). We did grind the faces of our ball peen hammer smooth.

Dixie Gunsmithing · January 3, 2015, 12:51 PM

It's a must to never use a mushroomed hammer. A piece can fly off and do damage, to the point of penetrating skin and muscle.

On punches, I generally spin the tip against a stitched polishing wheel with 120 grit applied. It doesn't take much to clean one up. I also have a collection of odd sized punches I've made, to fit oddball pins over the years, by reshaping them in a similar manner, or grinding them down, then polishing them for a final fit.

December 28, 2014, 11:26 PM	#1
JohnKSa Staff Join Date: February 12, 2001 Location: DFW Area Posts: 24,969	Pin punches and polymer... Be sure you properly maintain your pin punches, especially if you are using them with polymer parts. With hard use, the end of a pin punch can flatten and a sharp lip can develop around the edges. That's not good even for use in metal parts, but it's especially bad if you're using the punch with polymer parts. The lip increases the diameter of the punch and that, plus the fact that the lip tends to be sharp, means it can easily ream out the holes in the part to a larger diameter, creating a loose fit when the pins are reinstalled. It's a good idea to occasionally check the ends of your pin punches. If the ends start to flatten and develop a lip, carefully remove the lip with a file, a whetstone or even a piece of sandpaper. I go a step further with punches I use on polymer parts. They get a slight chamfer on the end. Not much, just enough to insure that the edges of the end of the punch are slightly rounded. That insures that even if I get a little sloppy or careless with the punch, it's unlikely that I'll shave the soft polymer material from the inside of the hole. __________________ Do you know about the TEXAS State Rifle Association?

December 29, 2014, 07:58 AM	#2
CowTowner Senior Member Join Date: October 17, 2007 Location: Cowtown of course! Posts: 1,747	I recall being taught this lesson in 7th grade wood shop (1971?). The instructor had an example of a mushroomed tip punch he showed every student. Then he would take each of us and show us how to use the stand grinder to correct the issue with other "practice" punches. Killed two birds with one rock. Punch safety and grinder safety/use. __________________ NRA Chief Range Safety Officer, Home Firearms Safety, Pistol and Rifle Instructor *“Today, we need a nation of Minutemen, citizens who are not only prepared to take arms, but citizens who regard the preservation of freedom as the basic purpose of their daily life......”* President John F. Kennedy

January 3, 2015, 12:28 PM	#3
4V50 Gary Staff Join Date: November 2, 1998 Location: Colorado Posts: 21,829	Good tips guys. We didn't get enough of tool maintenance at school. The program can easily be made into a three or four year program if they included more hand tools and their maintenance (as well as the artistic element and CNC operations). We did grind the faces of our ball peen hammer smooth. __________________ Vigilantibus et non dormientibus jura subveniunt. *Molon Labe!*

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January 3, 2015, 12:51 PM	#4
Dixie Gunsmithing Moderator Emeritus Join Date: April 27, 2013 Location: Ohio Posts: 1,923	It's a must to never use a mushroomed hammer. A piece can fly off and do damage, to the point of penetrating skin and muscle. On punches, I generally spin the tip against a stitched polishing wheel with 120 grit applied. It doesn't take much to clean one up. I also have a collection of odd sized punches I've made, to fit oddball pins over the years, by reshaping them in a similar manner, or grinding them down, then polishing them for a final fit.