VaughnT

The Dreaded Dimple!

Recommended Posts

When I make some of my hooks, I like to forge in a countersink for the mounting screws.  My go-to punch is made from a car coil spring, 5/8" in diameter, tapered and ground to a nice angle.  I might have heat treated it back when i first made it, but I can't remember.  I'm sure the HT has gone the way of the Dodo by now.

Anyhow, lately I've been getting this dimple forged into the end when I forge the countersink.  This one formed after just ten dimples were forged into the hooks.  That might not sound bad, but when you have a few dozen hooks to make, having to stop and dress the punch is both aggravating and changes how the countersinks look -- not a good thing.

Generally, I'll drive the punch in with three hits, then quench it in water.  Maybe I'll add a fourth hit before quenching, but cooling the working end is certainly on the list of things to do.  Most of the time, I drive it in until I can feel the anvil underneath.  Not all the time, but enough....

So what's the science behind this?  You wouldn't think the force of rebound off the anvil would upset the punch, driving some of it back up into itself.  But, for every action there's an equal and opposite reaction.

What can be done to eliminate the dreaded dimple so a punch will last longer?  So far, the only thing I've come up with that definitely works is to drill the screw holes and then use the punch to make the countersink.  This means the tip of the punch is actually traveling through air, not the steel, while the sloped portion forms the countersink.  It also means you usually have to go back and re-dril the holes to clean them up, but it does keep the dimple from forming.

Do the countersink first, though, and I seem to be stuck with the dreaded dimple.IMG_6372.thumb.JPG.d7dd54bc10a5f4dd83d97b059e0f1946.JPGIMG_6374.thumb.JPG.b0d4cad8638cda156cf30466259cc39f.JPG

Share this post


Link to post
Share on other sites

No doubt someone more knowledgable will be along shortly, but i'd hazard a guess that it needs heat treated again, and cooled more frequently when in use.

I've made several punches from coil spring, and put them through a fair bit of abuse to date, and none have done this.

Even striking them into cold steel to make a guide mark doesn't really affect the heat treated tips.

Share this post


Link to post
Share on other sites

I've used coil springs a lot to make center punches.  What comes to mind when I read your text above are these points.  Quench in oil, not water.  Don't drive the punch at all before quenching.  Heat treat the material first, normalize it, then heat treat again to non-magnetic and quench it.  Run the colors to a straw gold.  But, you probably have tried this.  So, Good luck and let us know what you find that solves the problem. 

Share this post


Link to post
Share on other sites

It is not a dimple, it is an eye punch. (grin)

Share this post


Link to post
Share on other sites

Ah, you grabbed the eye punch by mistake. Make another counter punch and save this on for something else. 

Oh, use  garage / yard, etc. sale chisel, punch, etc. for stock. All you need do is grind it's already heat treated to take impacts.

Frosty The Lucky.

Share this post


Link to post
Share on other sites

I would give that one another heat treat and then keep it as a perfect eye punch. Then make another for your countersink. And BTW, I like the way you countersink the screw holes - a method I have adopted from your previous posts. Thanks.

Share this post


Link to post
Share on other sites

Thanks gents.  The problem isn't repurposing this punch into an eye punch, something I've been considering.  But, the fact that it happens at all.  

When I saw it happen to the punch I made from a cheap chinese chipping hammer from the hardware store, I put it down to the garbage alloy they must have used.  I was wrong, apparently, because this dimple formed in just a few hooks.

What causes the dimple is a mystery.  The only thing I can come up with is some kind of rebound effect since the only odd thing about what I'm doing is feeling the anvil through the punch when I make that last hit.  It doesn't happen when I pre-drill the screw hole, even if I bottom out and the tip hits the anvil.  There's got to be some weird science going on.

Ausfire, it's an honor to have played a part.  I love what you've done with those nails!

Share this post


Link to post
Share on other sites

I get that effect on my round end power hammer punches when I either over-drive and work the tool down too close to the bottom die or when I try working a piece too cold.  

Share this post


Link to post
Share on other sites
1 minute ago, Judson Yaggy said:

I get that effect on my round end power hammer punches when I either over-drive and work the tool down too close to the bottom die or when I try working a piece too cold.  

That makes sense. Hypothetically, if the tip of the punch is hot (and therefore slightly softened) and the walls of the hole are cool (and therefore more rigid), I can see the downward force of the blow forcing the edges of the punch tip inward.

Share this post


Link to post
Share on other sites

Many smiths dip the punch in water after striking with it, two times.

Works for me.

I would keep the eye punch and smith a new 'countersink' one. 

Incidentally, You/this thread has given me a new idea for crafting some eye punches that will entail a little less work/time.

Thanks.

Regards,

SLAG.

Share this post


Link to post
Share on other sites

Does the stock you're countersinking have a corresponding bump in the bottom of the hole?  If so, it seems like that would suggest the slug of stock material is flowing to the point of least resistance which is the heat-softened point of your countersink.

I would be curious if you could make a countersinking taper that terminates in a cylindrical punch.  With a matching backing plate it seems like you could punch the slug and achieve your countersink without having to dress the hole or the punch.  Alternately, the cylindrical part could ride your drilled pilot hole to keep it from deforming during countersinking.

 

Share this post


Link to post
Share on other sites
1 hour ago, rockstar.esq said:

Does the stock you're countersinking have a corresponding bump in the bottom of the hole?  If so, it seems like that would suggest the slug of stock material is flowing to the point of least resistance which is the heat-softened point of your countersink.

I would be curious if you could make a countersinking taper that terminates in a cylindrical punch.  With a matching backing plate it seems like you could punch the slug and achieve your countersink without having to dress the hole or the punch.  Alternately, the cylindrical part could ride your drilled pilot hole to keep it from deforming during countersinking.

 

The stock does have a bump in the bottom of the hole.  The only thing I can imagine is that there's some kind of bounce-back caused when you get to that last strike and can feel the anvil jus like you do if you're trying to punch a hole.  

On this last go around, I was extra careful to quench the tool in water after every third hit.  Starting with a fresh grind, the divot formed in about ten hooks, or thirty strikes. 

I have been thinking about making some kind of punch like you describe.  It seems like it would be a very convenient way of doing it, and I've seen it done in industrial applications.  Not sure what alloy you'd want, though.  It'd have to be something tough that'd stand up to the heat and not wear round on the punching part.

Share this post


Link to post
Share on other sites

Interesting, never had that happen. And many of my punches are car spring and basically heat treated as you described.

Perhaps it's forged from "eye of China" steel.  ;)

Share this post


Link to post
Share on other sites

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now