Metal Hand Stamp via Forging

[mb44kar]

I recently gave myself an interesting problem - I wanted to be able to manufacture metal hand stamps, the kind hit with a hammer for marking metal, in the way they were made before CNC. Nowadays I get the impression they are hardmilled or milled and then hardened, using a vertical CNC mill. And I've seen one-offs done with an angle grinder and dremel.

But looking into it online, some posts on Practical Machinist seem to indicate that before CNC they were made by hot-pressing into a master die block. So a master die block made of some heat-resistant tool steel would be engraved (maybe via pantograph) and then hardened, and then the blank stamp would have its front end heated to forging temp and pressed into the die block engraving. Maybe touched up afterwards by light grinding or polishing, no idea there though.

I've tried to recreate this: I milled myself a pantograph attachment for my milling machine, and engraved a D2 block with a shape I want a stamp of (in this case a diamond, traced off of an old Black Diamond file). I hardened the D2 block and made a stamp-holder (forged and welded 1/4" mild steel plate) which attaches to the die block and holds the blank stamp. I've tried several rounds of heating up the blank and hitting it into the die block on my anvil, both with a 2.5 lb forging hammer and a 5 lb sledge. I know ideally the die block would be H13 but I didn't have any on hand when starting the engraving.

Here are some pics of my journey. Showing the engraved die block before heat treat, turning the stylus in the lathe to fit the diamond I wanted to copy, the setup on the anvil and the stamp blank holder attached to the die block. Last pic is the result so far after using the sledge. It stands proud of the surface by more than enough to feel with the finger tip, probably 0.010", but I need way more than that. I'm wondering if anyone here knows much about this manufacturing process before CNC came around and how to get better results.

Is this impossible with a hammer and anvil, do I need a big drop hammer or a hydraulic forging press? Maybe a better way to heat the blank than a MAPP torch? I was thinking it would be nice if I could get an induction forge and have the coil built into the stamp holder so that the blank passes through that and gets proper yellow hot right before the hammer blow, minimal heat loss from time spent getting into the holder. But those are out of my budget for the moment I think. Anyway let me know what you think!

[LeeJustice]

Was the end of your blank completely flat?  I am thinking that a domed or a raised dimple of material to provide the metal to form down into the die until the face becomes flat.

[mb44kar]

Yes it was completely flat, just faced off in the lathe and then given that slight taper. I'm turning these blanks from 3/8" O1 square stock.

I didn't think about giving it a starting form like that, really good idea. Probably I'll leave a nub approximately the width of the diamond when facing the blank, and maybe smooth the edges over so it doesn't have a hard corner to force into the die.  Then the hammer blows won't have to push back the entire face of the blank, they'll just have to form the nub into the die. I'm probably also dealing with the stamp holder sucking heat out as I fit the blank down into it. I left a 0.005" slip fit after welding (using a small square file), also taking into account the expansion of the blank by about 0.011" at 1800 degrees. Let me true up this test blank and give that dimple idea a try.

Edited September 18 by Mod30
Remove excessive quote.

[LeeJustice]

Great, I hope you get a much better result.

[JHCC]

51 minutes ago, mb44kar said:

I'm probably also dealing with the stamp holder sucking heat out as I fit the blank down into it.

You might try drilling some holes in the stamp holder to reduce its mass and the total area actually in contact with the blank, while still keeping the necessary rigidity to align the blank and resist the hammer blows. 

Keep us posted on how it works out!

[mb44kar]

On 8/16/2024 at 9:46 AM, LeeJustice said:

Great, I hope you get a much better result.

Pictured are the results using the nub shown, after facing off the last attempt (which took some annealing despite not being quench-hardened) and dressing the sides. Definite progress but the pre-forging nub needs better shaping, probably not as much length

On 8/16/2024 at 10:05 AM, JHCC said:

You might try drilling some holes in the stamp holder to reduce its mass and the total area actually in contact with the blank, while still keeping the necessary rigidity to align the blank and resist the hammer blows. 

Keep us posted on how it works out!

I hadn't gotten a chance to do this yet, I will try a few small holes.

[LeeJustice]

Maybe make the diamond die bigger?

[JHCC]

18 hours ago, mb44kar said:

Definite progress but the pre-forging nub needs better shaping, probably not as much length

Agreed. You probably want the total volume of the nub to equal the volume of the diamond, so that it fills the die without any non-compressible excess.

[mb44kar]

On 8/19/2024 at 8:21 AM, LeeJustice said:

Maybe make the diamond die bigger?

I should probably do this but the size is just about right for the application (stamping a knife). And would require figuring out how the positioning on my pantograph works more than I currently understand it. But it would give me an excuse to make a new die out of H13. Speaking of, where do you guys source your H13 from?

On 8/19/2024 at 9:34 AM, JHCC said:

Agreed. You probably want the total volume of the nub to equal the volume of the diamond, so that it fills the die without any non-compressible excess.

Yeah, it's going to take a few tries to guesstimate it properly. I tried drilling out the center of the nub that first time both to remove material and to pre-shape it a bit, but even after heating in the forge and letting it cool in the forge after turning off the propane, it was still too hard for my HSS center drill. A smart way is probably put some play-doh or something similar in the die and then scrape off the excess, then scrape out the amount that fills the die and form it into a cylinder and measure that.

[JHCC]

Certainly a good starting point!

[BillyBones]

23 hours ago, mb44kar said:

Speaking of, where do you guys source your H13 from?

I get mine from Alro. They usually have a few drops of tool steels available. I know there is one in Columbus, just not sure where. 

[mb44kar]

Okay here's the latest two attempts, I wasn't able to keep at this too much till now.

The light colored example was fairly successful in that the stamp blank fit into the holder when hot, and nothing untoward happened during the process. This was after using a much smaller nub than previously shown, with a much deeper center-drilled portion which may have been too much given that a circular divot is still visible in the final product. But in terms of correct amount of material, much closer.

The dark colored one never got quite into the holder, as it was an annealed prior attempt that was re-machined and still had some bend/bow from the first attempt. It still has its pre-forming nub intact. Just shows how tight the fit can be, even though the holder's square hole is about 0.016" oversize, after being in the forge the gap is more like 0.002" on each side I think.

 

Blanks can bend too easily in the holder, as its connection to the die is pretty horrible and prone to rotate about the axis of the bolts. I need to mill another die that has dovetails, and machine (instead of fabbing) a proper holder that has mating dovetail surfaces.

I also have yet to drill those heat-holes in the blank holder, but with these results (and how often blanks will have their faces come out at an angle), I need to remake the holder anyhow.

[Goods]

Have you thought about just heating the tip of the stamp with a small oxy torch in the holder, suspended just above the die?

Keep it fun,

David

[mb44kar]

I did, I was against it at first because I didn't want flame that close to the die block. It's D2 so not resistant to hot work and the impression would bend and wear with use. But If I'm going to remake it anyway, maybe I'll give this setup one last try that way before remaking it all. I drew up some much simpler plans for the die and holder, making them cylindrical since all this is way faster on a lathe than a mill. Only added difficulty from that is keying the cylindrical holder to the round die block. But I'll give both a try.

[Frosty]

D2 is way overkill for your die, you aren't going to be stamping a part every half second, it's a one off tool, don't heat the die to red or use a simple steel, say 1080. 

If your set up makes it so you can't drive the punch into the die while it's yellow your guides are too complicated.  Or perhaps you're trying to heat only the little button you machined to accept the pattern. If that's what you're doing you don't have a chance, the shaft WILL suck the heat right out of it. Heat the bottom 1/2" to yellow and drive straight down on the other end of the shaft or the die. Heck, you might get away with heating 1/4" even.

If you're bending the pattern end you aren't striking straight down the shaft. You can rig a sledge hammer and mount the anvil so it strikes the top of the punch moving vertical down, the handle will be horizontal. Make your guide open so you can press the punch blank in with tongs while you stomp the treadle. You could rig the torch so it's burning a couple inches from the guides so you can have it placed and hit in maybe one second after taking it out of the flame.

I think I've said all or most of this before already. People have been making pattern punches for a couple millennia, don't over complicate things.

Frosty The Lucky.

 

[mb44kar]

On 9/18/2024 at 12:34 PM, Frosty said:

D2 is way overkill for your die,

Frosty The Lucky.

 

I like to make things way overkill! What if 5 years from now I suddenly wanted to make 10,000 of these one-off stamps (by hand)? Kidding aside, I can actually get off cuts of A2/D2/H13 in round bar and square bar of considerable size much easier than I can get similar sizes of 1080 or 1095.

The guide is a tight fit at a yellow heat, some of the heat on the face has definitely dissipated by the time I strike on the back end. It takes a second or two of fiddling to get it in the guide, then a second to switch hands to the hammer and the other holding the guide and die, then the strike, usually 2 or 3 hits in quick succession. I've been heating the whole thing in a small propane forge, with the pattern face towards the heat source so it heats up that half to about yellow but the back is not yet red.

The stamp blank is allowed to bend due to the guide/holder rocking back during the striking, as it is only held onto the die by 2 bolts that are on the same axis, so plenty of freedom to rotate along the bolts' shared axis. But definitely true that if I were able to strike very truly straight then this degree of freedom would not matter too much. This is what I aim to fix in the next iteration of blank holder. With this other good suggestion about heating the blank while in the holder, I will try to add a port or a large opening for the flame to go through the holder and hit the blank. The current holder has some dead space between the end of the part that grips the blank and the die itself, open to air that can be used for heating.

I was also thinking maybe a treadle hammer is the way to do this and get serious force into it quickly. But that's a whole other can of worms to open up, building a treadle hammer in the middle of this project . I'd probably want to make one of the heavier style, with a solid round/square ram and the roller wheels around the ram, with a full welded frame. Maybe give the ram 50 or 60 pounds. Again I love to build overkill. I have even thought about building a larger drop-style hammer, just because it would be cool I think.

Many thanks for your help Frosty, I will try to mitigate my bends with better rigidity in the holder first, but treadle hammer is next on the list.

Edited September 19 by Mod30
Trim quote.

[Frosty]

You're making a common mistake here. Over kill does NOT mean overbuilding, more complex too often makes the design or tool less effective, weaker, etc. 

When I suggested an open guide I meant a V guide. Two pieces of angle iron welded edge to edge on another piece of plate or angle iron. I have lots of different sizes so I won't specify. The two lengths of angle iron welded together need to be pretty short, certainly no longer than the punches. This will get welded to the base plate but later. 

Make a center punch with the same dimension square stock you're using for the punches. and mark exactly where the point contacts the blank stock you're going to make your master die from. Trim the angle die so the master die is wedged firmly when in place.

Using the center punch mark as center carve your master die. Wedge and maybe clamp it in place ready to receive the abuse of a BIG hammer.

To hold the punch blank you can make a strong spring clip or a slide down bar. The bar retainer is as simple as a piece of steel that goes across the V guide and has a retainer to hold it in position. Lousy description but I'm bushed, I've been fighting to mount my snow plow and the landing jack is now wedged under a rock I'm going to have to dig out with a pinch bar before I can throw the locking latch. <sigh>

Anyway, you should be able to come up with an easy to drop in place retainer. 

Or modify a pair of tongs, one to hold it while you heat it and the other to hold it in the V guide. While you smack it with the hammer. A special tong might be more hassle than it's worth. I'm not thinking too clearly right now. I'm sure lots of the gang here can come up with better ideas than I have right now. I keep seeing different ways to index and hold the punch blank and the voices are starting to argue.

Frosty The Lucky.