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Radovan Geist




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PostPosted: Thu 05 Oct, 2017 8:12 am    Post subject: Blade-catcher dagger - method of manufacture         Reply with quote

Iīm researching a bit on blade-catcher daggers and got interested in this piece: https://www.flickr.com/photos/98015679@N04/21137350525/in/album-72157658156069811/
Interestingly, it seams that the blade is not made from one piece. Obviously, Iīm not talking about pivoted triangle pieces that are riveted in the slots, but the "comb". It seems that each piece was attached (forge welded?) onto the blade separately. If it were only for two-three pieces, it might have been later repairs, but when you zoom-in, you could see connecting lines on each, and the one missing piece broke exactly along that line.
In fact, that would make manufacture easier than making it in one piece, and then grinding narrow slots along the blade. What do you think?
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Michael B.
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PostPosted: Thu 05 Oct, 2017 1:13 pm    Post subject:         Reply with quote

That's exactly what it look likes. Good catch. That is a wicked looking blade, am I seeing the date right of 1620?
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Tim Harris
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PostPosted: Thu 05 Oct, 2017 7:42 pm    Post subject:         Reply with quote

I'd say you're right Radovan.

If I was replicating that, modern power tools would make it easier to cut and grind than forge-weld, but welding the teeth makes sense in period context.

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Radovan Geist




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PostPosted: Thu 05 Oct, 2017 9:40 pm    Post subject:         Reply with quote

Thank you, thatīs exactly what I thought.
Yes, it could be 1620. Iīm not sure how precise we could be, but I would put it to first decades of the 17th Century.
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Mikko Kuusirati




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PostPosted: Fri 06 Oct, 2017 3:40 am    Post subject:         Reply with quote

Looking closer, it seems that the triangular bits at the ends of the teeth are actually hinged, rather than riveted. Not only are a couple of them visibly rotated around their pins, but having them pivot out of the way (and then back, closing the trap) is also the only way for anything to actually enter between the teeth, since otherwise the triangular bits would close off the gaps completely, making the whole comb structure entirely superfluous.

I think that's the reason for the welded teeth, BTW, which if I'm seeing correctly (the image doesn't quite zoom in close enough to be sure) are made of two separate slats with a space left between them for the triangles to rotate into and out of the way: grinding such slots for the pivoting bits would have been really, really tricky if the whole comb assembly was made in one piece.

Such a curious thingie. Could be a very interesting late Renaissance curio if the dating is correct. Could also be a much later composite or whole cloth replica, though...

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JG Elmslie
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PostPosted: Fri 06 Oct, 2017 4:05 am    Post subject:         Reply with quote

I would be happy to place a bet those teeth are copper-alloy brazed onto the main body of the weapon.

there's a slight yellow discolouration at the bottom of each dovetail joint, rather than the sort of mark I'd see from forge-welds.
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Chad Arnow
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PostPosted: Fri 06 Oct, 2017 5:04 am    Post subject:         Reply with quote

Am I seeing this right? It almost looks like each tooth has a bulbous tang of sorts (below the straight line people are talking about) that keys into a shaped slot in the blade.
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JG Elmslie
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PostPosted: Fri 06 Oct, 2017 5:48 am    Post subject:         Reply with quote

Chad Arnow wrote:
Am I seeing this right? It almost looks like each tooth has a bulbous tang of sorts (below the straight line people are talking about) that keys into a shaped slot in the blade.


Yup. a dovetail joint, slightly rounded (because you dont want the stress raisers of a squared-off dovetail joint with a re-entrant angle cutting into the structural spine of the blade).

Welded with a silver/copper-alloy brazing filler, that would be a weld that, in theory, is almost as strong than the steel itself - even a relatively poor brazing gap of say, 0.2mm (which is pretty shoddy work, its not difficult to have a slot gap of 0.1mm, and sub-0.05mm gaps are certainly possible with practice) in a butt joint, yet alone a dovetailed mechanical fixture, will have an ultimate tensile strength in excess of 35KGf/mmē or 40,000psi. Bring that gap down to a decent .10mm, and the UTS rises to close to 65KGf/mmē or in excess of 75,000psi - stronger than a medium-carbon steel, and only marginally weaker than a high carbon steel.
That can be seen in the broken tooth, which has failed at the 90degree stress raiser in the tooth, rather than the dovetail where the brazing is.
Brazing is a remarkably strong welding method which is badly under-represented in historical reproductions.


The only downside would be that the main body of the knife is unlikely to be hardened when made with that method - but with the very thick section, it would be an awful cutter anyway. I'd love to see a couple of rockwell tests on that blade though. I bet you its low-40's HrC at best

Done like that allows each tooth to be fileworked individually, to make a channel (so its a '|_|' cross-section.), making the channels for the triangular hinged catches to be seated in, and its a pretty efficient use of steel for the main body of the blade too if its forgeworked. Though time-consuming, its not technically difficult to make.
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Radovan Geist




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PostPosted: Fri 06 Oct, 2017 6:19 am    Post subject:         Reply with quote

@Mikko: indeed, you are right, theyīre hinged.Otherwise it would not make sense functionally.
Iīm not sure about two separate pieces. If you look at the eight tooth from the right (counting also the third, missing one), id does seem as an U-shaped one-piece thing. But then, itīs really hard to tell from this angle.
In fact, things could be even more complicated. To make the catching effect work efficiently, I guess the triangular pieces should not revolve around the pivot. They must move just enough to make the blade move in, but then stop and trap the blade inside the teeth.
Now, I can think of four way how to achieve that. The first is to use some spring mechanism that moves the triangle bit back to its original position. I cannot say if itīs been used here, because the spring would most probably be at the back of each tooth, and we are seeing the front side, but it would have been quite a complex task, and I doubt that.
The second possibility is to make each triangular bit somewhat thicker at the protruding corner, to make it stop the rotation. From what I can see that is not the case.
The third option is to make the slot so short, that it would stop the protruding corner from rotating. Again, itīs not the case, because slots in teeth go really deep.
The fourth option is having the slots closed at the back side, to prevent bits from revolving. In this case, the teeth would not be U-shaped (either in one piece, or two separate pieces), but closed at four sides (bottom, sides, back), and left open on top and in front.
I cannot entirely dismiss the first possibility, but I would bet on the fourth one.
@JG: Indeed, you might be right. Thereīs a yellowish colouring visible.
@Chad: I was thinking about that myself. It would make the joint much stronger (especially if itīs really brazed, rather than forged). I donīt see signs of tang & slot at the missing tooth, the break line looks straight, but again itīs difficult to say from this angle.

Itīs an interesting piece. Of course, it could be much later collectorīs replica - I havenīt seen this variety with hinged rotating bits before.
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Mikko Kuusirati




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PostPosted: Sat 07 Oct, 2017 1:43 pm    Post subject:         Reply with quote

Yes, I see what you mean, Radovan - can't say for sure from this shot, but you're probably right. I really wish I could get a personal close look at this thing...
The subtle tongue, the sophist guile, they fail when the broadswords sing;
Rush in and die, dogs -- I was a man before I was a king.
-- R. E. Howard, The Road of Kings
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