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I Forge Iron

Hot fitting guards


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I'm considering hot fitting a wrought iron guard onto a hidden tang Bowie that I forged, ground and heat treated recently.  This will be the first trial at hot fitting a guard on a knife (did it once on a sword in a class), but I wanted to try it this time because when I punched the guard while forging it I got a nice "dimple" on the blade side that I'd like to keep rather than grinding that surface flush.

What I'm trying to figure out is how close to the ricasso I should file the slot before hot fitting.  The taper angle on the tang is fairly standard (maybe 15 degrees, though I don't have it with me right now, and I currently have it cold fitting down to around 3/4" from the final resting place).  I could probably do the math for thermal expansion ratio and the like, but there are a couple of variables that are not necessarily clear (like how much drifting of the slot can be expected from hammering it into place).  Any experienced folk have a general rule of thumb for this?  I'd like to get it close before I do the final shaping on the guard.


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I haven't found a tried and true formula for this. No matter how many times I do it there remains a "hit or miss" factor. If the tang is cold and the guard is @ forging temp the guard is going to shrink as it cools making a tight fit. I have never had a guard tear or split from shrinking but I have had a few shrink up so tight that I damaged the guard hammering it off cold. I mention this because my usual method is to set the guard before the edge bevels are hammered in and sometimes before fullering. Also I have done this with 5160 and mild/A-36 for the guard material, not wrought. If you have enough wrought to run some tests fits on various tangs it might save your finished work. As for the 3/4" you mentioned, I have had good results with a 16 degree tang hot fitting the last 1" with the tang at forging heat with light taps using a piece of "squished" 3/4" pipe as a sleeve over the tang to tap the guard down. I look forward to seeing pics!

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I have used up to .003" - .005" difference when heat shrinking hubs onto shafts. This was on a candy panning shaft that was over 2.5" dia. Heated the hub to a dull red and the shaft dropped right into it.  Cold press fits for bearings can be as little as .0005"-.001" , for heat shrinking I would say .003" would be a good place to start. You should not have to hammer it at all, just slide it onto the tang before it cools. 

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