Guard fitting question

oldanvilyoungsmith

oldanvilyoungsmith

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Feb 7, 2011
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Note: Please realize that my drawing is not exact, I purposfully emphazised the radiuses to make them obvious, I'm not implying they would actually be made that extreme on a knife.

Okay, recently my blue print reading instructor was telling us about thread reliefs, and as he was explaining, it seemed really similar to knife tangs. He explained that to have a sharp corner at a shoulder would weaken the area, just like diagram #1.

So, machinists would put in a radius to strengthen the area, just like #2. But, when they needed something to butt up to the shoulder completely, and still retaing the strength of the radius, they would inset it some, like picture #3.

So, my question, I know that my drawings aren't exactly to scale, but disregarding that, would it work better to make the radius more like #3, with a relief, that way the guard can butt up closer and you don't have to file in a curve?

I'm sure someone has tried this, so I'm curious as to why it's not used, is there something inherently wrong with it in our projects that wouldn't work? I realize it makes it somewhat smaller in that area, but unlike my rough drawing it would have to go in that deep, and it doesn't seem like it would weaken it that much. What am I missing?




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I prefer to use something like #2. As it leaves a little more beef on the bone and still allows for a tight fit at the outer edges of the guard the beefy area in the middle is covered by the guard itself. When you use a design such as #3 there is a weak area where the two radius's almost meet. Anyway that is my O2 on the subject!
 
I think the idea is that it's better to sacrifice material from the guard to achieve the correct fit, rather than sacrifice material at what is arguably the most critical stress area on the blade. That dosen't mean your reasoning isn't sound from a production standpoint and that is why machinists do it that way. Knifemakers tend to be particular about these things, that's why we're knifemakers, and the amount of hand-fitting that we do is one thing that makes our work distinct, even some of the parts you can't see.
 
Im guessing if your tang is decently thick and the radius was very small it wouldnt hurt really but I like #1 or a slight #2 better
 
If a machinist is planning on using #3 I would think he would use a piece of material more than thick enough to compensate and maintain the strength he needs. The tang of a blade is allready relatively thin so I wouldn't want to make it any thinner than necessary. I believe I'd use #2.
 
#3 will work, but it all depends on the scale of the parts involved. A small blade that won't be subjected to heavy stress, like a whittling knife, combined with a wide tang that won't be stressed, can have an inverted curve. Or, if the tang on your bowie is wide enough at that point that you don't have to worry about a reasonable ingress into the tang....

It's used a lot on carpenter's squares and machinist's blocks because it allows for a piece to sit snugly into that corner. Just drill a hole in the right spot and cut two straight lines in to it.

But, it's also just as easy to use tang #2 and it works on every knife of every size.
 
No point in leaving all the extra weight in the tang like on 3 when it is only as strong as the narrowest point........#2 is the way to go.
Darcy:)
 
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