pivot hole

[titaniumdoctor]

I seem to be having a problem with my reamed pivot hole in my blades becoming oblonged after heat treat giving me just a little bit of cam action at the beginning of movement of the blade in either direction. The blade moves nice and smooth and tight before heat treat, but becomes a little sloppy after. Should I be drilling my hole before hardening and reaming after to solve this problem? I've built three knives so far, all of which have this problem.

Thanks, Jeremy

[L6steel]

Jeremy, are you heat treating the blades yourself?
Do you clean the pivot hole after heat treat?
Are you sure there's no warpage of the blade during heat treat?
If the blades are stainless and you are heat treating them yourself, do you air quench them or do you use aluminum plates?
Don't mean to grill you, just would help to know these things. Might tell us what's happening to your blades.

[Ray Rogers]

Knowing the answers to L6's questions would help a lot in figuring out what's causing the distortion in the pivot hole.

However, there is generally more than one way to solve a problem. If you don't know what the pivot hole is out of shape then find a way to make a pivot hole after the heat treat is done. The way I do this is by pressing a bronze bearing into an oversized pivot hole. Even if the hole is slightly out of round the bronze will conform to it. Then, ream the pivot hole in the bronze and you will have a perfect, smooth, pivot hole at right angles to the plane of the blade - just what you were after in the first place......

[Chris_Crawford]

Jeremy,

Check to make sure that you are using a straight reamer and not a tapered reamer on your pivot hole. I have both a types in 1/8", and without paying too much attention to it, they look alike.

Thanks -chris

[titaniumdoctor]

I,m using carbon damscus for the blade and hardening it myself with an oil quench. Sometimes the blade will warp just a hair, maybe .002-.003 fom end to end, but not a whole lot. All my reams are solid carbide straight reamers. I have actually bought some bronze bushings, but have not used them as of yet. I may on my latest project just because I screwed up the the pivot hole and really have no choice. I heard they work good though.

Jeremy

[Kevin Wilkins]

Are you sure the pivot hole is round before heat treating? Test the run out on you drill press and make sure the table is perfectly square to the spindle. My *guess* would be your holes are already oval before heat treating. It seems unusual that a blade should warp in that way without substantial distortion throughout its length.

If you're using carbide reamers, leave your pivot slightly undersize and ream to size AFTER heat treating.

But check that drill press!

[Messinger]

I'm just a newbie, so my thoughts here might be groundless. I did have one idea though that might merit some thought (I hope).

Are the blades differentially heat treated? What if the blade is being hardened only partially throught the pivot hole leaving the top of the hole soft and the bottom hard. Since the hardened portion would be expanded, that would possibly deform the hole slightly. Also, I would think you couldn't get a round hole when reaming if one side of the hole is hard and the other soft - more matterial would be removed from the soft side.

I'm just brainstorming. What are your thoughts?

-Ben

[Frank Niro]

Is the hole being drilled at 90 degress to the blade? I have never seen heat treating create a problem of oval holes. Frank