folding knife/ pivot hole question?????

C

chad2

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Sep 2, 2011
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i have a very important question!!!!!!!

i am making a folding knife.

the pivot hole on the blade, i drilled it out smaller than what the hole needs to be because i know that during the heat treat the hole is going to shrink or expand a little, my question is which is it? will it expand or shrink? do i have to get a carbid drill bit and just drill it after wards or can i go one size up or one size down on the drill bits and be fine with sanding it out a little. the hole is supposed to be a 1/4" hole.

thanks for any advice

o yeah this is my first folder so i am kind of oblivious just kind of improvising on some things but taking my time

if you need more of an explanation i will try :D
 
the way i do it (and its only one way) is that i undersize the hole HT then used a carbide endmill to chase and clean the hole (4 fluts to keep the hole round not oblong liek a drill will)

so far this works reast for me and i dont have ot use carbide reamers
 
I drill my holes slightly undersized and then ream them to exact size with a reamer. This is all done prior to heat treatment. I have not experienced any schrinkage or swelling during this process. However it is good idea to lightly clean up the pivot hole after HT with some fine abrasive cloth and a rotary tool of some kind. Just be carefull not to overdo it and destroy the delicate geometry of the hole.

Brian
 
Gody said:
I drill my holes slightly undersized and then ream them to exact size with a reamer. This is all done prior to heat treatment. I have not experienced any schrinkage or swelling during this process. However it is good idea to lightly clean up the pivot hole after HT with some fine abrasive cloth and a rotary tool of some kind. Just be carefull not to overdo it and destroy the delicate geometry of the hole.

Brian
Click to expand...
I also do it this way but use the drill press with a barrel lap and ultra fine lapping compound to polish the hole.
 
As seen in the above posts, start with a hole that is already drilled, reamed, and polished to the size you want. After HT, either lap the hole or run a carbide reamer through it to clean it up. In a folder blade, there is very little dimensional change in the hole post HT.
 
This one I use on 3/32 holes. Turn down the music wire cut a slot at the end and solder
in a small piece of music wire for the eye, you can make them any size you want.
Ken
102_0385.jpg
 
This question has been answered, but I'll add my .02...

Steel changes dimensions after HT, but the amount and direction of change depends on the steel and the heat treat. Typically, some dimensions grow and others shrink, but it is only a couple thousandths per inch, so a 1/4" hole wouldn't change much.

It is not unheard of for a toolmaker to tweak their temper temperatures to get a tool dimension to fall into tolerance.

I remember once turning some go no-go pins in O1 and finding the diameter after HT had grown a thou in one direction, and shrunk in the other. It was about this time I started looking into a toolpost grinder...

Which reminds me. I've been thinking... I think a relatively fool proof way to size a hole in a hardened blade that would be very round (and square) and not bell mouthed (you lappers listenin?) would be to turn the blade on your lathe and dust off a couple tenths with a good die grinder (like an "air spindle" or similar) mounted in your toolpost. You might dig out your faceplate, but I figure you could just pin it to something through the hole then use clamps or even glue to hold it in place. Remember to turn it really slow, possibly even by hand. I'm going to try this...
 
Nathan the Machinist said:
This question has been answered, but I'll add my .02...

Steel changes dimensions after HT, but the amount and direction of change depends on the steel and the heat treat. Typically, some dimensions grow and others shrink, but it is only a couple thousandths per inch, so a 1/4" hole wouldn't change much.

It is not unheard of for a toolmaker to tweak their temper temperatures to get a tool dimension to fall into tolerance.

I remember once turning some go no-go pins in O1 and finding the diameter after HT had grown a thou in one direction, and shrunk in the other. It was about this time I started looking into a toolpost grinder...

Which reminds me. I've been thinking... I think a relatively fool proof way to size a hole in a hardened blade that would be very round (and square) and not bell mouthed (you lappers listenin?) would be to turn the blade on your lathe and dust off a couple tenths with a good die grinder (like an "air spindle" or similar) mounted in your toolpost. You might dig out your faceplate, but I figure you could just pin it to something through the hole then use clamps or even glue to hold it in place. Remember to turn it really slow, possibly even by hand. I'm going to try this...
Click to expand...

so should i keep it small then HT then ream it out?
 
chad2 said:
so should i keep it small then HT then ream it out?
Click to expand...

In my opinion, that's a pretty reasonable approach. One drill size under, HT, carbide reamer. Assuming you're setup for that. Of course the more experienced folder makers above are probably offering the best advice.
 
Nathan the Machinist said:
I think a relatively fool proof way to size a hole in a hardened blade that would be very round (and square) and not bell mouthed (you lappers listenin?) would be to turn the blade on your lathe and dust off a couple tenths with a good die grinder (like an "air spindle" or similar) mounted in your toolpost.
Click to expand...

Folder pivot holes would be pretty small

Would Diamond pins work for that?

grinding-pins.jpg
 
Nathan the Machinist said:
CBN would be better.
Click to expand...



Thanks Cubic boron nitride it is

I know they exist, but I've not used them before.

Since it's a through hole, almost any shape would work


What shape is better?

I would tend to use a
Spherical ball for gradual contact and not too critical set-up,


Is there more than one grit ?
 
I drill and ream undersized, heat treat, then lap.

Undersized reamers are fairly inexpensive, and are actually dirt cheap considering how many holes you get out of one...

Laps might as well be free once you are set up.

I don't worry about bell mouthing the hole, as I am only lapping a thou or two, and a bell mouth on one end isn't going to make a lick of difference on a folder anyhow.
It won't be much, and it won't go deep.
 
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