Perpendicular pivot hole

[John L]

As most of you know..when a folder is in the closed position and well built, the knife has its blade dead center between liners. This is due to truely perpendicular hole drilled into tang of blade and truely flat liner sides. How come I can't get this on a daily basis? I have checked drill press table and it checks out to within a thou or so for perpendicluar to bit. I hand lap stainless liners on sandpaper on granite surface plate. I start out drilling the pivot hole with 1/16" bit and increase to 3/32" or what ever the pivot pin will be. I am at a loss as to what else I should check for. I have used bronze bearings rather than straight pivot pins. Still no better. I think its just luck if I get a good centered blade.:grumpy: Any thoughts? Thanks

 

[Nathan the Machinist]

Is your problem caused by play (the blade can wiggle) or lack of square?

Drills bits don't make great holes. Drill bits are not even straight. The holes are not round, straight, or in true position. The holes are actually somewhat triangular in shape and tend to walk out of position, and drill at a bit of an angle to the surface. They do not have good surface finish. Drills are good for removing a volume of metal. Use them for clearance holes. A hole that counts should first be drilled undersized then milled, reamed or bored for good quality. I interpolate, but that's different discussion...

 

[Bill Vining]

Another thing to check is the thickness of the blade tang. If the thickness varies around the pivot hole, this will cause the blade to go off center as well.

Once you drill and ream the pivot to the exact sized needed, put the liners together and pin them with the pivot. Then clamp them together to drill any additonal holes. Even if your pivot holes are perfect, incorrect alignment of other holes for pins or screws will throw it out of alignment as well. Every time you drill an additional set of holes, make sure you pin them together before going on to the next one.

 

[synthesist]

Okay.............so I mill, ream, or bore my pivot hole.

CHECK.

Ohhhhhhhhhhhhhhh

I don't have a mill, any reamers, or a jig bore.

Grrrrrrrrrrrrrrrrrrrrrr

So can I use my drillpress to ream holes? Say it's a 1/4" pivot hole.... what size reamer, what speed do I use and is there anything I need to watch out for while I'm doing this? Do I use a cutting/lapping fluid for this operation? Any particular brand of reamer better then all the others? What about sizes? I'm thinking that reamers come in more sizes then drills,yes? How can you tell when a reamer is getting dull? (Carbide reamers? H'mmmmm?) I'm getting a headache here.

Thanks for sharing your communal wisdom btw.

Syn

 

[JCaswell]

I'd stay away from carbide cutters unless you're using a mill or unusually stiff drillpress. They'll just disintegrate unless your set up is really rigid.
I've had good luck with cobalt.

 

[george tichbourne]

We have discussed drill flex..if the finished pivot hole is going to be 1/4" use a 3/16" for the initial drill, not a 1/16" which will flex like the devil. I drill my liners for 1/8" pivots with a 1/8" drill straight out and get a perfect blade alignment.

Once the pivot hole is drilled shove a pivot into the hole to keep both liners aligned, clamp the liners together, then drill the tap size hole in the liners for the backspacer. With this set of holes as a drill guide drill the backspacer with the tap drill. Tap the back spacer.

Redrill the liners to enlarge the backspacer screw holes to the clearance size then counter sink them. 2/56 screws tap drill is #50 and clearance is #44

All of the above has been done with the pivot pin in place and the liners clamped solidly together to ensure alignment of all the holes that could affect the blade alignment.

Check the pivot to blade pivot hole clearance... there should be NO slop.

If there is slop the blade drill hole should be downsized by at least one number drill size until the slop is gone.

The same rule applies for bushings.....no slop.

If the blade is still off center after hole alignment and slop are taken care of then the grind is off center.

You can do without reamers but not without a set of number drills to custom size holes.

 

[Nathan the Machinist]

Okay.............so I mill, ream, or bore my pivot hole.

CHECK.

Ohhhhhhhhhhhhhhh

I don't have a mill, any reamers, or a jig bore.

Syn

You don't need a milling machine to use an end mill to clean out a hole or to use a boring head. A drill press will work fine. And either way will finish a better hole than just a drill bit. Or get reamer, which won't require you to clamp your work piece down.

I agree with J Caswell, I think cobalt HSS may work better for you than carbide. Carbide is expensive, and it tolerates little chatter before your edge flakes off, so speeds and feeds are not forgiving.

I have had bad luck with imported reamers, so I'd stick to USA.

I use water soluble cutting fluid when I ream. There may be a benefit to using oil, but I have not observed much difference and I don't use oil much because of the mess. But yes, cutting oil or tapping fluid should work well.

The steps between standard number drill sizes is several thousandth of an inch per step. I believe you will have better luck if your pivot hole isn't much more than .001" over your pin. For example, if your pin is made to certain dowel dimension standards, it will be between .2501 to .2503. So a good reamer size would be .2510, which is a standard size. If you measure your pin and find it is closer to .248, you can get a .249 or .250.

To sum up, drilled holes are not used for precision work, they're not round or smooth enough. I believe you will notice less play using a reamer or some other suitable tool to make your folder pivot holes.

 

[heatride]

As most of you know..when a folder is in the closed position and well built, the knife has its blade dead center between liners. This is due to truely perpendicular hole drilled into tang of blade and truely flat liner sides. How come I can't get this on a daily basis?


John maybe its not the hole that you are drilling that is the problem. Could it be that the tang to tip of blade is not straight ? I always check my blades with
a couple of pieces of PG steel to check this .

 

[Pinoy Knife]

try a straight flute drill bit then ream it .the straight flute drill doesn't flex that much

 

[JCaswell]

In addition to perpendicularity and accurate location of pivot holes, the other holes are important too. You can have nice, even, well located holes in the liners for the pivot and then if there's irregularity in the other holes holding the liners together, the whole thing gets tweaked a bit.
You may notice that some production knives are made a little loose so you can get everything aligned and then tighten it down. I think that's unacceptable, but it's done to varying degrees. :thumbdn:

I've had excellent success with pivot holes bored with an end mill then honed to final size. I like about .0003 over the actual pin size. This is done on a Sunnen honing machine. :thumbup:

I've never liked how reamers tend to be inconsistent reamer to reamer, and they tend to be difficult (or impossible) to get repeatable results in the tolerance ranges I'm after. Plus, they tend to cut a little conical which makes them a non-starter for pivots for me, but other guys seem to do well with them.

 

[KnifeHead]

After the blade is HT'd and before you start to finish grind, you should lay the blade on a known perfectly flat surface and make a NEW center mark on the tip of the blade. If the blade thickness is 1/8", measure up 1/16" on the blade tip, mark it and grind to that.