How to center slipjoint blades?

wkfl

wkfl

Joined
Oct 28, 2011
Messages
270
Curious to how you slipjoint folks are getting your blades dead center. I grind post heat treat, D2 or Cpm 154, plate quench using aluminum plates and a 6” milling vise. I know everything should be flat and parallel... but dang! I’ve tried surface grinding, lapping and such to no avail. My fit and finish are getting good, but centering is hit and miss. Could you please share details as per your technique in achieving this? A huge thanks in advance! Mike
 
Thanks, they are 3/32, I tried just drill bits alone, and I’ve tried a #43 drill followed with a 3/32 chucking reamer. I’ve used both drill press or mill. Hit and miss either way. No bushing.
 
Last edited:
wkfl said:
Thanks, they are 3/32, I tried just drill bits alone, and I’ve tried a #43 drill followed with a 3/32 chucking reamer. I’ve used both drill press or mill. Hit and miss either way. No bushing.
Click to expand...
A drill bit makes a triangular hole.
What size reamer?
Do you enlarge the hole post heat treat and after surface grinding?
In other words explain how you know your pivot hole is perpendicular?

The steps in order of operation in a slip joint is very Important and leaves no room for error and every operation is an opportunity to screw something up

So you need to be detailed in describing exactly what you are doing
 
Things to keep in mind.

Be sure the tip is dead center. Often times it is to one side because people "grind by eye" and not to a center line.

When hammering the pivot pin, hammer dead center on the pin. If you hammer to one side to much the pin can slighty bend moving the tip. Small thing at pivot magnified far away at tip.
 
One thing I do to be sure everything is where it is suppose to be is, I take spring clamps and grind a notch for the pin on the jaws.

I assemble the knife and put the clamps at each pin to hold the knife together.
If everything is right the tip will be dead center.
If not figure out why before you beat it together.
 
The reamer is 3/32, holes are all drilled preheat treat. As far as surface grinding... I suck. I can burn a blade faster than snot heat treated or not...shallow passes, coolant or dry. I’ve actually set that aside until I learn better techniques. Basically I drill the pivot hole on the mill with a 43 drill, followed with the 3/32 reamer then HT. I could not say if it’s perpendicular tho.
 
Thanks Adam, never would have thought that, but it makes total sense after hearing it. I’ve never paid attention to the blows, but I will now! So many facets that come into play.
 
Surface grinding. Dress the wheel with a diamond dresser. It’s burning because the wheel isn’t dressed. Or to heavy a cut. Take .0005 depth of cut passes and cross feed say a 1/4 turn of the wheel. Start with that.

If I recall my geometry, 1 degree variation is .017 per inch. On a 3” blade that’s a mile off at the tip. In other words you need to be within .0005”-.001” for your tolerance limits
 
wkfl said:
The reamer is 3/32, holes are all drilled preheat treat. As far as surface grinding... I suck. I can burn a blade faster than snot heat treated or not...shallow passes, coolant or dry. I’ve actually set that aside until I learn better techniques. Basically I drill the pivot hole on the mill with a 43 drill, followed with the 3/32 reamer then HT. I could not say if it’s perpendicular tho.
Click to expand...

the way I did it is surface grinding after hardening. Then open up the hole with a carbide reamer. Then you know it’s perpendicular assuming your mill and setup is square.
 
This may not help, but just remember that pocket knives have been made for a couple of hundred years without milling, surface grinding, reaming, bushings, washers, etc.
If the backspring and liners are square, the pivot hole can actually be quite a bit larger than the pin and everything will work just fine.
 
HSC /// said:
Surface grinding. Dress the wheel with a diamond dresser. It’s burning because the wheel isn’t dressed. Or to heavy a cut. Take .0005 depth of cut passes and cross feed say a 1/4 turn of the wheel. Start with that.

If I recall my geometry, 1 degree variation is .017 per inch. On a 3” blade that’s a mile off at the tip. In other words you need to be within .0005”-.001” for your tolerance limits
Click to expand...

HSC /// said:
the way I did it is surface grinding after hardening. Then open up the hole with a carbide reamer. Then you know it’s perpendicular assuming your mill and setup is square.
Click to expand...

Thanks, I will give that a try on the SG. I also will get a carbide reamer as well.
 
fitzo said:
Is the blade still flat after bevel grinding/polishing?
Click to expand...

No, not always. I typically try to lap them flat on a granite plate if not. PITA! I’ve had straight ones lean one way or the other though as well.
 
Bill DeShivs said:
This may not help, but just remember that pocket knives have been made for a couple of hundred years without milling, surface grinding, reaming, bushings, washers, etc.
If the backspring and liners are square, the pivot hole can actually be quite a bit larger than the pin and everything will work just fine.
Click to expand...

Def helps...thanks, and so true.
 
wkfl said:
No, not always. I typically try to lap them flat on a granite plate if not. PITA! I’ve had straight ones lean one way or the other though as well.
Click to expand...

Only reason I mention it is sometimes I have ground a thin blade like a filet knife with what I thought was reduced pressure only to find I had bent the bugger a bit. Still straight down the centerline, which is now a very wide arc. :(
 
Thanks for the input fellows, I’ll be implementing these strategies as we speak.
 
There used to be a good video out there on how to crink a blade to center. It's a technique that I have used many times on production slippies I had recovered and twice on my custom builds when they weren't falling right to center. Of course you'll want to do this after peening but before you grind the pin head flush. I'll keep trying to find the video and post up the link. It's easier to see what's being done than me trying to type and explain it.
 
You must log in or register to reply here.
Back
Top