Snap shut?

J

jkf96a

Well-Known Member
I'm having fits with this slipjoint I'm working on. It's my 5th slippie, and I wouldn't quite say I have it figured out. The previous four have turned out passable, but I'm seldom content with "OK." Problem on this one is that it won't snap shut right. I have decent snap at half and a nice click open, but can't get it to close up good. I don't have a mill. I have brass liners and .05 bronze washers, and lubed with a tiny drop of mineral oil. All parts polished to 400 grit.

Things I suspect include pivot pin too tight in the pivot hole, drag on the sides of the blade (but shouldn't the washers take care of that?), or the spring isn't strong enough (but then why the snap out?).

I could polish out the pivot pin a little. Haven't peened it yet. I could bend the spring a little more for more preload. Or I could take some off of the neck in between the pin hole and the bearing surface, but I don't know if that would make it stronger or weaker.

Any ideas?
 
If you have good snap at half and open, then your spring tension should be good. My guess would be the blade is dragging in the liners (but with the washers you should have good clearance).
One other possibilty is the bottom corner of the tang either is rounded too much. Did you sand the corner? Also are you flush at closed, open and half? If not the tang could be short on the bottom.
 
Sounds like you are losing tension in the closed position. It is kind of an awkward feat of physics in any light at this position, but I would say that this one position of the three is the hardest to get. Several of mine have done the exact same thing. You may try a little more spring tension by bending it...Have you heat treated it already? kind of hard to do after heat treat.

If you are using washers as you state, the only issue there could be a warped blade or a blade ground slightly off center. to check if it is rubbing, color the sides of the blade with a blue sharpie or layout die. Close it up and check it out. If you have drag, the liners will wipe the blue in the area of contact.

Too me, tha hardest part of getting a slippy right is that moment when you are peening the pivot, and you are trying to achieve both free movement in the opening and closing action, as well as no play when the blade is wiggled side to side. Very difficult to achieve. Again, part of the thing that is a real b*tch with slippys is there really is no turning back. Once you peen the pins, you can't just undo it. Sure, you can drill the pins out and dig out what's left, but you will likely mess up the bolsters or damage something in the process. You can't just unscrew the pivot like you can on a tactical folder or something similar.
 
J S Machine said:
Too me, tha hardest part of getting a slippy right is that moment when you are peening the pivot, and you are trying to achieve both free movement in the opening and closing action, as well as no play when the blade is wiggled side to side. .
Click to expand...

A good way to help with this is to use shims when peining. I use .002 shims inserted between the blade and liner when im working the pivot pin. This gives me some clearance so I dont jam the blade. Once I have the pin right I have .004 clearance just a couple of light taps closes that slightly. I have never had on get too tight this way.
 
Sean Cochran said:
A good way to help with this is to use shims when peining. I use .002 shims inserted between the blade and liner when im working the pivot pin. This gives me some clearance so I dont jam the blade. Once I have the pin right I have .004 clearance just a couple of light taps closes that slightly. I have never had on get too tight this way.
Click to expand...

Great tip. Thank you :)
 
Fold heat treat foil and put a piece under each side. Pein the pin with the blade in the half stop position so your liners are supported on all sides.
 
I messed with these alot since I figured out they didn't work. Broke one spring, so I re made it with a little more meat and pre-load in the original holes. Increased the tension significantly. Still didn't work. Talked at length with Craig B who suggested it could be the washers. Took them out, and also polished the pivot pin to a little undersized. Still no snappy. Got to looking back through various online tutorials, and carefully observed the open/close a zillion times. I really think it's something mentioned by Sean: the bottom corner of the tang was too rounded, which was causing the spring to lose tension a little in the closed position. By rounding the bottom too much, I was losing my leverage, and thus my snap. I rebuilt one of the blades but left the corners on, and it snaps OK out of the liners. I haven't heat treated the blade yet, but will likely do it this weekend and see if I can make it work. I've got three slippies all but finished, none with closing snap, all from the same batch. I have plans to make miniatures out of the fudged blades, and to re-make them to take advantage of the handle and liner work I've already done. If it all works, I'll post pics.

Thanks also for the tip on the HT foil. It is what I have been using, but I didn't think of peining in the half stop position. Makes alot of sense.
 
I suggest you go to the Knife Network forums, then to the folding Knife forum, and read some of the stickies. It's all there. Your tang geometry is off, and the stickies will show you how to get it spot on. The sticky on a Texas Toothpick should show you what you're doing wrong.
 
Don Robinson said:
I suggest you go to the Knife Network forums, then to the folding Knife forum, and read some of the stickies. It's all there. Your tang geometry is off, and the stickies will show you how to get it spot on. The sticky on a Texas Toothpick should show you what you're doing wrong.
Click to expand...

Yep, I agree. If the geometry is off, especially the relationship between the bottom corner of the tang and the kick, you will lose snap.
As for the corners, I usually work them by hand on 400 grit. I just want to take enough off to make it work smoothly. You would be surprised how little it takes to be too much.
I forgot to mention in my previous post, the best thing to use as a spacer when peining is a spark plug feeler gauge. You can pick up a set for cheap at any auto parts store. I pull out the .002 spacers and cut a small U shape in one end to fit around the pin. Ill try to get a pic up later.
Hope this helps.
 
Don Robinson said:
I suggest you go to the Knife Network forums, then to the folding Knife forum, and read some of the stickies. It's all there. Your tang geometry is off, and the stickies will show you how to get it spot on. The sticky on a Texas Toothpick should show you what you're doing wrong.
Click to expand...

I wasn't a member over there, but I did register. Apparently I don't have appropriate powers to view pictures in anything other than thumbnail size. Stickies look good, but hard to tell what's up with only tiny pics.
 
jkf96a said:
I wasn't a member over there, but I did register. Apparently I don't have appropriate powers to view pictures in anything other than thumbnail size. Stickies look good, but hard to tell what's up with only tiny pics.
Click to expand...

You may have to be a member. I don't know about that.
 
You may have seen this in my tutorial, and I figured it may be a little help here.

This is a direct quote from Mr Bill Vining's post on how to make a Texas Toothpick. This is the absolute best way I have ever seen this explained and he has permitted me to include this in this tutorial. Thanks Bill :)

The most difficult part of making a slipjoint is getting the geometries of the tang and spring to work in harmony. Many custom makers are designing their slipjoints so the backspring is flush with the back of the knife when it is opened, closed and at the half stop. The illustration below shows how the dimensions of the tang works in conjunction with the backspring. For illustration purposes, the dotted lines are for reference only. The distances from lines A, B and C to the center of the pivot must all be the same in order to obtain a flush backspring in all 3 positions.Dimension “A” should be approximately 10% longer than dimension “B”. This is to keep the blade from extending beyond the end of the backspring when the blade is rotated.

Geometry.jpg
 
Been looking at every tutorial in here and on the net! Definitely finding the right geometry on the tang has been my toughest challenge. Thanks for the drawing! I think I've been having too long a distance between my kickstop and the tang.
 
Thanks JS. Vining's was one of the tutorials I looked at several times. On the snapless knives I've got, the corner between B and C is too round.

Is there any benefit to shortening the distance between the two contact points along line C, the distance from the corner to the kick?
 
I wouldn't think so, but I'm no pro either. I'd like to hear Todd Davison's take on this.

That's the only thing I don't like about that particular area. Very hard not to hit the kick with a sander or overly round off the corner between B and C as you say. This will, as you know, make a drastic change.
 
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