Slipjoints with “adjustable” Spring tension

[DanF]

Case makes a slippie model they call “sodbuster”, which they adapted from an older German model folding butchers/meat cutters knife. Two construction techniques/materials used in this model is a cutlers rivet as a pivot pin (which to me sucks as it is rough as a cob and galls like crazy, and a tension spring that appears to have been made that way so the assembler could adjust the tension without losing a spring or liners from slightly misplaced holes.

The sodbuster is definitely a low budget production knife, but, the profile is very functional and could make a decent user with a few mods to the design. This type spring on this knife is the only one I have seen like it. Does anyone know of any other model knife utilizing this feature?

 

[Drew Riley]

Do you have some pictures of what you're referring to? I just pulled out an old sodbuster jr, and it appears to have a fairly standard backspring, as far as slipjoints go. As for the pivot, I'm don't think it's a cutler rivet, but a "birds eye" pivot with a brass pin and washers on both sides. It just looks like a one piece cutler rivet because of how it's peened and polished.

 

[DanF]

Two piece rivets, male and female halves. There were several threads I found from long ago while I was looking into the history of this knife mentioning the construction of these.

 

[DanF]

The spring has the center hole only. Where the hole to apply tension is, there is a slot that can be filed/ ground to take tension off without losing any parts from misplaced holes at that point.
That pin is visible in this knife when looking down between the liners.
I’ll have to pull out my SB Jr and see if it is the same.

 

[DanF]

Visually, my Jr constructed same, can see the tension pin. Only way to know about the pivot would be to take it apart.

 

[Drew Riley]

Ah.... I stand corrected. I see what you're saying about the spring now, and that's definitely a cutler rivet. Interesting!

 

[Tyson A Wright]

Just on a quick check, my Victorinox Alox Solo, A Wright & Son Lambsfoot, and Cudeman 456-L all have the rearmost pin in the spring visible. I seem to think I've seen this in other knives, too. I think this is a reasonably common design for slipjoints, although not as common as having that pin go through a hole drilled in the spring.

 

[Bill DeShivs]

It's not made that way to be adjustable-even though it could be adjusted at the rear. Lots of knives are made that way, including the Leverletto.

 

[DanF]

It's not made that way to be adjustable-even though it could be adjusted at the rear. Lots of knives are made that way, including the Leverletto.

Wasn’t sure what to call it, but noticed it could be used for that so I put it in parentheses for lack of better terminology.

 

[BradleySmall]

Aren't the fish knives similar as far as having the spring rest against a pin instead of having a hole in the back? Oops, I guess it is one of the Toothpicks, here s a picture from USAKM kit. The tail groove or hole, seems one is as good as another. When you are dealing with a fulcrum there is no need for a hole when a groove will do. Obviously, if you remove the blade and pivot, the spring can certainly spin freely. At least in the images I have seen of the finished Sodbuster, the "front landings" on the spring being how you want them already it makes sense to adjust tension at the back notch. It is certainly easier than moving the hole. Though, that is also not much different than adjusting the tension by leaving drilling the rear hole until last.

 

[Tyson A Wright]

I've never seen any reference to adjusting a backspring by moving the rear hole. I'm not even sure how that would work. I think you adjust the tension by thinning out the inside of the spring.

 

[Hubert S.]

I've never seen any reference to adjusting a backspring by moving the rear hole. I'm not even sure how that would work. I think you adjust the tension by thinning out the inside of the spring.

I think there are two parts to "tension", one being the preload on the spring and the other the stiffness or spring constant. You can adjust the preload by moving the rear hole, and the spring constant by thinning the spring. There is some interaction between the two, if you soften the spring by thinning it, the preload also drops for the same hole location.

 

[Tyson A Wright]

I think there are two parts to "tension", one being the preload on the spring and the other the stiffness or spring constant. You can adjust the preload by moving the rear hole, and the spring constant by thinning the spring. There is some interaction between the two, if you soften the spring by thinning it, the preload also drops for the same hole location.

Sure, but I believe the hole location is a design-time decision. When I see build-alongs (web pages, threads here on BF, videos) any adjustments to the spring during assembly seem to be happening by thinning out the spring. (Mainly in the part of the spring between the center pin and the end of the spring in contact with the tang.)

I am here to learn though - I would be fascinated to see more on how someone adjusts the tension by moving the rear pin. I have not seen anyone do that before.

 

[Hubert S.]

Sure, but I believe the hole location is a design-time decision. When I see build-alongs (web pages, threads here on BF, videos) any adjustments to the spring during assembly seem to be happening by thinning out the spring. (Mainly in the part of the spring between the center pin and the end of the spring in contact with the tang.)

I am here to learn though - I would be fascinated to see more on how someone adjusts the tension by moving the rear pin. I have not seen anyone do that before.

I have not seen anybody adjust the preload this way either, but it seems workable as long as you start out with a preload that is on the high side. The posts that I have seen here and elsewhere about adjusting the tension by moving the rear pin all involved making a new spring...

Bill DeShivs posted that this type of spring is not made to be adjustable, but did not say why they are made that way. Maybe he can elaborate, I am curious.

 

[Bill DeShivs]

They are made that way because it's an economical method. One less hole to drill.
I'm sure the design is worked out as far as tension before the punch dies are made for the backspring.
If you are making a custom knife, tension could be adjusted (lessened) by removing material where the rear pin rests.