Split spring question

[John L]

If a slipjoint has a split spring...does this mean a main blade at one end and two blades at opposite end....the main blade being the thickness of the other two blades plus the thickness of middle liner...all three blades using the two springs at the same time? So little time, so many things to learn.....

 

[zerogee]

Almost -- the single blade is the thickness of the two springs only (and yes, it uses both springs at once) -- the liner gradually tapers down in thickness to a point and stops - normally ending not much past the center backspring pin (the center backspring pin anchors the other end of the tapered center liner). The two blades at the other end each ride one of the springs.

Note: this is not the only way a splitspring knife is made - you can also have one with no center liner between the springs - the two blades are separated by a truncated liner that rests on top of the two springs and is about as long as the tangs of the smaller two blades.

Originally, the construction of a splitspring 3 bladed knife was exactly that -- a wide spring was split part way at one end during the forging - producing two springs at one end and one wider spring at the other.

We call such splitspring three bladed knives "whittlers" now, but for most of their history, they were just called three bladed knives, and that was just the way they were made.

 

[John L]

Thanks Zerogee: A question about the truncated liner. I guess this shortened liner is held by the pivot pin and...???? DOesn't any liner have to be held in at least two points? Is there normally a void left where the tapered liner ends..however small it may be? Thanks again.

 

[zerogee]

The truncated liner is thick enough that it sits on both springs, and it is usually fitted around the ends of the springs (think of the bottom of the truncated liner being basically "L" shaped) -- so even though there's only one pivot pin holding the liner, it cannot rotate with either of the small blades as they're opened since only one of the springs move at any one time. Technically, you could get the truncated liner to rotate slightly if you opened both small blades at the same time - but even then, once both blades are open, the springs are back into place and so is the liner.

The other oddity of the truncated liner splitspring is that the small blades are thinner than the springs (since the liner requires some of the spring width for itself). So the main blade is usually thicker than both of the small blades put together.

Yes, there is normally a void where the tapered liner ends - if done right though, the void should be very small. However, in many of the tapered liner splitsprings made by the great old knife companies, they would almost eliminate the void by fitting the springs together past where the tapered liner ends (the inside of the springs would then form a straight line while the outside of the springs continued to taper to the main blade). This meant that each spring was actually thinner at the main blade end, and the main blade didn't have to be quite as thick. I've also seen truncated liner splitsprings that tapered the outside of the springs - so again each spring was thinner at the main blade end and the main blade didn't have to be quite as thick.

-- Dwight

 

[Bastid]

Thank you Dwight. Excellent explanations!

 

[KnifeHead]

Here is a nice image showing the "split spring" config on a R.Bose Rogers whittler.

The "truncated liner" that zerogee is talking about is called a catch bit and was described pretty well. If I can't find an image of one I will shoot it and add one later of a Case Toenail that I have. In the case of the Toenail, the catch bit is tapered so that the relatively small pen blade will enter the trough at an angle so as to miss the main blade.

 

[zerogee]

The "truncated liner" that zerogee is talking about is called a catch bit and was described pretty well. If I can't find an image of one I will shoot it and add one later of a Case Toenail that I have. In the case of the Toenail, the catch bit is tapered so that the relatively small pen blade will enter the trough at an angle so as to miss the main blade.

Hmmm, I've only considered "catch bits" to be the extra bits of liner added to the full liners on one side or the other that allow a secondary blade to be thinner and the primary blade to be longer than would otherwise be typical. Though similar, the "truncated" liner on a splitspring is acting as a proper liner between the two secondary blades (though its thickness varies by how long you want to make the main blade - so in that sense it's acting like a catch bit).

I'm not arguing that calling it a truncated liner is correct -- that is just what I'm calling it for lack of a better term. But somehow calling it a catch bit doesn't seem quite right either, though maybe I'm just being a bit narrow in defining what a catch bit is. Would Tony like to wade in on this?

-- Dwight

 

[KnifeHead]

I thought you were describing a catch bit but apparently not. Some images with circles and arrows sure would be nice if you have any.

 

[zerogee]

Well, I can't post images here, but I can send you a couple I have handy - you could post them if you'd like. They're of an old Abrams Brooksbank whittler.

-- Dwight

 

[KnifeHead]

Sure...send the image to me and I'll post it. Email is on my profile.

 

[KnifeHead]

Thanks zerogee for the images you sent. Here they are...

 

[Tony Bose]

Thanks zerogee for the images you sent. Here they are...

These pictures show a catch bit. that's what it is called. They are used on paralell back spring whittlers. If it is a split back spring whittler it has a tapered cut liner seperating the springs at the back end. The picture Kerry posted of the whittler that Reese made is a split back spring whittler.

 

[Tony Bose]

PS on a split back spring whittle the master blade thickness is equal to the thickness of boyh springs and the back blades each are the same thickness as the spring setting on it. On a paralell back spring both spring equall the thickness of the master blade and the sum of the thickness of both small blades and the catch equal the thickness of both springs. If you think this is confusing try making one.

 

[zerogee]

Thanks for wading in on this one Tony! There's always more for me to learn, but that's a good thing. To complicate things further, a lot of the old parallel spring whittlers actually tapered the outside of the springs, so the springs were widest at the small blades and narrowest at the thick primary blade -- that old Abrams Brooksbank parallel spring whittler in the pictures is made this way.

-- Dwight

 

[John L]

Does anyone know of any diagrams on this subject? I think I'm more confused now than before the original question. I think........

 

[Mick57]

Does anyone know of any diagrams on this subject? I think I'm more confused now than before the original question. I think........

I'll second that.

 

[Tony Bose]

Thanks for wading in on this one Tony! There's always more for me to learn, but that's a good thing. To complicate things further, a lot of the old parallel spring whittlers actually tapered the outside of the springs, so the springs were widest at the small blades and narrowest at the thick primary blade -- that old Abrams Brooksbank parallel spring whittler in the pictures is made this way.

-- Dwight

You are right, some of the springs were tapered to give more room in the back, but that is going way back before they had steel sized like modern steel. It is really amazing what they did with water power and window light. But remember there wasn't any one man did it all. They specalized in one area and that's all they did, forger, grinder, etc. If you do something for 40 years you will get pretty good at it.

 

[malextwo]

Boy, I hope I'm not crossing any lines here, but, there's a Ruple splitback at Custom Knife Gallery, that, because of Bill's filework, shows one form of splitback that I think is being referred to here.

Mike