Slip joint general design advice needed

[Randy3000]

I have been seriously studying slip joint designs and trying many things out. I've made about 3 dozen slip joints and am capable of producing a well fitted and properly functioning knife, but my design needs serious improvement. The overall feel is usually good but the outline isn't appealing sometimes and frankly often times it doesn't all fit together into a neat package. My main issues are

1) i cannot hide the notch of the blade with the bolster without the bolster looking overly large or the blade not centered in the bolster when open.
2) i feel my tangs still have too much meat on them, and are often too long. If i try to shorten the tang i get the blade smacking the spring.
3) i often have the situation where i cannot round the bolster on the spring side and so it looks flat. If i make the bolster extend out further from the end it's just a lot of empty space and looks weird.

I typically use 3/32" 1095 steel. My springs are usually 1.25" - 1.75" from middle pin to the end, and have a height of somewhere between 0.060" and 0.090". For the tangs, i have usually 3/32" to 1/8" from the edge of the pivot hole to the notch. Adding it up, this gives about a half inch overall height near the pivot. The kick usually hits the spring 33% to 50% way down from the end. 50% is too long a tang, but 33% is too easy to smack the spring when closing.

The only solution i can think of is to make the spring about 0.150", take some off the belly of the spring near the middle pin so it won't be too stiff, and then taper the end from the back side down to maybe 0.060". Then i make the tang about 0.060" from edge of the pivot hole to the notch. Having a smaller tang will allow a stiffer spring and keep the same overall stiffness when opening and closing the knife. Tapering the end of the spring will keep the notch from being too deep and hard to hide.

My problem is when i try this, accuracy becomes highly crucial. I believe this is mainly due from nearly halving the preload i have been dealing with. I just ruined two knives in a row that felt good when fitting them in my ruple jig but after assembling the knife it became sloppy. I usually use the jig to setup my drill press to drill the final pivot hole in the liners, and everything went together perfectly straight and even as far as i can tell, like it always has, but just that little bit of error alters the fit up.

Any advice?

 

[tmerkl]

Do you work from a pattern when making your slip joints? There are some, like Todd Davison, that do it without them but I find it really helpful. I use a free program called inkscape to lay everything out, and I can pivot the blade to check for fit and clearances. The notch, or run-up usually does show on most unless you are designing what they call a "sunken joint". That is about pivot placement, blade design, and as you discovered, bolster design. With a couple dozen under your belt, i'm sure you know, one change affects many other parts and it's a real balancing act getting these things to go together right. That's why I find it so helpful to design it on the computer first so I know if I do my part on the bandsaw and grinder, it will come out right. You can check some of mine out on my instagram, tim.merkl, and I'll be happy to send you a pdf of some working patterns that i've made if you are interested. Good luck and keep at it! They are addictive!

 

[Randy3000]

I know many knives have the exposed notch but i always thought it seemed unattractive.

I usually draw the design by hand and then when making the parts i compare them to the drawing. Then I'll actually cut the drawing out and use it as an outline to cut liners. I've tried using templates but i don't get consistent results and so I've abandoned them since it seemed worse than going off my drawings. How consistent are you, knife to knife, when using a template? Maybe i should give it a try again now with more experience?

A main question i have is how do you transfer from fitting on a ruple jig to the handle liners and scales? I usually avoid cutting the liner until I'm completely done fitting the blade so that if i mess up I don't waste a liner.

 

[javand]

There's a lot of questions here, tough to respond to all of it without writing a thesis here.

I like sunken joint (hidden back squares) myself, and make most of mine this way, I think I've become pretty good at it. Yes, the proportions are very critical here, I'd argue it's that way with slipjoints in general. It's very easy to make as slipjoint that has a huge handle, and a short blade, the trick in pattern design is figuring out how to make the exposed/functional portion of the blade look as big or bigger, and can be very difficult with certain styles.

As to your blade hitting the spring if you remove material from the back of the tang, I'm uncertain what's going on here, the tip of the ramp, and the corner of the tang relationship, is what keeps the blade from hitting the spring, but the tip of the ramp, is the main adjustment to control where the blade edge lies in the closed position.


I personally made, but never use the "Ruple" style jig. It's too time consuming, and yes, you *must* have holes in your liners first and transfer the hole position of the front spring pin, and the pivot, to this jig, in order to be in the ballpark. Even still, you' almost always still require some adjustment.


I simply use my liners instead. Put it together with temp pins, check it, pull it apart, adjust, re-assemble. That's why I put handles on all my temp pins, and don't pinch them off. Since I use a lot of damascus or finishes that require separately finishing all the components before assembly, I may take a knife apart and back together 100 times. Although when you're doing all mono-steel work with handle material you can just glue to the liners, you can get away with not doing this, or even pinning the knife together if you put the handle material on with screws, even before you grind the blade, I can not. So it's crucial for me to keep it easy to disassemble quickly.


I do recommend making a loose pattern, but it's not necessary if you don't want, to base everything off a hard pattern. I usually only have a pattern for my blade and spring with many of my designs, that way I can easily adjust the liners and attitudes to make a knife that looks very similar, depending on bolster design and the finer details of blade grind (i.e. pinched bolsters, sunken, dovetailed or not, clip style of the blade, etc.) without having to have a bunch of specific patterns.

On the other hand, I do have some liner patterns for some of my stuff that's trickier to make look right, like my sway-back hawkbill pattern, where the handle can look really huge or "wrong" to the eye, if I don't get it just right. However, I still don't cut out my liners based on this pattern, I still get all my pin holes and my attitude adjusted in a rectangular piece of liner material first, then I glue a print out of the liner pattern over this, roughly lining up the pin hole marks I have in my pattern, and use this as a guide to get the basic shape and dimensions right, then do the final tweaks by hand, till it all "looks right".



Here's a shitty photo of my swayback hawkbill, this has sunken joint on a swayback which is even trickier to make look right, with a blade that's almost longer than the handle, integral wrought iron, with a rust blued carbon steel blade. There's some light trickery going on that makes it look like the grind is a little off at the top, but it's not. I'm just an absolute shit photographer.

 

[javand]

FWIW I still wish the bolster looked a little smaller, although it's better in person, I could have taken a little more off the front radius of he bolster under the ramp, and made it look smaller. On later examples I did. It didn't actually make the bolster smaller, but it gave the appearance of it.

 

[Frank Niro]

Just place your ideas of what it should be into the next one and continue with each folder as you are already doing. This will work especially well if you keep making over,the same model.
Frank

 

[javand]

Just place your ideas of what it should be into the next one and continue with each folder as you are already doing. This will work especially well if you keep making over,the same model.
Frank

I agree with Frank here. It's natural to want to make something different and constantly add complexity to your work with each next knife you make, it's the way I am by default, but it's really really advantageous when making slipjoints, to get enough of the "same model" under your belt to the point that you've "mastered" it, at least when you're early in your maker stages, so that you can judge the progress objectively, based on improvements over the previous work.

When you are constantly doing something different, especially when you don't have the deepest grasp of all the caveats (and trust me, I don't give a shit what your IQ or education is, if you think you understand the complexities of slipjoint component interactions, you're simply arrogant, naive, or both; just ask any of the top makers how much they still have to learn, decades or a lifetime deep making them in), then it's very difficult to determine where improvements have been made, and what worked better or worse.


I'm not saying just "focus" on this or that model forever, just saying, make a dozen of one "pattern" simply making targeted refinements to process and pattern, as you see discrepancies or areas that need attention, until you make a knife that you know is top, with no real compromises. Once you can do that, you'll be much better qualified to move on to the next style.

It'd be a waste of time for you to try and "build" a perfect hard pattern right now, without figuring out the interactions you're having issues with already, you'll simply duplicate those problems.

 

[Randy3000]

Alright, well i have been making a similar knife now for about the 4th time in a row, so I'll just at it. I made the ruple jig about a dozen knives ago. I don't like it. I had much more confidence drilling the liner first and pinning into some wood and doing the fit up there. I took a 6" piece of scrap and drilled a hole 1" from the end and pinned it to the wood, where the small end hit the sprint and i would mark where the big end was. The lever multiplied errors in blade fit by 5, and i could get pretty good results that way.

I'll go back to drilling the liners before fitting the blade. I may even toss the ruple jig, and just use the dial indicator instead if the lever thing i used to use to measure error.

Slip joints are a sickness with no cure!

 

[javand]

Alright, well i have been making a similar knife now for about the 4th time in a row, so I'll just at it. I made the ruple jig about a dozen knives ago. I don't like it. I had much more confidence drilling the liner first and pinning into some wood and doing the fit up there. I took a 6" piece of scrap and drilled a hole 1" from the end and pinned it to the wood, where the small end hit the sprint and i would mark where the big end was. The lever multiplied errors in blade fit by 5, and i could get pretty good results that way.

I'll go back to drilling the liners before fitting the blade. I may even toss the ruple jig, and just use the dial indicator instead if the lever thing i used to use to measure error.

Slip joints are a sickness with no cure!

Yeah, there are definitely a lot of different ways to skin this cat. I have all kinds of little "fixtures" and "jigs" I've come up with for certain steps myself, but when it comes to getting the spring flush at all positions, I prefer to just eyeball it till it's close, and then do it by feel. Having a "number" associated with the difference is very helpful for some, I think it's highly dependent on your thought process. To me, it's just an added tedium taking the thing apart and then putting it back in the jig, so many times. In the end, you still have to grind those thousands off by hand. Quicker for me to just slap the pins back in and feel it with my finger or fingernail. I don't even bother with the board myself.

There's no right or wrong way to do this though, all that matters is the results.

 

[kc custom]

I've really got to get to where I can put pictures up again. Randy I don't know what a Ruple jig is but an adjustable rise and fall indicator
works great for "wrapping the handle around the knife". It can be tough to fit a blade and spring to drilled holes on every knife. I'm not
exactly sure how you are doing it. Try drilling the center hole, the pivot hole, and then put pressure under the spring to drill the last hole.
Now you can trace the shape of the knife around the spring,-and then make the liners. I hope this makes some sense.
Ken.

 

[javand]

I've really got to get to where I can put pictures up again. Randy I don't know what a Ruple jig is but an adjustable rise and fall indicator
works great for "wrapping the handle around the knife". It can be tough to fit a blade and spring to drilled holes on every knife. I'm not
exactly sure how you are doing it. Try drilling the center hole, the pivot hole, and then put pressure under the spring to drill the last hole.
Now you can trace the shape of the knife around the spring,-and then make the liners. I hope this makes some sense.
Ken.

Ken, the rise-fall-indicator jig is what people have started referring to a "Ruple Jig", have no idea if Bill proliferated this or not, I've only recently begun seeing people refer to it as such.

I personally do them the way you describe, and don't bother with the jig. I just drill my pivot, temp pin the blade in there after I've cleaned up the tang, hold the spring in place in an attitude that "looks right" to me (open blade position, making sure I've cleaned up the spring end, and land, etc), clamp the spring to the liner and drill the front spring hole. After that I put a temp pin in that hole, and press the bottom back of the spring up to push everything together tight, then scribe a mechanical pencil line following the back of the spring. Then I remove the pivot temp pin, taking the blade off, and use that line as my guide for pre-loading. With a 3/32 hole, half the hole diameter eye-balled is a good rough guide IMO. I set the spring at that point, clamp the front of the spring to the liner, and drill the back pin hole.


After that, I just check where everything lands, and grind the liners to the spring, in whatever position is the lowest. You'll have to adjust the tang at that point at a minimum in the other positions to that. At this point I usually check the attitude open and closed, and make sure it's all landing where I want it, before doing the final spring flushness tweaks.

Obviously, all this gets way more complicated on multi-blades, especially ones with shared springs, etc.

 

[Randy3000]

Well i just tempered the spring and this is more like what I've been trying to do.

I have only seen the really small tangs work when there isn't a half stop. The spring is 0.110". The end of the tang is 0.120" and from the edge of the pivot hole to the notch is 0.060". I estimate about 0.050" preload.

I still need to finish the kick and heel, and I'll reprofile as i go. I think i may round off the top of the clip point where the sharpie line is, haven't decided though. I should easily be able to hide the notch on this one, i have about 0.030" off the top of the blade i can take off still near the notch.

 

[javand]

Your blade length could be quite a bit longer, the tip only needs to barely clear the end of the handle in the closed position. There's also no reason the spring heel has to go all the way to the 'bottom' of the handle, if you leave it a little shy you can get the tip damn near to the end of the handle in closed position easier.


Your ramp is not right for this style of knife IMO man, at all, and is causing you issues. Have it come to a point, slightly taller than the edge, and then have a choil notch there of your preference in style. This makes it easier to get your grind right, and sharpen the blade for you and your customer, without ending up with a recurve and an unsharpened section at the plunges.

The top of the spine above the back-square looks really high relative to the thickness of the spring, unless you've got the spring end engagement at an extreme angle, it looks like you'll have a lot of material to remove.

Let me see if I can get you a photo of what my single blade pattern looks like at this stage roughly.

 

[Randy3000]

I like the order you drill the holes in, javand. I'm going to start doing it in that order. I had been drilling the spring holes and setting preload by adjusting the notch, which is tricky.

Oh i have a ton of profiling to do on this blade. It'll clean up better. I guarantee it'll still be flawed. I'm interested to see your pics.

 

[Randy3000]

So i finished fitting the tang and tried out curving the top of the blade and i hate it. It made a very extreme angle when open and so i had to lose the curve at the blade tip to help straighten it out, and that wasn't enough.

Thinking about turning it back into a clip point, i have plenty meat to do so. Also it makes a fairly extreme angle when open which I've never had happen before. If i go back to a clip point i can curve the edge tip up a bit and make the knife look straighter when open, combined with some handle magic. I will end up with a decent gap then between the blade tip and the heel of the spring. To mitigate the blade to handle length ratio I'll grind off the heel of the spring closer to the pin.

Or, i can just keep the blade as it is and just grind off a bit more on the back and try to curve a tip a bit. And file the notch back a little further, just a tiny bit or I'll risk a sloppy lockup.

I'll probably choose wrong lol.

 

[javand]

What you don't have man, is enough length of the blade, to convert back to a clip-point, without having a really short blade relative to your handle length. You could grind the spring past the rear spring pin though, and put another pin in.


I'd recommend in the future, putting most of the curvature in your handle, progressing to a flat with a slight "down" tip attitude of the spine flat above the clip, progressing to a medium/long clip, with the tip, roughly centered to the middle of the bolster. This *looks* right, but more importantly, is intuitive to use. I think this is something that many (most) makers never consider; they put the point of the blade where they think it "looks" best, without any consideration to where it should be based on "feel", if it's drastically outside of centerline, except in highly specific, task oriented knife designs (i.e. sway back skinners, hawkbills, karambits, etc) then the user is *highly* unlikely to be able to control the point by feel/intuition without looking at it.

Any functional drop point, clip point, etc (standard, general use design) should have a point that's roughly centerline to the middle of the forward relaxed, or pinched grip of the knife, typically, centered to the bolster of a folding knife, or the ricasso of a fixed blade. Ultimately this translate to centerline of the void "cylinder" inside of a hand grip. If this is the case, you'll always know, intuitively, where your working tip is. If it's a "point focused" working knife, for fine detail cutting, this is critical. If it's a chopper, it's less so. For slipjoints however, we should mostly assume the former.

 

[stezann]

This is a HUGE thread!! Very interesting discussions goin'on here.
Randy, i have less slipjoints than yours under my belts, but i believe investing in making your own patterns pays a lot.
I started with paper, experimenting the "movements", but working with steel helps better fixing some "milestones" as your design developes.

When i am making the tang i always need to remember priming the spring position in opened mode as the lowest, that's because i find it easier lowering the half and closed position, when tuning flushness, what do you guys prefer?

 

[tmerkl]

This is a HUGE thread!! Very interesting discussions goin'on here.
Randy, i have less slipjoints than yours under my belts, but i believe investing in making your own patterns pays a lot.
I started with paper, experimenting the "movements", but working with steel helps better fixing some "milestones" as your design developes.

When i am making the tang i always need to remember priming the spring position in opened mode as the lowest, that's because i find it easier lowering the half and closed position, when tuning flushness, what do you guys prefer?

I set the open position first, then closed, then half-stop on mine for getting the spring flush. There's probably a better way, but this works pretty good for me.

 

[tmerkl]

Also, I do use a rise/fall indicator and find that it gets me close enough that when i transfer to the liners, only minor tweaks are necessary to dial everything in.

 

[Randy3000]

I set the open position first, then closed, then half-stop on mine for getting the spring flush. There's probably a better way, but this works pretty good for me.

If you take any off the end of the tang it will affect the heel and so affects the flushness at not only the half open position but also the closed position. This creates a moving target that is harder to hit. I prefer open, half open, and then closed.