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Build your first slip-joint - Tutorial


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Time to bring this build to an end!  Where I last left off, we had peened the main pivot pin.  The next step is to get the nickel silver spring pins in place.  Below you can see how long I leave the s

OK, let's make some liners so we can get into fine tuning the action.  I'm trying something new here and using brass for the liners.  I had some 0.050" (~1.25mm) thick brass sheet lying around so I su

Now you can carefully grind away most of the excess bolster material.  You need to go slow here.  Nickel silver heats up quickly, and you can get it so hot that you melt the solder.  

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OK, back tot he build.  One thing I haven't pointed out yet is how to thin down the spring to get the desired force.  Where I left of with this was to assemble the knife closed, and then to clean up the profile of the handle and spring so that they are even.  At that point you can be sure that you will not remove a significant amount of material from the outside of the spring.

 

You want to slowly remove material between the red lines along the red curve in the pic below.  Do not remove any material forward of the red line where the kick rests or you will disturb your closed position adjustment.

 

IMG_7979b.jpg

 

I had already thinned this spring down as far as it needed to go in this pic.  Sometimes I have to grind a bit deeper  It depends on how much I scale the drawing, and how thick I make the blade and spring.

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Another thing I haven't pointed out is how I handle assembling and disassembling the knife so many times.  I've already discussed using dowel pins as temporary pins to testing.  However, at this point in the build you have to also deal with compressing the spring each time.  I do this by putting in the blade pivot pin first, and then the center spring pin.  At this point nothing is under tension, and you can push the pins in by hand.

 

Then I grind a point on a dowel pin, and tap it down through the handle.  The point will align the holes in the spring and the handle as you tap it through. (You can just see the hole in the spring offset about half way across the hole in the scale)  

 

IMG_7975.JPG

 

When you disassemble the knife, use a pin punch to drive out one of the spring pins.  A proper fitting pin punch is a must for this.  Once one pin is out, all of the tension is relieved, and you can push the remaining pins out by hand.

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At this point I have the blade about ready to etch, but before I do that I want to add the nail nick.  I use a very rudimentary method for doing this, but it is within reach of a very simple shop setup.

 

All the cool kids use either a dovetail cutter, or a fly-cutter in a mill arrangement to do nail nicks that look like factory jobs.  I think Alan will jump in here to share his setup at some point to show how he does it.

 

First things first.  It help to mark the location on the blade where you want the nick.  I have started putting them out near the tip.  It looks kind of odd when the blade is open, but the nail nick is much more useful at that end than it is up closer to the pivot.  I just mark two lines so I an see where to stop cutting:

 

IMG_7980.JPG

 

I grind the nick in using a stone that is shaped to be domed on one side, and more or less flat on the other.  The stone fits in my dremel which I have mounted into a mini dremel brand router table.

 

IMG_7981.JPG

 

Then it is just a matter of keeping the spine of the blade flat on the table and slowly working between the lines to grind in a groove.

IMG_7982.JPG

 

Tada!

 

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Before etching the blade, I also like to assemble everything again to make sure the blade tip is centered.  In this case it was fine, so I didn't need to make any adjustments.  This is what you want to see:

IMG_7987.JPG

 

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I do use a dovetail cutter, so that means I'm a cool kid now? :P

 

I just like the look, it does look more "professional," for want of a better term.  You can always reshape that stone for your dremel to act like one.  

 

The first folder I made, I used a conical carbide burr on a dremel.  Being a complete idiot, I tried to freehand it.  First scrap blade of my folder career.

 

It then occurred to me that I have a milling attachment for my old lathe.  So I bought a 5/8" dovetail cutter and went to town.

20201108_120051.jpg

 

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I add the nick before grinding the bevels to make it easier to keep it tightly clamped in the milling vise with no chatter.  The blade is held between that 3/8" x 1" bar it's sitting on that keep it from bending under pressure and a piece of oak with a pin installed to hold the tang by the pivot pin hole.  Clamp it tight enough and it imprints on the tang, locking it in place.

 

The two things to be aware of if you do this are to keep a very close eye on the depth of your cut, because it sucks to grind through the back of the nick when you add bevels, and to not try to mill a longer slot in the direction the cutter is turning.  Machinists call this "climb" milling, and doing that will grab the workpiece and try to throw it forward.  That's why the nick pictured above is wonky-looking in the middle.  You can cut a long slot, but do it the right way.  A larger diameter dovetail cutter is also an option, but those things are not cheap.

 

If I were to try it without the lathe, I'd use Brian's method with a reshaped stone for the dremel.

 

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Another thing you can do for assembly/disassembly once the spring is in is to clamp the knife in a vise with narrow hard rubber jaws.  Or a set of gorilla grip pliers with the soft jaw covers.  Do this with the blade open, and clamp just forward of the center pin.  It can then be pushed right out, or in, as the case may be.  I got that tip from this site: https://www.allaboutpocketknives.com/knife_forum/viewtopic.php?f=38&t=10069

 

 

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Alan, that looks like it's probably a 60-degree cutter?  Any thoughts on that over a 45?  How fast do you run it?

 

My original idea was to shape the grinding stone to have the profile of a dovetail cutter, but I found that the fine edge of the stone wears away so quickly that it always ends up looking like a rectangular slot.  Maybe I should try grinding it to a much steeper angle...

 

That vise idea is pretty slick.  I'll have to try that.

 

 

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That's a 45 degree, and a 60 would give you a wider notch in the middle, which is not what I was after.  Speed is whatever the lathe is set on, which I think at the moment is around 600 rpm?  I had it at 1100 to do some wood turning, but I think I set it back down for this...  Change gears and belt-fed (two speeds on the motor pulley, four on the headstock) make it interesting to calculate with any degree of accuracy for a non-machinist like me.  I just go by what feels right for the job.   Quick change gears would be nice, though.  It does have back gears, and can be taken down to about 4 rpm for whatever you do with that, but the carriage isn't really rigid enough for heavy work. 1941 Atlas/Craftsman 101.

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This is the point where I get serious about final polishing and general finish on the parts.  I won't go into detail on sanding and such as everyone has their own approach to that.  However, It's worth pointing out that there is no need to go to your final level of polish on the bolsters.  These will get scuffed up a bit when I peen and file down the pivot pin.  The bolsters are at 400 grit.  The rest is at 800 which is where I'll stop on an every day carry kind of knife.

IMG_7993.JPG

 

Here are some random shots of the blade etching process.  I cover the tang area with fingernail polish to keep the etching process from messing with the critical dimensions there.

 

IMG_7991.JPG

 

IMG_7994.JPG

 

IMG_7997.JPG

Edited by Brian Dougherty
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I am using a pivot bushing on this knife.  This is not a must have item, and I didn't use one on my first few knifes.  The reason I like them is because I find it a little easier to peen the pivot without casing the pivot to tighten up too much.

 

I make my own bushings, but that is certainly beyond the idea of basic tools.  This bushing is made from bearing bronze, but I have also made them from A2 steel that I heat treat.  I like the bronze ones better.

 

If you want to use bushings, you can by them from various knife suppliers.  Just size the hole in the tang accordingly.  This bushing is a bit large for this tang, and doesn't leave as much steel as I would like, but I have all of my tooling setup for this size.  One of these days I need to setup for a smaller bushing.

 

Right now the bushing is thicker than the tang, and we need to thin it down so that there isn't too much space between the liners and the tang.  I have found that knives this size, and my assembly method, work well with a bushing that is 0.0008" (0.02mm) thicker than the blade.

 

First I need to know the thickness of the tang.  I zero my micrometer on the tang so I don't mess up the math in my head as I thin down the bushing.

 

IMG_7998.JPG

 

You can by tools like this, but I made my own fixture for sanding down the bushing.  It is just a cylinder this a whole through it that is a slip fit for the bushing, and a plunger to apply finger pressure as I sand.

IMG_7999.JPG

 

Kind of like this:

IMG_8001.JPG

 

Go Slow!  This bushing was about 0.009" too thick, and it only took a couple of minutes with 400-grit paper to thin it down.  Once I get with an couple of thousandths, I only make about 5 strokes between measurement checks.

 

Here is the finished bushing:

 

IMG_8000.JPG

 

Now I do one final test assembly.  I like to pinch the bolsters together as hard as I can with my fingers to get a feel for how tight the blade will be.

 

IMG_8002.JPG

 

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I taper the pivot pin holes in the bolsters so that the pin will swell into the space and lock into place.  For s 3/32" pivot pin, I use  #0000 tapered pin reamer.  The green ink is from sticking a sharpie in the hole to ink up the inside.  I do this so I can see how far in I have run the reamer.  I like to taper the hole to about the thickness of the bolster, and leave the liner the original diameter.  However, I don't try too be to exact with this.

IMG_8005.JPG

 

We need a pivot pin that is long enough to have material to peen over on each side.  I measure the thickness of the assembled knife at the bolsters, and add 0.100" (2.5mm) to that number to get the length of my pivot pin.

 

For this knife the pin will be nickel silver.  The pin will lock into the bushing, so the blade will be rotating against the bearing bronze, and not the pin.  I put a slight taper on one end of a rod and then cut off a little extra material.  Then I cuck the pin up in a drill and grind the cut end at an angle until get the right length.

 

IMG_8006.JPG

 

I grind in the little taper because I feel that it helps get the peening process started evenly.

 

This is what it looks like before the hammering begins:

 

IMG_8007.JPG

 

Then what it looks like after peening.  I keep going until I get the blade to feel solid when it is open, but stop before it gets so tight that it won't snap closed anymore.

 

IMG_8008.JPGIMG_8009.JPG

 

Edited by Brian Dougherty
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Much to carefully read and absorb.....
Slight cop-out, there are at least 2 brilliant slipjoint makers in SA that don't do nail nicks, I'll just follow their example for now :ph34r:
Honestly, the only type I really like is a match-striker pull......any idea how those are made?


I've using a fueler gauge jammed into the gap while peeing to keep the gap, tip I got from Swiss Army knife modders, but I really like your pivot bushing idea.......just for the life of me can't figure out where I'm going to get bushings like that....
 

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4 hours ago, Gerhard Gerber said:

...just for the life of me can't figure out where I'm going to get bushings like that....

 

The bushings are easy to make if you have access to a lathe.  The local machinist you've used can probably make them for you pretty cheaply.

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7 hours ago, Gerhard Gerber said:

only type I really like is a match-striker pull......any idea how those are made?

 

Those are stamped, usually hot.

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16 hours ago, Brian Dougherty said:

 

IMG_8008.JPG

 

 

I forgot to mention this- There is a reason that the ink is still on the bolsters until after I peen the pivot.  Years ago, in another hobby, I was taught a way to keep pins from "Ghosting".  Basically, once the hole has been reamed to size, you want nothing to touch the surface, or edge of the hole until the pin is in place.  The idea is for the edge to remains a crisp as possible to minimize any gap that can form.

 

I don't know how important that really is in this situation where I am mushrooming the pin to fit into a tapered hole.  However, old habits die hard, and it doesn't hurt anything to do it this way.

 

 

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18 hours ago, Brian Dougherty said:

The bushings are easy to make if you have access to a lathe.  The local machinist you've used can probably make them for you pretty cheaply.

Fortunately have a machinist I call friend, spoke to him yesterday, I recently gave him a piece of 14mm brass rod because there's none available in town......nada......nothing!  He can make me a little Mcgafter like that, but we're in for a wait for the materials.
Phosphor bronze is out like cookies in the orphanage, think brass will work?

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Brass might wear a little faster than the bearing bronze, but we are talking a slip-joint here, not a flipper that people will open and close incessantly :)

 

I did a few with tool steel bushings as well.  I used A2 so I wouldn't have to oil quench it thinking that gentle heating with a torch an cooling on a fire brick would reduce warping.  However, I would think even Namibia would have some sort of drill rod available.

 

The fit to the pivot pin is not the critical part.  The pin swells to lock into the bushing anyway.  The important part is the fit between the blade and the bushing.

Edited by Brian Dougherty
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Time to bring this build to an end!  Where I last left off, we had peened the main pivot pin.  The next step is to get the nickel silver spring pins in place.  Below you can see how long I leave the spring pins before peening.  I put the pins in long, and then grind them down to the length I want.  I also tend to grind them at an angle that matches the contour of the scales.

 

IMG_8010.JPG

 

Then it is just a few more minutes of "Tappa tappa tappa" Until I finish them off to where I want them.  It's wise to open and close the knife every now and then to make sure you haven't caused something to tighten up too much.

 

IMG_8011.JPG

 

Then I use a file to remove the excess pivot pin material.  I sometimes do this on the grinder, but nickel silver files quickly, while the grinder screws things up quickly.

IMG_8012.JPG

 

After filing, and some clean-up with abrasive paper:

 

IMG_8014.JPG

 

At this point, there isn't anything left to do except finish polishing up the desired level.  This is going to be an EDC knife for someone, so I only took the bolsters up to a 400-grit brushed finish.

Here are a few finished pics:IMG_8015.JPG

 

IMG_8016.JPG

 

IMG_8017.JPG

 

IMG_8018.JPG

 

Here is a quick video snippet showing what I feel a slip-joint should behave like when opening and closing:

https://youtu.be/o3elmz4B53M

 

Thanks for riding along with me on this.  I hope it helps some people out, and I'm happy to answer questions.  I also hope that it demonstrates how easy it is to make one of these without a machine shop.  Bigger/fancier tools would allow me to do this with fewer iterative steps, but it is doable with not much more than a drill press.

 

You can skip the surface grinding by purchasing precision ground tool steel stock.  The bushing nonsense isn't a must have, but even if you want to use them, you can purchase bushings from many suppliers.  The precision fitting of the bushing I did with sand paper on a piece of granite counter top scrap.

 

Is there anything I would do different?  Yeah, no knife is perfect.  I think this design would look a bit better with smaller pins.  I also need to setup for a smaller diameter bushing for knives in this size range.  This one didn't leave as much tang material as I would prefer.  However, I already have the reamer and bushing sanding block made for this size, so I just went with it.

 

Edited by Brian Dougherty
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Brian, this has been one of the most detailed WIP's I've seen posted.  I dont plan on making slip joints anytime soon, but when I do I'll be sure to return to this thread.  Well done sir!

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Fun read.  Thanks for putting this together, Brian.  It kinda makes me want to get into slip joints.  

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Brian thank you for posting this. I’ve saved both your patterns to use on future knives, (in the past, I used patterns from store bought. well, A.M. Mayhall did too!)

I like this coke bottle, good pocket-size and full size blade. I like Alan’s small folders as well and want to try some too.

i know the photos aren’t easy but I picked up pointers as if I was standing there and everyone’s input was really good!

Gary LT

 

 

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Thanks very much Brian. A valuable resource. One day when the folder bug bites I will definitely be turning here. Kinda hate to ask, but

7 hours ago, Brian Dougherty said:

It's wise to open and close the knife every now and then to make sure you haven't caused something to tighten up too much.

how would you fix this?

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On 2/17/2021 at 2:36 PM, Brian Dougherty said:

Brass might wear a little faster than the bearing bronze, but we are talking a slip-joint here, not a flipper that people will open and close incessantly :)

 

I bought stainless sheets in 0.7mm and 1.2mm and they have phosphor bronze in 14mm rod, no smaller, but fortunately not ridiculously expensive.  Will cost a bit more to have it drilled and turned down, but not impossible.

Thank you very much @Brian Dougherty for taking the time, very much appreciated.  Hope to show my effort in the not too distant future.  

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5 hours ago, Charles dP said:

how would you fix this?

Charles, It will depend on what is going wrong, but there isn't much you can do to reverse it.  Stopping before you make it worse may be the only recourse.   If the spring is perfectly flat, and the right thickness, then nothing should tighten up.  However, nothing is ever perfect, and at the end of the day, you are hammering on something that is supposed to be precisely fitted together.  Weird things can happen.

 

It would be possible to remove the spring pins and back up to fix something.  Removing the pivot pin would be much harder,

 

 

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