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Build your first slip-joint - Tutorial

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OK, I'm going to try something new here.  There has been some interest on the forum of late for building folders.  A handful of folks, including me, have started building them in the last year or two.  I thought I would walk through the process I use in great gory detail in the hopes that it will help some folks.  I'm not an expert at this by any means.  I've only build about a dozen slip-joints, and I do something different each time.  However, they say that nothing is as educational as trying to teach something, so I'm hoping to learn too.  If nothing else, it should stimulate some conversation.


Today boys and girls, we are going to build this knife:


It is my own design and the pattern is here for you to download.  The design is heavily influenced by the work of Steve Culver.  I highly recommend his book on slip-joints:  https://www.amazon.com/Slip-joint-Folder-Designing-Building-Culver/dp/1545388326/ref=sr_1_1?dchild=1&keywords=steve+culver+slip+joint&qid=1611879565&sr=8-1


With the exception of two steps, I will not use anything more sophisticated than a drill press and my 2x72 grinder.  The two steps where I do use bigger machinery can be eliminated with good results.


I've done a WIP while making this design before, but that was just a few pics I took along the way.  In this tutorial, I will try to explain why I do each step, and what I have learned is and isn't critical.  Feel free to add any info I missed, or ask questions along the way.


I'm a few days into building the knife, and am pretty motivated to finish it up, so hopefully I'll add to this thread every day or two.

Pattern 9-30-19 (1).pdf

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To start with, you need a piece of steel for the blade and another for the spring.  In my case I am using a piece of pattern welded material for the blade and 1075 for the spring.  This is the first place where I use a big piece of machinery - a surface grinder.


It is important that the blade and spring material be exactly the same thickness.  You can get away without a surface grinder if you simply buy a piece of precision ground tool steel to cut both parts from.


In my case I like using pattern welded material, and I am not good enough to forge my bars out to that exacting of a tolerance  :D


Here you can see my two pieces of steel along with the paper patterns cut from the drawing.  I scaled the pattern to 90% in this case which results in a blade a little under 3".  (76.2mm)




I ground the steel to be a touch over 0.100" (2.5mm) thick, but I'll thin the finished parts down to about 0.095" (2.4mm) before it is all over.  It would be fine to start with the material at the finished thickness.  Doing it this way just gives me the luxury having a little room to clean things up if I goof.  I think you could easily make the same knife with much thinner material if you wanted to.


The next step is to superglue the paper patterns to the steel:




You want to get them glued down real well.  It also helps to coat the paper with the super glue.  This way the pattern will hold up better to dunking in water to cool the part as you grind to shape.  One of Culver's tricks is to use the plastic shaft of a Q-tip as a rolling squeegee to spread the glue out. 


My starting pieces will waste a lot of material.  Usually I try to be more frugal with the steel, especially the stuff I make.




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Hi Brian

Thank you very much, I've got two sizes of your knife ready up to this point, so I'll be going along with you as far as possible.

And I've learned something already, for the life of me don't know why I didn't think of using super glue instead of contact adhesive. :ph34r:

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I use a lot of super glue when building a knife, but none of it ever remains in the finished product :)  It is my "go to" material when I need to stick two parts together temporarily.



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I use a lot of it too, in fact on the same piece of steel I have the broken back spring SUPER GLUED on to trace out the new one :lol:
Feel doubly stupid remembering that.
Template ripped a bit during drilling, not critical, will just fix what's left in place.
We called super glue The Light of APGAI on a fly fishing forum, revolutionized my fly tying :lol:B)

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fortunately my soul looks worse than my workshop, but my flat is another matter.
bachelor with day job + knife making = stay away




Edited by Gerhard Gerber
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Well for tonight's installment we'll drill some holes.  The pattern has the center of each hole marked, to make it easier to use a center punch to start the drill.  You want to be reasonably careful to get the punch marks centered, but as you will see later, the required accuracy is well within what a human can do by hand.




I'm using 3/32" (~2.4mm) pins for this build.  That is actually a little large for the spring and scale pins, but I already have drills, reamers and pin stock for that size, so I'm just going with it.  I think a 2mm pin would look better.


I drill the holes undersized and then ream them.  I feel this allows for a much better fit with the pins.  Here I am using  #43 drill bit followed by a 3/32" reamer in the spring.  We are only drilling the rear hole now.  The center hole will get drilled after the stop points for the blade have been adjusted.




Do you like my highly calibrated piece of MDO plywood?  I don't know why I do it, but I have always preferred to have a piece of MDO on my drill press table when I work on small parts.  You'll see what the notch is for later on.


A note about pins and reamers: You can't put a 3/32" pin in a 3/32" hole.  Well, you can but it will be a press fit which is not what we want.  During the multiple test assemblies I will be doing, I will use commercially made dowel pins that are about 0.0002" undersized (Yes, that is 2 tenths of a thousandth) These will slip nicely in the reamed hole, but not have any slop.  You can also buy reamers that are slightly oversized to get the same result with a full-sized pin.


I also drilled a 3/32" hole through the blade pivot pin location while I had the drill chucked up.  Not everybody thinks a pilot hole is a good idea, but I find it makes it easier.  Then I open the hole up to a #14 drill so that I can ream it to 3/16" later.  (I'll do that after I grind the profile to shape)




Ready to head to the grinder!





Edited by Brian Dougherty
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On this knife, I felt it was important for the pins in the center of the handle to be symmetrical so the second spring hole position is fixed by the hole in the liner.  I'll use the liner to locate the hole in the spring after the preload is set.


If I were machining the parts, I could locate the hole in the spring ahead of time on the pattern.  However, a few thousandths of an inch of variation in the spring tip or blade tang will result in a big change in spring tension.  Since these parts are all made with simple tools with the resulting variability in size, I have to wait a while before I can decide the final hole location.


I'm not sure I described that very well.  It will be more clear once I set the preload on the spring and drill the second hole.


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I didn't take a picture while grinding the profile of the blade and spring, but it's worth talking about a few points that I look out for. 

  1. Going slow and keeping the heat down will help keep the paper template in one piece.  It will also reduce the amount of burnt super glue that you put into the air.  I can only imagine how bad for you it is when you can smell the super glue when you are grinding.
  2. Leave the tip of the spring a little bit long so you can fine tune the open angle of the balde later
  3. Everything about the blade except the tang area is pretty arbitrary.  Go ahead and grind to the line.
  4. It's better to leave a little material on the inside edge of the spring where it contacts the tang so that you have room to make adjustments 
  5. Leave plenty of material around the tang, and hand file that area to the final size.



When I file the tang area I like to start by keeping the open and closed facets parallel to each other.  I just measure points A and B with calipers and adjust my filing until I get them within a couple of thousands of an inch to each other.  (The absolute dimension isn't that important as long as you don't remove so much material that you can't position the spring in a way that exerts enough force.)


Tang Grind Tip 1.JPG


I also try to keep the hole equidistant from all 3 edges.  To do this I check to make sure that this dimension is the same in all 3 places:


Tang Grind Tip 2.JPG


I also ream the pivot hole at this time.  You can probably do this earlier, I just got into the habit of doing it after all the harsh grinding was done.




You can see how things are starting to line up.  We need to get some liners cut so that we can start adjusting the open, half-stop and closed positions.  This is where things will get interesting, and that nice "Square" tang that we worked so hard to file into shape will end up with all sorts of funky angles before it is all done.


This is also a good time to file in the sharpening notch before it gets forgotten.  I use small triangle file with a safe face up against the kick.  A round file would look better and create less of a stress riser, but this way is so easy that I just keep doing it.







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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 super glued the patterns to the sheet and roughed them out on the grinder.



Now we have to drill some holes.  It is very important that the holes line up perfectly.  The position of the holes has to be within less than a thousandth of an inch if you want a nice clean assembly.  How do you do that with a just a drill press?  Easy...


First off, you get one free move.  You can drill a hole anywhere in two plates and pass a pin through them.  It's only when you add a second set of holes that you get yourself in trouble.  Let's start by centerpunching the pivot pin holes in each liner:




You can see that I'm not perfectly centered here.  No worries as long as there is enough material around the edge of the lines to clean things up in the end.


Then drill and ream each hole to 3/32" (2.4mm) so we can slide a dowel pin through.  Clean and deburr the faces of the liners that go together.  Then super glue them together using the dowel pin as an alignment tool.  You have to line up the other end of the liners visually.  (There he goes with the super glue again...)  Note that the pivot pin hole is not on the centerline of the liner.  That means you have to keep track of the inside and outside faces of the liners.




Now drill and ream the back spring hole, and slide another pin in before you do anything else.  Yeah, I know it would be a lot faster to drill all of the remaining holes, and then switch over to the reamer.  Trust me, super glue is evil and will let go on you when you least want it to.  Put a second pin in now to keep everything properly aligned.




Then you can drill and ream the rest of the holes.  Strictly speaking, only the two spring pin holes and the pivot pin holes need to actually line up between the two liners.  However, I find that having them all perfectly aligned is an advantage during various phases of the build.  If you do this right, you will be able to put pins in all 5 sets of holes with no binding whatsoever.  If you can't push the pins through with your finger tips, then something is out of whack.




Now we are starting to get somewhere.  Ignore the blade busing for now.  I'll cover that a bit later.  If you are following this tutorial, you are probably new at slip-joints.  In which case I would suggest skipping the bushing all together as it isn't that important.  If you don't use a bushing, simply ream the blade pivot hole to match whatever you are using as a pivot pin.






Looks pretty crusty at this point doesn't it.  Don't worry, it will start looking like a knife soon...

Edited by Brian Dougherty
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On 1/28/2021 at 7:57 PM, Brian Dougherty said:

It is important that the blade and spring material be exactly the same thickness.


It is impossible to emphasize this enough.  It absolutely must be precision-ground, or flat in both length and width to within 0.0005" / 0.015 mm, or it will cause problems.  I found this out the hard way after finishing several folders using precision-ground O-1 and having zero problems related to thickness, then switching to AEB-L which is not readily available pre-ground.  Turns out doing it by hand with a disk grinder is not precise enough...  

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OK, it's time to get nasty.  We need to adjust the spring and blade tang so that the blade positions are all correct.  If there is part of making slip-joints that is irksome, then this is it.


First, keep in mind what we are trying to achieve:

  1. We want the blade opening angle to be correct
  2. We want the blade to be locked up tight when it is open (i.e. not feeling "springy")
  3. We want the half-stop position to be about 90 degrees from open
  4. We want the tip of the balde completely inside the liners when closed
  5. We don't want the blade edge to come into contact with the inside edge of the spring when it snaps closed
  6. We want the outside edge of the spring to be flush with the liners in all 3 blade positions.

Adjusting any one of these things can impact the others, and it is easy to take off a bit too much material resulting in a scrapped balde or spring.


First I start by grinding a roughly 45 degree chamfer on the inside corner of the spring tip to create a bit of clearance.  By the way, I do all these adjustments with a 320-grit AO belt.  Once the adjustments are done, you don't want to be sanding on these surfaces anymore.




Now slowly grind back on the tip of the spring until the blade stops at the right angle when open.  I like to leave the spring and blade pinned to one liner so that I can easily grind a touch and then flip all the parts in place to check the open angle.  It helps keep me from getting impatient and taking off too much.




The proper open angle is a somewhat aesthetic choice.  I prefer it to be a bit more open than this:




This is one scenario you do not want to be in.  Do you see how the spring is bearing along the entire top facet of the tang.  This invariably means that the tip of the spring is not in contact with the blade, and will result in a mushy feeling blade when open. 




If this happens to you, then you need to carefully file the top facet of the tang so that the spring contacts at the tip and at the corner of the tang only.  This is much better:





At this point I like the open angle so I am going to call this adjustment done.  It also means that I have defined where the spring will be when the knife is open.  As I adjust the other two positions, I need to not only get the blade in the right place, but also make sure the spring is in exactly the right place as well.




Edited by Brian Dougherty


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27 minutes ago, Alan Longmire said:


It is impossible to emphasize this enough.  It absolutely must be precision-ground, or flat in both length and width to within 0.0005" / 0.015 mm, or it will cause problems.  I found this out the hard way after finishing several folders using precision-ground O-1 and having zero problems related to thickness, then switching to AEB-L which is not readily available pre-ground.  Turns out doing it by hand with a disk grinder is not precise enough...  




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Now that we have the open position adjusted, it is time to do the half-stop position.  Not everybody puts the half-stop in, so just round this facet over if you don't want to mess with it.


This is the easiest of the 3 positions to adjust, and it is also the position I shift any error to when it is all done.  Nobody seems to nit-pick just how well you do the half-stop :)


Here is the tang as we first roughed it out.  The paper pattern guides you to leave enough extra material in place that the blade will be at noticeably less than 90 degrees open.  To correct this we need to grind away material along the red line I drew in the pic.



The angle of the red line is what controls the angle of the blade.  However, you want to try to preserve the top left corner of the tang (as oriented in the pic) because we will grind parallel to the red line to adjust the position of the spring relative to the liners.  If you take that corner out too early, you may find that you have the spring below the level of the liners, and then you have to go back and adjust the open position again.  (Remember we are trying to get the spring flush with the scales in all 3 blade positions)


I'll explain more about how to know when you get the spring height right in the next post.


I like to file a small concavity in the half-stop tang facet because it makes the position feel more solid.  The tang and spring surfaces will never be perfectly flat, and will rock a bit.  This way you get two points of contact instead.  I actually filed this hollow in after I had adjusted the closed position, but now is a good time to talk about it.  You'll see that the kick in the pic below is in its final form.



Edited by Brian Dougherty


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Now we have to adjust the closed position.  The kick in the pattern is way oversized so if you were to try to put the knife together, it would look something like this:




There are two things we need to adjust for here, the angle of the blade when it stops, and our old friend spring position.


The angle is controlled by a line from the top left corner of the tang as it is oriented in the pic through the kick.  Just like the half stop, the spring height is controlled by grinding parallel to the line that sets the blade angle. (The blade angle will change a little when you do this, but I find it easier to think about it as two steps.)


Here I overlapped the blade with the spring so you can see what we are trying to accomplish.




First I need to clean up the inside edge of the spring a bit so that there is a clean surface for the kick to rest against.  All I did here was move the shoulder back a bit.  You do not want to grind anything off the part of the spring that touches the tang facets or you'll mess up all the adjustments you've made so far.




Then it is just a matter of creeping in on the right closed angle by grinding a little bit off the kick at a time..






Then all you need to do is adjust the spring height.  I do this by measuring the position of the spring relative to the edge of the liner  in the open position and then matching that dimension when it is closed.  In this case, the liner is sitting 0.021" (~0.5mm) proud of the spring when I hold everything in the open position.  So I ground away on the tang until got the same measurement when holding it closed.




I like to clean up the hollow left in the closed facet at this point to give it a nice clean curve.




And here we are:







Edited by Brian Dougherty
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I wasn't going to share this part because it is all about the complexities of surface grinding, and I wanted this to be for the make who only has a drill press.  However, this might help someone with more advanced tools so here goes.


As Alan said earlier, not only do the blade and spring need to be exactly the same thickness, they also need to be very flat.  Unfortunately, my starting stock was not flat at all.  The 1075 was pretty flat, but had a bit of warp to it.  The pattern welded steel was even worse.


My friend's surface grinder has a magnetic chuck (as do most)  The magnet is strong enough that it will suck a slightly warped piece of steel down flat against the chuck surface.  The result is that you can make the part a very uniform thickness, but you can't make it perfectly flat.


If you've ever spent much time id a wood shop, it is like trying to take the cup out of a board with a surface planer.  To my knowledge the don't make a jointer for small metal parts :(


Both my parts had about between 0.0005" and 0.001" of warp.  I put the concave side down against a piece of abrasive paper on my marble slab, and gently sanded until I got one side flat.  Then I went back to the surface grinder to even out the other side.


You can still see a bit of the concavity in the pic here:




If you are using precision ground stock, you don't need to worry about this.

Edited by Brian Dougherty


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My next step is to locate the second hole in the spring.  To do this, we need to set the pre-load on the spring so that it places the right amount of force on the tang


Here I am holding the spring tightly against the blade in the open position and measuring the distance between the spring and the edge of the liner with the tail of my caipers.  I will then move the spring inward (towards the edge of the liner I am measuring from) by 0.030" (~0.75mm), and place the second pin hole so that the spring is in this position when at rest.


0.030" isn't a magic number, but it seems to work well with the springs I make and the size of knifes I make.  




I mark a line that I am measuring along to keep the calipers at the same angle in the next step.  I also write down the measurement, and what my target dimension is on the liner because I am getting feeble minded in my middle-age.


Here I have removed the blade, and clamped the spring into place.  I gently tap the spring to shift it until it is the right distance away from the edge of the liner. (The rear pin is placed through the spring and liners during this whole step)




Once I get the spring positioned correctly, I carefully drill through the liners to create the second hole in the spring.  You'll see that I have both liners clamped to the spring.  I do that so that the guide hole I drill through is deeper.  This makes it easier to line the drill bit up accurately.  Remember the notch in my MDO plywood?  That creates clearance for the c-clamp.




Then I unclamp everything and ream the hole to size.




If you do it right, you should be able to slide the dowel pins through by hand.  You can see that the tip of the spring is much lower than it would be if the blade was in place.


At this point, we have to get the spring and blade heat treated before we can put the knife together again.




Edited by Brian Dougherty


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Before I heat treat the blade and spring, I like to make sure that the back section of the spring is polished down to a final finish on the inside.  It's not a critical surface, but it is visible when the knife is open.  There is no point in finishing up much of the area in front of the center pin yet as we will be adjusting the spring tension by grinding away that area after heat treating.



I didn't photograph much of the heat treating process.  There are far more knowledgeable people on here than me when it comes to that.  However, I will point out that I like to coat the parts with anti-scale so that the areas with finely tuned dimensions don't get altered.



My shop is heated with a kerosene heater, and I use it to bake on the anti-scale while the oven heats up.  It's also a great place to warm up my oil while I wait.  My large blades are heat treated in my forge which is in a shed out away from the house.  However, folders I do in my garage using a little burn-out oven, and a jar of canola oil.



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While I wait for all of the heat treat cycles to happen, I'll get the bolsters and scales going.


I'm using 1/8" (~3mm) thick nickel silver for the bolsters.  First I cut off a couple of pieces that have quite a bit of excess.  I like for the bolster to end about half way between the pivot pin, and the front scale rivet.







I use a piece of abrasive paper on a marble slab to make sure one face is flat.  The bar stock is not very flat, and if you don't do this you will get an uneven solder joint that stands out.



I also use the 2x72 to grind the rear edge of the bolster square so that they will match up well with the scale material.




This is what you want:



Then I tin the area of the liners where the bolsters will go.  You want this to be a pretty thin coating.




I also tin the back of the bolsters.  I usually lave a little more solder on here to make sure I don't starve the joint.



Scribe a line on one liner where you want the bolster to stop



Reflux everything, and set the bolster on the liner in the correct position:



Then gently heat until the solder flows


Edited by Brian Dougherty


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So, how do you get the second bolster soldered on so that it lines up perfectly with the first one?


I'm sure others have a more direct method, but this is what I do.  Remember I said it is handy if all of the holes in the liners are perfectly aligned, not just the holes for the through pins?  Well, this is one of the reasons why.


I pin both liners together using the center pin/rivet holes.  Then I put the pair in my file guide so that the back edge of the first bolster rests on the file guide.




Then I reflux the second bolster and liner and hold in in place with a couple of spring clips.  Be careful here!  If you use too much clamping pressure, you will squeeze out all of the solder and the bolster will come loose.




Then reflow the solder as before.  If you are careful, you can get just the second bolster to flow.  However, the clips will hold everything in place if you get the fist one too hot.


It also helps to put some  liquid paper on the inside of the liners so that you don't inadvertently solder them together :)




You can clean up any solder where the back edge of the bolster meets the liners using a brass rod hammered flat, and ground into a chisel edge.

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Next I drill through one bolster from the inside using the hole in the liner as a guide.  The oversized bolster helps me keep it flat against the table.




Then pin both liners together, and drill back through the other direction 



Once the hole goes all the way through, run back through with the reamer



You should be able to slide the dowel pin through with a finger tip...


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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.




Here I am cleaning up any excess solder using the home made brass chisel trick I mentioned earlier.


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Now that we have liners with bolsters attached, we can put on some scales.  I'll be using "Jigged Bone" scales.  This is cow bone that has been machine jigged and dyed to look a bit like antler.  I like this material as it is inexpensive, but wears very nicely in the pocket.


The material I buy is nominally 1/8" thick.  However, it is actually closer to 0.160" (~4mm) thick which is too bulky for a knife this size so I usually have to thin it down a bit on the grinder.  I don't have a disk sander, so I do it on the belt.



This results in a back side that is not perfectly flat.  In order to maximize the glue bond strength, I like to flatten the back side on my trusty granite slab.  I use the same method you use to flatten a water stone.  First scribble some pencil marks on the bone:



Then rub it on the abrasive paper on the granite slab until all the pencil lines disappear.  Here you can see the progress as I sand out the high spots:



Next I grind one edge square so that it will mate nicely with the bolster:




Then I clean the parts with acetone, and get ready to glue on the scales.  I have been using Gflex epoxy.  However, on this build I thought I would try Alan's approach and use Loctite 330 structural acrylic adhesive:




The advantage to 330 is that it sets quickly, and has a ideal adhesive thickness that is half of what is required for epoxy.  I just followed the directions by applying the activator to the liners, and the adhesive to the scales. (The instructions recommend applying the activator to the least porous side of the joint)  Here are the parts clamped up.  The only trick here other than following the instructions is to make sure you get a tight fit at the joint between the scales and the bolsters.



Once the adhesive is cured, you can rough the scales to the shape of the liners.  I leave quite a bit of extra material at this point.


Edited by Brian Dougherty
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