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2020, the year of the slipjoint


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I'm getting a bit ahead of myself, but I've cleared a major hurdle, some 3mm thick 1070 headed my way soon.

Correctly or not, I figured my chances of getting the blade and backspring the same thickness any other way was slim, still no joy with the VW Beetle torsion springs.

 

I have a little wooden Canoe pattern knife kit that I plan to use as a template, one blade only for a start.

Plan on using engraving brass for the liners and solder on bolsters.

 

One thing I'm unsure about is my plan to use 4mm brass rod for the pins.  I use these regularly on my knives so I have 4.1mm drill bits ready to go.

So is 4mm too thick?

Should I rather drill the blade 4mm and fit the pin as tight as possible?

 

The part I dread the most is assembly and peening the pins, my only plan so far is to make a jig using some massively thick MS flatbar I have lying around.  Basically just duplicate the pin holes in the flatbar.

 

Is it feasible to only add the scales after the worst of the above is done?

 

How long & hot to get a spring temper on the 1070? 

 

Edited by Gerhard Gerber
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I've been using 1075 for my springs.  I quench just like I do the blade, then temper the spring to 530F (276c).  The spring usually gets tempered with the blade each cycle, and then one extra cycle at the higher temp, but I just do this for convenience and have no idea waht it does to the metallurgy.

 

I've been using smaller pins than that, but I think it depends on the scale of the knife.  Lately I have been using 1/16" (~1.5mm) pins to hold the scales on and the spring in place.  I like using 1/8" (~3mm) pins for the pivot.  My blades have been between 2.5" and 3".  I literally use a 1.5oz hammer to peen the pins.  Lots of light taps.

 

I try to get the holes tighter than 0.1mm.  Depending on the pin stock you are using, you may be able to get away with the exact drill size.  Alternately, I use some 0.001" over-sized reamers.

 

Edited by Brian Dougherty
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5 hours ago, Gerhard Gerber said:

Is it feasible to only add the scales after the worst of the above is done

 

To add to what Brian said (and I use 3/32" pins for pivots and bolster, 1/16" for scales),  if you want to pin the scales you have to do that before final assembly of the knife.  They work by having a little countersink inside the liner.  You could conceivably have the holes drilled and countersunk, and add the scales last if you put a chunk of steel the exact width of the blade channel in the knife to act as an anvil, but I wouldn't trust it.   It's really best to attach the scales with the liners off the knife.

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Thank you very much for those practical tips.

The Canoe is rather small, might look okay at the pivot but probably not the rest.

My only alternative is brazing rods, would that work?  Will try to find steel alternatives.

We're limited to drill bits in 0.1mm increments so I'll drill on size and fiddle a bit.

11 hours ago, Brian Dougherty said:

I Forgot to say that I'm happy you are going to try folders this year!

Thank you again for the design you shared, that will be my next attempt B)

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A set of calipers or a micrometer will help immensely with the pin stock and drill bits. I have found that most of the pin stock I get is a few thousandths over the stated diameter, and rarely ever matches the drill bit well enough. I usually have to "dress" my pin stock with 320 grit sandpaper and a drill, even after using a reamer to open the holes a little.

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On 1/24/2020 at 3:07 PM, Joshua States said:

A set of calipers or a micrometer will help immensely with the pin stock and drill bits. I have found that most of the pin stock I get is a few thousandths over the stated diameter, and rarely ever matches the drill bit well enough. I usually have to "dress" my pin stock with 320 grit sandpaper and a drill, even after using a reamer to open the holes a little.

I put in a bid on a  micrometer between a lot of tools but I never heard from the guy, can't afford the rest available in town....

 

Been watching a lot of videos on the topic, and the nett result is mostly worry..... 

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It's really not as hard as some make it look, and you don't "need" a micrometer.  A cheap set of calipers is fine.  I got some $9 digital ones because I have to wear magnifiers to see a vernier anymore...

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3 hours ago, Alan Longmire said:

It's really not as hard as some make it look, and you don't "need" a micrometer.  A cheap set of calipers is fine.  I got some $9 digital ones because I have to wear magnifiers to see a vernier anymore...

 

I agree.  I am indeed adjusting some tolerances in the +/-  0.005mm range, but that is eeking out the last 15% of performance.  The first 85% can be had measuring with standard calipers reading to +/- 0.01mm.

 

After making quite a few of these, I would recommend you sort of "slap" the first one together to get an idea how it goes.  Let it turn out a bit rough.  The value of the knife will be in learning how all the adjustment points work along the way.  Then start fine tuning your process on the second one.

 

There is a bright side to folders.  I can hand sand a 3" slip-joint blade from off the 320 belt to 800 grit and ready for finishing in an hour or two.  :)

 

 

 

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I wish I could find and link the series of videos......

One tip from the videos is concaving each step on the tang, I assumed this prevents wobble in the blade at the stops.

 

I have concerns about my template not being accurate enough, what works in a small wooden kit might not translate well to steel....

 

And the nail nick.......not looking forward to that! :D

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Don't count your chickens they say....

Murphy's Law they say....

 

My 1070-dreams are in tatters, got somebody to smuggle 20kg of steel over the border, only to be tripped up by the inability to pay via EFT, transaction has failed twice, guess their bank doesn't belong to the right club :angry:

 

:(

 

Back to hunting for VW Beetle torsion springs

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  • 11 months later...

Good morning All

......and a Happy New Year to you all.

2020, obviously on January 23rd nobody could've guessed what this year would bring, for me it turned out to be my least productive year since I started making knives.
I poisoned my environment working from home for several months and I couldn't make myself go into the shop.

Several years ago I bought a slipjoint kit for a friend in another town, not knowing much at that stage we later found out the blade and spring were 14C28N and we couldn't heat treat it at that stage.
Fast forward about 4 years he returned the kit to me, deal was I'd try to make the folder for him, if I fluffed it I'd refund him.  Not a great deal for me, but he's a good human being.
The kit consisted of the blade and spring blank, 2 brass scales and SS bolsters, holes were marked but I had to drill them.
I cleaned everything up, ground the blade, did the heat treat including tempering the spring at 540C.
Used micarta for the scales but I was still scared of peening on the scales, so I'd drilled an extra hole in the backspring and scales, peened the 2 structural pins and hid them below the scales.

I had a rather serious problem during the dry fit, walk & talk felt good but very quickly got worse, and when I took it apart the blade had gouged a bad groove into the backspring. My first assumption was the advice on the temperature to get a spring temper for 14C28 had been incorrect, but I ground out the gouge, smoother and polished the shit out of everything.....which seems to have worked.
The only consequence (I think) is about 1mm of lock rock :ph34r:
I don't like the fact that it's a kit, and the lock rock is not great, but other than that this knife literally made my year, I reached my goal, even if it was in the dying moments.

The knife was sharpened and sent to my friend 30 December 2020 :lol:

I had a few weeks leave which I spent either on the couch or in the workshop, I was very busy with a knife for a young man who has a birthday on the 6th, had to inlay tusk from a warthog he'd shot in the handle, commissioned by his dad.

 

Only sharpening left to do and the sheath is being made, so yesterday afternoon after lunch I decided I would just mark out the next folder.
Then I thought I'd just trim some of the waste.
Then figured why not do the drilling, if I mess that up the rest is a waste anyway.

Called it quits by about 6pm when I had all the components roughed out.......and by 9pm I found myself back in the shop busy with a file doing some fine tuning.

I'll post some photos soon:ph34r:

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Congratulations on a successful year-goal. Well done sir!

The only other thing I can say is about that spring on the new knife. It looks like you over-sized it in anticipation of doing some retuning grind to make the fit up. This is a good way to go about it. However, you may want to consider taking material off the bottom of the spring, rather than the top of the spring, or a little of both. I only say this because I am not holding the knife in my hand, so I don't know how it looks when the blade is closed. That little tail on the back end of the edge should contact the spring when the blade is closed. This keeps the edge from banging into the spring.  Getting that spring shaped so that there is enough material for the tang notch and still have that tail stop the blade, is the crux of slip joints.

 

Oh yeah. I almost forgot to mention.....You want a canoe?

Edited by Joshua States
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On 1/6/2021 at 4:54 AM, Joshua States said:

 

 

Oh yeah. I almost forgot to mention.....You want a canoe?

Got one ;)

Thanks Josh, I've been learning that dance this week :ph34r:

So my leave ended monday, but it was so quiet at the office I phoned the boss and asked if I can take more leave......since I have a burning obsession.....

I made a second similar knife and I've been busy with them the whole week.
I did the post-HT grinding and started with the scales this morning, just got one set ready and assembled the knife for the first time post-ht.
It felt like a fixed blade, I assembled it open, when I went to close the spring snapped :(

I tempered the springs with the blades right after HT, and then they tempered for another hour at 290C, they looked blue on the way to purple.

IMG_20210108_121740[1].jpg

IMG_20210108_121822[1].jpg

IMG_20210108_121838[1].jpg

IMG_20210108_122042[1].jpg

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Bummer. :(  Is this the 1070?  The ASTM guide says to austemper for springs, but since you don't have a salt pot that may be difficult...  Heat to 815 C, quench in molten salt at 315 C, soak one hour then air cool is what they say.  Maybe, just maybe, you could quench in really hot oil and immediately temper at 300 C?  Jerrod is going to object that's in the blue-brittle range, but sometimes we have to ride the ragged edge of disaster to get the desired effect.  

 

I haven't broken any of my O-1 springs, but I have snapped an AEB-L one.  On the O-1 I found it helps to really thin out the spring from top to bottom between the center pin and the blade end.  Leave the part the blade rides on full thickness, but grind the part between as thin as you dare, with a nice rounded transition of course.  The thinner the spring, the better it will bend without breaking.  Usually... :ph34r:  Kind of like below:

 

20201206_135345.jpg

 

For the record, when I assembled this one I learned that the spring between the pins has to be truly flat/parallel and the same thickness as the tang of the blade.  If the slight taper between the center pin and the blade continues past the center pin, the knife will bind in a most annoying manner. It worked fine during the dry fit, but once the pins were peened it binds no matter what.  That's item #190 on my list of things I've learned what not to do on folders...<_<

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10 minutes ago, Alan Longmire said:

Jerrod is going to object that's in the blue-brittle range, but sometimes we have to ride the ragged edge of disaster to get the desired effect.  

Nope, that is just below the range.  

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1 hour ago, Jerrod Miller said:

Nope, that is just below the range.  

The ragged edge of the range? ;)  

 

I think we should start a thread in Metallurgy about temper embrittlement and how it works, since it's been coming up a lot lately.  Just to keep the info easy to find, what do you think?

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13 minutes ago, Alan Longmire said:

I think we should start a thread in Metallurgy about temper embrittlement and how it works, since it's been coming up a lot lately.  Just to keep the info easy to find, what do you think?

I'll put something together.  

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Hopefully I didn't steer you the wrong way on the temperature Gerhard.  Here is a pic that shows one of my springs.  You can see how much it is relieved (thinned down) in the area where it flexes.  I can say with absolute certainty that if I try to close one without that relief, it will snap the spring.  (Yes, I had to learn that lesson twice)

 

IMG_20200428_181128841_HDR.jpg

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On 1/8/2021 at 11:08 PM, Brian Dougherty said:

Hopefully I didn't steer you the wrong way on the temperature Gerhard.  Here is a pic that shows one of my springs.  You can see how much it is relieved (thinned down) in the area where it flexes.  I can say with absolute certainty that if I try to close one without that relief, it will snap the spring.  (Yes, I had to learn that lesson twice)

 

 

Hi Brian

I believe you did, but no worries, school fees!
I employed my best google-foo and found a non-knife site with the needed info, I was actually looking for it to link it here but I couldn't find it again.
Anyway, according to this guy 700F is the right temperature for a 1070 spring, interesting part was he said you can use molten lead to temper the spring since lead melts at 700F.
I tempered the other spring and the broken piece at 370C, tested on the broken one.  

Second spring worked but was way to stiff so I ground that area you both indicated much thinner....but not thin enough, slightly stronger than a fingernail breaker, but the knife is together and works!
 

Thank you all for advice and more importantly inspiration!

 

@Alan Longmire, Brian, I do have another question about the spring, when not tensioned should the front part  sit a bit lower than it's position when assembled? 

I have a million questions actually, but my impression from this week is there might be a million answer depending on the pattern and the assembly method.

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5 hours ago, Gerhard Gerber said:

 I do have another question about the spring, when not tensioned should the front part  sit a bit lower than it's position when assembled? 

One of the tricks is getting the spring flush with the scales in all 3 positions.  (Open,Closed, and Half-locked if you do that)  I start by fitting the open position so that the others leave the spring a bit proud, and then file/grind away carefully on the tang to tweak the other positions.  

Edited by Brian Dougherty
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And yes, by about 0.5 mm.  Getting the tension right is one of the harder things for new folder makers, myself included.  It's a delicate balance between too stiff and non-functional.  That's how I break springs, I grind a bit too much off one position on the tang, so I have to equalize the other positions, and then the spring is loose.  Put the spring in a three-point bending setup in a vise to tweak it by 0.3mm, and if overdone, TINK! :(

 

The way I was taught o do it is to not drill the center pin hole until everything else is done.  Fit it up, mark where the hole will be with everything tight, then drill the hole slightly further down the scale.  Ideally, that pin will slip in when you compress the spine with the knife assembled.  

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30 minutes ago, Alan Longmire said:

The way I was taught o do it is to not drill the center pin hole until everything else is done.  Fit it up, mark where the hole will be with everything tight, then drill the hole slightly further down the scale.  Ideally, that pin will slip in when you compress the spine with the knife assembled.  

My approach is similar.  I get things set to where the spring is nearly flush in all 3 positions with a few thou (~0.1mm) extra to allow me to grind everything perfectly flush once the center pin hole is in position.

 

Then I clamp the spring to one liner in position with the blade open.  Next I pull the blade off, and measure from the belly edge of the liner to the spring so I can calculate what my new target for this dimension is once I put in the pre-load.  Then I slide the tip of the spring towards the belly about 30 thou (~0.75mm) and reclamp it.  Once I check that the dimension is what I want, I drill through the center hole in the spring to put the pin hole in the liner.  Put the second liner in place, and drill back through to create the center hole in it as well.

 

Once the center spring hole is in place for both liners, you can grind the spine flush and start thinning the spring for tension.  I leave it a bit strong at this point because I inevitably end up taking a little off the back side to clean things up.  You can always thin the spring down a bit before final assembly if it is still too strong.

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