Folding Knife Pivot Interface To End Free Spinning Pivots

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Jan 27, 2006
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497
I thought I would put this idea out into the public domain in detail as "Prior Art", so that it can be incorporated into the knife world freely and without restriction for manufacturers as well as tinkerers. I initially thought about applying for a US Utility Patent on this, but the last one cost me $12,000+ and still counting. It was more complicated than most at over 50 pages, but still even a simpler US Utility Patent Application can cost serious money.

So,....presenting this publicly means that no one else can file for a US Patent on the idea either, and as far as I know I know,...no one has used this simple process to interface the knife pivot to the liner or frame of a folding knife.

What I did was use a 1.2 mm round carbide bur to create a "cup" at a depth of about 1/2 the diameter of a 3/64" 440C stainless steel ball bearing from the supplier below. I chose 1000 ball bearings for $13.85 shipped, but smaller and larger quantities are available such as 500 for $9.95 or 200 for $7.60.

https://www.bcprecision.com/collect...ss-steel-ball-bearings-g25?variant=6185690501

The 3/64" ball bearing is 0.046875 inch in diameter, and the 1.2 mm ball shaped cutting bur converted to inches measures 0.0472441 This gives you a little room for error in cup positioning, as the bur is just very slightly larger than the ball. But it's pretty close.

Here's where I bought the burs, costing $5.85 for a 6 pack plus shipping. You have to go in and choose the 1.2 mm size, as the page defaults to the smallest bur they make on this page.

https://www.stuller.com/products/18-10000/?groupId=121459&recommendationSource=SiteSearch

If you work slow and don't heat up the bur,...you can get several cups done before the bur begins to dull. I like to use a fairly fresh bur to "start" the cups so that it's less likely the bur will move on you when starting a hole,...and then once you have a cup started finish it off with a bur with a little more use on it.

I'm using a hand held Foredom flexible shaft machine (but with 40 years experience and I used it extensively daily for 35 of those years as a bench jeweler),.....so I have to brace my hands as much as possible and drill slowly when starting the cup.
A manufacturer can have a dedicated drill press with precision depth controls, so it's very cost effective and precise in that case.

Before I get into the interface photos,...if you're wondering how I got my Hinderer XM-18 3.5" apart with all the usual Lock-Tite on the pivot thread,.....I used a US Nickle as a spanner wrench after fitting it! BTW, that's a phosphor bronze washer that I drilled out, and added a larger diameter cup (using a tapered bur) to the blade facing side to better hold the moly/oil lubricant combo I prefer:
xF1a6PS.jpg


Here the cup has been cut to 1/2 the depth of the ball bearing diameter, awaiting the pivot...
MFzDglO.jpg


The next step is to add a similar "cup" to the inside ledge of the pivot. Note the ball bearing is in place waiting for the pivot. I found that after the first assembly, the ball bearing tended to stay in place for subsequent disassembly unless I picked at it with tweezers. If you happen to lose it, they are inexpensive to replace as shown in the link previously.

NOTE: On all of my Hinderer XM-18 knives, I positioned the ball in the same location, centered between the "D" and "E" in "Hinderer" on the frame. I also positioned the cup on the Pivot in the middle (perpendicular to the slot), so that I knew where the cup and ball was on all of my knives and could quickly get them lined up.

5nivVhe.jpg


I found it best to cup the liner or frame first, place a ball bearing into the cup, and then hand spin the pivot for a little while to get a light "line" to show on the pivot's inner lip to show where to add the "cup" on the pivot. I didn't try it, but adding a layer of magic marker to the lip on the pivot might show the line you need to see for cup positioning a little faster. I tried to get the initial "cup" position in the frame centered along the pivot seating ledge, but it's usually not critical as long as the matching pivot "cup" lines up over it.

The idea is to get the ball bearing to interface and lock the pivot to the knife when it's all tightened up, so that the pivot is no longer "Free Spinning". To do this the cups for the ball bearing have to be positioned in the same plane, one over the other,.....and creating a fine line to the inner ledge of the pivot helps you to get it right by seeing where you need to drill out the pivot cup using a Round high speed steel Bur in the approximate size of the ball bearing your are using. (round burs are available in packs of 6 at jeweler supply houses such as "Stuller"). It's best to "lock up" your hand holding the flexible shaft hand piece to keep the spinning ball bur from traveling when starting the cut. This can be done using thumbs and fingers in various ways to steady both the part and hand piece, and best to practice on a scrap piece of steel or brass to get a feel for the process.

You can tune the fit a little by slightly enlarging a hole if you can't get the pivot to lay flush with the ball in place, without rocking. (signaling either one or more of the cups is not deep enough, OR one cup is not directly OVER the other).

If both cups appear to be 1/2 in depth of the ball bearing diameter when it is placed in each cup and you still get a little rocking when test fitting the pivot, then you probably have one cup that is not directly over the other. You can slightly enlarge a cup's width in the needed direction to get a flush pivot with no rocking, but best to get it right the first time.

Keep in mind that the more you have to enlarge the cup's width for a flush pivot fit, the more a slight movement of the pivot is possible. If you can keep the cups fairly tight to the ball, the ball can't move and therefor the pivot can't either.

It's actually pretty easy once you've done a few,...so it might be good to practice on a cheaper knife first. In the end, if you mess up you CAN always position a 2nd cup in the liner or pivot and try again. No one will know you messed up the first time, as all the work is covered by the pivot anyway. :)

Using this procedure will simplify assembly, disassembly, and help to keep the knife's pivot tension more stable. A locked in pivot will not tend NOT to unscrew the pivot tension screw, and generally alleviate the need to use any Lock-Tite on that screw. There is some vibration when you flip open any knife, and that can slowly loosen any screw over time. But this is nothing like how quick a free spinning pivot will loosen the pivot screw!

Personally, I like the simplicity of being able to adjust the pivot tension with just my thumbnail if needed,...and that's only after many dozens of opening cycles. Realistically, if you're using a knife for a tool and not a flipping "toy" (we ALL do that so I get it! :), you could go months without need to even use your thumbnail.

IF you want a little resistance to the pivot screw,...I might suggest coating a few of the later pivot threads at the slotted end of the XM-18 pivot in a light layer of clear nail polish or thin super glue, perhaps, and letting it dry before you add the pivot screw. Just a touch will create some resistance once the screw reaches it, so that even opening vibrations will not affect it's adjustment, and will probably be good between regular service times.

All three knives that this worked very well on were my Hinderer XM-18 3-1/2" and 3" folders. After this system was added, there was no need to Lock-Tite in the pivot screw, and the screw stayed in place for many opening and closing cycles. (100 or more, and no need for their special $75 pivot tool either).

Even though the pivot is not spinning, vibration from opening (when the lockbar clicks into place mainly), will eventually cause the screw to move a little. However, with this feature added I can simply use my thumbnail to retention the pivot screw, and I'm good for lots more opening and closings! You will, of course get many more adjustment free opening cycles of the knife if you open the knife in a controlled manner, rather than flipping it open "hard" which creates a lot more vibration.

OK,...I just signed up to Imgur and uploaded some photos, but I have a job to get done and will have to figure out how to load individual photos here. For NOW you can go to the link below and the 1st three photos show the modification. I also added some other mods I made to the this Hinderer XM-18 later in the link.

https://imgur.com/a/Uob8A

Cheers,
Joseph Tousignant
Ti Rod Tactical
 
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Whats the longevity of this? Will these burr cups break or wear out?
 
I edited my original post to add some Imgur images in a link, but will also add the link here as I signed up to Imgur and uploaded some photos. However, I have a job to get done and shipped today (my local Colonie mall in Albany, NY has a USPS Branch with clerks open on Sundays til 5:00p PM! :)

I will have to figure out how to load individual photos here. For NOW you can go to the link below and the 1st three photos show the modification. I also added some other mods I made to the this Hinderer XM-18 later in the link.

https://imgur.com/a/Uob8A
 
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That's actually pretty slick...good job:thumbsup::)

~Chip
 
Whats the longevity of this? Will these burr cups break or wear out?

Since there is no movement to the pivot, there is not much than can wear out. Using this interface means you shouldn't have to use Lock-Tight, and I wouldn't advise it anyway. It will only make disassembly unnecessarily more difficult, because you will have to keep tension on the back of the pivot or else it will ride up and over the ball at some point.

The whole point of adding this interface was to eliminate pivot movement AND any need to use Lock-Tite at all,... and also no need for a special tool to hold the back of the pivot when unscrewing the pivot screw. Being able to adjust pivot tension with just your thumbnail after extended opening and closing cycles is a piece of cake with this, so keep the Lock-Tite away! :).
 
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I'm trying to figure out what the deal was with the nickel. A spanner wrench seems like it would have been the right tool for that job.

Either way, nicely done on the mod!!! Looks simple and functional, like the best inventions.
 
I'm trying to figure out what the deal was with the nickel. A spanner wrench seems like it would have been the right tool for that job.

Either way, nicely done on the mod!!! Looks simple and functional, like the best inventions.

Hehe,... I didn't have a spanner wrench, but I have LOTS of Nickles! Even if I had a spanner wrench, I doubt it would fit the pivot slot as well as the one I hand fitted here! :)

Nickles are harder than pennies, which some folks sometimes use to make a tool like this. BTW, If you use a penny to make a makeshift spanner, use one from 1981 or earlier, as sometime in 1982 they changed the penny to copper plated ZINC. Some 1982 pennies are copper, and the easiest way to tell is to drop it on a hard surface. If it "rings",..it's copper. If it sounds dull and lifeless,...it's zinc!

Real copper pennies contain about double the $.01 face value in actual copper value,...which is why they switched to zinc, and a Nickel (which is mostly copper but the added nickel gives it the white color and added hardness),...is also worth about double it's metal content. The US Mint loses money on every Nickle too because the metal content has a higher value than the coin's face value,... so at some time the metal content will probably change like they did with the penny. (and with changing the 90% silver content to clad with the dime, quarter, half dollar and dollar coins after 1964)
 
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Back in 2005-2006 we sold pivots with the hole on the backside of the head. We updated the design to have a .0005" raised area on the shaft next to the head. The raised area make the pivot be a press fit into the scale/liner and still allowed the blade to pivot freely without the pivot turning.

Chuck
 
Thanks Chuck,... I'm glad I didn't spend the dough to start a Patent Application! The ball bearing idea is a little different, but similar in function to lock the pivot. I've also seen a partial cut out in the shelf in a liner, and have a corresponding raised notch on the pivot to interface.

The ball bearing idea is the one practical modification than can be retrofitted easily on many different knives already in user's hands, such as all the Hinderer knives using the same basic proprietary pivot system as used on the XM-18 models and others.

I might just start a retro-fit business Ball Bearing Pivot Locking "division" :) as a side line to my Ti Rod Tactical Titanium Self Defense Sticks!

By the way, the first knife I tried this mod on was my Zero Tolerance ZT-0562CF , because the Torx head on BOTH sides of the pivot were driving me nuts! :) I only had ONE proper fitting Torx screwdriver at the time, but have since duplicated the most used sizes. I wanted to get that one apart to add a finger choil, AND smooth and round over the edges of the flipper. I also wanted to add a mixture of moly/machine oil to the KVT Bearings.

Here's how she came out, except that now I have a custom black G10 scale on it that offers much better grip due to some nice looking and deeper cut in pattern going lengthwise. (Cost $55 plus $6 shipping, and came from a Russian maker named "marsilero" on ebay. It fit wonderfully and feels GREAT, lots more grip!!) (2 available as of this post in the link below)

http://www.ebay.com/itm/Hinderer-Slicer-0562-ZT0562-Scale-Model-Line-G10-Knife-not-included/252660792493?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

The first photo is from the ebay listing, but shows what this G10 scale looks like:
uN18AHB.jpg
The added finger choil came out very nice, and is comfortable when using the knife needing added close up control.
9QqobDM.jpg

For those of you wishing to do the same, use that useful US Nickel again as a guide to fitting a uniform and good looking finger choil.

Iw2gGAh.jpg


The ball bearing modification was a bit close on the ZT, because at that time the only ball bearings I had on hand (from a bearing race I believe I purchased from you folks) were about 1.5 mm in diameter. The KVT bearing system on the ZT-0562CF didn't leave a lot of thickness to the bearing shelf in the frame, and I had to be really careful not to accidentally pierce the frame and into the KVT bearing area. It worked out OK,...but that's when I decided to order a supply of ball bearings a little smaller so that would be easier on similar knives with ball bearing systems.

I made another modification on my ZT-0562CF,....slightly reshaping the flipper tab to get rid of that pointy shape digging into my finger during deployment,...which was a bit rough on my longtime damaged index finger tip.

This is what the stock flipper tip looked like before the change. That slight "hook" had to go! (for me especially):

CIJgeXs.jpg


....and after the reshaping on the pointy side and beveling the edges of the flipper. Not a huge change, but is meaningful in resulting comfort to deploy!:

2yFIiIc.jpg

sqTOLJh.jpg

e68HFuu.jpg


I find the flipping is not hindered in any way with this change,...but it's so comfortable to flip now that even my uninjured left hand index finger appreciates it!

Cheers,
Joe T
 
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I really like this idea, I think it is an easy fix for free spinning pivots.

Some manufacturers use the female bit insert on both sides, making disassembly easy. However, other manufacturers only utilize one side; something that puzzles me:confused: I've found ways to cope with one-sided pivots, but it is always an annoyance.

I wouldn't mind seeing this design on knives in the future, it really thinks outside of the box and is simplistic. It definitely adheres to the K.I.S.S rule.
 
The same thing could be added to the shaft of the pivot screw, by drilling a dimple in the shaft and in the side of the pivot hole slot. Either way this would add almost nil to manufacturing costs while allowing a knife to have a simple pivot design (which decreases costs) but still be captive.
 
I thought I would put this idea out into the public domain in detail as "Prior Art", so that it can be incorporated into the knife world freely and without restriction for manufacturers as well as tinkerers. I initially thought about applying for a US Patent on this, but the last one cost me $12,000+ and still counting. It was more complicated than most and was over 50 pages, but still even a simpler Patent Application can cost serious money.

So,....presenting this publicly means no one else can file for a US Patent on the idea either, and as far as I know I know,...no one has used this simple process to interface the knife pivot to the liner or frame of a folding knife.

What I did was use a 1.2 mm round carbide bur to create a "cup" at a depth of about 1/2 the diameter of a 3/64" 440C stainless steel ball bearing from the supplier below. I chose 1000 ball bearings for $13.85 shipped, but smaller and larger quantities are available such as 500 for $9.95 or 200 for $7.60.

https://www.bcprecision.com/collect...ss-steel-ball-bearings-g25?variant=6185690501

The 3/64" ball bearing is 0.046875 inch in diameter, and the 1.2 mm ball shaped cutting bur converted to inches measures 0.0472441 This gives you a little room for error in cup positioning, as the bur is just very slightly larger than the ball.

Here's where I bought the burs, costing $5.85 for a 6 pack plus shipping. You have to choose the 1.2 mm size, as the page defaults to the smallest bur they make on this page.

https://www.stuller.com/products/18-10000/?groupId=121459&recommendationSource=SiteSearch

If you work slow and don't heat up the bur,...you can get several done before the bur begins to dull. I like to use a fairly fresh bur to "start" the cups so that it's less likely the bur will move on you,...and then once you have a cut started finish off the cup with a bur with a little more use on it.


MFzDglO.jpg


The next step is to add a similar "cup" to the inside lip of the pivot. Note the ball bearing is in place waiting for the pivot. I found after the first assembly, the ball bearing tended to stay in place for subsequent disassembly unless I picked at it with tweezers. If you happen to lose it, they are inexpensive to replace,......I found 1000 pieces for about $13.00 shipped after a short internet search!

NOTE: On all of my Hinderer XM-18 knives, I positioned the ball in the same location, centered between the "D" and "E" in "Hinderer" on the frame. I also positioned the cup on the Pivot in the middle (perpendicular to the slot), so that I knew where the cups and ball were on all of my knives.

5nivVhe.jpg


I found it best to cup the liner or frame first, place a ball bearing into the cup, and then hand spin the pivot for a little while to get a light "line" to show on the pivot's inner lip to show where to add the "cup" on the pivot. I didn't try it, but adding a layer of magic marker to the lip on the pivot might show the line you need to see for cup positioning a little faster. I tried to get the initial "cup" position in the frame centered along the pivot seating ledge, but it's usually not critical as long as the matching pivot "cup" lines up over it.

The idea is to get the ball bearing to interface and lock the pivot to the knife when it's all tightened up, so that the pivot is no longer "Free Spinning". To do this the cups for the ball bearing have to be positioned in the same plane, one over the other,.....and creating a fine line to the inner lip of the pivot helps you to get it right by seeing where you need to drill out the pivot cup.

You can tune the fit a little by slightly enlarging a hole if you can't get the pivot to lay flush with the ball in place, without rocking. (signaling either one or more of the cups is not deep enough, OR one cup is not directly OVER the other).

If both cups appear to be 1/2 in depth of the ball bearing diameter when it is placed in each cup and you still get a little rocking when test fitting the pivot, then you probably have one cup that is not directly over the other. You can slightly enlarge a cup's width in the needed direction to get a flush pivot with no rocking, but best to get it right the first time.

Keep in mind that the more you have to enlarge the cup's width for a flush pivot fit, the more a slight movement of the pivot is possible. If you can keep the cups fairly tight to the ball, the ball can't move and therefor the pivot can't either.

It's actually pretty easy once you've done a few,...so it might be good to practice on a cheaper knife first. In the end, if you mess up you CAN always position a 2nd cup in the liner or pivot and try again. No one will know you messed up the first time, as all the work is covered by the pivot anyway. :)

Using this procedure will simplify assembly, disassembly, and help to keep the knife's pivot tension more stable. A locked in pivot will not tend to NOT unscrew the pivot tension screw, and generally alleviate the need to use any Lock-Tite on that screw.

One knife I had that this worked very well on is on one of my Hinderer XM-18 3-1/2" folders. After this system was added, there was no need to Lock-Tite in the pivot screw, and the screw stayed in place for many opening and closing cycles. (100 or more, and no need for their special $75 pivot tool either).

Even though the pivot is not spinning, vibration from opening (when the lockbar clicks into place mainly), will eventually cause the screw to move a little. However, with this feature added I can simply use my thumbnail to retention the pivot screw, and I'm good for lots more opening and closings! You will, of course get many more adjustment free opening cycles of the knife if you open the knife in a controlled manner, rather than flipping it open "hard" which creates a lot more vibration.

OK,...I just signed up to Imgur and uploaded some photos, but I have a job to get done and will have to figure out how to load individual photos here. For NOW you can go to the link below and the 1st three photos show the modification. I also added some other mods I made to the this Hinderer XM-18 later in the link.

https://imgur.com/a/Uob8A

Cheers,
Joseph Tousignant
Ti Rod Tactical

Awesome work. Well done.
 
Just thought I would add a tip that I think should be out there. SO SIMPLE I wonder why I haven't heard of it before,...BUT if you want to always have an easy way to work on you knife without the armorer's tool being necessary (or making the Nickle tool I used and show early in this thread)....

....... just shorten the Hinderer XM-18 Pivot Screw about 2-1/2 to 3 threads and fine finish it up,...so that the end lays flush with the bottom of the pivot slot, as shown below. (Note: The Hinderer "Skinny" 3-1/2 inch XM-18 Pivot Screw is short enough to do this on a standard 3-1/2 inch XM-18, and you can order one as far as I know! :) Even an unaltered penny will hold it in place to remove the screw if you don't want to add the pivot locking interface, but a well fitting Gunsmithing "flat sided" screwdriver is the best match to the pivot slot.

The part of the screw you cut off is doing nothing anyway, as it just exits the threads and is doing nada,.... except irritating me and you! Just 10-15 minutes work,.. and you carry a few "copper" pennies with you. You can even drill a hole in the penny and add it to your everyday carry key ring.

ltnq1f5.jpg


Use a penny from 1981 and earlier,...as they are 95% copper which is harder than the copper coated zinc penny you show here. A lot of 1982 pennies are copper also, but that was the transition year so millions are the softer zinc ones too. To Determine 1982 pennies composition,...if you drop them onto a hard surface about 1 foot up,...the copper versions "ring" a little, the zinc ones sound "dead" and lifeless. :)
 
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