Folder detent and bonus CF sealing/finishing questions

FlaMtnBkr

FlaMtnBkr

Joined
Oct 20, 2004
Messages
4,704
Hi,

This probably isn't the perfect place for this as it's based on a production knife but I figured the guys making knives would know best. As a (now disabled) mechanical engineer I like to know as much as possible (AMAP?) about things and hope no one minds me asking here.

I wanted a decent flipper so I recently bought a ZT 0804CF which is a Ti framelock running on bearings for anyone not familiar with the knife. The knife may not matter (?) but it is what it is. I know frame lock flipper knives need a somewhat strong detent to allow force to build up before releasing and letting the blade snap open. I don't have a problem with the opening detent but closing is a bit of an issue. It requires a bit of force to get the blade to push the lock bar over and get the ball onto the blade tang. The bigger issue, as I see it, is that the blade has to close roughly 45° before contacting the ball bearing which means my thumb has been off the lock for a while and I'm no longer holding it over so the blade can more easily move past that point. Instead, I have to change my hand position to get a better grip and more leverage and to move any fleshy bits from the blade path. Changing grip feels like I'm compromising my grip and that I could potentially drop the knife.

Can a knife break in enough to over come such a design characteristic? I don't want to keep a knife that I'm uncomfortable with so I haven't been flipping or even holding the knife so as to minimize any loss of value. Being disabled and not working doesn't allow much of a knife budget and I want to make sure it's a knife I will enjoy. I'm not a big fan of frame locks and feel it is a design of compromises, but one that I can overlook for a nice flipper. I like the rest of the knife design and the materials and although I'm not crazy about the black DLC coating, I would like to figure out a way to keep the knife.

Is there a reason for knife makers not to grind a notch or ramp into the blade tang to allow the bearing to ease onto the blade? It seems like this would not only allow the blade to more easily close but would also reduce a lot of wear to the bearing and slow the formation of a flat spot that many develop over time. Since designs sometimes limit bearing/detent placement, it seems like a ramp would be a good addition but I've only seen it on a few knives though that means little. Is there a downside to the ramp?

Is it possible to add a ramp to a hardened vanadium rich steel like M390/CTS-204P? Or should I say is it easy enough? Would just breaking and slightly rounding the hard/sharp edge be enough to make closing easier? How would others go about this? Or should I just find a different knife model to like? I have access to milling machines and probably some sizes of carbide tooling, though I don't have extensive knowledge using the machines. There is also a bench grinder with an aluminum wheel coated in diamond to sharpen said carbide tooling. Though I imagine I would probably damage it except to maybe slightly round the edge where the bearing makes contact?

Lastly, is there a way to seal already machined and finished carbon fiber? Without causing an uneven surface or built up ridge of glue? I have a different knife that has some pin holes and rough areas on the edge where it looks like maybe there wasn't full saturation with resin? There is also a 3D machined surface that feels smooth to the touch but that seems to grab fibers from cloth and hold onto them. I imagine either voids or small ends of carbon fibers protruding from the resin that are grabbing loose fibers. And that maybe some type of sealing will stop this? Thoughts or suggestions?

Thank you for any type of comment! Sorry this got so long!
 
Thin CA will fill small gaps and pores. As to the modifications and such, I am going to move this to Tinkering and Embellishment.
 
Carbide tooling won't be a good choice to cut full hard steel. The tool will wear out rapidly and leave a surface that isn't flat. If the tang is a little bit softer (in the 50's Rc or less) it will cut okay at reduced speeds.

The aluminum grinding wheel you described is most likely not diamond coated but rather CBN (cubic boron nitride) coated - CBN can be used to readily grind full hard steel cleanly - diamond can not without damaging the wheel. When diamond abrasive is used at speeds high enough to throw sparks, the steel will leach carbon from the diamonds and destroy them much more quickly than when they're used for carbide or nonferrous metals.

To repair the carbon fiber one method would be to procure a UV resistant epoxy (otherwise it will yellow after continued exposure to sunlight) and use a brush to paint it on, then sand it up to whatever finish you'd like after it fully cures. As Mr. Apelt noted, CA will probably work just fine too though. I'd say choose the method depending on how much area needs to be coated.
 
I use carbide on fully hard steels often and the tools don't wear- at least drill bits don't.
I have never heard of diamonds "leaching" carbon.
Please tell us more about this phenomenon.
 
Thanks for the replies and that is great info!

I've tried thin CA on wood scales in the past using cheap watery liquid super glue. It left a very uneven finish that had to be sanded flush and buffed to a polished finish. Certainly couldn't put it on a 3D machined scale without some skillful sanding and cleaning up which I wouldn't trust myself with currently due to my health. Thanks for the suggestion but was hoping for something that could be applied and then wiped off so it is nice and smooth. More like a stain vs polyurethane on wood, though not the best analogy.

I figured knife makers that have gone thru a few iterations of the design, test, modify process with flippers and detents would know best and I'm most likely to find them in the knife makers forum. As I was once a fairly frequent visitor and poster to both the shop talk and tinkering subforums, I figured the makers would be able to most likely give a knowledgeable response. But I'll go along with whatever someone thinks is best. I've found very little discussion about detent design and blade tang ramps so it was probably a long shot anyways.

Thanks
 
In all the liner locks I make I use a 400 grit belt to place a tiny "ramp" on the edge of the lock.I place this at a very sharp angle. I originally started this for concerns the hardened edge of the blade lock would shave off the detent ball.
Frank
 
Bill DeShivs said:
I use carbide on fully hard steels often and the tools don't wear- at least drill bits don't.
I have never heard of diamonds "leaching" carbon.
Please tell us more about this phenomenon.
Click to expand...

Actually for full hard plain carbon steels you might get better tool life. I was thinking of HSS when I made that comment (OP mentioned M390). Even cutting full hard plain carbon steel the carbide tools will still wear pretty rapidly compared to cutting softer steels though. Not sure what kind of tools you're using that don't wear - I have yet to come across carbide tooling that doesn't wear even on soft steel.

The carbon leaching is a pretty well known phenomenon, at high temperatures (such as a bench grinder running a wheel fast enough to cause sparking) steel will absorb carbon from the diamonds. The diamonds then gradually erode/dissolve away. Here's a first-page Google link describing the specifics:

http://www.gearsolutions.com/article/detail/5499/hard-choices-diamond-or-cbn

I've seen this happen firsthand plenty of times in machine shops I've worked in. It happens pretty quick too. I used to keep my own diamond wheels just so I wouldn't have to use the ones other guys destroyed by doing this. To picture the damage, basically imagine a regular bench grinder wheel that someone has abused and not dressed - runout, severely rounded corners and big grooves in the part of the wheel that should be straight.
 
Frank or anyone that knows,

Does putting a notch or ramp significantly reduce the force needed to close the blade? I would assume it does but don't want to alter it and find it still hard/awkward to close one handed. I guess I will decide how much I like the knife or if I would rather put it towards a different model flipper.

If I did add a ramp/round the edge, I'm thinking I will cover the edge with plastic and tape it up real good and go real slow with abrasives and dunk in water often. I'm thinking I would have a little more control than trying to use a mill. Especially without some sort of jig to position the blade. Anyone have any thoughts on this considering it's nearly full hard M390?

Thanks!
 
Technically a ramp won't change the amount of force needed to close the blade because the amount of resistance - the spring strength of the lockbar pressing the detent against the blade tang as you are trying to close it - won't change. But - and I'm no physicist - my understanding of the ramp is that it distributes the pressure as you close it so it feels smoother. For example, like walking up a 2foot-high-one-foot-long ramp would feel weird but be less abrupt than walking up to a 2foot high wall until your toes touch it and then jumping straight up to the top of it.

If the knife is significantly difficult for you to close then I would look at getting a different knife. But you could probably make it perhaps up to 20% smoother in closing by using the grinding wheel to make a ramp but as rounded (not flat) and as polished as possible - a curved polished ramp will help reduce friction and distribute the force better as you close it. I would do lots of finish work on the ramp by hand with sandpaper
 
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