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Aiden CC

Stainless Steel for Frame Lock

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I've wanted to make another locking folding knife for a while, and thought that a frame lock might be a fun project. I'm trying to keep the budget manageable, so that means in all likelihood using a steel instead of titanium for the frame. I want the whole thing to be corrosion resistant, which means the steel will have to be stainless. I already have some CAD and have picked a few of the parts I might use, which I will probably put in a Design and Critique thread later down the line.

Anyways, I have been looking at a few different options. One option would be to use some blade steel, though this might be the most expensive, since I would need to buy a fairly thick piece of steel. It would mean I could make the blade and scales from the same stock, though that would involve more machining, since I plan on the scales being 3/16" with a 1/8" blade. Also, I already have some 440C in 1/8" bar so I don't need to buy blade steel anyways. I haven't looked into it much, but it also seems like getting the properties I want may be difficult in a steel designed for high hardness rather than spring applications.

Another steel I have considered is 17-4 PH. It seems like I would have a lot of options if I bought a piece in the solutionized form and that the high strength could work for this application. It's also available in a convenient size on McMaster Carr where I might order all of this stuff from. One downside is that I've heard it can be difficult to machine (although apparently it's better if you harden it first?) which could be problematic since I have lots of drilling and counterboring to do.

The final thing I've been thinking of is either 410 or 416 (though these aren't available on McMaster in convenient sizes and I would have to order from somewhere else/use a piece I have which may be big enough). I think the strength on these will be high enough after heat treating. Also, would a 300 series work at all? I'm sure it depends on the spring geometry, but I want something that will work with a wide margin so I don't mess this up. Also I may be able to get some budget from this from my school, so if I can keep it to under $100, price isn't a huge consideration.

Any thoughts would be appreciated! I'm currently leaning towards 17-4, but that depends a lot on how it is to machine (heat treatment looks pretty straightforward, just an aging cycle at ~500 C). This is mostly based on it being available in a convenient form and having s simpler heat treatment than 410 (the box furnaces I have take forever to get up to ~1000 C and it would complicate things if I had to do an oil quench), plus if I can get money to buy new stock I would rather do that than use things I bought for myself. If a 300 series would work without heat treating that would be the easiest (though I kind of like heat treating stuff).

Thanks for reading!

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I have made liner locks with unhardened stainless blade steel for the liners, and have also used work hardened brass and nickel silver. As I see it, there is no real problem using unhardened material, provided that you over bend the lock a fair bit, and design it so the lock cannot be counter bent in use, which may be an issue with a frame lock. The only potential problem I see is that the bearing surface of the lock will tend to wear faster in a softer material, but so long as the angle of the heel of the blade exceeds the arc of the lock, this should never become a problem (I also leave the heel of the blade unhardened or temper it right back so I can do fine adjustment with a file after hardening...).

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I get that you might prefer the look of titanium or stainless, you probably even know what I'm about to say, and if so, pay me no mind... 

Brass historically is a very good material for this type application. Special bearing bronze is even better. It's a lot slicker than steel on steel, and has better wear resistance. Lots of Industrial parts (and pocket knives too) will have an alloyed copper for wear resistance. 

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4 hours ago, jake cleland said:

I have made liner locks with unhardened stainless blade steel for the liners, and have also used work hardened brass and nickel silver. As I see it, there is no real problem using unhardened material, provided that you over bend the lock a fair bit, and design it so the lock cannot be counter bent in use, which may be an issue with a frame lock. The only potential problem I see is that the bearing surface of the lock will tend to wear faster in a softer material, but so long as the angle of the heel of the blade exceeds the arc of the lock, this should never become a problem (I also leave the heel of the blade unhardened or temper it right back so I can do fine adjustment with a file after hardening...).

Not having to work with hardenable material could make machining a bit easier. Hopefully with a thicker lock bar (3/16") and some angle to the heel it will take a long time before wear is an issue. I don't think I will be able to leave anything unhardened on the blade since I will likely do a plate quench, but since I'll be using foil, there hopefully won't be too much damage to the surface and I'll be able to go closer to the finished geometry before heat treatment. The over-extension thing is a good point, since there isn't a scale to stop the travel like in a liner lock. It looks like heat treated 17-4 has over twice the yield strength of a 300 series stainless steel, which could address that, but maybe I should do some analysis to see if I really need that strength.

17 minutes ago, Zeb Camper said:

I get that you might prefer the look of titanium or stainless, you probably even know what I'm about to say, and if so, pay me no mind... 

Brass historically is a very good material for this type application. Special bearing bronze is even better. It's a lot slicker than steel on steel, and has better wear resistance. Lots of Industrial parts (and pocket knives too) will have an alloyed copper for wear resistance. 

I was planning on using washers made from some kind of bearing bronze, and either a pressed in bronze bushing or a bronze pivot for the action. Not as sure about a bronze lock-bar. The elastic modulus is lower than steel so I wouldn't need as deep of a relief cut, but over-extension could be a problem and I would be worried about permanently bending the lock bar on accident.

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Woops...  Thought you meant for the liner. Reading comprehension is not a strongsuit of mine... 

Good luck!

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first mc masters has a bit of everything but they make you pay for it i would look at ebay for ti no heat treat and nothings going to hurt it if your fancy i do recommend a replaceable contact point for the lock bar as ti has a tendency to lock up to well i carbidize mine but i only get a few years of constant use before it starts to show were

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On 7/6/2019 at 7:14 AM, Aiden CC said:

heat treatment looks pretty straightforward, just an aging cycle at ~500 C

That is only if it is already hardened.  Hardening 17-4PH is a solution treatment at 1025-1050 C (1875-1920 F) then oil quenched.  After that you age at about 480 C (900 F) to get a hardness in the low 40s HRC.  

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4 hours ago, Jerrod Miller said:

That is only if it is already hardened.  Hardening 17-4PH is a solution treatment at 1025-1050 C (1875-1920 F) then oil quenched.  After that you age at about 480 C (900 F) to get a hardness in the low 40s HRC.  

I believe most of the stuff I’ve seen has been in the solution treated state. After aging does it behave anything like a lower alloy steel would at that hardness?

 

On 7/7/2019 at 10:18 AM, dragoncutlery said:

first mc masters has a bit of everything but they make you pay for it i would look at ebay for ti no heat treat and nothings going to hurt it if your fancy i do recommend a replaceable contact point for the lock bar as ti has a tendency to lock up to well i carbidize mine but i only get a few years of constant use before it starts to show were

That’s a fair point about McMaster. I looked on eBay a bit and couldn’t find much Ti over 1/8”, which is a bit thin for what I want to do. I have also experienced the galling Ti can exhibit with steel, though I found that applying then wiping off oil mostly fixed it. Is the replaceable surface on the lock bar or on the blade? With a frame lock there’s a lot of lock bar to wear, which should help longevity. 

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I really shouldn't have used the term "hardened".  Solution treated is the right wording.  It was still a little early for me after a long weekend.  I'll talk to our machinist tomorrow to get his thoughts on machining it, but we have no problems machining it that I am aware of.  You're looking at having ferrite stringers in a martensite matrix.  Better than having austenite, which gums things up!  

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I did speak to our machinist today.  He said 17-4PH isn't too bad if you you get the right feed and speed.  Keep the chip load fairly light or you get work hardening effects.  

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On 7/8/2019 at 6:59 PM, Aiden CC said:

I believe most of the stuff I’ve seen has been in the solution treated state. After aging does it behave anything like a lower alloy steel would at that hardness?

 

That’s a fair point about McMaster. I looked on eBay a bit and couldn’t find much Ti over 1/8”, which is a bit thin for what I want to do. I have also experienced the galling Ti can exhibit with steel, though I found that applying then wiping off oil mostly fixed it. Is the replaceable surface on the lock bar or on the blade? With a frame lock there’s a lot of lock bar to wear, which should help longevity. 

yes the replacement is the contact point on the bar it does last a wile but even with the carbonizing i did to mine after two years of edc it has some play.

 

on ebay try using bar or plate as search terms for thicker than 1/8 ti

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Posted (edited)
On 7/9/2019 at 8:30 PM, Jerrod Miller said:

I did speak to our machinist today.  He said 17-4PH isn't too bad if you you get the right feed and speed.  Keep the chip load fairly light or you get work hardening effects.  

Thanks! That sounds good. I did manage to find speeds for 17-4. The mill I would use is a knee mill with CNC on the X/Y axes. I'll probably just be drilling and counterboring manually, but if I get ambitious I may cut the profile with CNC (though using a bandsaw and grinder might honestly be less hassle).

 

On 7/10/2019 at 6:32 PM, dragoncutlery said:

yes the replacement is the contact point on the bar it does last a wile but even with the carbonizing i did to mine after two years of edc it has some play.

 

on ebay try using bar or plate as search terms for thicker than 1/8 ti

Was the knife a liner lock or frame lock? I'll keep looking into Ti, though it is a bit of a pain to work, especially if it were 3/16-1/4" thick like I plan on making the frame. Do you have any pictures of the knife? It would be interesting to see how the replaceable contact point works.

Edited by Aiden CC

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