Quick folder question from an inexperienced maker

C

Cubane

Joined
Apr 16, 2007
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242
I have make half a dozen fixed blade knives now and I would like to get into making some slip joint folders. I will do doing some the traditional way of pinning the handles and pivot together. I would also like to do some more modern screw together slipjoints. I have a couple of questions about designing them though. I have some precision ground 3/32 O1 steel I will be using for the blade and the spring. What I am unsure of is how wide I should make the spring. I am guessing about 3/32 would be a good start point. How do other go about determining this thickness? Would you make it thicker for longer blades? This seems to make sense as the pivot point is further away.

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Also if I am making one to screw together should I thread the spring as well as the liner to hold it together. So I would have a liner countersunk for flat head screw then a threaded spring and a threaded liner. Or should I leave the spring unthreaded and just have it held together with the screw through the liner?
 
The width of the spring is dependent upon size of blade. For a 3" blade, for example, I think a 1/8" is about correct. A lot depends upon spring tension you build into the device. I have a 1/4' spring in some large 5-51/2" folders.
Do not thread the spring for screw together folders. You want a clearance hole only...no slop. If you are using 0-80 or 72's or 56's....use the largest pivot screw that you can. There is a lot of tension on that pivot.
 
Thanks for that. It is exactly what I needed to know. I was thinking overnight that I could just start with a thicker amount and then grind it down to an amount that feels good for the play of the blade.

I have seen that tutorial before, I will be referring to it I am sure during the process of making my first folder. Unfortunately it doesn't cover designing your own blade. It does a really good job covering the construction aspects though.
 
I just finished my first slipjoint and the Chris Crawford tutorial was very helpful.

This site also has some good tutorials on designing a slipjoint and a liner lock. http://www.herbst.co.za/tutorials

You can always take apart some old slipjoints to see how they work and use as pattens.
 
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