Problem with slipjoint design

C

Cubane

Joined
Apr 16, 2007
Messages
242
Hi everyone.

I don't know if you saw the recent thread I had on making my first slipjoint http://www.bladeforums.com/forums/showthread.php?t=525561. Well I have been using it for a week or so now and I have noticed a mark on the inside of the spring where the tip of the blade is hitting the spring when it is closing. However when the blade is in its normal closed position it doesn't touch the spring. Now I am wondering if the problem is just that I haven't left enough room between the blade and the spring or if there is something more inherently wrong with my design. I can imagine that the strength of the spring and the location of the kicker on the spring and how far the spring raises as the knife is closing could all influence how far the tip of the blade can move inward of its resting position when it is closing.

How should I solve this problem? Do I just allow more room or do I need to do more a redesign to fix the problem in the tang/spring area? Since this is my first folder I am not to accustomed to solving issues like this.
 
It could be the tip is hitting when the blade is closing, if the spring is strong it may push the tip a little farther than its resting position. It does look like it is pretty close to the spring. I would leave a little more room. Is the spring really strong?? looks a little thick which would make it pretty strong.
 
I could be that the spring is a bit strong but the knife isn't insanely difficult to open or anything. If I press on the spine of the blade when the knife is closed the spring pushes up a little and I can see the tip touches the spring. If the answer is just to leave a little more room then lucky the knife is screwed together so I can fix it :) If the kicker was up a bit further on the spring I could see it would be more difficult for it to apply pressure to the spring and wouldn't be able to hit the spring as well.
 
In this picture you can (hopefully) see how to adjust the blade to the spring. Set up your spring and blade on a board of some kind. Then adjust the blade down to the desired clearance. If you get it to close to the spring the exact problem your having will happen. The spring tension will actually let the blade slap the spring if the tolerance is to close. Now for the fix on your knife I would
take the blade down (as in grind the edge off then put the edge back on . I would guess about .010 to .015 off the blade.



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heatride said:
In this picture you can (hopefully) see how to adjust the blade to the spring. Set up your spring and blade on a board of some kind. Then adjust the blade down to the desired clearance. If you get it to close to the spring the exact problem your having will happen. The spring tension will actually let the blade slap the spring if the tolerance is to close. Now for the fix on your knife I would
take the blade down (as in grind the edge off then put the edge back on . I would guess about .010 to .015 off the blade.
Click to expand...

Yep, that's what I would do since you can't stretch the handle out. :D That is a common problem (called "spring rap") and it sometimes occurs even in finished production knives. The Texas Toothpick seems to be the worst offender since the blade is really long and the kick is short, allowing over travel of the blade when you let it snap shut.

Follow heatrides suggestion on this one and build more space into your future designs. Or, you might try that handle stretching technique. :)
 
well I'm no expert on slip jointsbut it seems to me that your only choice for this knif is to do as suggested and regrind the tip of the blade for more clearance. Thenon the next one I think that if you move the center pivot closer to the center it will help to alleviate this problem. You may still have to leave a little more room though.
 
Thanks for all the replies. I think I will do as suggested and grind the tip down. How much gap do you normally leave? I have around 2mm gap and thought that would have been enough. I was talking to another knifemaker today and he suggested in future designs moving the spring pivot forwards to minimise the movement of the spring as well which will make the spring tighter and less likely to allow the blade to hit the spring.
 
There is an excelent tutorial at TKN.It covers everything from design to fitting.
 
I really did not give that gap much thought until now. Looking in my pocket at my EDC its about 1/4". Too big would look awkward like the tip had broken but 1/4 looks fine. You and just take it down to where it no longer touches. You can use a felt marker to mark where the blade was hitting, remove a little and close to see if it still hits.
 
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