Slipjoint blade thickness

K

KenH

Well-Known Member
Hello all, Should the blade on a slipjoint be thinner than the backspring? If so, how much?

It seems if the blade and backspring are the same thickness, the blade would tend to rub the inside of liner when closed? Am I missing something? How is this blade rubbing prevented?

Thanks to all for guidance,

Ken H>
 
Ken
From all I have gathered the backspring and blade are thesame thickness. Many slipjoint makers relieve theinside of the liners .005 or so to allow the blade to open withoutrubbing. Check out the attached how-to’sfrom Steve Culver and Phil Tham. It showsthis very clearly and both are very well done.
DeMo

http://www.culverart.com/Culver-Building%20a%20Slip%20Joint%20Folder-Part1.pdf
http://www.culverart.com/Culver-Building%20a%20Slip%20Joint%20Folder-Part2.pdf

http://www.ptartistry.com/slipjoint-knife-build.html
 
Ken there are three ways of doing it.... maybe more :0

first, you can do nothing and make the blade and spring the same thickness.... trouble here is you get a folder that works but will get half moon scratches in the side of the blade from rubbing on the liners. works OK but looks bad.

Second, you can do as DeMo said and re leave the inside of the liners and create an island for the blade to rotate on and act as a bushing/washer. the relieved area doesn't need to be very deep, maybe .002 - .005 max. this works great but you need to have a milling machine to do it easily. I have seen guys use a drill press when in a bind.

Third, you can use washers. you will need to thin the blade by the net thickness of the washers you are adding. for example, if you plan to use .005 thick bronze washers, you will thin the blade .010 compared to the spring..... I happen to have the luck I got a surface grinder this past summer and it makes it really easy to do this, but I have done folders before that and used a disk sander and lots of coffee to get the job done.

there are a couple of wips on sight you can look at to get the idea of milling the scales or adding washers

Erik
 
Ken,You have a milling machine so that would be the easiest way for You to mill out what I call anti scratch relief. Then your blade and spring would be the same thickness.
 
Milling the relief is what I've been doing, which prevents the area around blade pivot from showing any scrub marks. Even with this area milled out, doesn't that leave the space between liners (inside where blade folds into) with the same width inside as the backspring is thick? UNLESS of course, the bevel of blade always extends above liner so the full thickness of blade is above liner? That may be the case, this last slipjoint I'm working on has "higher" liners than normal perhaps preventing the bevel of blade to peek above sides.

Not sure I'm explaining myself clearly - if not, I'll try again.

Ken H>
 
ken I think in most cases the blade doesn't fall completely into the liners. there is usually some of the spline outside with only the bevel entering into the liners so you have your clearance being made by the cutting edge.

Erik
 
Yep Erik, you said exactly what I was trying to say. I'd not noticed that problem before when I made smaller/slimmer folders. This time I was making a bit heavier model for myself. First thing I noticed when I folded this blade down was the scruff mark on blade just above the bevel. The only folder I have to look at is #1 the wife took. Just as you say Erik, the grind line is just above the liner allowing only the bevel part to extend into the liner keeping flat part of blade clear.

Thanks to all for comments - just took me by surprise when I saw that scruff marks today.

Ken H>
 
a little distal taper will allow some clearance even above the bevels, past the liners milled zone, if necessary due to the deep sunken blade.
As an emergency measure (damage already done) i would try to sand the outer rims of the liners in the contact area or sand in some distal taper on the blade.
Multiblade slippies get often very creative with the grinds due to clearance issues, but also single blade's may face similar challenges.
 
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