The Knives Have Ears

[btrwtr]

This subject has come up here on AAPK before but I am adding to the topic with some pictures.

I have always referred to the little tabs of metal that are a result of lack of lubrication of the blade tang and back spring contact point as ears. Without proper lubrication the tang contact can begin to wear and form a thin tab of metal that will eventually bind between the back spring and liner. The end result is loss of blade walk and talk that we all so love to here on our slip joint knives. The knife may still have plenty of spring tension opening and closing but the binding of this ear tab prevents the walk and talk. This lack of lubrication wear can also result in the spring contact eroding but more often than not it is the blade tang that will develop these ears and becomes a problem.

To fix this problem taking the knife apart and resurfacing the tang may be necessary but I prefer to try and resolve this by first employing some minor surgery to remove the ear without taking the knife apart. This can be done by a number of methods. It is sometimes possible to snap off these ears by using a prying method with a thin razor or utility blade. Precision files can also be used to carefully file off the ear. I have also used a thin cutoff wheel in my Foredom Flexshaft to grind off the ears. Like any repair the method can vary depending on the knife and it's condition. Just as with auto mechanics, doctors and plumbers much of the cure is dependent on the diagnosis.

As an example the first picture shows an extreme case that would require disassembly of the knife and welding as a fix. I show this picture just as an example to show what these ears can look like.

The following pictures are an old Case Bros. knife that had no snap on the master blade. Opening and closing the blade at first felt like there was grit in the gears. Even after oiling the joint the knife had a grind while opening and closing. Examination of the joint with some light magnification revealed tiny ear slivers on both sides of the master blade tang. The pile side ear was removed using precision files and the mark side ear was actually cut using a single edge razor blade. These pictures show the mark side ear after it was cut and before it was pulled out. It's hard to see but looks like a small curled piece of hair. You can see how small this little trouble maker is in pics 2,3,4 and 5. I then pulled the piece out using some needle nose pliers, img 4119. Img 4122 shows just how tiny this ear was in my hand.

After filing off the pile side ear and cutting off the ear on the mark side this old Case Bros. jack walks and talks like new. As with any type of repair the less intrusive the better. This knife was fixed without taking it apart, a much preferred method for me.

Comments welcome.

[jerryd6818]

And here all this time, I've been laboring under the misconception that the loss of "snap" was caused by so much wear on the tang that there wasn't enough rise on the back spring to cause the spring tension the blade needed to close properly.

I have some on which to test your fix. Thanks for the post.

[muskrat man]

Good post! Worn tangs have become a normal repair for me, 98% of the time the ones I get are so bad they need to be welded. I have attributed a lot of the worn tangs to poor temper as well as lack of lubrication. In most cases it seems the tang area is softer then the back spring as the backspring is rarely worn. I used to krink the spring and reshape a tang to get snap back in a knife but if some was severely worn it still did not make it 100%, welding brings them back up to proper size and always ensures those badly worn tangs snap like new again. Plus with welding you only need to remove the pivot pin in most cases so the rest of the knife stays together. As with anything it's always good to have multiple ways to approach a problem.