What is a catch bit?

J

John L

Joined
Oct 28, 2004
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What is a catch bit, what does it look like, and how does it work? I realize it is a spacer of sorts...but when is it used? Say you have a double bladed muskrat with a blade at each end on a single spring....would you use a catch bit on both ends to gain a bit or room to close both blades? Or...what? Thanks and pcis sure would help.
 
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John,

A catch bit can be used on one end or in some cases both ends. The main benefit of a catch bit is it allows the opposing blade to be full length. Without a catch bit the opposing blade can only be as long as the plunge cut. The pictures that are shown here is of a modified canoe with single spring.In this case there is a catch bit on both ends of this knife. The catch bit thickness is the difference between the tang thickness and the spring thickness plus .0005 (at least thats what I shoot for).

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This is a double end serpentine jack with a catch bit only on the one end. This allows the master blade to be full length while the secondary blade is much shorter. This knife has a single backspring.

Ken
 
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Note that the center wedge between the secondary blades of a whittler is also a catch bit -- if it's made thick enough, it allows the main blade to be somewhat longer since it can now pass between the secondary blades and be full length.
 
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This is a muskrat with a catch bit on both ends

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Whittler with center tapered spacer acting as a catch bit allowing master to be full length
 
Thanks very much Ken and Zerogee. The pics help immensely. They also act as a washer and therefore....you need to relieve liners only opposite the catch bit...I guess. The clearance is to eliminate interference with spring so that it has good contact with blade? Seems so. Am going to have to try one. Now...what knife to build? Hmmmm. I just hope they look something like the knive shown. Doubt it though.:D
 
John L said:
They also act as a washer and therefore....you need to relieve liners only opposite the catch bit...I guess.
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John,

I relieve the catch bit also, otherwise it will scratch the tang just as an un-relieved frame will. I just do not relieve it using the mill. I use my belt sander and gently taper it way. If you look close at the double end jack you can see some space between the tang and catch bit. (sorry the pic is a bit out of focus)

Ken
 
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