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Old 02-07-2018, 03:37 PM
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Ray Rogers Ray Rogers is offline
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Join Date: Jun 2002
Location: Wauconda, WA
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Fillet Knife KITH!

It's about time for the next KITH!! We normally try to design these exercises so that they encourage you to try
something you may not have done before and this one is intended to do exactly that! In this KITH the goal will be to
build a fillet knife that is flexible. Not all fillet knives are flexible nor do they all need to be but for this KITH flexibility will be the goal. You can make the knife any size that you wish and use any materials that you want as long as the blade is flexible. I suggest that a blade length of 7" is probably the minimum you'd want to try and that most of you will want to use carbon steel although stainless is possible if you can handle it.

There are basically two ways to make your blade flexible: one is by the heat treatment and the other is by its geometry. You can choose to give up some edge holding in exchange for flexibility (this is what most inexpensive commercial fillet knives do) and that is fine for this KITH if that is your choice. The other way is by geometry or a combination of geometry and heat treatment. The one thing I would NOT suggest is that you try to do a differential heat treatment (or a hamon) on this knife because fillet knife blades are too narrow to make this practical. If you are very careful you might be able to use a torch to draw the spine just a little but even that is iffy. If your blade is stainless then nearly all the flex will have to come from the geometry.

The attached picture will illustrate what I mean by geometry. Starting with steel that is 3/32" (.093) or so you can do a distal taper as shown in Fig A. At least as important as that taper is the profile of the blade, indicated in Fig B. Depending on the steel you choose and the heat treatment you use the profile will vary from Fig B but something similar will be need to get the right flex.

What is the right flex? If you look at Fig C and Fig D you can see that the tip of C has bent faster than the rest of that blade. This is what can happened if the last few inches of the blade get too thin too fast. A blade like this can cut the meat in a wavy line as the too flexible tip 'floats'. Ideally, your goal would be more like Fig D.

You should make a cover or a sheath for your fillet knife. I usually make a kydex cover which is simply a sheath without a belt loop which offers protection for the knife (and the user!) when it is in the tackle box. You can make a sheath or a cover using kydex or leather as you prefer.

There is no need to make this a fancy knife but you can if you want to. I have attached pictures of a couple I have made for reference but there are many others on the internet. One of mine is fairly fancy with a stabilized wood handle, the other has a simple and practical Neoprene handle.

This KITH will run until Halloween so there is plenty of time for you to perfect your blades. Anyone who wishes is invited to participate all I ask is that you post a response below if you want to join in. There is no deadline for joining, you can wait until the day before Halloween if you want to, but the sooner you can let us know the better . Have fun!
Attached Images
File Type: jpg fillet8.JPG (10.5 KB, 64 views)
File Type: jpg fillet flex.JPG (48.4 KB, 76 views)
File Type: jpg filt1a.JPG (41.3 KB, 61 views)


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Last edited by Ray Rogers; 02-07-2018 at 03:39 PM.
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