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Advanced Sharpening techniques: Coote 3HP Belt Grinder: Knife Thinning and Differential Grinding
In this video, as a part of my series of videos on advanced knife sharpening techniques I begin by demonstrating some details of of a second belt grinder that I have assembled. I then use the grinder to demonstrate a few specific sharpening techniques.
The Grinder is a 2x72" Coote Belt grinder - http://www.cootebeltgrinder.com/ It doesn't come with a motor. I'm using a 2" pulley wheel on a 1" motor shaft and a 4" diameter wheel on the shaft of the grinder which turns the 10" contact wheel, I am using a 3 HP motor with a peak RPM of 1800. The motor and wheel came from http://www.electricmotorwholesale.com/ Contact is Ed Frye - a superb person to work with. If you are going to do a project like this - he's your man. Tell him Ken sent you
The VFD or variable frequency drive is used to control the motor. Both the motor and the VFD are completely enclosed to avoid failure from dust - a necessity. The motor uses 3 phase 240 volt current. The input line voltage is a 30 amp line of 240 volt single phase current. The VFD converts single phase to three phase current and controls the motor by adjusting frequency. There are specific motor requirements for this eg the motor must be inverter ready, etc.
The footswitch takes over control of the VFD to run the motor in the forward or reverse direction and must be programmed and wired for this task. Programming can control a large number of parameters (almost 100 parameters with multiple possible values). The potentiometer (knob) on the VFD varies the speed which is displayed on the control panel, which can be set to display either RPM or frequency or arbitrary units. Using this potentiometer to control speed is one of several possible approaches that I chose from for my needs.
The footswitch is connected to the ioda (input/output) board which, among other things provides isolated control circuits for the VFD. These can be programmed (details available but beyond the scope of this video) as switches, analog and digital inputs, etc etc). I needed to rewire the original footswitch pair for my needs for this project - purchased separately. I show the ioda board and wiring hookup in the video.
Next I demonstrate speed and torque available from the setup, showing the extremely slow speed and the unit at full power. One of the most impressive things about this setup is the ability to produce LOADS of torque at low speed. Precise speed monitoring is a big plus and the ability to go in both directions is a major advantage, especially for leather belts and (in the future) nanocloth belts.
ON TO TECHNIQUE!
So I demonstrate sharpening / polishing a single bevel knife - a Nubatama White steel Deba using the flat platen and hands free on / off capability to enable precise sharpening so that the shinogi line is not adversely affected.
Next I demonstrate an advanced - and somewhat dangerous technique - thinning a knife and differentially not wearing off the labeling on a knife. Do this at your own risk. For this I use a Richmond Artifex using M390 steel. http://www.chefknivestogo.com/riar21gym3.htmlThis is one of the highest quality stainless type steels available. The particular belt being used is an A3 belt structured AlOX abrasive at 4000 grit.
Finally, I show how to selectively grind a specific area of a knife using a custom knife made by Farid, an outstanding knifemaker specializing in highly abrasion resistant steels. In this case it is a knife made using CPM Rex 121. I have put a convex grind on the knife using diamond belts. There is no distinct bevel on the blade - the two sides simply meet, giving a maximally acute angle for the edge - which this knife handles quite nicely.
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