KNIFE BEVEL GRINDING JIG.

By Langdon Wilson

 

 

 

 

Contents

 

1. Design Philosophy

2. Components Required

3. Construction Method

4. Setting Up The Jig For Grinding

 

 

 

 

1. Design Philosophy

 

The fundamental concept of this design is that it will assist in the accurate grinding of the primary bevels of knives, with adjustability in the bevel angle, as well as adjustability in the “arc” of the cutting edge.  Obviously the edge is not always a perfect arc, but this will not be detrimental in most but the larger sized knives.  So essentially this jig is targeted at the beginner who wants to make a good looking knife but who does not have sufficient experience to grind a neat bevel “free hand”. It requires a small angle grinder [115mm] with threaded auxiliary handle holes [M8] on either side of the unit.  Throughout the tutorial, the convention will be used where sizes I used in my original design are indicated in square brackets [ ].  This will obviously vary per country depending on what is available, and as per your requirements

 

2. Components Required

 

·        Small angle grinder [115mm]

·        Machine vice [65mm]

·        Threaded bar/rod for upright [M12 x 400mm]

·        Threaded bar/rod for guide rod [M8 x 700mm] (this must match the thread of the handle hole in grinder.)

·        3 x nuts for upright [M12]

·        2 x nuts for guide rod [M8]

·        1 or 2 small metal drill bits [1.5mm]

·        Larger wood drill bit  [11mm] (slightly narrower than upright thread bar)

·        8 x woodscrews [4mm x 35mm]

·        4 x fender washers [M6]

·        Small piece of metal scrap [60mm x 40mm x 5mm] (Should not be less than 5mm thick)

·        Paperclip

·        2 x Timber pieces [150mm x 650mm x 20mm & 120mm x 120mm x 20mm]

 

Tools and consumables required would include: variable speed drill (drill press preferably, but not required), hand file, angle grinder and cutting disc or hacksaw, sharpened steel nail or centre punch, oil, screwdriver, vernier calipers, wood glue (not essential but useful).

 

3. Construction Method

 

3.1.

First up is to make the hinge: We do the same procedure on two nuts, one the larger [M12] and one the smaller [M8].  Use the centre punch to punch two holes in the centre of two opposing nut faces, and drill narrow holes [1.5mm] slightly short of through to the centre hole of the nut. If you go too far it’s not a tragedy.  So this will be 4 holes drilled in the nuts in total.  Drill slowly and use the oil to lubricate, and if using a hand drill, drill as perpendicular as possible.

 

Using the piece of scrap, drill two holes on two sides of one edge, about [5mm] from the edge, and midway through the thickness of the piece. Drill sufficiently deep so when we later cut out the middle section, the holes are exposed. (through holes)

Put the two nuts side by side and measure across the flats of both together. [32mm]  This is the width we will have to cut out of the metal scrap piece. Using an angle grinder with a cutting disc, or a hacksaw, cut out this section from the scrap. (It is advisable to cut slightly smaller so we can file to the exact dimension later) Cut out chunks until you are able to file flat the remaining bits of metal. 

 

The following image shows the dimensions which I successfully used for my jig:

 

Make sure you have cut out far enough that the nuts will rotate freely.  File to size and make sure the nuts fit flushly between the two legs of the newly made bracket.

Using the cylindrical section (top part) of the drill bits used to drill the holes, cut 3 pins at the required lengths to hinge the nuts between the bracket.  Make sure when the outer pins are inserted, there is a slight recess in the outside hole.  Put the whole mechanism together and then bend the paperclip in a ‘C’ shape, with the ends hooked into the pin recesses on the outside of the bracket. (This is essential as the vibrations generated by an angle grinder will shake the pins out in a hurry!)

 

3.2.

Cut the timber to required size [150mm x 650mm] and attach the extra block on one end using 4 wood screws and wood glue.  In the centre of the block, drill a hole a millimetre or so smaller [11mm] than the threaded rod for the upright. This is to ensure it fits in place rigidly with no freeplay.  Sharpen the tip of the threaded rod slightly and cut about 4 longitudinal grooves around the same end, and no longer than about 20mm.  (This is to let you ‘cut threads’ in the wood while you screw the rod into place)  Screw the threaded rod into the hole, just short of right through, and then lightly tighten a nut against the wood block to secure the rod.

 

3.3.

Place the machine vice on the other end on the timber and trace the slots on the wood with a pencil.  Drill holes in the centre of the traced lines and then secure the vice with the remaining 4 woodscrews and fender washers.  This is a nominal position for the vice and new holes can be made to mount the vice closer to the upright rod for a smaller arc (ie. That is for knives with a smaller cutting edge arc)

 

 

3.4.

Thread the hinge mechanism down the upright thread rod and then when in a suitable position, thread the guide rod through the mechanism.  Thread the grinder on the loose end and secure in place with the remaining nut.

 

  

 

 

 

4. Setting Up The Jig For Grinding

 

To get the correct bevel grinding angle, the height of the hinge mechanism is adjusted on the upright threaded rod, and this is obviously easier done with the guide rod removed!  Once the hinge mechanism is at the desired height, then the guide rod can be threaded in.  It should be adjusted so that when the grinder is attached, the centre line of the disc shaft is approximately above the cutting edge of the blade. 

 

 

The guide rod should then be threaded into the handle hole of the angle grinder and secured with a nut tightened against the handle hole.  This jig will give a characteristically hollow grind bevel, and depth of the hollow grind can be increased by increasing the angle of the grinder relative to the knife edge.  (The more oblique the grinder is, the more hollow will be the grind)

 

The best technique to use with this jig is to grind one side of the blade to completion before changing the knife around and finishing the other bevel.  Thereby the alignment of the blade can be easily maintained by measuring the distance between the grinding surface and the bottom surface along the length of the cutting edge and ensuring it is consistent.

 

  

 

 

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Last updated 07/07/20