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