Sharpening Draw Knives September 2019

BowBuildingSchool.com

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Publisher and owner:
Matthias Wiltschko
Gross Gundholz 25, 3920 Gross Gerungs, Austria
www.BowBuildingSchool.com
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All rights, copying, distribution and translation rights are with the
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Text, photos, translation and layout: Matthias Wiltschko
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of the customer/reader and third parties is taken over by the information
provided and by the objects produced therefrom (eg bows, arrows,
tools . . . ). Each customer/reader is responsible for his/her own
safety and safety in dealing with his/her bows, arrows and tools. It is
at the measure of the customer/reader to assess and avoid dangerous
situations with bows, arrows and tools.

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On the Sharpening Block
The 90cm/35” long and 12cm/5” wide usable surface of the sharpening
block allows very quick formation of a new bevel geometry. The biggest
advantage of the sharpening block is the creation of a straight cutting
edge across the whole tool. With small waterstones, this is not feasible.
New draw knives or knives with severe damage can be processed
within a few minutes to have a straight cutting edge again.

Although the bevel geometry on new draw knives is given, the cutting
edge is severely jagged. The lower picture shows the rough grinding
burr of a brand new knife: you cannot cut wood with such a blunt tool.

With both thumbs, the abrasive linen is stretched and positioned between
the jaws. When clamping, the jaws should not be pressed against
the abrasive linen so that it can slip into the gap.

Start sharpening the bevel with 180 grit paper. The movement begins
on the left outer edge of the knife and in the middle of the sharpening
block. It ends with the right edge in the middle of the grinding linen.

After sharpening the bevel, a burr forms on the cutting edge. The mirror
is also ground on 180 grit. Here the angle must be kept as flat as possible
(picture below). The photo perspective belies a very blunt angle.

Grinding with 180 grit. The lower the contact pressure when sharpening,
the finer the burr. Now the bevel and mirror are sharpened with 400
grit: the burr becomes smaller and the cutting edge sharper.

Here ends the work on
the sharpening block. The
slightly crowned bevel geometry
is formed and the
cutting edge is free of nicks
and coarse sanding marks.

The sharp edges still need to be rounded. They create a risk of injury to
the bowyer and the bow. Take 120 grit sandpaper on a small sanding
block and round them generously. Do not forget to wear gloves!

Professionally rounded edge. Although the cutting edge visually makes
a good impression, it still needs a fine touch.

With clamps the draw
knife is fixed so that the
cutting edge is freely
accessible for further
sharpening.

With a 1000 grit waterstone, held with both hands, bevel and mirror are
ground. Put the stone in the water until it is completely soaked. Once it
is too dry, submerge it again.

The cutting edge gets the finishing touches with the other side of the
stone (6000 grit). Keep the slightly crowned shape of the bevel and
make sure you keep the mirror angle as flat as possible.

On the Rotating Waterstone
As with any new draw knife, the blunt cutting edge can be seen here.
The light reflection indicates the dull drop of the cutting edge geometry.
Old knife smiths say, “The white must go!“

I also work commercially on the small Tormek T4. With many knives
and scissors a narrower stone is an advantage. The fan sucks off the
vapors of the warming rubber drive wheel.

At an angle of about 45 degrees, I begin to work out the bevel on 220
grit. If the knife was held perpendicular to the direction of sharpening, it
could start to jump and this would produce an uneven cutting edge. At
the cutting edge a uniform and continuous burr has to be formed.

The sharp edges of the blade are generously rounded on the outside
of the coarse 220 grit stone.

After grinding the bevel, the burr will be bent to the opposite side (mirror).
Now, the mirror will be ground on 1000 grit at the flattest possible
sharpness angle. The overall tool angle remains at about 45 degrees.

True off the stone regularly to remove the chatter marks and to achieve
a uniform grinding pattern. Only the cutting edge of the mirror has been
sharpened and not the whole surface.

The fine burr is not ground away, but broken as close to the cutting
edge as possible on a rotating leather disc. After several passes, the
burr will be gone completely.

Top: Fresh out of the factory. Bottom: Finely sharpened draw knife.