Sharpening Draw Knives September 2019




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Imprint<br />

Publisher and owner:<br />

Matthias Wiltschko<br />

Gross Gundholz 25, 3920 Gross Gerungs, Austria<br />

www.BowBuildingSchool.com<br />

Publisher and media owner takes no legal responsibility or liability.<br />

All rights, copying, distribution and translation rights are with the<br />

owner and publisher.<br />

Text, photos, translation and layout: Matthias Wiltschko<br />

No legal responsibility or liability for injuries and damage to property<br />

of the customer/reader and third parties is taken over by the information<br />

provided and by the objects produced therefrom (eg bows, arrows,<br />

tools . . . ). Each customer/reader is responsible for his/her own<br />

safety and safety in dealing with his/her bows, arrows and tools. It is<br />

at the measure of the customer/reader to assess and avoid dangerous<br />

situations with bows, arrows and tools.

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On the <strong>Sharpening</strong> Block<br />

The 90cm/35” long and 12cm/5” wide usable surface of the sharpening<br />

block allows very quick formation of a new bevel geometry. The biggest<br />

advantage of the sharpening block is the creation of a straight cutting<br />

edge across the whole tool. With small waterstones, this is not feasible.<br />

New draw knives or knives with severe damage can be processed<br />

within a few minutes to have a straight cutting edge again.

Although the bevel geometry on new draw knives is given, the cutting<br />

edge is severely jagged. The lower picture shows the rough grinding<br />

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<br />

the jaws. When clamping, the jaws should not be pressed against<br />

the abrasive linen so that it can slip into the gap.

Start sharpening the bevel with 180 grit paper. The movement begins<br />

on the left outer edge of the knife and in the middle of the sharpening<br />

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<br />

is also ground on 180 grit. Here the angle must be kept as flat as possible<br />

(picture below). The photo perspective belies a very blunt angle.

Grinding with 180 grit. The lower the contact pressure when sharpening,<br />

the finer the burr. Now the bevel and mirror are sharpened with 400<br />

grit: the burr becomes smaller and the cutting edge sharper.

Here ends the work on<br />

the sharpening block. The<br />

slightly crowned bevel geometry<br />

is formed and the<br />

cutting edge is free of nicks<br />

and coarse sanding marks.

The sharp edges still need to be rounded. They create a risk of injury to<br />

the bowyer and the bow. Take 120 grit sandpaper on a small sanding<br />

block and round them generously. Do not forget to wear gloves!

Professionally rounded edge. Although the cutting edge visually makes<br />

a good impression, it still needs a fine touch.

With clamps the draw<br />

knife is fixed so that the<br />

cutting edge is freely<br />

accessible for further<br />


With a 1000 grit waterstone, held with both hands, bevel and mirror are<br />

ground. Put the stone in the water until it is completely soaked. Once it<br />

is too dry, submerge it again.

The cutting edge gets the finishing touches with the other side of the<br />

stone (6000 grit). Keep the slightly crowned shape of the bevel and<br />

make sure you keep the mirror angle as flat as possible.

On the Rotating Waterstone<br />

As with any new draw knife, the blunt cutting edge can be seen here.<br />

The light reflection indicates the dull drop of the cutting edge geometry.<br />

Old knife smiths say, “The white must go!“

I also work commercially on the small Tormek T4. With many knives<br />

and scissors a narrower stone is an advantage. The fan sucks off the<br />

vapors of the warming rubber drive wheel.

At an angle of about 45 degrees, I begin to work out the bevel on 220<br />

grit. If the knife was held perpendicular to the direction of sharpening, it<br />

could start to jump and this would produce an uneven cutting edge. At<br />

the cutting edge a uniform and continuous burr has to be formed.

The sharp edges of the blade are generously rounded on the outside<br />

of the coarse 220 grit stone.

After grinding the bevel, the burr will be bent to the opposite side (mirror).<br />

Now, the mirror will be ground on 1000 grit at the flattest possible<br />

sharpness angle. The overall tool angle remains at about 45 degrees.

True off the stone regularly to remove the chatter marks and to achieve<br />

a uniform grinding pattern. Only the cutting edge of the mirror has been<br />

sharpened and not the whole surface.

The fine burr is not ground away, but broken as close to the cutting<br />

edge as possible on a rotating leather disc. After several passes, the<br />

burr will be gone completely.

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

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