How to make a do-it-yourself knife sharpening machine

Recommendation points

• Machine base
• Assistant device
• Fixing mechanism
• Sharpening angle adjustment
• Carriage and replaceable blocks
• How to sharpen correctly

The advent of the Edge Pro grinding machines revolutionized without exaggeration. Prices are really high, but no one bothers to copy the principle and create such a device yourself. We offer the design of a simple machine for sharpening knives, chisels and any other blades that you can do yourself.

Machine base

Most parts for a sharpener can be made from literally anything, following the general principle of the device. As an example, let us take laminated or polished box plywood 8-12 mm thick, which was widely used in the manufacture of cases of Soviet radio engineering.

The base must be heavy – about 3.5–5 kg – otherwise the machine will be unstable and unsuitable for sharpening heavy chopping tools. Therefore, the inclusion of steel elements in the design is encouraged, for example, the base of the case can be “shod” with a 20×20 mm angle.

Two pieces in the shape of a rectangular trapezoid with bases of 170 and 60 mm and a height of 230 mm must be cut out of plywood with a jigsaw. When cutting, leave an allowance of 0.5-0.7 mm for the machining of the ends: they must be straight and exactly correspond to the marking.

The third part is an inclined plane made of a plywood board measuring 230×150 mm. It is installed between the inclined sides of the side walls, while the trapeziums of the side walls rest on the rectangular side.

In other words, the base of the machine is a kind of wedge, but the ramp should protrude 40 mm at the front. Along the ends of the side walls, use a thickness gauge to set two lines indented by half the thickness of the plywood. Drill three holes in each plank to secure the parts with screws. Transfer the drilling to the ends of the inclined part, temporarily connect the base parts.

At the rear, the side walls are connected with a 60×60 mm bar, which is attached to the end with two screws on each side. A 10 mm vertical hole must be made in the bar with a 50 mm distance from the center, that is, 25 mm from the edge. To be sure of verticality, it is best to first drill with a thin drill on both sides and then widen. From above and below, screw into the hole two sleeves with an M10 female thread, and in them – a 10 mm stud, 250 mm long. Here it may be necessary to slightly adjust the bottom sleeve if its thread does not match the stud.

Assistant device

Remove the flat inclined part from the base – it needs to be finalized, equipped with a device for fixing and pressing the tool being processed.

First, set aside 40 mm from the front edge and along this line with a hacksaw, saw down a groove about 2 mm deep. With a sectional or boot knife from the end of the board, split the two top layers of veneer to form a sample into which you can insert a 2 mm steel plate flush with the common plane.

The handrail consists of two steel slats 170×60 mm and 150×40 mm. They need to be folded together along the long end with uniform indents along the edges and make three through holes of 6 mm. The strips along these holes must be tightened with bolts, placing the caps on the side of the upper, larger plate. Arc welding bake each head, welding it to the plate, then remove the beads of metal and grind the plate until a perfectly flat plane is obtained.

Attach a narrower striker to the notch on the edge and relocate the holes with a drill, then bolt the handlebar. Before installation, it can also be magnetized with direct current, this will help in sharpening small blades.

Fixing mechanism

The second part of the handcuff is the clamping bar. It also comes in two pieces:

1. Upper L-shaped bar 150×180 mm with a shelf width of about 45-50 mm.
2. Lower striking plate of rectangular shape 50×100 mm.

The parts need to be folded in the same way as the parts of the handcuff were folded, placing the striker at the far edge of the upper clamp. In the center we make two holes with an indent of 25 mm from the edges of the small part, through them we tighten the parts with two 8 mm bolts. They need to be started in opposite directions, while the head of the upper (near) bolt is located on the side of the clamping bar. The bolt heads are also welded to the plates and pre-grinded to neat rounds.

On an inclined plank with an indent of 40 mm from the edge, draw a line with a thickness gauge, and make one 8 mm hole 25 mm from the top and bottom edges. Connect the edges of the holes with a marking and make a cut with an allowance with a jigsaw. File the resulting groove to a width of 8.2–8.5 mm.

Fasten the hold-down and strike plate through the groove in the plank. Tighten the bolt protruding from above with a nut so that the bar retains minimum movement, then lock the connection with the second nut. To press or release the strap from the bottom (in the base niche), screw the wing nut onto the second bolt.

Sharpening angle adjustment

On the stud screwed into the base bar, throw a wide washer and tighten the nut so that the rod does not rotate in the sleeves.

The adjusting shoe must be made from a small block of solid material with dimensions of about 20x40x80 mm. Take carbolite, textolite or hardwood.

At 15 mm from the edge, the block is drilled into a 20 mm end on both sides, the hole expands to 9 mm, then we cut a thread inside. With an offset of 50 mm from the axis of the hole made, the second is drilled, but in the flat part of the part, that is, perpendicular to the previous one. This hole should have a diameter of about 14 mm, and it should be flared strongly with a round rasp..

The block is screwed onto the stud, so it is possible to relatively accurately adjust the height of the eyelet without a complex system of screw locks, as in the original machine, which is a little more difficult to implement in practice. In order for the block to be motionless during operation, it must be counterbalanced on both sides with M10 wing nuts.

Carriage and replaceable blocks

For a sharpening carriage, you will need to coaxially weld 30 cm pieces of M10 hairpin and a smooth, even bar 10 mm thick. You also need two solid blocks with dimensions of about 50×80 mm up to 20 mm thick. A 10 mm hole should be made in each bar in the center and with an indent of 20 mm from the top edge.

First a wing nut is screwed onto the bar, then a wide washer and two bars, again a washer and a nut. Rectangular sharpening stones can be clamped between the blocks, but it is better to make several replaceable sharpening stones.

As a basis for them, take a light aluminum profile with a flat part 40-50 mm wide. It can be a rectangular profile pipe or pieces of an old eaves profile.

The flat part is skinned and degreased, with “Moment” we glue strips of sandpaper of various grain sizes from 400 to 1200 grit. Choose a fabric-based sandpaper, and on one of the bars glue a strip of suede leather to straighten the blades with an abrasive paste.

How to sharpen correctly

For correct sharpening, make several templates from plywood with angles of 14–20? for cutting and 30–37? for chopping edges, the exact angle depends on the steel grade. Lock the blade parallel to the edge of the handrail and press down with a bar. According to the template, adjust the angle between the planes of the sharpening block and the inclined tabletop.

Start sharpening with a coarse (P400) bar if the edge does not have the correct angle. Make sure that the descent strip takes the form of a straight strip without convolutions and waves. Reduce grit and work on both sides of the blade with a P800 bar and then a P1000 or P1200 bar. When sharpening the blade, slide the bar lightly in both directions.

After sharpening, the blade needs to be corrected with a “leather” bar on which a small amount of GOI paste is applied. When dressing the blades, the working movement is directed only towards the edge (towards itself), but not against it. And finally, a little advice: if you sharpen knives with polished blades and engraving, cover them with masking tape so that the crumbling abrasive does not leave scratches. It also does not hurt to paste over the surface of the handcuff with vinyl self-adhesive.