The folding knife project

Sheffield was once the centre of the UK’s knife making industry but this has now declined to the point where only a few master craftsmen remain, although there are people interested in preserving and learning such skills. In this joint research project, contemporary Sheffield knifemaker Grace Horne and multimedia designer Nicola Wood have worked with some of the remaining traditional Sheffield craftsmen and developed learning materials to support those wishing to learn the skills needed to make traditional folding knives.

Initial ideas

Decide on the basic shape you are trying to achieve; you might have seen a knife you like, admire a particular blade style, or fancy a folding version of a fixed blade knife. If you are not familiar with slip joint folding knives you might find it useful to read about different locking mechanisms and look at some of the knife makers on the links page.

Whilst you're about it handle as many folding knives as possible:
  • look at them both open and closed - look at the way the shape of the back of the blade works (or doesn’t) with the shape of the handle
  • feel the movement of the blade and think about what you like and what you don’t
  • look at pictures of folding knives, think about what you like and don’t and print out pictures of those you like
Sketch a few rough ideas for the knife you’d like to make … nothing formal at this stage, in biro on the back of an envelope is fine … just get a few ideas down about the size, type of blade and ideas for a handle.

Here you can see knife designer Jeff Durber talking with Grace and Nicola about what influences his knife designs:

Drawing your knife

Start with a horizontal line - the knife will be on this line where the blade flows into the handle and can fall below it anywhere but should not rise above it.

1. Draw your knife to scale; sketching in where the blade will be when it is both open and closed.

  • the length left for the tang should be approximately the same as the depth of the handle at this point - draw a circle here and the centre of the circle is the blade pivot point
  • mark out a further 70mm on the handle to show approximately where the blade will go when folded - a further section will be needed to secure the end of the spring (at least 10mm)

2. Draw on the position of the spring
  • the middle pin should be around two thirds of the way along the knife
  • at the tip, the spring needs to be 3mm deep
  • at the middle pin, the spring needs to be 6mm deep
  • the end of the spring needs to be large enough to give the knife stability and take the end hole

Here you can see knife designer Jeff Durber developing sketches for a knife with Grace and Nicola:

Create a template

Whilst you can do this with tracing paper or cardboard, you will find it much better with some thin transparent plastic you can cut easily with scissors. Look out for suitable flat pieces on packaging - plastic milk cartons come highly recommended!

1. Carefully trace around the closed outline onto your plastic, mark on the position of the spring and pins:

2. Cut it out and cut the spring portion away from the rest.
3. Put pins through the spring to hold it in place on the drawing, put the remaining piece in position, spike a point through the pivot and turn it out into the open position.
4. Draw the blade shape you require on this piece, remembering any alterations you make to the back of the blade will alter how it looks closed, so keep turning it into the handle to check - do not alter the part of the blade inside the handle in the open position.

5. Cut around 5mm from the length of the spring; it needs to be longer than the pivot point but not go as far as the end of the knife.
6. Put the spring back on the drawing, put the blade in the open position on top, then carefully scribe onto it where it will meet the spring (back square) and cut this portion from the blade.

7. Turn the blade into the handle again, put another piece of thin plastic over the top and sketch off the handle shape, making any necessary adjustments to cover the back square or to expose more of the blade to make it easier to open - carefully mark on the position of the pins - cut it out.

Here you can see knife deigner Jeff Durber making up a template for his knife:

Making a model

A perspex model gives you the opportunity to refine where the blade and spring meet so you will get a good opening and closing action. Use perspex approximately the same thickness as your steel to give you a similar feel.

1. Scribe around the plastic pieces onto perspex, saw the pieces roughly to shape, then file towards the scribe lines, leaving a little extra around the tang of the blade and tip of the spring for fine tuning.
2. It it is really important that the holes line up exactly on the handle and spring, so drill one side first then use it as a drilling guide for the other side and spring.
3. At the same time drill these three holes in a piece of wood that is large enough to take your knife open; you will use this to get the blade and spring working together.
4. Put the spring into position on the board, put the blade in the open position on top, lining the angle of it up with the drawing underneath, then look for where the back square of the blade and the end of the spring need adjustment to fit.

5. File carefully and slowly to fit - this needs to be an exact, tight fit at this stage - any sloppiness here might cause problems later - if you take too much off anywhere it is better to cut a new piece from perspex and refit it than accept an error now that might magnify further down the line.
6. Put the blade into the closed position (don’t try to pivot it on the board yet or you will snap your spring) and mark where the kick and spring will meet - again file slowly and carefully until it is exactly right.

7. Put the blade into the half stop position and mark where the spring will meets it - this is the bare minimum length of tang - if it is any longer the spring will be raised at the half way stage - this might not be an issue for a knife for personal use but if it is for sale and will be displayed in this position for any length of time it might weaken the spring - again file slowly and carefully until it is exactly right.

8. Gently round the corners of the tang until you get the opening and closing action you require, making sure they do not cause the spring to be lifted clear of the back of the knife.

9. Finally, assemble it off the board with the handle sides - now you can refine the overall form looking at how the back of the blade flows into the handle shape and how it feels in the hand - be careful about taking too much off the back of the handle leaving the spring weak - again file slowly and carefully until it is how you want it - don’t be afraid to remake pieces that aren’t right, it’s far easier to do it in perspex than steel!

Here you can see knife designer Jeff Durber developing a model for his knife:

Making up the knife

The board and pins you used to develop the perspex prototype can be reused to get the steel spring and blade working but, before attempting to turn the steel blade on the board, put one of the perspex sides down first to support the pins or they will tear out of the wood

1. Using your perspex prototype as a template, cut your blade and spring out of steel and drill the holes.
2. Carefully file up to your scribe lines, leaving a little material for adjustment around the tip of the spring and the tang of the blade.
3. Put them on the board with the blade in the open position and fit the spring to the back square:

4. With the blade in the closed position, shape the kick of the blade:

5. Heat treat the spring then put it back on the board and check the open and closed positions still work (it might warp as you heat treat) then gently round the corners of the tang until you achieve the opening and closing action you require (you might want to bend the spring a little to put more pressure):

6. Cut the sides out of sheet metal thick enough to take the pressure of the spring without further scale material - 2mm brass is good for this job then assemble the knife within these sides and retest the opening and closing action, taking it apart to refine the shape as necessary.
7. Make the final adjustments to the overall shape of the handle and blade so they look as you wish both open and shut:

Finishing your knife

There are various other things to consider to be able to finish your knife:

Nail nicks: these make the knife easier to open by giving you something to catch hold of on the edge of the blade
  • on some folding knives only a little of the blade protrudes from the handle so you need a nick near the edge of the blade to help you pull it open, there is help on how to make one here 
  • not every blade will need one - Grace's knife pictured in the header of this page has a soft opening action and plenty to catch hold of so has no nail nick

Scales: the scale material needs to be rigid enough to support the pressure caused by the knife opening and shutting.

  • Traditionally, there would be two thin brass liners with bolsters soldered on - at least at the pivot end for strength, but often at both ends - with wood, horn or mother of pearl in between:
  • The scale material would originally have been simply pinned to the liner with a rivet, then more firmly fixed with the other rivets that hold the knife together - nowadays you can use glue too!
  • The liners could simply be cut from metal thick enough to support the knife alone:
  • Thick liners could be entirely covered with scale material:
  • If you have access to a milling machine the liners can be cut from even thicker steel and the central section milled out for scale material:

Pins: the knife is held together with pins; the one at the pivot needs to be particularly robust to withstand the blade’s rotation. The centre pin is subject to strong outward pressure as the spring flexes.

  • Traditionally the pins which were just pieces of rod cut a little longer than the knife and the ends riveted:

  • A more expensive solution, which gives you the ability to take the knife apart again easily, is to use fine nuts and bolts or threaded tube and small screws, although these will impact on the overall look of the knife:

Walk & talk: before finally fixing the pins review again how it looks and how it opens and closes; this fine tuning makes all the difference to the look and feel of a knife.

  • Check the blade is in line with the back of the handle
  • Check the spring is flat to the handle when both open and shut.
  • Check the blade opens and shuts smoothly
  • Check the blade point is inside the handle

Development: to start again from scratch each time is not advisable unless you’ve had a complete disaster - if you make the same design three or four times over it will get better and better with each one as you overcome problems - then you’ll be ready to start on a new design.