Making a 3-blade

Take a look at the 3-blade folder design page.
Most of the techniques as the same as those used in Making a sliplock folder.

Sanding the square backs of the main blade and its companion. The two blades have been glued together with cyano-acrylate.

The square backs sanded to 800 grit

The round end marked

On the two-blade folders, I use a steel plate, about 12mm thick. I drill the holes in the liners for the pivots as well as the spring pin. I then drill all these holes in the steel plate as well. (I use old drill bits for pins).

The liner is put on the plate, pins in place, one blade on its pin, and the spring on its pin. The most important bit is to make the spring too big. Make it too long, and on the inside at least half a mm too wide.

Marking the spring length as well as the pre-tension for the main and sheepsfoot blades

Now you can work the spring down to its correct length on one end. It is a pain, because you get one chance only to do it right. I do this after the spring has been hardened and tempered, just sanding off the layer of scale after heat treating can cause the spring to be too short.

With the one blade in position and the spring fitted, place the other blade on its pin. You will see that the spring extends over the second blade both in length and width. If the springs extends over the blade (width) more than one mm, you can work it down a bit after you have shortened the blade to fit.

I have found that 0.7 - 1mm pre-tension on one side is just enough for a knife with a closed length of 80mm or less. For a longer knife I would allow 1.5mm pre-tension.

By making the spring wider than on the plan (or template) you get the necessary pre-tension. If you, by accident, cut your spring exactly to size, but you have not yet drilled the holes in the liner or the mounting plate you can compensate by dropping the spring pin hole by .5mm.

The thick mounting plate keeps the holes in the liners from working into an oval because of the number of times you have to fit and refit all the parts.
The one I use already has a number of different knives' holes drilled. To drill the liners for the next knife I clamp them to the plate and drill the holes from the rear.

The three blades and both springs in position.

Mark the center liner and cut using a jeweller's saw.

It is easier if you fit the blades with loose pins and then do the grinding. This way you can continually check to see if the blades fit.

The grinding procedure on a two blade and a e three-blade is slightly different:

Two-blade:
First grind the inside of the large blade, then the inside of the small blade. Switch between the two until both close without jamming. You will then have a good indication of where your cutting edges are going to be, and you will be able to take a bit off on the outsides so the blades don't touch the liners.

Three-blade:

Mark the cutting edge of each blade.
First grind the outside (liner side) of the small blade until it clears the liner. On the picture below you can see that the blade is still touching the liner and needs to be grinded a bit more.

Grind the main blade as you would for a normal single blade folder.

And now the fun begins. The small blade clears the liner, and the large blade is done. In the picture below you can see the sheepsfoot blade jamming on the small blade, in the second picture you can see the sheepsfoot and the main blade jammed when both are in the open position. Grinding the sheepsfoot will solve both these problems.

A flat grind works ten times better on a multiblade than a hollow grind. I grind my blades on my diskgrinder, having a vertical platen on a beltgrinder makes grinding these to fit a pleasure.

When all the blades are opening and closing without jamming it is time to mark and cut the nail nicks.

Mark the inside of the liners for the relief. The relief is cut to keep the blades from rubbing against the liners.

I use a slight unconventional method of milling the reliefs, as I do not own a milling machine. With the liners glued to a steel disk using CA adhesive, I mill out the relief with a 5mm 4-flute mill in my drill press.

I use a flat riffler file to remove the milling marks, then rubber polishing wheels, the type used by jewellers, to polish the inside of the liners. The liners are then removed from the steel plate by soaking the adhesive with acetone for a few minutes.

Placing a bolster alignment clamp in position on the liners makes placing and drilling the bolsters for pinning to the liners much easier than working to a scribed line.

When the bolster pins peened grind them flush on both sides, be careful when working on the liner side as any unevenness on the raised section of the liner might cause the blade to stick.

The secret to fitting bolsters on both sides is to make sure that the inside edge (handle or cover sides) are not parallel. Put them at a slight angle relative to each other. Then you make the covers at the same angle and just slide them into position.

Take a look at www.knifepurveyor.com , especially the work of Tony Bose, Eugene Shadley and Terry Davis. (There is an index according to the maker's name)