The main three tasks before sanding and finishing the handle are: creating the round overs, drilling the holes for the nuts and bolts and sawing the slot for the saw blade. These can be done in any order.
Before cutting the slot, copy the line from the design onto the handle blank or shaped handle to mark the depth of the cut to be made.
Note: If you are making a new handle for the Spear and Jackson 9500R it is better to cut the slot for the saw blade before drilling the holes for the nuts and bolts. This will enable you to mark the holes out in the right position.
Cutting the Slot for the Saw Blade
A Slitting Saw
To start the kerf for the slot you could use a slitting saw on a mill or a drill press. It’s a small horizontal circular saw of which you can dial in the height. The thickness of the kerf should match the sawblade. This should be exactly in the middle of the saw handle. Make a shallow cut all around the position of the slot. To make the full depth of cut place the handle in the vise and use a handsaw or a tenon saw to finish the cut.
Using a Saw Blade instead
Another option is to use a sawblade or a panel saw and clamp it on top of a slat of wood that brings the sawblade to the right height. Clamp this on top of a flat plate or benchtop and move the sawhandle along the sawblade to saw the slot.
The thickness of the important piece of wood can be found by measuring the thickness of the saw handle. Then subtract the thickness of the sawblade and then divide the outcome by 2.
Example: the thickness of the handle is 24 mm. The thickness of the blade is 0.6 mm. The thickness of the piece of wood will be 24-0.6 / 2 = 11.7 mm
The kerf of the sawblade should be the thickness of the sawblade you want to mount your new handle to, or a fraction thicker to allow it to fit more easily.
Checking the assembly
By using a marking gauge and you can find the midpoint of the kerf by marking from two sides of the handle. Check if the slitting saw or mounted sawblade has the right point of contact on the saw handle.
Compare heights and adjust accordingly. If the height of the sawblade is too low you can bring this up accurately with paper shims.
Cutting the Slot
When the height is right, mark the start and end of the kerf on the sides of the handle and proceed cut the kerf. Make sure that you stop a little before the marks.
The slot can be deepened and finalized by using a panel saw, a backsaw, or by extending the sawblade further out so the above method can cut deeper.
Note: Make sure the saw is straight and flat for the most accurate results and has the right kerf thickness. This becomes easier when using the same saw for both steps by clamping a panel saw in the assembly with the block of wood.