New Marking Tool

When making a knife, specifically when shaping the bevel on the blade, it is important to ensure both sides are symmetrical.  I achieve this with the Bevel Jig (see earlier post in this blog) to ensure a smooth grind of equal angle on both sides.  However, in order to gauge whether the amount of material removed from the left and right remains evenly balanced, most bladesmiths score a double line down the centre of the blade before grinding.  This provides a guideline for how far to grind the bevel without having to measure it as you go.  The photo below shows an example of the parallel lines before grinding.

Originally, I crafted a simple device as shown in the photo below, which was basically a masonry nail, ground to a chisel point and mounted through an adjustable bolt onto a block of wood.

It worked ok, but was very difficult to adjust and was usually not accurate enough.  So ... I made a new, better one!

I had an old Vernier calliper at home, which worked, but was a bit worn and scruffy and besides, I recently received a new, better quality one as a gift.  So, I came up with a way to repurpose the old Vernier in the design of the new tool.  First, all the unnecessary features had to be ground off and the long spine of the calliper was cut shorter, to a bit more than 100mm (4”).  After a thorough overhaul and clean-up, the device was running smoothly once more.  Then came the shaping of the new attachments, for which I used 6mm (0.25”) aluminium and a thicker block for the base, 12mm (0.48").

The head of the Vernier is secured with epoxy glue upside down to the base block.  The aluminium plate secured to the rear side of the Vernier is used to hold the cutting tip, which is a bar of High Speed Steel – very hard steel that is typically used for cutting tips in a metalworking lathe.  The position of the tip can be adjusted, although the need to do this is highly unlikely.  The idea is that the cutting tip can be raised and lowered by sliding the Vernier to a precise distance above the surface, accurate to 0.05mm (2 thousandths of an inch).  The little securing screw prevents it from slipping inadvertently during use.

"Front" of the tool, with cutting tip raised to 2.15cm (0.85"):

"Rear" of the tool:

Cutting tip:

Tool lowered to its zero position.  The cutting tip is flush with the surface of the cutting mat.  It appears to be floating because the grid pattern is printed on the underside of the glass mat.

Now, when marking a blade prior to grinding the bevel, the blade is placed flat on the surface of the cutting mat, the height of the cutting tip is set at half the thickness of the steel minus about 0.5mm (0.02"), and a line is scored all the way along where the bevel is to be ground.  Then the blade is flipped to the other side and a second line is scored parallel to the first.  The distance between the 2 lines will be somewhere around 1mm (0.04"), depending on the type of blade and thickness of the material.

The photo below shows the orientation of the marking tool beside a completed knife to illustrate how the lines would be scored (I did not have any unfinished blades at the time of taking the photo).

Now to put it to work!