Marking Knife Blade & Collet Manufacture

Marking Knife

Making the Blades

Although for those earning a living a HSS  blade is perhaps preferable for stiffness and edge holding I think for occasional hobby use the knife blade need not be particularly thick or over exotic.  I make mine from old worn out Hard Point Saw blades.
Having sawn the old blade into suitable strips and dressed them to desired width, removing burs etc. I then polish the faces on a diamond and/or oil stone, surprising how coarse the grind is on the average saw blade and it shows up if you subsequently heat treat. I then grind the Vee edge and sharpen the edges with a chamfer, at this point as long as you have not blued the edge when grinding, the blade will hold an edge for a considerable time with occasional use.

If however you wish to harden it to retain the edge longer, heat to Cherry Red.----------- and Quench.

At this point the blade is now very brittle and easily snapped and will require tempering.

To do this, polish the metal back to a bright finish and reheat Gently at a distance back from the edge and watch for the colour bloom to move towards the cutting edge, when it reaches straw colour immediately re-quench. The blade can now be polished & cutting edges re-lapped on your preferred sharpening medium, but final sharpening may best be left until mounted in the handle.



Making the Collets

Cut a suitable piece of Brass Rod to length and saw in half lengthwise. Ensure the inner faces are smooth and flat & glue together with CA with a strip of card sandwiched between. 

Place in Lathe Chuck and turn down one end to a little under bore size required for Knife blade. HSS wood tools are fine for this. Remount in chuck and turn diameter to a fraction larger than blade bore diameter, dome the end and a few millimetres back from end form a taper down to first turned diameter at chuck jaw face.

Finished collets should be somewhat like this. With sharp knife split collets apart and sand off cardboard residue.
With careful attention to Blade width, drilled blade locating hole diameter and collet diameter, the blade should hold in the handle with just a push fit of the collets.