Archive for March 21st, 2020

Drag Knife Blade Lengths

The distances from the sharp tip to the top end of the edge, measured parallel to the shank axis:

  • 60° = 1.3 mm
  • 45° = 0.7 mm
  • 30° = 0.6 mm

Here, the angle goes upward from the paper / Tek CC deck / whatever to the shank axis, so the 60° blade at the top of the picture has the longest blade edge.

Drag Knife Blades - unused 60 45 30 degree
Drag Knife Blades – unused 60 45 30 degree

That’s for one trio of blades from a single eBay seller. I expected no consistency between sellers and that’s exactly what I got when I sorted my collection by peering through the microscope:

Drag Knife Blades - inconsistent cap colors
Drag Knife Blades – inconsistent cap colors

Red seems consistently 45°, but blue & yellow caps can cover either 30° or 60° blades. The actual blade angle lies mostly within ±5° of the nominal value, with 45° between 40° and 50°, but I doubt my few samples span the QA space.

The flat shaping the backside of the blade should put the point 0.25 mm from the shank axis and, because the blades are 1.0 mm ⌀, also 0.25 mm from the OD. A few spot measurements suggest the point offset can be up to 0.4 mm from the axis, so any fancy calculations you might think of making seem pretty much irrelevant.

There’s not much practical difference between the 30° (“window tint”) and 45° (“vinyl”) blades, particularly given the angle and offset tolerances, but 60° blades (“card stock”) seem better suited to cutting the 0.3 mm to 0.4 mm thick laminated Tek Circuit Computer decks than the 45° blades I’ve been using.

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