Sharpmaker grits : medium/fine ceramic

The Sharpmaker medium and fine rods were used to sharpen ten standard Olfa blades with the 15 degree setting using the corners. The sharpness was examined by cutting light thread and poly with a 500 gram load. The shallow cutting ability was also checked on 3/8" hemp (push cut and slice). As a reference this was repeated with a new 600 grit DMT rod (fine/red). Averaging (median) the performance of all then blades :

Sharpness comparisons between Sharpmaker ceramic rods and fine DMT rod
Finish Thread Poly Hemp
push slice
grams cm lbs
Fine ceramic  65.0 +/- 2.3 0.70 +/- 0.03 21.0 +/- 0.9  9.8 +/- 1.6
Medium ceramic  95.0 +/- 3.6 0.95 +/- 0.05 22.5 +/- 0.7 11.5 +/- 1.6
Fine Diamond 150.0 +/- 5.3 1.50 +/- 0.06 29.5 +/- 1.3  9.0 +/- 0.5

The thread and poly performance was quite consistent with little deviation from one sharpening to the other (less than 5%). The performance on the hemp rope showed more variation on the draw as this is a more complicated cut and thus prone to greater influence from technique, the variance was still only ~10% . All of the above finishes will readily shave fine hair and push cut newsprint. The fine ceramic finish will actually cut hair above the skin and push cuts newsprint like it was not even there.

As expected the performance on the thread increases with the polish of the abrasive, the fine ceramic showsing a many to one improvement over the fine diamond. The same type of improvement is seen on the hemp push cuts however the increase is not as high as a significant component of the force is due to the wedging action of the geometry which is identical for alll blades. Still about a 50% improvement is seen from fine diamond to fine ceramic illustrating how critical an optimal sharpening is for cutting ability.

On the slicing, the finer grits still do better, as the blades are so thin and acute that they push cut so well through the rope they require little draw. A similar influence is seen on the hemp rope, though the power of the more coarse grits stronger. While the fine diamond does not pull ahead of the fine ceramic, it makes a huge increase relative to the push cutting performance which shows how critical the type of abrasive used is for getting optimal performance.

Considering that the fine DMT rod (red) is known to be 25 micron and examining the finish of the medium and fine ceramics under 20x magnification, they estimated to be at 12.5 +/- 1.0 and 6.5 +/- 1.0 micron respectively.

Comments and references

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More information on the Sharpmaker can be found on the Spyderco website. Other grit information :

Last updated : Jun 11 : 2004
Originally written : Jan 9 : 2004