Thread: Rasp sharpening again

Despite my best attempts to moderate my natural scientific curiosity, my brain and my habit of problem solving when drifting on that pond between wakefulness and sleep has conspired against me.

Why did the diamond stone cut the steel so quickly?
Why did the rasp go from cutting abysmally to cutting so well I used useless terms like 'cuts fantastically'

The answer was in front of me. Zoom into the photos of the rasp and notice the variation in the size of the flats (cut on the teeth); there's a big range from very obvious through to barely or not perceptible.

So, the teeth were quite different heights and the diamond stone was borne by fewer than the full contingent of teeth, perhaps relatively few.

This explains:

Why the diamond stone cut the steel so quickly.

Why the rasp was so bad to begin with. The high teeth would have been doing the lion's share of the work, leaving a coarse finish and dulling quickly. Once dull the rasp essentially stopped working.


The diamond stone sharpened the dull teeth, but also importantly, allowed the whole contingent of teeth to start doing their fair share of work. This is why honing this rasp made such a big difference, not only to the speed of cut but the quality of the finish.

I haven't checked the machine made Nicholson I fettled, but I suspect its teeth are much more uniform.

I now have to look at my cache of Chinese-made hand-stitched rifflers, some of which are so bad they're better termed RSO's (rasp shaped objects)

more food for thought

Edit: I have a new appreciation for the skill of the hand stitchers; not only do they have to manage some semblance of uniformity in the pattern of teeth, but also strike so consistently as to raise the teeth to a consistent height.


Cheers
M

Well, at least I can see how this method could refresh the leading edges of the teeth, unlike the acid-bath method that simply takes an even layer off, leaving teeth that are cleaner, perhaps, but still rounded.

I've got a very tired Liogier modeller's rasp that I've worked to death on very hard woods and it struggles to cut anything much harder than balsa now. There's nothing to lose with that one, so it's going to get a lick or two of diamond file later today. I'll let you know if I have the same successful outcome. I'll be overjoyed if I get any improvement at all, that rasp is a favourite so extending its life by even a little would be a bonus....

Cheers,