Stropping base

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DaveHb

Joined
Oct 18, 2021
Messages
106
Critiques and pointers welcome.
Reading “Science of Sharp” thought I would experiment.
He discovered alternating stropping type compounds seemed to be better at removing bur than using same progressively finer grits of same compound, but still at times if remember correctly using up to 50+ strokes.
Not having equipment to be as technical as him, I’ve been experimenting with different backers, and what I apply compounds on.
This was sharpened free hand on 600 grit diamond plate (edge trailing) followed by 800 grit diamond plate with alternating, brushing, edge leading strokes for initial debur. ~15 per side.
Moved to plain paint stick with 6 micron diapaste applied directly to the wood @ 10 laps per side. (An s30v blade I sharpened last night did take 15ps to get where I felt but was sufficiently removed).
Next was bark river black, applied to leather glued down on backer board, for 5 per side.
Next was green compound with same per set up as black for 10 per side.
Last was 3 micron diapaste also apply to leather strop glued to wood backer for 10-15 per side.

The stropping compound applied directly to the wood has seemed to significantly reduce the need for excessive stropping
Video of results below.
One drawback is stropping compound looses its effectiveness faster when applied strait to a wood surface. MDF seems to have the same issue.

Any other substrate the compound could be applied to that would last longer?
Have done M390, S30V, CPM M4, and Rex 45 with this process so far and achieved similar results.
https://imgur.com/a/WGYyinG
 
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The quicker loss of effectiveness of compound on a wood backing is likely due to the greater aggressiveness of the method itself. In other words, compounds applied on wood or other hard backings will generate much more swarf, much more quickly. A lot of us are aware of how such hard strops blacken with swarf very fast. All that swarf will more quickly load up & clog the strop, which diminishes it's effectiveness. The firmer backing makes the grit of the compound dig more deeply, therefore removing metal much faster than it otherwise would, if used on a softer & more compressible backing like leather. Hard backings increase the unit pressure exerted, and a softer backing will do the opposite, i.e., decrease the unit pressure.

For the same reason, this is also why the need for excessive stropping is also reduced. It's because the method's greater aggressiveness gets the task done in much fewer passes.

I consider all of the observed hard backing behaviors to be good things, rather than not. A hard backing makes the compound work better & faster - this means doing much less work to get the same (or better) result. Additionally, the hard backing's resistance to compression or deformation under the blade means the finished edge will stay crisper, keener & sharper, instead of risking the rounding issues at the apex, as can happen on a softer backing - especially if stropped excessively on such a backing. So, if a hard strop of wood loads up & clogs more quickly, I consider that a relatively minor price to pay, in the form of more frequent cleaning & resurfacing of the strop, as compared to the greater benefits afforded by the same method.

There are times when extreme subtlety is advantageous, in stropping. If an edge needs just a tiny bit more attention to get it perfectly sharp according to your expectations, stropping on plain leather or leather with a very light application of compound might be all you need, without overpolishing or removing more additional metal than is necessary.
 
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Paper wrapped around a hard surface like the coarse side of a combination stone is a good alternative, just not with most diamond pastes. Toss it when it loads up. Diamond added to silicon carbide or AlumOx compounds works just as well or better than straight diamond.

In my own testing, use of a multi grit size honing compound produced the best effect.

You can also use a dollar bill, baking parchment, anything that does not have a lot of give. If you are going for a softer effect or a more delicate finish, several sheets of paper can be used. Being able to toss it after it loads is helpful, or just rub it down with a paper towel.
 
DaveHb said:
Did you make your own or buy it?
Click to expand...

I wound up making my own. A few years back I used to sell a reduced footprint underplate that worked like the serrated contact wheels available for belt grinders. Intended to be freehand used under sheets of wet/dry sandpaper or plain paper and compound. Whipped up a compound to go along with it.

Had a relatively small amount of 20 micron SiC blended with a lot of 6 micron SiC and 15% diamond at 3,000 mesh. This blend reliably was able to better recondition dulling blades and did a fantastic job as a follow up to moderate and fine hones. Did a great job on high vanadium steels as well - everything really. I speak in past tense but still have and use this material. It makes a slight haze, not a mirror, and reliably restores lightly worn edges back to tree-topping. Subjectively it makes about a 4k-6k finish. If I microbevel on an 8k waterstone I don't bother with it.

A couple of other manufactured compounds use this approach, namely Flexcut Gold and Lee Valley honing compound. I recall some people yelling about the inconsistency with the LV and found a response to the effect that it works better and is for getting work done, not for cosmetic polishing.

I did a LOT of testing trial and error before a clear trend began to emerge, and then more testing to narrow it down and define how much diamond needed to be added to keep it disposable yet still be effective (10% by abrasive weight). I added another 5% on top of that for insurance- going higher than that yielded no improvement and slightly reduced performance on lower RC and low alloy content steels (!) compared to SiC and AlumOx.
 
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