The importance of stropping edge tools

[D_W]

I always strop the face (non-bevelled side), flat against the media, as well as riding the bevel on the strop. I go from one to the other a number of times. My thinking is that by doing so I'm weakening and eventually causing the remnants of the wire edge to fail in a clean break. I've been reading this thread with interest and despite the many fascinating revelations it contains, I still think what I'm doing works because of why I think it works. Am I wrong? BTW I use a piece of flat mdf loaded with a bit of autosol as a strop.

The most important thing is that it works. The rest just satisfies our curiosity.

I like autosol and dursol a lot as strop pastes, and in the event I imagine that I need sharper than the washita, I just work the bevel side a little on horse butt with one of those. I haven't noticed the back side to make any additional difference unless the last stone was coarser than a washita or soft Arkansas.

I bare strop after it, or palm strop.

 

[D_W]

A good way to test how well you did with the strop is to shave hair with both sides of the iron. If you do an incomplete job, it will shave well on one side but not the other. This is true even if you use the finest of synthetic stones.

 

[Trafalgar]

Actually, if the ruler trick works, it would be logical to presume stropping the back of the blade would as well. Does anyone do it?

Absolutely, and with a slight lift for a few strokes which completely obviates the need for back bevels, ruler tricks, etc. except on cutters or chisels in horrible condition - profoundly humped and/or pitted -- which shouldn't be in service in the first place. A straight chisel out of one's carving set meets the occasional need for a low angled chisel ground on both sides to a knife edge, that is unless your job is to cut sash pockets all day (see my post above).

On a softish strop you get the same effect without lifting as the material deflects, the slight lift is only needed on a very firm strop. Its easy enough to see the polish imparted all the way to the cutting edge and it doesn't take much work -- ten strokes or less -- less is more. Use restraint. It's like taking aspirin to prevent a heart attack or stroke -- stick to one, two may cause you to bleed to death. More is not always better, in fact it rarely is.

If you're stropping a cutter or chisel's back by pulling you're already likely concentrating pressure at the tip for that extra bit of polish and removal of rag, very slight lift assures that you are. No need to wonder, just take a look and you ought to see a brighter line of steel on the back at the cutting edge. This ought to completely go away the next time the item is honed on stones or other media. This is assurance that you have not created an unintentional back bevel.

 

[Derek Cohen (Perth Oz)]

phil.p wrote:
Actually, if the ruler trick works, it would be logical to presume stropping the back of the blade would as well. Does anyone do it?

With BU plane blades that have a high secondary micro bevel (created with a honing guide), it is not practical to strop the face of the blade (the secondary bevel is too small, and you may change the bevel angle if doing this freehand).

Consequently, when I needed to give the edge a lift, I would strop the back of the blade. Although the blade was kept flat, this process was essentially the same as using the Ruler Trick. It works well.

Regards from Perth

Derek

 

[bridger]

This guy covers it:
https://scienceofsharp.wordpress.com/20 ... opping-do/

That suggests to me that stropping is more a burnishing process (plastic deformation - moving metal around) rather than an abrasive process (removing metal). Putting it another way, the main effect seems to be slightly reshaping an edge by deforming metal to where it's wanted to make a better cutting edge, rather than by abrading it to form a new edge in new metal.

From a purely personal observational point of view, that rather confirms what I find when using a slate polishing stone. There seems to be only slight metal removal, but when I treat tool edges by only trailing them on the stone (rather than the usual honing practice of back-and-forth), I end up with edges that seem sharper than almost any other way I've tried. I've noted the same effect on an ultra-fine ceramic stone too. That practice seems to both remove the wire edge from the main honing stone (fine India in my case, or medium ceramic in the past), and burnish the honed edge to a better 'finish' than the honing stone leaves.

That effect does not happen if I use the same back-and-forth technique on the slate as I use on the India, or at least, not as quickly.

I've no proof of this whatever, but my suspicion is that leather, palm of hand, piece of hardwood dressed with compound or undressed, or polishing stones, all do the same thing - burnish rather than abrade.

I suspect that there's an awful lot in that and I'm tempted to believe that the notion of e.g. the palm of the hand giving the final touch is not a bit of baseless fantasy but rather the result of somebody noticing that it produced a definite effect. However, the key question must surely be, "How long does the effect last?" If this final touch, which involves relatively little mechanical force, gets the wire off followed by a hint of beneficial deformation, how many strokes of a blade on wood will cancel it out? The freshly sharpened and stropped blade is no doubt optimal but I can't imagine that it does anything other than quickly go to "normal" (i.e. perfectly satisfactory) sharpness, depending on the species of wood worked. Of course it makes sense to start from the best sharpness you can achieve. It's just that I suspect it is not available to you for very long. Also "best sharpness" might be more than enough on woods which plane easily but just about enough on some of the more outrageous tropical woods.

Human skin- however dry and callused- contains considerable oils. Otherwise your skin would crack and rupture when you flexed your bones. Those oils, transferred to the tool provide a bit of lubrication in the cut. Think the squiggle of wax on the sole of a plane.

Skin, whether a human palm or the finest horween shell has mineral content. Not a lot and quite fine, which makes for an excellent final process in sharpening. A little dust and dirt at the surface can raise that mineral content quite a bit. Think of the last thing handled before stropping on the palm- it was probably a fine grit stone....

Friction is a funny thing. The effects scale up and down pretty much to infinity. Sliding hard steel over smooth leather with the slightest pressure- even less than the weight of a razor for example- results in plastic deformation of the hard steel, even if only in a layer a few molecules deep at the surface. Given that a well honed edge is only a few molecules wide it's not a stretch of the imagination to accept real effects to sharpness.

Stropping is not one thing.

 

[Trafalgar]

If that were the case then stropping would be just as likely to ruin an edge than make it perform better. If the passes weren't exactly equally divided from front to back, with the exact same amount of pressure the edge would be ruined. In fact, most tools seem to benefit from even fairly haphazard stropping and by the relatively uninitiated.

Coaxing the correct 'plastic deformation' of an edge only 'a few molecules thick' would be the most ticklish of operations. But in reality it's not.

 

[bridger]

If that were the case then stropping would be just as likely to ruin an edge than make it perform better. If the passes weren't exactly equally divided from front to back, with the exact same amount of pressure the edge would be ruined.

I don't follow your reasoning. What is it ruining the edge?

In fact, most tools seem to benefit from even fairly haphazard stropping and by the relatively uninitiated.

Coaxing the correct 'plastic deformation' of an edge only 'a few molecules thick' would be the most ticklish of operations. But in reality it's not.

 

[Trafalgar]

One of your posts made me afraid that if I turned the shop fan on too high I might lose the edge...

 

[bridger]

One of your posts made me afraid that if I turned the shop fan on too high I might lose the edge...

Don't try to strop your tools on the moving blade and you'll be OK...