Effectiveness of leather strops (and polishing compounds)

[HRRLutherie]

Saw a very interesting web article comparing leather strops to micro mesh abrasives:

http://www3.telus.net/BrentBeach/Sharpen/Stropping.html

 

[bugbear]

http://www.inthewoodshop.com/WoodworkTe ... paste.html

BugBear

 

[David C]

Have always had an unfounded prejudice against stropping. Brent seems to provide some evidence !

Best wishes,
David

 

[Paul Chapman]

I used to use a leather strop with jewellers rouge, which gave a very good polish but I think tended to round over the edge because of the compressibility of the leather. I now use a piece of wood with Solvol Autosol, which gives just as good a polish and no rounding of the edge. My blades are super sharp

Cheers :wink:

Paul

 

[Racers]

Solvol autosol? I can only find solvol metal polish these days!
Used tubes of the stuff on motorbikes years ago!

Pete

 

[HRRLutherie]

Are honing compounds at 0.3 Micron or less readily available?

I read, for example, Lee Valley advertise their green honing rouge as have an average 0.5 micron particle size. The compound is only as fine a grit as the lowest grit it the compound, i.e a 0.01 micron compound is really a 10 micron compound if it contains those particles.


But again, bear in mind that I have absolutely no experience in practice, so what I'm saying might be utter...

 

[David C]

Pete,
Autosol paste in tubes, should be available in car accessory shops or garages.

David

 

[custard]

I get all the arguments about soft stropping substrates "dubbing over" edges, so I'm not arguing in favour of stropping, nor am I saying stropping is better than using 3M film...but still, there has to be something that's just plain wrong with those photos!

I've seen carving chisels go from having that frosted matt look after sharpening on even the finest arkansas stones, to then becoming polished after stropping. But those photos suggest the exact opposite.

I think I'll trust the evidence of my own eyes, and hundreds of years of accumulated craft experience, and say stropping can improve edge sharpness after sharpening on oil stones.

 

[HRRLutherie]

I suppose it just depends on the polishing compound your using, for there must be some really fine compounds that go above and beyond those of Lee Valley.

 

[Steve Elliott]

I did a test that confirms what Brent Beach found, namely that a well-honed edge can be degraded by stropping on leather. I took my standard sharp edge honed with 1 micron diamond on cast iron and refined it by "stropping" on boxwood charged with 1/4 micron diamond. After 80 strokes the scratches were so fine that my 540x microscope couldn't see them, in fact I doubt any optical microscope could. Then I started stropping on uncharged leather and saw scratches begin to reappear.

When diamond is used on a wood substrate the grit embeds quite deeply. Maple and especially cherry need a lot of diamond paste to work well. Boxwood was a lot better and didn't absorb nearly as much paste.

Leather would allow abrasive to sink in quite deeply so that the effective grit size would be smaller than the actual grit size, but leather seems to have abrasives of its own. My real objection to stropping on leather is the dubbing it causes at the edges.

Here's a link to an image that sums up my experiment using boxwood and uncharged leather:
http://bladetest.infillplane.com/StroppingTest.jpg

 

[matthewwh]

I notice he didn't test neat chromium oxide.....

Starting with a blade honed to 0.5 micron I would expect to find the same results as Brent did - the compounds that he tested made things worse.

Indeed, straight Chromox at 0.3 micron would also have a minimal effect on a blade that has been honed to that standard, I doubt it would worsen the situation but any improvement would be so marginal it wouldn't be worth talking about. The point of stropping is that it is fast and smooths out irregularities at the edge. A freshly honed edge of that quality has no irregularities so there is nothing to strop.

In a way it's like a microcosm of the secondary bevels argument, (if you can get ten fresh edges by honing a tiny secondary bevel between grindings why would you waste steel by taking a tormek to the edge every time.)

There are two assumptions at work that I believe have caused Brent to reach the conclusions that he has.

1. If any wear bevel is present the tool is no longer sharp.

2. Wear bevels are the same all the way along the edge.

Taking the first assumption I would suggest that wear bevels begin to develop from the second the blade enters the wood. Given that you are able to make a second and third cut without honing there must be a degree of wear that is acceptable - a tolerance.

Now remove the assumption that wear bevels on an edge are uniform: why would they be, wood isn't uniform and if you are anything like me you hang a corner out here and dig one in there to get the timber the way you want it).

A quick stropping will bring the irregular edge closer to the uniform, even wear bevels that you would get if you extrapolated Brent's diagrams along the entire edge. Under lab conditions a blade with any wear bevel seems like exactly the situation we are trying to avoid, but in practice a smooth evenly worn edge will still cut and will cut better than a ragged one. Up to a point an edge will come back to you (or move further inside it's working tolerance) with a quick stropping. Once the wear bevels grow to the point where they are outside tolerance, honing is the only medicine.

I never thought I'd be arguing in favour of freehanding a rounded bevel but for managing the condition of the last 1/100th of a mm of steel I believe it is more viable than doing nothing.

 

[Derek Cohen (Perth Oz)]

I think that stropping has its place. It is not a replacement for traditional methods when those methods are readily available. I rarely use a leather strop anymore, but this is because it is not necessary to do so as I have a dedicated sharpening station alongside my bench. It is, in fact, easier to use a ceramic waterstone, such as a Shapton, at the station than pull out a leather strop from under the bench and find a spot on the bench to use it.

There is evidence that a leather strop can degrade a bevel's sharpness. There are a few issues that this finding raises:

(1) Should this be interpreted as a criticism of the honing compound, or of the compound substrate? I resist using MDF as it contains impurities that are released and contaminate the honing process. Leather, even horse butt, is soft enough to alter the angles as well as containing its own contaminants. Hardwood seems to be a better choice, but some contain a high degree of silica. Now what does this say about plain leather?

(2) One does not throw the baby out with the bathwater. If stropping does nothing for an edge that comes off an 8000 grit waterstone, it still can do a lot for an edge that comes off a 4000 grit waterstone, an extra fine (1200 grit) diamond stone, or a 2000 grit oilstone.

(3) The resultant dubbed edge off leather is not the same as a dulled edge. It is not rounded. It is, instead, given the equivalent of a tapered micro bevel. This is still sharp (look at the recent interest raised in the sharpening method of Paul Sellers and our own Jacob).

(4) There are some blades that are not negatively affected by a tapered micro bevel and for which there are few alternate methods of sharpening, such as carving blades.

There are modern alternatives to the traditional leather strop now available: diamond paste on cast iron and diamond film on glass or a wooden form. I have a little on diamond film here: http://www.inthewoodshop.com/WoodworkTe ... dFilm.html

Regards from Perth

Derek

 

[David C]

I do think it is important to keep in mind, that the fine "stones" used by Paul Sellers and Jacob are around 1,200 grit, and their edges will certainly benefit from some improvement.

Hard Arkansas used to be considered extra fine, or "surgical". However it is not in the same league as 0.5 miicron film or paste. So we have two scenarios which bear no relationshio to each other.

best wishes,
David Charlesworth

 

[David C]

My local saddler told me that untreated leather was abrasive!

David

 

[Jacob]

I do think it is important to keep in mind, that the fine "stones" used by Paul Sellers and Jacob are around 1,200 grit, and their edges will certainly benefit from some improvement.

Could be sharper yes - but not necessarily worth the time and effort, depending on the job in hand, bearing in mind that very sharp edges are very quickly blunted. I do find myself going on to a finer stone when needed, and occasionally stropping too. It's all a compromise.
NB Paul Seller's 3 diamond plates idea is very very quick and good enough for almost everything.

Hard Arkansas used to be considered extra fine, or "surgical". However it is not in the same league as 0.5 miicron film or paste. So we have two scenarios which bear no relationshio to each other.

best wishes,
David Charlesworth

Neither of these are much use to woodworkers. Surgeons and Barbers perhaps, oh and sharpening enthusiasts of course. :lol:

 

[Jacob]

.....
I never thought I'd be arguing in favour of freehanding a rounded bevel........

Glad to hear you are getting there, albeit slowly!
It's only a few woodworkers who have this modern phobia about rounded bevels. They were normal - and still are in many other areas of sharpening.
I think the phobia is a good example of the "viral" dissemination of misinformation.

 

[shim20]

i sharpen free hand, way i was tort and its the way it was done years ago, i do it little and often only takes a little time that way, i often just buzz over on a medium then fine oilstone. i tried waterstones but at work i found them to messy, as for strops i do have a bit of leather on a block but most the time i don't use it, my 2ps worth :lol:

 

[woodbrains]

Hi,

Putting a tiny (rounded or not) microbevel at the tip of the cutting tool to eek a little more working time out of a tool before re sharpening, is something we all probably do from time to time. This is not the same as the total bunkam of rounding under, that Jacob continuously prattles on about. Let us face it, the Fine India stone which appears to be his staple, has a grit size of 42 microns. I don't think any reasonable person would even consider that sharp enough for anything finer than an axe. And how anyone can say with any amount of seriousness that a sharper edge just dulls quicker anyway--words fail me I have to say. It is pityful we have to put up with such twaddle.

I don't think stropping is of much use to those who sharpen with waterstones to a fine enough grit or those who use 3M lapping film. Oilstones don't get any finer than about 9 micron (surgical Arkansas) so stropping after these would definitely give a better edge.

I don't buy into the idea that stropping on a cushioned substrate (leather) gives the paste a softer effect, either. 0.5micron chrome oxide is 0.5 micron no matter what it has been coated on to. The idea of the leather is to create a micro bevel so it doesn't take so long to actually achieve a polish with such a fine, cutting abrasive.

Mike.

 

[Jacob]

H.....This is not the same as the total bunkam of rounding under, that Jacob continuously prattles on about.

If you, or anybody else, could explain why "rounding under" is bunkum, I could stop prattling on about it it. But you can't, and neither can anybody else.

Let us face it, the Fine India stone which appears to be his staple, has a grit size of 42 microns

. 1200grit (whatever that means) according to DC see above, but I do go finer if I need to

I don't think any reasonable person would even consider that sharp enough for anything finer than an axe. And how anyone can say with any amount of seriousness that a sharper edge just dulls quicker anyway--words fail me I have to say. It is pityful we have to put up with such twaddle.

Twaddle yourself. Not exactly "dulls quicker", more loses it's uber sharpeness quickly and becomes averagely sharp, which deteriorates more slowly. Thats why if you want to keep a very sharp edge sharp you have to strop very frequently, as everybody knows, except you perhaps.
It might help with these threads if they were labelled either "hobby/enthusiast sharpening" or "sharpening for woodworkers". Several people pointed out in an earlier thread that sharpening is a hobby in it's own right, which creates crossed lines!

 

[Karl]

I think these last two posts demonstrate something fundamental here.

How sharp is sharp enough?

To an extent I agree with Jacob in that as long as the edge does the job, it is sharp enough. I have spent plenty of time putting an extreme edge on blades (particularly for wooden planes), and then losing some of that "ultimate" edge in setting up the plane and taking test cuts! If you're working a plane hard it may need re-sharpening after 10/15 mins anyway, and putting a super-sharp 0.3grit edge on the blade doesn't make any difference to the work in hand. With the exception of smoothing planes, where I tend to go the extra mile as the blade is only used for a few swipes in any event.

For general work, if it shaves the hair on my arm, it's sharp enough - regardless of what the grit says.

Cheers

Karl