Thread: convex paddle strop - why?

I've just finished getting this this old paddle strop back in shape, and wondered what the point of the convex stropping surface was:



As can be seen, one face is leather, and the other is bowed wood, under tension from an aluminium spring underneath.

Apart from the reason for the convex stropping surface, which I hope someone can explain, I also feel that even if you want a convex stropping surface, this is a funny way to go about it. The springing is strong, so the wooden bow is absolutely solid, and has no flex in normal use. Seems massively over-engineered, is it something designed to catch a customer's attention rather than perform any useful function?

The wooden stropping surface originally had what appeared to be bits of green compound on it, and I did see one other identical strop on eBay Germany on which the wooden bow was entirely green. Sadly I forgot to save the pictures for comparison.

(The wood between the original paddle and the leather is my addition, the original paddle was both badly warped laterally and bowed lengthwise)

Any ideas? Many thanks!

that is odd. does seem to be made that way. I've only ever seen them made flat but with a space underneath the stropping surface to allow for some flex. they do use wood (usually balsa) as a strop with something like Chromium Oxide on it (which would be the green you are talking about) as a pasted stropping surface.

Originally Posted by tintin

that is odd. does seem to be made that way.
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No doubt it was made this way. Damn shame I forgot to save the pictures of the other one I saw, it was in much better shape. The wood (for the stropping surface) looks like pine or cedar maybe? Light and fairly wide-grained.

This one was filthy and black when I got it, I forgot how black until I dug out this pic:



When I had removed the black, there was green compound in the pattern on the wooden stropping surface.

I found an ad for a T. Reynor convex strop here from 1879. It is the second ad down.

https://www.irishtimes.com/news/offb...-ads-1.3714430

Originally Posted by 32t

I found an ad for a T. Reynor convex strop here from 1879. It is the second ad down.

https://www.irishtimes.com/news/offb...-ads-1.3714430

Very interesting! Shame there is no illustration. I will try to figure out what it might be called in German, and do a web search, given that the two examples I've seen have been in Germany.

With respect to the function, I tried stropping a blade on it. It probably won't be much practical use to me for two reasons; firstly, because despite my best efforts to clean the wood, quite a lot of abrasive remains, and it is too coarse to be useful for me, and secondly, historic nicks in the wood mean it is tricky to come up with a stroke with covers the whole edge on the return stroke.

Having said that, trying it out suggested two possible reasons for going down the convex road. The first is that the convex surface means you are always stropping 'into' the strop, and it seems to be much harder to lift the spine when stropping with this strop. Another idea is, given that there was undoubtedly a relatively coarse compound on the strop, maybe it was intended to create an ever-so-slightly concave bevel, so that stropping on the leather would have been focussed on the edge and not the whole bevel.

In the add it says good for gentlmen that live in the country that find it hard to have their razors sharpened. Does that mean honed? That would explain the course compound.

A few thoughts I have had without holding it.

Would you strop away from you on the side nearest you and to the top and towards you on the other end. Never going over the top/apex.

If you went relatively slow and kept the spine on the surface it would keep the same arc as advertised for the "special" hollow ground blades.

This one seems a little weird even to myself but what if you put the rounded side on a table and only used the leather side. If the spring was right it would limit the pressure that you would be able to exert while stropping. I am thinking this is wrong because it doesn't look like the spring side is variable pressure.

It would be fun to hold one in my hand!

Originally Posted by 32t

In the add it says good for gentlmen that live in the country that find it hard to have their razors sharpened. Does that mean honed? That would explain the course compound.
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I found this picture on the web:



I assume that the case is for the paddle-style strop, so when we see 'convex strop', it doesn't necessarily refer to the same style as the one I have, it seems some strops were convex laterally, not longitudinally as with mine.

Originally Posted by 32t

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Would you strop away from you on the side nearest you and to the top and towards you on the other end. Never going over the top/apex.

If you went relatively slow and kept the spine on the surface it would keep the same arc as advertised for the "special" hollow ground blades.
...

I guess you could do this, though I'm not sure why. The curve is constant, obviously, and the strop is not that long, leather stropping surface is 22cm, the wooden one a centimetre or so less.

Originally Posted by 32t

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This one seems a little weird even to myself but what if you put the rounded side on a table and only used the leather side. If the spring was right it would limit the pressure that you would be able to exert while stropping. I am thinking this is wrong because it doesn't look like the spring side is variable pressure.
...

The wood and the aluminium combine to make the whole thing pretty rigid, the pressure of stropping certainly doesn't flex the bow.

I spent and hour and a half going through completed listings on eBay trying to find the other one I saw, it wasn't that long ago that I saw it, but no joy...

Originally Posted by Montgomery

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With respect to the function, I tried stropping a blade on it. It probably won't be much practical use to me for two reasons; firstly, because despite my best efforts to clean the wood, quite a lot of abrasive remains, and it is too coarse to be useful for me, and secondly, historic nicks in the wood mean it is tricky to come up with a stroke with covers the whole edge on the return stroke.

I decided to re-appraise this conclusion, and cleaned up both the leather and the wood:



The leather was lightly dressed with neatsfoot oil, and after a few days to soak in, it was lightly sanded with #600 wet and dry (to smooth one part of the leather which was snagging a microfibre cloth), cleaned with chamonix milk, and given the tiniest smear of a quality wax polish. The wood was just sanded with #180 sandpaper.

I then tested both surfaces with a razor on which I had polished the bevel, following the method laid out by @Euclid440

Originally Posted by Euclid440

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You can also test for grit by stropping a polished bevel and see if it scratches the bevel
Polish a bevel with a good metal polish. Make a paddle strop from a piece of cardboard, inside of a cereal box. Paste 3-inch X’s, 3 inches across one edge, then strop a razor or knife bevel on the edge of a table or workbench.

About 100 laps will remove all the visible stria from the bevel of an 8k edge. 60-100x magnification will help, a Carson MicroBrite 60-100 scope is $10-15.

...

Though the leather looks great, and is very slick, which I like, there are still fairly coarse abrasive particles in the surface, which appear to be coarser in comparison with my Herold green pre-pasted loom strop.

The sanding does however seem to have taken the coarse abrasives off the wood, which now leaves only very fine scratches on a polished bevel.

So, it seems I can paste the wooden side. I could paste with a Solingen green paste, though I don't have any and don't find this to be an essential paste. On the other hand, I recently started using Solingen red paste, which I find useful, and currently only have a fabric hanging strop with this on. Then again, would red paste really allow me to fully explore the possibilities of this strop? I could also experiment with how to take advantage of the curved stropping surface, and try a coarse paste with razors with a wide-ish bevels, to test the idea that a coarse compound on a convex surface would create a concave bevel, which would focus subsequent stropping on the edge.

I have several options for the leather side:
-sand/scrape the surface of the strop to create a napped finish and hopefully get rid of the abrasive particles, then paste with a known paste (maybe Solingen red, and paste the wooden side with Solingen green, as above, which would be an occasional refresh or post-honing strop)
-replace the leather with a new piece, and use unpasted (and possibly paste the wooden side with red paste, which would make a useable travel strop); the downside is that it disturbs the integrity of the piece (!)
-leave it as is, because it looks so good and is so tactile
-paste it with a coarse paste like Solingen green

The most useful idea seems to be paste the wood with Solingen red paste, and put a clean piece of leather on the other side.

Ideas welcome!

I would paste it as close as possible like the green to keep its originality.

Try it and if you don't like it either don't use it or sell it to some one that likes it.

By the time you put new leather and wood on it etc. you might as well make a modern version of it.

Hmmm... food for thought, thank you! I could always try it with red, and put green on afterwards if I don't like it.

As you rightly imply, we have already moved quite a way from the original, we will end up in a situation like Trigger and his broom...

https://youtu.be/56yN2zHtofM