Leather strops versus balsa wood strops

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Khromo

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I have been making strops using leather belt blanks for some time. I usually use the smooth side, and I have charged the strops with diamond compounds from 10 down to 1 micron. I attach the leather to an MDF or plywood panel with double-sided carpet tape. The results have been pretty good, offering up brilliantly polished bevels and freehand BESS scores below 150.

I have noticed that the surface of the leather is rarely flat, with some surfaces never touching the blade. I tried to level one with sandpaper on a flat surface, but that didn't work so well as the leather didn't seem to be firm enough to take a level surface. I realize that doesn't make much sense!

I recently cobbled together a few strops using balsa wood and the same polishing compounds, and the surface can be leveled much better than leather. The balsa seems to be more firm and less likely to wrap around the apex if I get too enthusiastic and apply too much pressure. I'm thinking the balsa looks like a better alternative than the leather overall. The results are encouraging so far.

I would like to get more educated on the advantages of one over the other! Please offer suggestions and comments! I need all the help I can get!
 
It's not advantages over each other. It's two separate tools. That do two jobs.

The harder the strop. Then less deflection it will have as it moves across the blade edge. Hard won't push against the burr as much as soft. Oak, basswood, balsa, all have a different compression.

Let's say you've sharpened an edge to 1000. Then go to 2000. Well, 2000 is the hone. You've formed a micro burr. Leather has enough flex to where it'll push against the burr. Breaking it off. Now you have an edge with tiny serrations from the burr separation.

So if you want to micro hone that micro edge. You use a wood. You can go from soft to hard. Start with balsa and end with oak.

Then again, you can do the same with leathers. Cow is more spongy then horse. Kangaroo, I believe, is somewhere between the two.


It all boils down to how the strop material deflects at the very apex of the edge.
 
Consider basswood. It holds up much better than balsa when used with knives. I do like balsa for razors, if I'm refining with diamond paste before the mandatory stropping on unpasted leather.

My favorite knife strops, though, are kangaroo leather, which is thin and tough, and Nanohone's strange diamond resin stones. I use the kangaroo, unpasted, on simple carbon steel knives, and the Nanohone 3 micron on stainless and hard-carbide steels.

I have leather strops that are very flat, so there must be some maker's trick to accomplish that. I don't know what it is.
 
Balsa seems to imbed compound much more readily than leather will, and in a very dense application. Net result is, it can be a very fast, aggressive polisher. The evidence of how fast it can be is seen in how quickly a balsa strop will blacken when used with compound. All that black stuff is the metal swarf being removed from the bevels. Balsa is more needy for maintenance & upkeep, as it can use periodic cleaning to remove the accumulated swarf, and also because it's soft enough that the surface can become dented, cut or otherwise less than perfectly smooth & flat. A small hand plane is an easy way to shave off a thin layer from the top, down to clean wood, and also making it flat & smooth again for a reapplication of compound.

Can also get similar results to balsa by using a fabric strop with a hard or firm backing, such as denim or linen over hardwood. Again, the fabric will take and hold a very dense application of compound. So it'll also work very fast as a polisher. If you like polished convexes, this works very well.

I tend to feel that leather is best used without compound, or with a very minimal application of it. Use it mainly for the very last fine touches to the apex, for the sake of aligning a shaving-sharp edge and for cleaning up loose remnants of burrs. If you prefer to preserve a toothy bite in your edges without overpolishing it away, this minimalist approach will help with that. Balsa and other wood strops work very well for polishing though.

So, each type of strop can fit into a particular niche, depending on what you're aiming for in results. As mentioned earlier, each type of strop is a different tool for varying purposes. Doesn't necessarily imply that one type is better than another, but rather which is best suited to give you specifically what you're looking for.
 
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Khromo said:
I would like to get more educated on the advantages of one over the other! Please offer suggestions and comments! I need all the help I can get!
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It sounds as if you've already considered all the basics. I have a few strops made of a variety of materials, but the couple that I use almost exclusively are home made experiments. I was thinking of getting some balsa. Since I'm impatient and didn't want to wait, I found some paint stir sticks in the garage. I cut them up and made a couple strops. They worked so well that I forgot about getting real balsa, and I quit using my other strops.

P.S.
Sandpaper will contaminate your strops. Be careful with that.
 
If sanding leather, use a coarse grit and DON'T use SiC sandpaper.

Something like 100 grit or so, in sandpaper made for wood using garnet or aluminum oxide grit, will easily work for that. The garnet or AlOx grit is large enough and resists breaking down. So if any comes off the paper, it won't imbed and it'll be easy to detect and clean up from the leather - you can actually feel it with your fingertips and brush it off. It doesn't present the same risk for imbedding and contamination as would a SiC grit, which is friable and breaks down into fine dust, and would be much more difficult to fully clean from the leather.

The above is how I cleaned & resurfaced my own homemade strop blocks, when I was using those. It worked well and was very easy. Leather sands very easily with the coarse grit and a very light touch. No need to use pressure at all. Wrap the paper around a small sanding block and just brush the surface with that.
 
Khromo said:
I recently cobbled together a few strops using balsa wood and the same polishing compounds, and the surface can be leveled much better than leather. The balsa seems to be more firm and less likely to wrap around the apex if I get too enthusiastic and apply too much pressure. I'm thinking the balsa looks like a better alternative than the leather overall. The results are encouraging so far.

I would like to get more educated on the advantages of one over the other! Please offer suggestions and comments! I need all the help I can get!
Click to expand...


Well f🤬king duh! 🤣 You will tend to convex your edge less with something firm as opposed to something which gives. Leather is softer, wood is firmer. If you push down hard on a soft material then you are guaranteed to convex your edge because the soft material will contour itself around the edge and cause that edge to become more rounded.

If you actually want to convex your edge then leather is great. However, wood is better if you want more control over whether you want to keep your edge straight or convexed depending on how you strop it, because wood is more rigid than a piece of leather.

Am I wrong in thinking that this should be obvious?
 
Obsessed with Edges Obsessed with Edges , thank you for your very informative post.

I have a balsa block strip that is in need of cleaning and refinishing, but I am using it with the cheap wax based stropping compounds and I don't plan on running a hand plane through that mess.

I guess I am planning to wipe off as much as possible, an try a hand plane or sand paper on my flat surface. 100, 150, 220. And see how it comes out.

I have found that some of the balsa grain is softer than other parts, so the surface does get worn in funny patterns, and the waxy build up adds to the problem.

However, it has worked well for me for the final sharpening step after the dmt green sharpener, which is still a bit course, even for my working edges.
 
There are obvious differences in hardness which theoretically do different things. In practice, I get better results with leather, so I generally use leather. I prefer a hard leather, but not rock hard. I like suede for 3-7 micron compounds and smooth for finer grits. I believe it's mostly down to one's individual technique and preferences. But before you give up on leather, I would buy a dedicated leather strop, because belts are really designed to keep your pants up, as opposed to honing knives. :p
 
I always thought that's why there's a range of stopping compound. Diamond emulsion.

Softer the strop, the lower the grit. Wider edge pocket knife, cow (600 grit edge). Finer and thinner edge (1000grit with a 2000grit hone) horse leather.

The options. 9 micron to 0.1. Using wood and leather. Cow would do better with 6 or 9 micron. With horse used for 1&3.

0.5 for balsa and 0.1 for oak.
 
Some good info in this thread.

I'll just add that if you start with a piece of leather, you may get better results if you use something like a (clean) heavy roller to compress the leather before affixing it to the base.
 
As far as I understand there is always some 'wrap arround' on micro level when using strops no matter if it's made of hard or soft leather, denim, linen or wood.
You will always get some level of convex edge on the last few microns of the bevel after stropping.
Wood strops have micro fibers on the surface and those fibers make 'wrap around' and remove the burr. Strops were not invented to polish the edge and make it more shiny but to remove the burr.
There is a lot going on on micro level when stropping. Some things you won't be able to see with 30x or 60x loupe or even with optical microscope on highest magnification.
Type scienceofsharp in Google – among other things you will also find 4 articles about strops with photos made with electronic microscope (magnification up to 10000x).
 
You don't need to see pictures of the effect. People have been sharpening things since stone knives. There's nothing new under the sun.

Especially the desire for the sharpest edge. The desire and pursuit for the pentacle of, what we understand, as sharp.

The only thing Scienceofsharp does. Is try to explain out what we do. Why we do it. They're the X-Files of grit pushers.


.....

And Yep, it's all about the deflection of the strop material and how it interacts with the burr. Stop compounds, are really a cutting compound. It's micro sharpening. As people marvel at a 30000 grit stone. That also has deflection. Never comparing it to 0.01 diamond emulsion on oak.

I'm surprised, there's no strop plates made of sapphire. A big slab, of microscopically flat sapphire. The lack of a ceramic plate is also interesting.
 
Ok.... I guess?
No need to see those photos? So, how do you know what's going on when stropping on different strops?
 
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Obsessed with Edges said:
If sanding leather, use a coarse grit and DON'T use SiC sandpaper.

Something like 100 grit or so, in sandpaper made for wood using garnet or aluminum oxide grit, will easily work for that. The garnet or AlOx grit is large enough and resists breaking down. So if any comes off the paper, it won't imbed and it'll be easy to detect and clean up from the leather - you can actually feel it with your fingertips and brush it off. It doesn't present the same risk for imbedding and contamination as would a SiC grit, which is friable and breaks down into fine dust, and would be much more difficult to fully clean from the leather.

The above is how I cleaned & resurfaced my own homemade strop blocks, when I was using those. It worked well and was very easy. Leather sands very easily with the coarse grit and a very light touch. No need to use pressure at all. Wrap the paper around a small sanding block and just brush the surface with that.
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I appreciate the help, David!

As per David's instructions, I got a fresh sheet of AO 80 grit and a flat sanding block, and used very light pressure over the surface of a couple of my used DIY leather-on-plywood strops. Here are the important results.

None of my leather strops were flat. They all had wobbles and dips to the point where a good deal of the surface was not contacting the blade at all. The wood panels were flattened before taping on the leather, so I am convinced this good consumer grade leather is uniform enough for belts and harnesses, but not quite square enough for my strop. You could easily see the low spots after the first few strokes of 80 grit paper.I didn't trust the plywood, but I trusted the leather. My mistake!

The coarse AO sandpaper and a truly flat block handled the task perfectly, leaving a level surface about midway between the smooth side and the rough side of this leather. I tried getting a finer finish with finer sandpaper, but the leather seemed to resist getting any smoother. It feels fine enough, even for 1 micron diamonds. The process was very quick using sharp paper, and as David points out light pressure is key to a flat surface. You don't want to press the leather out of shape, as it will not spring back flat.

I re-surfaced and loaded a couple of strops at 5 and 3.5 microns. Sanding the old, loaded surface off and getting a smooth, flat finish took less than 5 minutes per 10-12" x 3" strop, by hand, using a half sheet of new paper. I used a fresh sheet for different grits, which may not have been necessary.

The solvent based Kent's diamond paste worked into the leather smoothly, probably easier than when loading the smooth side before sanding. I warmed up the leather and the paste in the hot southern California sun. I think the warm paste soaks into the warm, dry leather a little better than it does at room temperature.

Well worth the time. I expect much better results from these strops. I will do this out of the box from now on. Here are the finished products. I should have taken pictures during the flattening process, but I am lazy, disorganized and probably lucky I got as far as I did!

blzQIg3.jpg


My next scientifical experiment will be to compare new, flat strops in balsa and leather, to see if I can get better results on the BESS machine with one or the other.

The LionSteel Roundhead (sharpened at 20 dps on a DMT fine diamond, then stropped at 5/3.5/1) in the photo tests 155-160, I will sleep better after I get it closer to double figures.
 
^^Yes, there's not much need for sanding with fine paper. The coarse paper will do all that's needed, and very quickly.

The finish on the leather will pretty much be limited by the fineness of the leather's fibers when they're newly exposed and lifted by sanding. The leather will have a nice velvety nap to it, after that happens. That's a good thing and will really help the leather take and hold new compound. After some use in stropping, the leather's surface will become smoother and perhaps somewhat shiny as the nap of the leather lays down and becomes more compressed.
 
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