softwood strop question

[forrestdweller]

inspired by some recent threads i'm planning to make a softwood strop. yesterday i harvested a piece of balsa (presumably part of a raft discarded by locals) when walking the beach with my little friend Biscuit. today i started processing it BUT that stuff is that soft that i easily can depress the surface with my thumb which makes me wonder how long it will stay nice and flat (even) and if something slightly harder might be better...
unfortunately i've no way to (scientifically) determine hardness other than the "thumbnail test" used to determine it a piece of wood is suitable for friction fire -- would this work as a guideline?!

 

[Robson Valley]

The essential concept is a base platform which is smooth and hard. Balsa isn't.
Leather on wood was the only smooth, flat material for centuries. Leather is none too hard as well.
Now, anything hard and flat will do as the base. I use offcuts of granite kitchen counter top. Sheets of modern float glass, sticks of laminate flooring. All sorts of diameters of dowels and tubings, even a tennis ball for my elbow adzes. Just as long as the material is hard and smooth, I'll consider wiping $50.00 - $100.00 carving blades on it every 20-30 minutes to keep them carving sharp.

 

[forrestdweller]

thanks, that makes my quest for a solution much easier

 

[Robson Valley]

Next thing, is to select some sort of honing compound. They are all abrasives with very fine particle sizes. All steels are soft and pliable at very thin edges. That is a physical fact that many will try to deny. They are wrong.

The essential concept is to prepare a fine edge for the task but with enough steel for support behind that edge to keep it from folding over. That will be visible as a reflective surface under a very hard light, such as a focused LED.

Chromium Green (CrOx) is a green color and the trade polishing standard has a nominal particle size of 0.5 micron. Aluminum Oxide (AlOx) is snow white and trade usually sells the nominal particle size of 0.25 micron. I buy solid waxy bars of a mix of those two.

You can buy 40 bazillion grit stones from strange places on earth and they are all a waste of modern money. Back in their day and time, they were of extreme value and importance. No more.

I carve mostly western red cedar here in the Pacific Northwest. Most of my tools are adzes and double-edged crooked knives which I have built up from buying or repurposing the blades. My strops are any old hard tube thing. No leather. I like 4" x 6" office filing cards with CrOx & AlOx scribbled all over it and wrapped around.

I lay those out flat to tune up any of the 5 cleavers which I have in my kitchen for 40+ years.

If you got this far, you're in for quite a ride, exploring steels, honing compounds, strops and successful edges in woods. I'm done. I have a path to follow that I need not think about any more. It works. There are maybe 5-6(?) other techniques to putz around with.

 

[C_Claycomb]

I am not sure, but my reading of RV's first reply sounds like he is saying that balsa is unsuitable for a stropping surface.

For a strop I disagree with the statement that "The essential concept is a base platform which is smooth and hard. "

Stropping by definition requires a soft surface. Lapping uses a hard surface. Both can produce sharp polished edges. This subject is a spectrum, not a single case since it ranges from mechanical burr removal without abrasive (stropping on the palm of ones hand) to edge polishing with abrasive, from heavy convex forms to dead flat (which is what RV is describing very well).

Balsa could probably be used as is if acquired in a thick enough section, I would think it would need to be over 1 inch. In the commercial model making stuff that is sawn to thickness, a 10mm slat is glued to a plywood or similar backing to give it support.

Whether the surface of the balsa compresses and dishes with use and whether this matters are two related but separate questions. I use my balsa strop for plane irons and chisels, these are straight edges and what load there is is spread across a fairly wide front in most cases. It is good for the surface to remain flat. If the surface gets dented and grooved I can sand it flat with good resin bonded 60 grit paper on a glass sheet without much fear of the balsa picking up large grains. For a knife strop, there is more chance of the surface being compressed from the narrower pressure on a knife belly, but in most cases knives are less fussy about dead flat surfaces, unless one is going for super flat carving blades.

If the aim is to have something that will do a similar job to a wood-backed leather strop for knives, then a bit of denting on the balsa surface is of no real significance.

 

[tombear]

I'm having good experiences with the lime/linden/ basswood backed on to a big lump of oak.

I'm going to make a bigger version with a handle underneath when have a new blade on the bandsaw or become less lazy. Once it's glued together I'll true up the limes surface with a sheet of sandpaper taped down to the big piece of tin float glass I scrounged for smoothing out the bases of planes I've restored. The 3 inch wide version is fine for 90 % of my sharpening but on occasion bigger will be better.

ATB

Tom

 

[forrestdweller]

I'm having good experiences with the lime/linden/ basswood backed on toast big lump of oak.

I'm going to make a bigger version with a handle underneath when have a new blade on the bandsaw or become less lazy. Once it's glued together I'll true up the limes surface with a sheet of sandpaper taped down to the big piece of tin float glass I scrounged for smoothing out the bases of planes I've restored. The 3 inch wide version is fine for 90 % of my sharpening but on occasion bigger will be better.

ATB

Tom

thanks for the replies everyone -- learned something new again

it was tombear's other thread which brought me to this idea -- leather is a bit tricky to obtain around here + tropical rainforest isn't the best climate for it, therefore my plan to use softwood instead....
i started processing a piece of the balsa i brought back from the beach yesterday afternoon, but sanding it lengthwise (both #40 and #120 grit sandpaper) removed fibres from the surface and just handling it resulted in dents in the surface, hence my question. i know someone who has a small woodworking shop (so "milling" a piece nice and flat isn't a problem once i'm past the experimental stage), he also rides a Harley so CrOx/ AlOx should be easy to obtain

 

[demographic]

Some woodworkers/woodturners use MDF scraps as strops.
Some just use a flat bit for plane blades and some glue a few bits together then turn a circular bit.
It holds honing compound and its cheap.

 

[Stew]

My wicked edge sharpener has balsa strops....

 

[FerlasDave]

Balsa wood makes for an excellent strop. Just add some compound into the grain of the wood and it will do well, I probably would use a planed section as sanding would likely clog the soft grain. It really doesn’t matter if it’s flat for a knife edge anyway.

 

[Kadushu]

I've stropped on the palm of my hand. I suspect balsa is harder.

 

[Robson Valley]

Let's agree to disagree. I am not willing to alter a technique for putting carving-sharp edges on gouges, adzes and crooked knives. Running $50 - $100 per blade for me to haft, I won't ruin any of them on soft strops. I abandoned my good leather strop more than 10 years ago when I could see it rebounding and rounding the steel tool edges.

 

[C_Claycomb]

Let's agree to disagree. I am not willing to alter a technique for putting carving-sharp edges on gouges, adzes and crooked knives. Running $50 - $100 per blade for me to haft, I won't ruin any of them on soft strops. I abandoned my good leather strop more than 10 years ago when I could see it rebounding and rounding the steel tool edges.

No one is trying to get you do do anything different.

What I am disagreeing with is what I see as your "this is how I do it, so this must be the one and only way that is best for all people, everywhere in the world, all the time" perspective on the matter. This does appear to be a theme with your advice. Maybe this isn't your intent, but it is how the posts come across.

Soft strops do round the edge with use. That is kind of the point and reason for using a soft strop. For most people for it to become noticeable it needs to be repeated use, not just two or three times between sharpens. Softer strops are more forgiving of angles, they remove burrs from coarser grits more readily and they tend to convex the edge which is often seen as good for a good compromise between strength, finish and angle.

If you are finishing to high grit anyway, want to maintain an angle for precision craft work and can hit your angle easily, say with a wide bevel and long practice, hard backing works better to maintain the edge.

 

[TLM]

Most tools are clearly softer than knives that also makes a difference to how they are sharpened. I don't do any stropping to my knives but then I don't shave with them.

 

[Robson Valley]

I am very happy to share a technique which consistently holds carving sharp edges. Some other techniques, I have never tried. Some I have abandoned, such as water stones, leather strops and diamond plates.
If you're still exploring technique to find a method which is fast and effective in your shop, try them all.

 

[forrestdweller]

small update: i split some of the balsa into thin boards and after a few days of sunshine and lower humidity they've dried up and gotten a bit harder, so i can't put dents into the surface with my thumb anymore. means now they look more suitable for my project

 

[Robson Valley]

Good stuff. Putz around with it for results. Have another rock hard strop (glass/plastic/wood flooring, etc) for comparison. I need to use rods and tubes like copper and aluminum pipe.

Buy good honing compound. Most use green Chromium Oxide for the basic bulk. No, it never needs to be spread absolutely evenly. Your honing strokes cannot be exactly repeated.

Industrial supply houses here sell CrOx as a polishing compound. It's a fine abrasive, you can't see the scratches so the surface looks shiny. The better ones have more predictable control over the nominal particle size. So, you can get a sense of predicting the honing results.

 

[C_Claycomb]

Interesting examination of the effect of strop material

The Pasted Strop – part 3

In the previous installment of this series, it was shown that (sub-micron) abrasive stropping produces convexity in the last few microns of the edge; this result was defined as micro-convexity. In…

scienceofsharp.com