How does wood dull steel?

[Jamie Buxton]

So here's a question to ponder...

Exactly how does wood dull steel? Steel is much, much, harder than wood. Yet somehow that soft stuff manages to dull a steel edge. Consider a hand plane, planing some nice clean (that is, no included grit) piece of lumber. Sharpen that blade to a surgical edge, plane for a while, and the blade is dull. What is happening here? Is that nice soft wood managing to rub metal atoms off the blade? That seems pretty unlikely -- except that the blade tip does wear away.

[Kevin Gerstenecker]

Jamie, that is an excellent question.......you should win a prize or something! Wood dulls wood pretty much the same way grass dulls a lawnmower blade..................Silica. Wood contains silica, just like a blade of Turfgrass does. There are other things involved as well, but the biggest culprit is the Silica Content of a given wood species. Some wood contains a higher content of Silica, that is the reason that some woods will dull cutters very quickly. Some Exotic Species are loaded with Silica, and they can and will dull a cutter QUICK.

(Build up of pitch and sap can cause heat build-up, which can attribute to the blade losing it's edge prematurely as well. It pays to keep 'em clean.)

[Dennis Peacock]

Well....I can't add to what kevin said.....he summed it all up in a nut shell.

Good job there Kev.!!!!

[Alan Tolchinsky]

Jamie, that is an excellent question.......you should win a prize or something! Wood dulls wood pretty much the same way grass dulls a lawnmower blade..................Silica. Wood contains silica, just like a blade of Turfgrass does. There are other things involved as well, but the biggest culprit is the Silica Content of a given wood species. Some wood contains a higher content of Silica, that is the reason that some woods will dull cutters very quickly. Some Exotic Species are loaded with Silica, and they can and will dull a cutter QUICK.

(Build up of pitch and sap can cause heat build-up, which can attribute to the blade losing it's edge prematurely as well. It pays to keep 'em clean.)

Kevin, Thanks for that info. I didn't know that and always thought it was just the hardness of the wood that dulled blades etc. But silica makes sense since wood is softer than metal and wouldn't be responsible for dulling by itself. There had to be another culprit. Thanks Alan

[Kevin Gerstenecker]

Your welcome Alan. Wood Density does play a part..........but generally, the harder the wood, the more Silicate content. Abrasive stuff, that Silica. Just imagine trying to cut your grinding wheel with your nice Forrest Saw Blade! That of course is an exaggeration, but you get the idea.

[John Miliunas]

Hey, "thanks" to both, Jamie and Kevin! A very worthy inquiry with a fascinating answer! I was aware of silica content in some of the exotics, but never gave it much thought to all woods having it as part of their makeup. Very interesting, but no, I'm not switching to 100% Pine!

[thomas prevost]

Kevin is right on the money. Ask any sawyer about silica. But for most of us it is heat build up due to resins in the wood adhering to the blade. You will notice that pine, spruce, and hemlock dull faster than oak or cherry. Thus, keeping a blade clean not only keeps wood from burning but also adds life to the blade as it runs cooler.

[Dale Thompson]

Silica is common in sand, quartz and other mineral stuff. I know that for a fact because I once took a tourist boat trip on Lake Superior. It was along the north shore of the Upper Pennisula of Michigan. The beaches are pure sand (silica) and the winds can become very strong. One of the things that the Captain emphasized was that the winds from "Superior" are strong enough to pick up the sand from the beaches and blow it into the trees with such force that they become part of the the tree. The local lumberjacks then harvest these trees and turn them into sandpaper.

That story sure made ME a believer! Would a Captain LIE?

I alreddy new dat i wus a inteleckchual tipe. Kevin jus PRUVED it!

Dale T.

[Jamie Buxton]

Jamie, that is an excellent question.......you should win a prize or something! Wood dulls wood pretty much the same way grass dulls a lawnmower blade..................Silica. Wood contains silica, just like a blade of Turfgrass does. There are other things involved as well, but the biggest culprit is the Silica Content of a given wood species. Some wood contains a higher content of Silica, that is the reason that some woods will dull cutters very quickly. Some Exotic Species are loaded with Silica, and they can and will dull a cutter QUICK.

(Build up of pitch and sap can cause heat build-up, which can attribute to the blade losing it's edge prematurely as well. It pays to keep 'em clean.)

Hmmm....how does the silica get inside the wood? (Disregarding Dale's special case of gale-force winds on the Great Lakes!)

[Kevin Gerstenecker]

Jamie, I just KNEW someone was gonna ask that. Without digging thru volumes of my Horticultural Text from my College days, I do remember this much. The earths crust is made up of many elements, of which one of the abundant ones is Silica. If memory serves me correct, it has to do with the content of silica in water, and soil, which is then stored in the pores of the tree structure. Petrified wood is petrified due to the presence of Silica. The reds, pinks and browns you see in petrified wood is cause by other minerals, like Iron. Thus, one of the big hazards of Saw Dust is the Silica content that gets into your lungs thru the microscopic dust particles. The body can expel larger particles of dust, but not the harmful small ones. It is similar to Asbestos, in that it just stays in your lungs. Silicate is very harmful..........check out the warnings on a bag of Silica Sand used for sandblasting, or the MSDS for the same. BAD STUFF..............wear a respirator when woodworking..............it is no joke. I hope that sheds some light on where the Silica in wood comes from.............that's the best I can do for ya off the top of my head!

[David Rose]

I think Kevin is right. It doesn't enter the tree in the form of sand. It is the mineral silica disolved in the water. Have you even seen mineral rich water build up in a dog water pan or a pipe? It is not in solid form when it travels. The evaporation allows the sediment to resolidify.

I've followed the magnified pics of hand plane blades with interest. The molecules of steel actually seem to flow from the thin edge to areas behind the edge thickening them while rounding the thin edge. I guess that is an abrading effect too.

Now can we get to a more serious question? Do any of you believe Dale? As he said I'm sure that his Captain would not lie. The problem is in the fact that it came FROM the Captain THROUGH Dale. Or did it? How do we know? Has anyone seen any of Dale's Lake Superior sanding blocks? I didn't think so. I mean... I would NEVER accuse Dale directly of doing anything wrong. Indirectly? You decide!

David

[Dan Stuewe]

So do I have silica in my whiskers? Or is it just a ploy by Gillette to get me to buy more razors and I could be using the same one I first used in High School? Or maybe we should all get plastic cutting boards so our knives won’t dull when cutting meat on a wooden cutting board (vegetables on the other hand probably have the same dulling properties as wood).

Sorry for being a bit sarcastic, and I sure that Kevin’s explanation is a big key, but I don’t care what you make the blade out of, it will get dull no matter what you use it to cut. Sharp is a pretty precise thing. I think the difference between what we would consider a sharp blade and a dull one is pretty small (a dull blade still cuts, just not a well). In other words, it doesn’t take much to dull a blade made of the strongest or hardest metal.

I believe I read in Lee’s book on sharpening that if we were able to get a blade to the ideal perfect interface of two planes, the blade would never dull. But since we can’t get there, the edge will eventually degrade and not be as sharp.

[John Christiansen]

So do I have silica in my whiskers? Or is it just a ploy by Gillette to get me to buy more razors and I could be using the same one I first used in High School? Or maybe we should all get plastic cutting boards so our knives won’t dull when cutting meat on a wooden cutting board (vegetables on the other hand probably have the same dulling properties as wood).

Sorry for being a bit sarcastic, and I sure that Kevin’s explanation is a big key, but I don’t care what you make the blade out of, it will get dull no matter what you use it to cut. Sharp is a pretty precise thing. I think the difference between what we would consider a sharp blade and a dull one is pretty small (a dull blade still cuts, just not a well). In other words, it doesn’t take much to dull a blade made of the strongest or hardest metal.

I believe I read in Lee’s book on sharpening that if we were able to get a blade to the ideal perfect interface of two planes, the blade would never dull. But since we can’t get there, the edge will eventually degrade and not be as sharp.

Finally! The other half of the story.

Sure the Silica content in wood will dull an edge. But it does it by erosion. The removal of metal molecules. Any substance harder than the cutting edge of the tool will do this.

But there is also the simple dulling of an edge by the movement of molecules. If you continually bombard a steel edge with anything, I don't care if you use wood, paper, water, air, or tomato soup, you will eventually move the molecules in that edge to a point of "dullness". Dull and sharp being arbitrary terms, the fact remains that all molecules move. Some molecules need nothing more than gravity to change position, others need a little more persuasion.

I can't go into greater detail, because, well, I'm 50 some years old now, and all that junior high science stuff has for many years now eluded my mental filling system.

[Dale Thompson]

Hi folks,
This thread has been ANYTHING but DULL. In fact, it has been very informational. Thank you all!! As you know, intelligent conversation confuses me so I have spent the last day or so watching the CARTOON Channel.

The "Silica Theory" is indisputable because it is proven science. In essence, it the reason that steel cuts wood. Science is a funny thing. It says that a solid steel bar will float - in a pool of Mercury. It also explains why boulders "float" to to the surface of farm fields. Some soils are denser than rock.

The "Erosion Theory" is also indisputable. If you doubt it, explain to us how the Colorado River created the Grand Canyon.

GREAT WORK, GUYS!!

David is my only problem. In response to his comments, my tan sanding blocks come from sand impregnated Maple. My emory sanding blocks come from impregnated Black Walnut, etc., etc.. I just spend a buck two seventy-five to sharpen my chain saw chain and head for the Upper Pennisula. I can get all the sanding blocks that I want just from free "fallen" trees.

I don't know why David is the only one on this entire forum who questions serious science. Though he is in total "denial", let's all continue to encourage David to seek the psychiatric "restructuring" which he obviously needs

Dale T.

[David Rose]

Dale, if I am your only problem, you have given me a great load to bear. Most of us have way more than one problem, and you should too. I'll do my best "for" you, but...

If you plan to chainsaw many sand filled block, be sure to take extra files and maybe a few spare chains. Try sanding a piece of wood then hitting it a lick with a freshly sharpened plane.

Dale, I am impressed that you think I am smarter than anyone on the forum, but sir! that ain't at all so! I do deny that with all my heart. I am by far one of the least knowledgable here. Or was that merely a suggestion of getting a frontal lobatomy? My personal molecules resent being moved around that much.

David