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Wood hardness scale?


When I select plywood or hardwood from the materials list in GWizard then pick “more”, it has one entry and the hardness is listed as zero.

I presume GW uses Rockwell hardness for metals.

Can you please clarify how GW relates to hardness of wood species and wood products types?

I found a Janka wood hardness chart here

I am no expert but it appears that the Janka scale is whats used within the wood products industry.

I can see value in GW managing the materials list so all GW users benefit but,

can I add material specs to the list under the more option?


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Best Answer

This has been brought up fairly often, so it’s good to get a chance to put an answer down here for the future.

The relative hardness of metal is much more crucial to successful feeds and speeds than is the relative hardness of wood or plastics.  Yes, there are scales like Janka available, but the hardness of an HSS or especially a Carbide cutter is so much harder than those scales measure that it just doesn’t matter.  There is no material effect on feeds and speeds.

Why then have different categories at all for soft materials?

The answer is that they make chips differently and there are other factors that enter into determine the feeds and speeds “sweet spot” for these materials.  “Hard” vs “Soft” Plastics are industry terms used by the cutter manufacturers that refer to how these plastics make chips.  With “Soft” Plastics, chips can be sliced off cleanly.  With “Hard” Plastics they tend to fracture like glass and turn into dust.  Many plastics melt if they get too hot wild wood burns.  The amount and behavior of sap in wood matters a lot in the decision of “Hard” Wood vs “Soft” Wood feeds and speeds.  Composites like Plywood and MDF have lots of grit embedded that is very abrasive to cutters.  It’s due to how these materials are manufactured.

So, we don’t use Hardness with woods.  We settle for categorizing them into broader groups which is what the various cutter manufacturers do as well.

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