Blade wear advice re cutting jatoba and hickory

[rudy de haas]

So next week I'm starting into the prep work for a major renovation. A big part of this will involve rough shaping a bunch of hickory and jatoba so it can acclimatize for a few months (Lethbridge is very dry) before I finalize things and put it in place. My question is a simple one: is it smarter in terms of minimizing blade wear to make a few big cuts or many little cuts?

The tools have lots of power, hickory splinters if you cut too deep, but both woods will take 3/32" cuts with the grain. To minimize the number of blades I use, do I set for a bit less than 1/16th and cut many times or set for a bit less than 1/8th and cut about half as many times?

In this context my time is "free" - but blades are not.

[Jamie Buxton]

I take it that the blades you're talking about are planer blades, right?

As far as I know, blade wear isn't related to how deep you cut. If you have multiple feed speeds, you get less wear at the faster feed.

[Bill White]

I ALWAYS take light cuts. Don't know about the wear factor, but it keeps the tear out to a minimum.
Bill

[glenn bradley]

I'm with Bill. I would always make a few more passes (even if it is a few more on a couple dozen boards) rather than lose good stock to tearout. My shift to insert cutterheads resolved this however.

[rudy de haas]

The question applies to all kinds of knives - planer, jointer, and moulder.

if I understand correctly blade wear is most directly affected by heat production, so your advice to use the higher feed rate rings true because that produces less retained heat at the blade/wood intersection. Doesn't that imply, however, that deeper cuts would encounter more silica (in jatoba) each time, but produce enough less heat to net out better?

[J.R. Rutter]

I would only use light cuts if the deeper cuts don't produce a good surface. I've planed lots of jatoba over the years and quickly went to carbide knives on everything. Good plan to let things acclimate as much as possible. Jatoba especially will end check overnight if it is too wet and is cut in a dry environment.

[Dennis Ford]

Fewer cuts will cause LESS wear but the above points about tear-out are correct.

[rudy de haas]

Thanks!

I'll get some carbide knives and see how making thinner cuts at higher throughput works.

[Peter Quinn]

Ditto to JR's comments, jatoba goes better with carbide, hickory's biggest problem is knots if rustic, hickory is hard but the knots are killer, I'd do all my rough planing on a set of knives then switch to a fresh set for final thicknessing. Definetly leave jatoba long, it end checks bad as it acclimates and these can go pretty far into a board, 8"-10" extra would not be uncalled for if available.

[Simon Dupay]

Actually deeper cuts cause less tear-out, remember that a cutterhead cuts in a arc so there's more chip support with a deeper cut.

[Tom Walz]

Keep your tools sharp.

Roughly, roughly as you cut you will wear your knives down from a sharpness level of 10 to 9 the first hour, 9 to 7 the second hour, 7 to 4 the third hour and so on.

Those are pretty much nonsense measurements but they do illustrate the wear curve. We typically measure the radius of the cutting edges in real tests.

Feeding clean lumber helps edge retention.

If you really care following are my 17 possible causes of carbide wear that I use for failure analysis.

17 Factors ThatCan Contribute To Carbide Wear
1.Wear – thegrains and the binder just plain wear down
Wear is often assumed to be straight abrasive wear.The just plain rubbing of material againstmaterial always plays a part. However there can be a whole lot of other factorsinvolved.
2.Macrofracture –big chunks break off or the whole part breaks
3.Microfracture –edge chipping
4.Crack Initiation– How hard it is to start a crack.
5.Crackpropagation - how fast and how far the crack runs once started
6.Individualgrains breaking
7.Individualgrains pulling out.
8.Friction Weldingbetween the carbide and the material being cut
9.Physical Adhesion– the grains get physically pulled out. Think of sharp edges of the grainsgetting pulled by wood fibers.
10.Chemical adhesion– think of the grains as getting glued to the material being cut such as MDF,fiberboard, etc.
11.Chemical leachingthat will dissolve the binder and let the grains fall out.As with any chemical reaction of this sortthe acids create a salt that protects underlying binder until the salt isabraded away so grain size and binder chemistry are also important.
12. Rubbing can also generate an electrical potential thatwill accelerate grain loss.
13. Part deformation - If there is too much binder the partcan deform.
14. Metal fatigue – The metal binder gets bent and fatigueslike bending a piece of steel or other metal
15.Heat – adds tothe whole thing especially as a saw goes in and out of a cut.The outside gets hotter faster than theinside.As the outside grows rapidlywith the heat the inside doesn’t grow as fast and this creates stress thattends to cause flaking (spalling) on the outside.
16.Compression /Tension Cycling - in interrupted cuts the carbide rapidly goes though thiscycle.There is good evidence that mostdamage is done as the carbide tip leaves the cut and pressure is released.
17.Tribology – asthe tip moves though the material it is an acid environment and the heat andfriction of the cutting create a combination of forces.

[Andy Pratt]

I have carbide insert knives and have noticed zero difference between exotic woods and domestic woods. Even over years of use I notice no difference, I think you don't need to worry about it too much.