Bite size and blade life

[Edwin Santos]

I learned many of my woodworking practices from a mentor who advised to take light passes when using machines with rotating blades i.e. jointer, planer, router.
His logic was that numerous lighter passes will not only be easier on machine, but more importantly easier on the cutting edges. Not to mention reducing the risk of tear out and grabbing grain.
So my practice has always been to take very light cuts even if it means more time and more passes. Often times sound is a good feedback. The sound of a lighter cut is normal to me, but when the machine is taking a heavier cut I'm conditioned to wince.

The thing is I can't scientifically prove whether this belief is a fallacy or not. After all, could the physics of taking 1/32 depth cuts instead of 1/16 or 1/8 really make a meaningful difference in cutter life?
Does it make a difference if the cutter is carbide vs HSS?
What do you think?

[Edward Weber]

IMO, Yes, it makes a difference.
I tend to lean toward lighter passes as well when applicable. As you said, it does increase machine life by not taxing the tool. It does lessen the chance of tear out and if it does happen, it's usually not as bad. It keeps the cutting edge cooler which is generally a good thing.
As you said, it may not be scientific but after decades of using power tools, I'll stick with what works for me.
Interested to hear others opinions on this, everyone uses tools differently

[Phil Gaudio]

I have my jointer set to take about a 1/64" bite: Minimax Xylent segmented head. I rarely take more than twice that when running the planer. I get better results with this strategy as opposed to hogging off larger amounts per pass. Wear on cutters: lighter cuts means more passes which in turn has to increase wear on the cutters. But I am a hobbyist and am in no hurry to process lumber. I'd rather get the best finish, and I disregard cutter life: these carbide blades seem to last forever.

[Justin Rapp]

I also tend to take lighter passes for the reasons mentioned above. I see no reason to hog out 1/8, making the machine work harder. If i had a 10hp jointer, maybe it would be ok.

[Jim Becker]

Some of the faster wear with heavy cutting could possibly come from more heat generated from friction. I've always preferred light cuts for a more practical reason, however...less chance of overshooting, tearout and other things that happen with a cutting edge bites into the material.

[Mel Fulks]

The manufacturers and sharpeners say that slow cutting is not good . Makes more heat and more wear and non-smooth surfaces as the
saw has room to wiggle.

[Rod Sheridan]

Hi Jim, for maximum cutter life, the thickness of the chip has to be sufficient to carry away the heat of cutting.

For this reason you do feed rate calculations when machining, most people feed far too slowly, resulting in reduced cutter life.

Take the thickest chip that produces the required finish, and stays within the tooling recommendations from the manufacturer and stays within the machine capabilities as specified by the manufacturer.

Regards, Rod

[Lee Schierer]

On a router, jointer or a planer a bigger bite gives a greater potential for reversed grain tear out. If your take a light cut on the first pass you can see the areas where tear out may occur and take steps to avoid further damage.

[Jared Sankovich]

Hi Jim, for maximum cutter life, the thickness of the chip has to sufficient to carry away the heat of cutting.

For this reason you do feed rate calculations when machining, most people feed far too slowly, resulting reduced cutter life.

Take the thickest chip that produces the required finish, and stays within the tooling recommendations from the manufacturer and stays within the machine capabilities as specified by the manufacturer.

Regards, Rod

This. You can calculate the ideal chip load. Light passes are not where you have maxium tool life.

[Andrew Hughes]

I take at least 1/32 pass on my jointer when facing rough boards. Sometimes even more. The idea more passes the less wear sound like Bs to me.

[Patrick Kane]

Yeah, i never understood the "light passes=greater tool longevity" theory. You are cutting more material surface area. I try to take one 1/8" pass at the jointer to get my face flat/straight, but i will take 1/4" or more if the edge is very bowed. I take 1/8", or whatever the biggest bite allowable by my planer, for most passes. Do you make one pass at the table saw, or do you raise the blade in 1/2" increments?

If you have the power, then i have to imagine the faster feed rate and heavier cut will make your tooling last the longest time. If you strive for the best surface finish or your tool is underpowered, then go with lighter cuts at the expense of your tooling. Remember, tooling is disposable! It will need to be replaced or sharpened, and thats just part of the gig.

[Kurt Wyberanec]

Talking heavy passes scares me on a router and anything figured... on the j/p I tend to stick around 1/32 but will often start with heavier passes and finish light.

On router I have mixed feelings and experiences. When I've gone trade shows and the like i always see demo guys taking full passes worth large profile bits and getting good results fast... I've never really tried because i tend to use pricey lumber and likewise can't risk big blowout even though I'll still get some light. I think a lot of it matters on the grain of your material. Profile bits I tend to work in passes because of what I said but recently doing plunge routing like cutting interior circles or cutouts in taking full cuts....I had a conversation with Onsrud recently and they told me you really don't want to step with spiral plunge bits as that will only heat the tip and wear out faster... they told me to take full plunge, around 18k, and at 3 sec a ft or faster!...I understand the logic but taking full plunges in hardwood or BB seems really hard as well (I use dewalt 618s) ... I bought a rougher but from them and can't tell you how pleased I've been... I've been trying to keep my feed rate fast even when it starts to sound like it's fighting a bit and so far so good.... over $100 for the bit so it's risky. I've tried it faster, slower, and higher and lower rpm and it seems like their recommendation is actually the best overall.

Experiment and see what works for you.

As for the j/p it larger depends on the power of your machine, type of material, and how you like to work. On my a3-41 I can pretty much take whatever I want... have yet to bog down the machine in any way and have not really noticed any significant different in quality of cut.

[Rod Sheridan]

Hi Kurt, take a ripping blade with 24 teeth, a chip thickness or load of 0.015” and a blade RPM of 4,800.

24 X 0.015 X 4,800 = 1,728 inches per minute or 144 feet per minute.

For a fine finish (glue line) use 0.010 chip load = 96 feet per minute.

Know you know why stock feeders have one or two speeds up in the 60 feet per minute range.

When I set up gang rips for a living the machines were 50 HP, I was often running 3 or 4 blades in 8/4 or 12/4 hardwood at 80 feet per minute…Rod

[Kevin Jenness]

Cutter life and surface quality are sometimes at odds. The heat that dulls edges is carried away by chips so the longest cutter life comes with low rpms/high feed speed to get the optimum chip load. Cautious, slow feed and light cuts may be called for to get an acceptable surface in figured or gnarly wood but it will be at the expense of blade life. The more linear feet of material a cutter sees the more wear, so heavier cuts will prolong its life

[johnny means]

It's much more nuanced than that. In theory, and carbide blade, If cooled, and kept perpetually clean, could cut wood indefinitely with out dulling. There's nothing in (most) woods that would cause wear on a carbide tip. Yes, the first cuts with a brand new blade would cause some micro fracturing on the edge, but but the edge would very soon acquire a slightly blunted edge, on a microscopic level, that would be incredibly durable. Heat is what causes blade wear. Controlling heat generation is going to be the most important aspect of prolonging cutter life. Cutting speed and depth are only limited by the capacity of the machines spinning the tooling.

[Jim Becker]

Just to clarify, I'm very familiar with chip load calculations, especially with my CNC work, and my previous comment wasn't about speed...it was about the "bite". Taking too much does nasty things and can exacerbate heat from friction which in turn plays not-nice with chip load being able to pull off enough heat. That's in addition to the other risks I mentioned. I also took this thread to be more about machines like jointers/planers and so forth, rather than router tooling, although I now reread the OP and see that routers were also mentioned. There are interesting dynamics for any cutting tool for sure.

[Greg Quenneville]

For what it’s worth, some woods (like most of them in Australia) have a high silica content, and they dull edged tools fast. You learn to take a big a bite as the machine and the material can stand. Very often material sympathy and edge life are mutually exclusive, so then its back to feathery cuts and holding your breath.

I think that edge mileage is limiting, and feed and DOC (depth of cut) should be considered. Obviously working in wood isn’t the same as metal, which is supposed to be uniform* I have never had a situation working wood where I valued my tooling more than the material.

*except Chinese cast iron , which can contain unmelted taps and drill bits.

[Bill Dufour]

In metal working the standard is every horsepower will cut about one cubic inch of steel per minute. Pretty much true for any type of machine that has a single direction cutter. Any less is wasting time any more will not be able to keep up the cut. There are calculators that show too life vs material removal rates. Lower rates the tools last longer. It is a balance between tool life and cutting speed. Wood shops tend not to be as exact on their measurments and the materials being cut are more variable. For home shops tool life is more important then a few extra seconds per cut.
Bill D.
Bill D

[Edward Weber]

I have to echo the last few comments and say there is a big difference between machine life and cutter life, feed rate vs depth of cut But there is still a balance to be struck.
All of this has been calculated in the world of machine tools and metal work and some of it, not all can be used by woodworkers.
As Greg Quenneville's said
"Obviously working in wood isn’t the same as metal, which is supposed to be uniform* I have never had a situation working wood where I valued my tooling more than the material."

Some wood is often better treated as metal (like cutting aluminum) due to it's density and high mineral content. Higher tooth counts and lighter passes are sometimes necessary.
JMHO

[Jim Becker]

It's also important to not lose sight of the fact that tooling is "disposable", per se. (Yes, some can be re-sharpened, but ultimately, it may need replaced) The point about some species being rough on edges also applies to manufactured wood products like plywood and MDF. Some of the resins used to make the product wear tooling quite quickly in some cases.

[Tom Bender]

A shallow cut makes fine sawdust. It takes more work to make fine dust. More work = more wear and concentrated on the tip of the cutting edge.

And fine dust is more hazardous since it settles slowly and stirs up easily.

Just two more factors to consider.