Saw blades, fine or coarse?

[RussellT]

Hi Everybody

This is probably a silly question, but on the basis that there's apparently no such thing as a stupid question...

I'm not really a woodworker, but I do work with wood as needed for other projects, and I've just been fitting a new kitchen.

When it came to doing the cornice mitres I borrowed a mitre saw from a friend (a Festool Kapex 120) and I was amazed at the quality of the cut.

I was so amazed that I decided to buy a new blade for my table saw (a Triton workcentre with an Elu circular saw) and after looking at what's available I've been wondering about fine and coarse blades. A fine cut blade might have 80 teeth and a coarse cut blade only 20, so why not use a fine cut blade all the time because with all those extra teeth it will take longer to go blunt and it doesn't cost that much more

I'm sure that there are other features of coarse blades like chip clearance etc, but for most of my work I don't see that that would matter.

Am I missing something?

Russell

 

[Inspector]

The coarse blade is most likely designed to rip wood and the fine blade for cutting plywood so the veneer doesn't chip out or for crosscutting where you want a clean cut and no chipped edges. If you use a high count blade for ripping the teeth can't clear the chips and the gullets (spaces between the teeth) fill up. The friction from that may cause burning of the wood (blackened places along the cut). There are combination blades (about 40 teeth) that can do both but not as perfectly as a specialized blade.

Pete

 

[Eshmiel]

A blade with more teeth cuts through the wood with more teeth per inch (and per second) than a blade with less teeth. This creates a lot more friction and therefore a lot more resistance to pushing the wood through the blade and a lot more heat that can burn the wood, especially as its going past the blade more slowly because of the increased resistance. Higher-count teeth blades are generally used for thinner sections of wood or board that don't offer so much resistance as a thicker workpiece; and on which you want a cleaner cut edge with little or no spelching or saw marks.

A blade with fewer teeth will cut thicker and harder timbers more easily - but most also leave more saw marks and spelch.

You'll sometimes see low tooth blades advertised for ripping (cutting with the grain of the wood) and higher tooth blades advertised for crosscutting (across the grain) and for veneered boards that might easily spelch or fracture. Ripping cuts are usually (not always) longer than cross cuts so less teeth means a faster feed rate is possible.

You'd not use an 80 tooth blade to rip or a 20 tooth blade to make a fine cut on a veneered board, even though you could try. There are "combination blades" of 40 teeth (on a 10 inch diameter sawblade, pro rata for other diameters) that are meant to serve as both rip and cross-cut blades, so you don't have to change blades when performing different kinds of cuts in different kinds of material. But if the material is potentially problematic (rock hard, very thick, prone to spelch, etc.) you're better off changing the blade for one with the ideal tooth count and configuration.

There are various qualities of blade and geometry of teeth. It pays the shop around and understand what kind of qualities and capabilities (especially finish-of-cut) are available.

The quality and type of the blade isn't the only factor in making good cuts. The power of the motor (output, not input) and the quality of the arbour & its mounting can affect cut quality, as can the accuracy of other parts of the saw such as the flatness of the table and the resilience/set-up of the fence or mitre gauge. Some timbers/boards cut more easily than others. Some are hard to cut, some burn easily and some have hidden surprises in the form of inner tensions or even "stones" (lumps of rock hard silicone and calcites).

You might find this useful:

https://www.axminstertools.com/ideas-advice/axcaliber-saw-blades/