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/

 

[RussellT]

Thank you both.

I think that makes things a bit clearer, and I have learnt a new word (spelching).

I think that for most of the work I do I will be able to stick to a fine cut blade. I seldom cut thick or hard timbers and only rarely rip stuff.

One thing I am still wondering about is the optimum height of the saw blade. From a safety point of view I would expect the blade needs to be just above the surface of the material being cut, but if the blade is higher then each tooth will have a shorter path through the material and the cut will be more downward and less likely to damage the surface - or am I missing something?

Russell

 

[Eshmiel]

Thank you both.

I think that makes things a bit clearer, and I have learnt a new word (spelching).

I think that for most of the work I do I will be able to stick to a fine cut blade. I seldom cut thick or hard timbers and only rarely rip stuff.

One thing I am still wondering about is the optimum height of the saw blade. From a safety point of view I would expect the blade needs to be just above the surface of the material being cut, but if the blade is higher then each tooth will have a shorter path through the material and the cut will be more downward and less likely to damage the surface - or am I missing something?

Russell

There's a lot of different opinions about the optimum height of a table saw blade for a given workpiece thickness. Some recommend minimum height, partially because its "safer" for those who insist on working with no guard but also because of various arguments about the quality of cut. Others suggest higher for the reasons you mention.

Personally I tend to keep the blade high, because lowering it can mean that the guard (which is attached to the riving knife behind the blade) can begin to act as a stopper or jammer of the workpiece when it, along with the blade, is lowered. I can't find any other significant difference between use of high or low blade, really. As long as I can always keep the guard on, a high blade is not a greater risk than a lower blade if basic safety procedures are followed (guard, riving knife, feather boards and pushing device, no leaning over the table, no hands anywhere near the blade and no standing in line with the blade).

 

[Delaney]

I have read that having a blade high, can cause wobble and is best to cut with the blade just high of the peice.

Another factor in blade choice is tooth pitch.
A more aggressive pitch smashes through the wood instead of cutting.
So for example, a pitch of 15 degrees or less will give a finer cut. Over will give a more smashing cut.

Another factor is tooth shape. The most common is alternate teeth but the best cut comes from hollowed straight teeth.

So to summarise, if you wanted the finest cut, a high tooth count, shallow pitched, hollowed straight tooth, would be best and good for cutting veneers etc.

There is a company called Swedex who make excellent blades and can help advise.

 

[Katomi woodsmith]

Well others have covered most of my advice
From personal experience a 6tpi blade is more lightly to grab if pushed to hard.
Work slow and don’t rush the tool

 

[HOJ]

From personal experience a 6tpi blade is more lightly to grab if pushed to hard.

With respect @Katomi woodsmith I would suggest you read the OP's post he is asking about blades for a table saw.

 

[Doug71]

I'm a keep the blade high kind of guy, it cuts more efficiently and reduces the chance of kick back........and I always keep the guard on.

 

[Katomi woodsmith]

Yes table saw mine is a hobbyist max cut depth is 38mm of the same brand
With a 6 TPI blade it kicks when I push to hard, I was ripping down old rough wood

 

[Phil Pascoe]

Where do you get 6tpi for a circular saw blade? Usually they just quote the tooth number.

Instinctively I keep the blade down, but it tends to lift the wood, so a bit higher is better.

 

[eribaMotters]

I guess I'm fairly typical and have 3 blades for my circular saw table. They are 12" and 24tpi for ripping, 72tpi for plywood and cross cutting and finally a 48tpi for general purpose or when one of the other is in for sharpening.
I have my guard set tighter than a finger thickness above the timber, which generally means have the blade set to slice through the timber at a fairly shallow angle and so reduce breakout/spelching due to the less aggressive cutting angle.

Colin

 

[TRITON]

Novelty saw blade enters the conversation...

 

[RussellT]

OK. That's all useful, thank you.

I think that means that if I want the cleanest possible cut on the top, then blade high, if I want clean cuts on both sides then blade low - and use the guard!

Russell