Saw blade height - why?

[Anonymous]

Well, I often wonder about the sage advice offered down from people who have years of experience and accumulated knowledge.

The placing of the hand plane on its side etc. is clearly one that was recently discussed.

Another is the idea that one should set the height of a table saw blade just above (6mm or so) the workpiece height.

Anyone know why this is recommended?

I suspect is stems from the days where there were no crown guards and a low blade presents less danger if one should reach across. Or maybe there is some idea that it reduces kickback is the riving knife is missing?

Modern saws in the UK have both safety features as standard.

The thing is, that after much table saw use, i find that a high blade (maybe 40mm above the top of the wood) works best in 2 ways. First of all, the sawdust is dragged down into the cabinet and sucked away rather than being squirted out of the back of the saw and also i get a better quality finish on the cut.

What say you?

 

[Slim]

Hi Tony,

I thought the blade should project above the workpiece by the length of the teeth, so it doesn't get clogged up with sawdust.

 

[Paul Chapman]

The only circular saw I have is a hand-held one. Like you, I've always read that it's best to have the blade projecting only slightly more than the thickness of the wood. However, I've also found that the cut is usually better with the blade projecting far more.

Cheers :wink:

Paul

 

[lugo35]

my theory is there is less strain on the machine with less projection due to the cut being more of a shear cut rather than 90degrees.

 

[MooreToolsPlease]

I would have thought that the reverse would be true lugo?
with the saw blade higher, there is not so many teeth in contact with the wood at any one time, so there would be less friction bogging the motor down?

 

[TonyW]

To date have only used a hand held circular saw. Instructions stated saw blade should project a few mills more than wood thickness. Like Paul I found better results with the blade projecting more. Maybe related to Simons comment so it does not get clogged up with sawdust.

Cheers
Tony

 

[lugo35]

see your point

 

[Niki]

Tony

I'm using normally "High" blade.
I think that, as you said, the low blade setting is from the times that nobody used blade guard and you will find this advise also on many American sites because they are known as "I removed the splitter and the guard from day one and I don't know even where they are"....in this case, yes, it's better to cut a 1/4" of the hand instead of all the hand but.....

From a book (I will not say by who, but he wrote at least 4);

"When the blade is set low, each tooth spends more time inside the wood, increasing the risk of burning the wood" (as I understand, hotter blade that can lead to deformation)

"When the blade is set high, the cut is at it's cleanest and most efficient"

Personally, I like high blade (maximum height).
From my experience (that is not much), when I'm cutting the 30mm oak, the feed is faster and no burning marks (unless the blade is not clean or sharp) but when I use low blade, the motor is telling me "it's too hard for me niki"....

I don't have any problem with high blade...the guard is there and my hands are never around the blade in a position that they can "slip" into the blade.

Regards
niki

 

[tnimble]

The cutting teeth are placed at an angle to the axis of the blade (besides having a certain amount of set along the axis aternating to the left and richt). This angles determines the hight of the blade above the center of the wood.

When the blade is set to low, most of the travel path the teeth rub against the wood. When the blade is set to high, most of the travel path the teeth negatively scrape through the wood. Somewhere in between those extremes the teeth cut most effectively along the path though the wood.

For most positive angled blades the blade must be pretty high above the wood to have the most effective cut.

 

[lugo35]

to be honest have learnt all this in college but brain gone to mush and forgot it

 

[andys wood shed]

Tony

Take a look here for an explanation

Andy

ps page 15 if you are in a hurry :wink:

 

[Paul Chapman]

"When the blade is set low, each tooth spends more time inside the wood, increasing the risk of burning the wood" (as I understand, hotter blade that can lead to deformation)

"When the blade is set high, the cut is at it's cleanest and most efficient"

I think the point about having somewhere for the heat to escape is significant in all this. When I have cut thick pieces of wood and had to do half the cut from one side and half from the other, I have always found that the cuts aren't as good as when cutting thinner wood in one go. I have always put this down to the blade being buried in the wood and the heat having nowhere to escape.

Cheers :wink:

Paul

 

[Harbo]

I recently read (somewhere - complete with diagrams [but not the Freud site]?) that a lowish height is best i.e. maximum number of teeth cutting at one time.

With a high height fewer teeth are doing the cutting so the cut is not as efficient.

I generally cut with about 10mm protruding - it just looks safer?

Rod

 

[OPJ]

Have you ever tried ripping a thin (3/4" or less) length of timber with the blade on an industrial saw exposed at full height? (about 6"?)

It can vibrate or jump like hell! :wink:

 

[Anonymous]

Tony

Take a look here for an explanation

Andy

ps page 15 if you are in a hurry :wink:

Ta

So, at least the height of the tooth above the wood and higher if one wants.

 

[engineer one]

i wonder whether a lot of the thought about the blade height has anything to do with cutting man made boards???

depending on the board and the blade that you use, the slightly lower blade will i think give less break out and a better finish on man made materials than a high one.

paul :wink:

 

[Pete W]

So, at least the height of the tooth above the wood and higher if one wants.

Or less! What it actually says is this:
"The sawblade's projection (T) with respect to the workpiece must be at least equal to the height of the blade's tooth (fig. 10). Increase or decrease the projection of the sawblade to improve the quality of the cutting finish."

So... a pretty definitive answer, I think :? :lol:

Pete, with no more than a theoretical interest in table saws

 

[Keith Smith]

It all depends what you are cutting and what blade you are using, for instance.

A negative rake blade cutting MFC is best with a 2-3mm projection. (for reduced chipping)

A rip blade is usually best if the gullet is level with or above the timber (helps chip clearance)

 

[Scrit]

Well, I often wonder about the sage advice offered down from people who have years of experience and accumulated knowledge

So are you saying that accumuulated knowledge is of no worth?

Another is the idea that one should set the height of a table saw blade just above (6mm or so) the workpiece height.

Anyone know why this is recommended?

I suspect is stems from the days where there were no crown guards and a low blade presents less danger if one should reach across. Or maybe there is some idea that it reduces kickback is the riving knife is missing?

Blade height for "quality" cutting of materials such as MFC, plywood, etc is often set so that the quality of cut is maximised - this generally means having the blade set low. Try cutting MFC with the blade set 4in above the table and the break-out on the underside will convince you of why a low blade setting is needed. In fact with a low blade setting the potential for kickback is may be increased due to the increased contact area between the edges of the teeth and the timber, although the attack angle will most likely result in backwards ejection of the workpiece as opposed to the upwards ejection you can experience with a high blade.

And as for "a low blade presents less danger if one should reach across" then all I can say is that only a complete silly person willingly reaches across an unguarded spinning saw blade, even if he's got a push stick in his hand.

On the flip side for course ripping on a purpose-made rip saw a high blade is often used because the saw itself doesn't have a huge range of vertical adjustment. I find that single-purpose rip blades often make cleaner cuts when the blade is raised in the same way that hand ripping requires a higher angle of cut than cross cutting

So to sum up - low blade will cause less break-out on cross grain cuts and cuts in brittle materials whilst high blade can yield some advantages in ripping. In either case don't lean over the blade, use a riving knife and crown guard and a rip fence set appropriately for the cut.

Scrit

 

[Anonymous]

Well, today I rceived a link to a tablesaw 'primer' in my latest email newsletter from fine woodworking magazine.

Might be interesting to some members

http://www.taunton.com/finewoodworking/ToolGuide/ToolGuideArticle.aspx?id=29509