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How high to raise the blade

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Forum topic by Karamba posted 12-31-2015 06:47 AM 850 views 0 times favorited 20 replies Add to Favorites Watch
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Karamba

116 posts in 399 days


12-31-2015 06:47 AM

A common recommendation is to keep the table saw blade as low as possible. That is deemed to be safer as the teeth protrude only a quarter of inch or so. Then there is an absolutely opposing suggestion to keep the blade as high as possible. That ensures more vertical direction of cut and as the result less chance of a kickback.
So what is the ultimately safest blade height ?


20 replies so far

View MrUnix's profile

MrUnix

4224 posts in 1662 days


#1 posted 12-31-2015 07:02 AM

From Freud:


• The sawblade’s projection (t) with respect to the work piece must be greater than the height of the blade’s tooth (fig. 18). Increase or decrease the projection of the saw blade to improve finish quality.

• The number of teeth cutting the wood simultaneously must be between 3 or 4 for ripping and ideally 5 to 7 for crosscutting. With less than 3 teeth cutting the sawblade begins to vibrate leading to an uneven cut. If you want to cut work pieces with increased thicknesses (T-fig.21), but wish to maintain the same diameter saw blade, then use a blade with less teeth. If instead you want to cut work pieces with a reduced thickness, but also maintain the same diameter saw blade, then use a blade with more teeth.


Also, kickback starts at the rear of the blade where it gets lifted, not the front where it is being pushed down. Raising the blade too high will not only produce a worse cut and more tear-out, but increase the capacity for lifting at the rear of the blade, increasing the chance of kickback.

Cheers,
Brad

-- Brad in FL - To be old and wise, you must first be young and stupid

View Karamba's profile

Karamba

116 posts in 399 days


#2 posted 12-31-2015 07:37 AM

Thanks Brad,
That is very useful.

View AlaskaGuy's profile

AlaskaGuy

2406 posts in 1772 days


#3 posted 12-31-2015 08:48 AM

I have a number of blades. I believe in changing blades to get the best cut. I don’t generaly use combo blades.

I find each blade has a “sweet” spot (meaning blade height) that give me the best chip free cut on the top and bottom of the material being cut. For me it has nothing to do with safety but quality of cut.

Keep the guards on or keep you fingers out of the blade and won’t mater (safety wise) how high the blade is.

-- Alaskan's for Global warming!

View InstantSiv's profile

InstantSiv

259 posts in 1058 days


#4 posted 12-31-2015 11:34 AM

There’s pluses and minuses to a higher blade and lower blade. I set mine to where the gullets are fully exposed.

View Woodbum's profile

Woodbum

729 posts in 2528 days


#5 posted 12-31-2015 11:38 AM

Low blade clearance or high? For me it’s very simple. In case of a mishap…lacerate or amputate? The whole tooth extending through the top of the stock is all the height I need for both quality cuts, and a bit more safety. Less kickback too. It has worked for me for 35 years without a TS cut on my body.

-- "Now I'm just another old guy wearing funny clothes"

View rwe2156's profile

rwe2156

2193 posts in 944 days


#6 posted 12-31-2015 11:58 AM

My experience depends on what you’re doing.

For ripping normally just about to the bottom of the gullet.

For xcutting higher depends on wood character if tear out it occuring or if blade is a little dull because I’m too lazy to take it to sharpener ;-)

Sometimes I catch myself “wow that blade is really high” usually when in a hurry.

With riving knife or good splitter probably not as important nowadays.

-- Everything is a prototype thats why its one of a kind!!

View sawdustdad's profile

sawdustdad

131 posts in 348 days


#7 posted 12-31-2015 12:02 PM

The rule of thumb I use is 1/4 inch above the wood I’m cutting. I keep a combination blade on the TS unless I’m ripping a bunch of stuff or cutting veneer plywood and need a finer cut.

-- Murphy's Carpentry Corollary #3: Any board cut to length has a 50% probability of being too short.

View knotscott's profile

knotscott

7211 posts in 2839 days


#8 posted 12-31-2015 12:31 PM

It depends. Optimum safety and optimum cut performance don’t necessarily use the same logic. What’s ideal is a little different for every blade, every saw, every board, and every cut. A little higher can reduce burning and resistance…. a little lower can provide a slightly cleaner cut but by increasing the resistance, you also increase the pressure required to push the board through, which is a bit less safe. A higher blade height tends to pose less resistance, thus needs less pushing pressure, but will also take more flesh in the event of an accident. Brad’s reply was excellent and supplied some solid theoretical info. I don’t get too anal about it and usually just set the teeth slightly above the above the board so that the gullet is about fully above the piece. Changing blades to a blade optimized for the cut is best, but sometimes a slight blade height adjustment will suffice.

Considerations/factors:
- sharp blades that are optimum for the task
- suitable kerf width for the saw…3/32” TK blades pose less resistance than a 1/8” full kerf blade
- clean blades pose less resistance (and stay sharp longer)
- low friction saw surface that allows wood to glide easily (waxed, cleaned, etc)
- flat straight work piece that doesn’t wobble or shift during the cut
- hold downs, featherboards, and/or push shoes
- good blade, fence, and splitter/riving knife alignment
- stiff throat insert that doesn’t flex
- sufficient motor power
- blade guard
- riving knife or splitter

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View bearkatwood's profile

bearkatwood

1202 posts in 475 days


#9 posted 12-31-2015 12:42 PM

Thanks for the Freud diagram, I wonder if Dr. Ruth has a diagram about using the table saw. Probably not suited for this forum ;) Have a great day and keep the teeth off the wood.
O.K. That was a little blue sorry, had to. It was there.

-- Brian Noel

View MadMark's profile

MadMark

977 posts in 916 days


#10 posted 12-31-2015 03:09 PM

Bottom of gullet at top of board. Enough rise to reduce kickbacks, enough attack angle to cut well. Too much blade reduces kickback risk but increases cut risk. Low blade has more kickback risk but less cut risk. Given a choice kickback is less damaging than cut so go with less blade exposure.

All that math is moot. Thats theoretical woodworking for setting up production manufacturing. No-one is going to do the math before every cut.

M

-- Madmark - Madmark2150@yahoo.com Wiretreefarm.com

View Richard H's profile

Richard H

489 posts in 1144 days


#11 posted 12-31-2015 03:38 PM



Bottom of gullet at top of board. Enough rise to reduce kickbacks, enough attack angle to cut well. Too much blade reduces kickback risk but increases cut risk. Low blade has more kickback risk but less cut risk. Given a choice kickback is less damaging than cut so go with less blade exposure.

- MadMark

I never understood the logic of “Low blade has more kickback risk”. My understanding is kickback occurs at the point where the blade exits the table on the upward spin. If the blade at that point contacts the wood there is enough upward and forward force to push the workpiece at the user at high speed. My one major experience with kickback the piece didn’t slide across the table as if being pushed across the table it flew off the table and hit the wall well above the height of the tablesaw top. I just don’t see how the height of the blade can make any difference in kickback at all other than to change the force vector to a steeper angle. Now number of teeth in the wood and cut quality makes complete sense to me.

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MadMark

977 posts in 916 days


#12 posted 12-31-2015 03:49 PM

Force vector, the kickback force is less as the angle steepens. A riving knife and a zci are more important than blade height.

M

-- Madmark - Madmark2150@yahoo.com Wiretreefarm.com

View Andy Ponder's profile

Andy Ponder

232 posts in 1171 days


#13 posted 12-31-2015 04:21 PM

Every time I set my blade depth I remember what my high school (1965) shop teacher said, “You want the blade to protrude through the wood as far as you want it to cut into your hand if you slip”.

I do raise the blade until the whole tooth clears and always use push sticks etc.

-- AP--I thought growing old would take longer.

View Richard H's profile

Richard H

489 posts in 1144 days


#14 posted 12-31-2015 04:31 PM


Force vector, the kickback force is less as the angle steepens. A riving knife and a zci are more important than blade height.

M

- MadMark

The amount of force put on the piece of wood is the same as it’s based on the velocity of the teeth which is constant regardless of how high the blade is set because it’s based on the diameter of the blade and the RPM’s of the saw. I looked at the new woodworker video where he deliberately setup kickback and in that video I noticed two different forces at play.

1. The force that caused the wood to lift off of the table saw top. This is based on the force applied by the spinning blade to the back side of the wood and I just don’t see how more or less height is going to make a difference here.

2. The force applied after the bottom of the piece of wood cleared the top of the blade. Once the piece of wood cleared the top of the blade the teeth on the blade pulled it away from the fence in a counterclockwise motion and catapulted it behind the saw pulling the operators hands towards the blade in the process.

I guess one could argue that if you set the blade really high than the amount of energy required to move the kickback into step 2 would be higher. If the operator was applying enough downward force to prevent the piece from escaping the space between the blade and the fence than the kickback would be limited to the piece jumping up off the table and slamming back down again. Even than that’s a lot of ifs and it’s making the big assumption you can overpower the saw in the time it takes to lift the piece past the blade height. That’s a big if in my book.

View 716's profile

716

502 posts in 380 days


#15 posted 12-31-2015 05:15 PM


The amount of force put on the piece of wood is the same as it s based on the velocity of the teeth which is constant regardless of how high the blade is set because it s based on the diameter of the blade and the RPM s of the saw. I looked at the new woodworker video where he deliberately setup kickback and in that video I noticed two different forces at play.
- Richard H

Very wrong. If you lower the blade so it barely protrudes over the surface of the table all forces will be directed almost parallel to the table towards the operator. As you gradually raise the blade the vertical force increases and horizontal decreases. If you could raise it to the point where the the wood piece is on the same elevation as the center of the blade ( not possible on the table saw, maybe on some chop saws ) there will be no horizontal force just vertical towards the table.

-- It's nice!

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