What is the recommended height of the blade on a table saw while operating?

26

1

I have been watching a lot of videos lately about table saws. In those videos I usually see cuts are being made with the blade just barely clearing the piece. For example:

Low blade cutting wood

Image from HammerZone

Conversely I see some where the blade is very high above the piece.

High blade cutting wood

Image cropped from Wikipedia

In the second example I do not see a reason to have the blade up that high to cut the piece. There would be a obvious safety issue with more blade being exposed but is there a reason to keep the blade up that high?

Matt

Posted 2015-04-20T19:16:28.620

Reputation: 13 424

8Two answers put forth the claim that you need to have the blade have clearance above the workpiece to allow the gullets to clear. That's in error because the blade cuts on the down stroke, emptying itself at the bottom. The back of the blade shouldn't be doing any cutting on its way up through the table unless you're feeding the wood backwards, and that's just begging to get yourself hurt. – FreeMan – 2015-04-21T02:00:05.523

@FreeMan You should definitively add an answer. – Maxime Morin – 2015-04-21T12:30:33.687

@MaximeMorin, I get ya', but that's not really an answer, which is why I put it here as a comment. I suppose I could cut and paste a comment to each of the answers that brought it up... – FreeMan – 2015-04-21T20:31:10.087

In a case where you are more bothered by taking a corner off the top surface of the wood than leaving a rough edge on the bottom surface, it might be advantageous to have the blade high, so that it's biting in at a sharper angle. But my guess about the reason for the high blade in some videos is because that's what the person running the machine thinks is the right way to do it, whether it is or isn't. – Steve – 2017-11-17T23:56:05.210

Answers

18

If you call up Freud and ask, they'll tell you that you want one full tooth to clear the top of the wood, but no more.

There are a couple of reasons for that recommendation- first is safety. A tooth that clears the surface on the up swing then re-enters on the down swing may not follow the same planar path due to harmonics and vibration related physics. A tooth that is held firmly by the material it is cutting is less likely to catch.

The reason why you want a whole tooth to extend through the work surface has to do with the shape of a tooth and debris clearance. Circular saw blade teeth (even carbide ones) are often wider at the tip than they are at the base. This tapering allows for less binding and cleaner cuts than a straight tooth would.

TX Turner

Posted 2015-04-20T19:16:28.620

Reputation: 3 927

1may not follow the same planar path due to harmonics and vibration related physics is a very good point. Leads towards keeping it down. Thanks. – Matt – 2015-04-20T19:41:08.700

I would say that's very unlikely to make a noticeable difference in terms of the accuracy levels worked to with a ripping saw cut. – WhatEvil – 2017-11-09T16:56:04.403

10

The common argument for raising the blade is that the front of the blade is making a more downward cut, theoretically reducing the chance of kickback and increasing cut quality. While this may produce a better-quality cut in plywood, the kickback argument relies on flawed logic, since kickback is often produced by the kerf pinching the back of the blade or by a workpiece or offcut getting pinched between the back of the blade and the fence. It also means the back of the blade is following a more vertical path as it exits the table, increasing the possibility that your workpiece or offcut will be raised off the surface of the table and out of your control.

The argument for lowering the blade is that less exposed blade means you have a smaller chance of an amputation if you accidentally position your hand in the line of the cut and make contact with the blade.

There are various modern recommendations, all of which are very similar:

  • the blade should be raised so its peak is 1/8" to 3/8" higher than your workpiece
  • the blade should be raised so 1 full tooth is exposed above your workpiece
  • the blade should be raised to expose half of the gullet (if there are multiple depths of gullets as in some combination blades, this recommendation applies to the shallowest gullets)

As TX Turner briefly noted, the purpose of having some clearance above the blade is to allow the gullets to empty. If the gullet does not have adequate clearance, it may not be able to dump its payload before its corresponding tooth takes another bite. When this happens, the gullet becomes packed with sawdust, producing friction on each subsequent pass, commonly causing the blade to wander and/or burn the wood.

rob

Posted 2015-04-20T19:16:28.620

Reputation: 15 938

You should be relatively unlikely to cut through an appendage with a ripsaw blade anyway. You're more likely to cut a finger off on a bandsaw because of the speed of the blade and size of the teeth (and indeed they use bandsaws for meat cutting). I know from something that's happened to somebody else while I was there, that if you do accidentally touch a ripsaw blade it's much more likely that there'll be a big "bang" and your hand/finger will be pushed away. Though it will do damage, it's not how you might think in that it'll instantly cut through your (multiple) fingers. – WhatEvil – 2017-11-09T16:59:40.840

9

I set the blade to the minimum height that is required to make the cut, typically about 1/8" above.

There isn't really a need to have it higher for purposes of clearing the sawdust. If you look at the geometry of a table saw blade, the cutting action is happening at the front of the blade, as the cutters push through the wood. The gullets will fill on the down stroke, and inertia will clear the gullets down into the body of the saw.

Kickback occurs when the piece being cut is picked up by the back side of the blade, usually due to the saw kerf being pinched. Having the blade lower reduces the length of the blade that is in the kerf, which can help reduce the chance of kickback (although a splitter or riving knife is far better).

LeeG

Posted 2015-04-20T19:16:28.620

Reputation: 6 092

1Nice video! I also like your point that there is less blade in the kerf when the blade is lower. – rob – 2015-04-21T17:39:51.477

3

Generally I'd put the blade only as high as necessary to clear the top of the board being cut. There is, however, one occasion when raising the blade significantly above the work piece is valuable. That would be when you're making a stopped cut. In this case, the higher the blade is, the more vertical the cutting surface is, thus making a cleaner stopping point.

FreeMan

Posted 2015-04-20T19:16:28.620

Reputation: 2 522

1

Well I noticed two things about the pictures you posted. The first is a ripping blade and the second is a cross cut blade. That might have something to do with it.

The first is a crosscut blade and the second one is a 'cross' between a rip saw and a cross saw, doesn't have the kicker on each tooth. (though there still might be a reason for height between cross cutting a board and ripping).

However, what I was able to find was that the more blade you have showing the more blade is available to be grabbed and cause a kick-back (pinching the blade). Cross cutting a piece of wood is less likely (IMO) to cause a pinch and kickback. So that might be part of the reason for the differences.

The different comments also suggested a good riving knife will help reduce the chance of kick back in these situations too.

I personally just like it closer to board height to have less exposure to the spinning teeth of the blade.

bowlturner

Posted 2015-04-20T19:16:28.620

Reputation: 12 431

I didn't intend to have those two different pictures but perhaps it worked out for the best. I thought it was just an obvious safety thing but I glad to know if could be more than that. Thanks. – Matt – 2015-04-20T19:50:36.447

I'm not so sure if the difference between a ripsaw blade and a dual-purpose (rip and crosscut) blade is just whether there's a "kicker" on the teeth or not. There are plenty of rip blades with no "kickers" and as far as I'm aware it's more to do with tooth pitch and tooth rake angle. – WhatEvil – 2017-11-09T17:06:08.197

@bowiturner I'd say the more you hide that blade and think your fingers are safe because of the wood there, you are kidding yourself. I like to keep the operation visible. The material could collapse, fracture, etc and send your finger into the blade. The more you are aware that there is spinning danger zone...better. – Andyz Smith – 2015-04-28T12:39:31.943

3@AndyzSmith I look at it, if I slip, the less blade that is showing will take a smaller bite out of me. – bowlturner – 2015-04-28T12:51:44.097

@AndyzSmith In this case, it's a through cut so you can see exactly where the leading edge of the blade is. – rob – 2015-04-28T18:48:31.950

Commenter is suggesting that by lowering the blade below/just below the cut wood height , it's safer. I differ. Raise it on up, so you can see what is going on. – Andyz Smith – 2015-04-29T03:44:36.653

1@AndyzSmith Maybe I'm missing something but I don't see how your interpretation of bowlturner's suggestion makes sense for a through cut. I think bowlturner is responding to the pictures in the original question and suggesting lowering the blade so it's only slightly higher than the top of the workpiece, rather than exposing, say, 1/2" or more of the blade above the workpiece. – rob – 2015-04-30T17:17:13.697

@rob I think if you put that blade a 1/8 inch above and think that is safe it is a completely false sense of security. I keep mine up above, half inch or maybe a bit more. I can see the blade clearly, I can see move clearly if there is some pinching. I think if you are just barely cutting through you can't see as well. And thinking that it is safer is just NOT. If they material collapses and you are depending on that material being there to protect your digits....it's just better to be aware of the danger. – Andyz Smith – 2015-05-02T02:11:50.580

1@AndyzSmith I don't agree with your logic at all, but you're certainly welcome to post an answer of your own if you think the other answers here are incorrect. Since you're refuting a safety recommendation prescribed by several reputable modern woodworking publications, I would highly recommend including a reference from at least one such publication to support your reasoning. – rob – 2015-05-02T03:56:19.887

-1

I don't have time to read through the litany of guesswork by armchair engineers, but many pages into this no one mentions that the saw blade gullets should protrude above the cut by 1/4" "or so" for proper blade cooling. Hot blades dull quickly. 90% of these are cautionary guesses by people scared of saw blades. Rightly so, that's why people in the business make guards, and use push-sticks.

Dennis

Posted 2015-04-20T19:16:28.620

Reputation: 7

That is very interesting to hear. Do you have any sources for this as that would help this answer stand out among the others. Also your first sentence might be taken the wrong way by some readers so you might want to rephrase it. Welcome to WW.SE! – Matt – 2018-01-12T20:07:15.243

If you didn't bother to read the other answers, how do you know 90% of them are cautionary guesses? :) Do you have any reference for the cooling aspect of your answer, such as a manufacturer's recommendation? – mmathis – 2018-01-12T20:50:20.403

I only raise my blade about 1/8" above the work being cut, and I've never run my table saw for long enough to have a hot blade at the end. Even when I ripped a mind numbing number of stickers for stacking wood, the blade was still cool to the touch at the end. – Charlie Kilian – 2018-01-12T22:58:43.703

Dennis, don't be a jerk ;-)

– Graphus – 2018-01-13T07:05:19.570