Why did I get kickback?

[JeromeM]

[quote author=Packard link=topic=75084.msg727093#msg727093 date=1736455675]
I wanted to see what kick-back on a track saw looked like.  Google provides some looks.
[unsure]
I do not see what this guy did wrong.  I could see myself making the same cut.  But I always use two hands on the saw.  This guy weirdly keeps one hand inside his apron.

[/quote]
His YouTube page contains this information
After a serious car accident in May, 2018 | suffered nerve damage and lost the use of my dominant right hand and arm.
I admit it did take more than a few seconds to get this information  [unsure]

 

[woodferret]

How dangerous is kick-back on a track saw?

I know it is dangerous on a table saw, and the equivalent (climbing the stock) is very dangerous on a radial arm saw.  But what kind of damage is possible/likely from a track saw.

After all no riving knife is required on circular saws sold in the USA.

=26s

A track saw takes a similar trajectory.  As Michael said a while back, the shoe of the tracksaw pops down usually by the time it gets to your leg (mostly).  Not going to try it.  A secured track does keep the lateral forces that cause the majority of climbouts at bay too.  The makita smile I've seen usually does make some arc to the left of side of the rail.  The TSC K with the electronic stop sometimes still nicks the right side near the splinter guard, but tends to not make such a dramatic artifact.

Most though look like this.

 

[woodferret]

[member=74278]Packard[/member]

Here's another video... slightly more pertinent to the current OPs kickback as the setup is similarly unsecured.


The playback slowmo, you can see the rail starts moving wrt to the piece (actually the pieces moves out from under the rail) and then the saw climbs out.  It's pretty violent and happens fast.

In general, I think these videos should be shown to track saw users.  I've seen plenty of YT and tictok influencers hold down the rail behind the saw with their off-hand. 

View attachment 1
(courtesy of "DAS ist der GRÖßTE FEHLER beim Arbeiten mit HANDKREISSÄGE & TAUCHKREISSÄGE! | Jonas Winkler")

 

[Packard]

The thing about kick-back (on a table saw, radial arm saw or a track saw) it that it seems to ambush you. 

If you take off the guard on a table saw and you touch the moving blade, then a reaction might be, “F**k! Stupid, stupid, stupid.”

But kick-back kick-gets you when you least expect it. Ambush.  And the reaction might be, “Geesus!  What just happened?!  darn.”

I am entirely self-taught in woodworking.  No classes.  No mentor.  Just books, magazines and later, the Internet.  I was aware of kick-back from articles on the subject, and yet I got kick-back on the table saw twice.  The first time I was standing aside the cut piece as the articles warned. No damage.  No injury.

But none of the articles warned about cutting very short pieces. I got what I called “kick-up” and ended up in the emergency room (I tore off my fingernail).

So, on the subject of track saw kick-back, the closest I thing I come to the situations that might cause it, is cutting plywood boards that are 12” wide and 16” wide.  I would first rip them to the 12” or 16” width x 96” and then cut them on the radial arm saw.

So, would cutting a 96” long x 12” board to shorter lengths, say 16” or 24” put me at risk of kick-back? 

I normally cut over a sheet of expanded foam insulation and cut about 3/8” into the foam.  So to cut a 3/4” thick board, I would set my blade depth to 1-1/8”.

I would use a TSO squaring arm, and the short piece of track (32??).

Would that be risky?

2” x 4” lumber I would cut on my 12” miter saw (chop style).

Boards to 16” I would cut on the radial arm saw.

Before the track saw, I would cut long boards to manageable lengths using a circular saw (hand held) and make the final cuts on stationary equipment.

 

[woodferret]

So, would cutting a 96” long x 12” board to shorter lengths, say 16” or 24” put me at risk of kick-back? 

I normally cut over a sheet of expanded foam insulation and cut about 3/8” into the foam.  So to cut a 3/4” thick board, I would set my blade depth to 1-1/8”.

I would use a TSO squaring arm, and the short piece of track (32??).

Would that be risky?

Depends on how wide that cut is.  If your track doesn't make consistent contact, then you're back to the videos at hand.  12" tends to be wide enough that you can claw-hand down and forward on the TSO bracket so the board doesn't drift.  Narrower pieces like 6-7" (I've tried) have a tendency to subtly move if you're trying to get a non-plunge cut since the weight of the tracksaw tips the rail.  You either have to use clamps (I set up the pistol one FS-RAPID/R for these types of cuts) or you take the quality/safety hit and do a slow plunge cut (blade at full speed) with the kick stop behind the saw.  The OP's method of rail support in front of the cut also helps if you want to do a pre-plunge - they only missed securing the piece from the right side.

 

[JeromeM]

I am entirely self-taught in woodworking.  No classes.  No mentor.  Just books, magazines and later, the Internet.  I was aware of kick-back from articles on the subject, and yet I got kick-back on the table saw twice.  The first time I was standing aside the cut piece as the articles warned. No damage.  No injury.

But none of the articles warned about cutting very short pieces. I got what I called “kick-up” and ended up in the emergency room (I tore off my fingernail).

So, on the subject of track saw kick-back,

Like you I am self taught, though long before YouTube existed.

I had the advantage of getting an old English table saw with a short rip fence so I have never managed to get kickback.

When I got a track saw I got table dogs and used them in the places that made logical sense, which is that any force pushes into the stops

So, would cutting a 96” long x 12” board to shorter lengths, say 16” or 24” put me at risk of kick-back? 

I normally cut over a sheet of expanded foam insulation and cut about 3/8” into the foam.  So to cut a 3/4” thick board, I would set my blade depth to 1-1/8”.

I would use a TSO squaring arm, and the short piece of track (32??).

Would that be risky?

I also cut on foam, however if your setup would be risky depends on how the long pieces are constrained.
I would use tall bench dogs, you have some, to but the foam and workpiece against. I don’t have a very short rail so would use an 800mm one with the TSO jig.

 

[Packard]

I have a lack of trust for friction holding the track in place.  I almost always use two Festool clamps on the track.  Is that a recipe for avoiding kick-back.

I understand how kick back occurs on a table saw, and that understanding allows me to avoid kick-back.

However, I do not understand the mechanism that creates kick-back on a track saw.  Can anyone explain? Does the blade bind between two pieces of lumber that are being cut?  Long cuts would make that unlikely.  The dropped piece on shorter cuts could bind as it nears the completion of the cut.  Are my guesses correct?

 

[woodferret]

You get kickback the same way you do as on a table saw.  The wood, instead of being sheared cut starts riding on the back saw teeth.  Just flip yourself upside down and look at the TS55 as it's an upside-down table saw.

Any time the wood closes into the teeth behind the back half of the blade, it doesn't as much cut as it just gets pushed.  Because on a track saw, the wood is pinch between your table/foam and saw, it's more likely to push the saw upwards, as oppose to itself riding up.  Once the saw starts riding up, it presents an even weirder angle to the wood and starts a runaway chain-reaction, just like why full kickback pieces running up a table saw also has an arc smile as it pulls itself across the saw teeth.

A drop piece, if unsupported will get randomly flayed around.  But since it isn't pinched, it can't impart substantial force back onto the saw blade even if it hits it wrong.  Much like the offcut side of a table saw cut may kiss the blade, but doesn't do much damage.  On the table saw, if one captures the offcut between the fence and blade, then it starts swiveling back into the back teeth of the blade.  The fence isn't going to move, and neither is the blade, so the wood moves.  If one places a stop on the offcut side of a track saw (or even miter saw), the same thing happens.

Tension binding on a track saw operates the same as on a table saw, hence the desire for a riving knife by most people.

 

[Crazyraceguy]

Though [member=72072]woodferret[/member] comments are 100% true, that is not the only source of pinching, and certainly not the case in this situation. A cut as short as cross-cutting a 2x4, would not involve the riving knife at all.
The issue here is far more likely to be from either bowed wood, unsupported track, over constrained off-cuts, or a combination of them.

As an aside...The pinching, on a table saw, can also come from the wood spreading as much as closing.
The part can push off of the fence, adding pressure to the side of the blade, which is the point of riving knives and splitters. It is also the point of the shorter fences that are generally called "European", though they may not know it as such.

 

[Michael Kellough]

Though [member=72072]woodferret[/member] comments are 100% true, that is not the only source of pinching, and certainly not the case in this situation. A cut as short as cross-cutting a 2x4, would not involve the riving knife at all.
The issue here is far more likely to be from either bowed wood, unsupported track, over constrained off-cuts, or a combination of them.

As an aside...The pinching, on a table saw, can also come from the wood spreading as much as closing.
The part can push off of the fence, adding pressure to the side of the blade, which is the point of riving knives and splitters. It is also the point of the shorter fences that are generally called "European", though they may not know it as such.

Before tracksaws, if the bandsaw wasn’t available, I’d clamp an auxiliary fence to the tablesaw fence that stopped around the front of the blade so squirrelly wood could bow towards blade. Only did it a few times. If the wood is that bad it isn’t good for much of anything and might as well recycle it.