Why did I get kickback?

[woodferret]

What does kick-back on the track saw look or feel like.  What are the typical causes?  I did not even know it was a possibility until this thread.

Low grade, underpowered track saws will bind and slightly lift if it's a kerf closer.  The higher torque saws will climb completely out and produce the Makita smile (what I call it) which is an arc over the rail towards your crotch given how it's weighted to the left.  That said, there's plenty of festool tracks out there that have the smile too even with our riving knife, and that's why we have the back stop we're suppose to place behind the saw during a plunge.  Makita has an after-sale kickback stop that locks into their anti-tip rail. 

Kerf closing is the most typical one, although the rail shifting because of sawdust, or just plain user-error of pushing the saw laterally can also cause it.  Plunging during startup or too fast is also another user-error one.

 

[Michael Kellough]

[member=82497]GreenCheck[/member] good call on stopping and asking "what just happened".
As others have said kickback is caused by the blade getting trapped by the workpiece.

I've attached a marked up photo of your workbench, is it flat?  it looks like there are gaps under the 2x4's that suggest the workbench has a high spot in the middle, this could make the timber unstable and cause the rail to move.

Bob.

While the workbench may have a high spot in the middle, I don’t know, the pieces are construction 2x4s that are probably not flat in any orientation the front and back supports with the rail positioning clips are unlikely to move much if at all and even if they do they are probably irrelevant and won’t have any effect, the gap shown one the centre piece that is clamped on the right is rather different as the piece when cut could spring up and that could pinch the blade. This seems to be the off cut piece and as such I can’t see any reason for it to be clamped any many for it to be free

[member=82497]GreenCheck[/member] it would be helpful if you would confirm which are the important pieces.
It is usual to have those to the right of the saw, it seems you may have reversed this.
There are a few occasions when the important pieces are under the rail but this is not the way that most people use the saw.

Maybe you wrote the opposite of what you mean?

With a tracksaw the important piece is usually under the guide rail, partly to take advantage of it’s mild clamping ability but mostly because the splinter guard matches the left side of kerf so you know what the length of the piece will be. Otherwise you have to consider the kerf thickness to know what the length of the offcut will be and that is inconvenient.

 

[Michael Kellough]

What does kick-back on the track saw look or feel like.  What are the typical causes?  I did not even know it was a possibility until this thread.

Low grade, underpowered track saws will bind and slightly lift if it's a kerf closer.  The higher torque saws will climb completely out and produce the Makita smile (what I call it) which is an arc over the rail towards your crotch given how it's weighted to the left.  That said, there's plenty of festool tracks out there that have the smile too even with our riving knife, and that's why we have the back stop we're suppose to place behind the saw during a plunge.  Makita has an after-sale kickback stop that locks into their anti-tip rail. 

Kerf closing is the most typical one, although the rail shifting because of sawdust, or just plain user-error of pushing the saw laterally can also cause it.  Plunging during startup or too fast is also another user-error one.

Another possibility in this case is plunging too close to the stock. Although there is a surplus of rail before the stock it is not supported so maybe the OP started with the saw too close to the stock to avoid bending the rail. In that case you can get an abrupt slamming down of the front of the saw but not much kick BACK.

You get the scarier kick BACK (that can produce the Makita/Festool/etc. smile) when the stock closes around the back of the blade. This causes the saw to jump back and up and the natural response is to hold the saw down but since our reaction is too slow the spinning blade comes in contact with the top of the rail cutting an arc (the smile). If we let the trajectory of the saw continue a few more inches the shoe would spring down on it’s own covering the blade and making it safe. Not something many people care to rehearse.

This can sometimes happen with poor quality plywood but the kerf closes slowly enough that a riving knife prevents the kerf from closing on the blade. It’s more likely to happen when poorly supported or positioned heavy stock moves into the blade as the kerf is created. In that case the riving knife might not be in the kerf yet so it can’t help but the newer saws have an electronic anti kickback feature that will limit this and the other kinds of kickback.

 

[ElectricFeet]

[pic]
I think those are the themes - anything I'm missing or misunderstanding?

Just one: With the clamp to the right of the two exit-side dogs on the workpiece, you risk the work pivoting about the clamp. Like this:

[attachimg=1]

I would swap the position of the clamp and the right-hand dog, like this (‘scuse the crappy drawing ):

[attachimg=2]

Another approach would be to get into the habit of always clamping the workpiece with two clamps. In a production environment, this might be too time-consuming. But it certainly reduces cognitive load, if this is what you prefer. Two clamps = not budging, wherever the pivot point might be.

 

[GreenCheck]

[member=64013]ElectricFeet[/member] excellent point! I should have thought of that. The end stop "should" prevent that pivoting, but it's foolish to rely on it unnecessarily, especially as that's not its purpose and there is indeed some play in it depending on how hard you lock it down. Some very basic common sense can go a long way, and seems to be something I'm lacking in this endeavor.

 

[Michael Kellough]

In my last post I was assuming it was the first board you were cutting.
Not sure my comment(s) are very relevant now…

 

[ChuckM]

The rule of thumb for crosscutting is to let the offcut end cut loose.

That means on the tablesaw, the sawfence must not be used as a stop, and on the miter saw, the stop should be placed on the side where the workpiece is clamped down.

I've seen some Youtubers doing the exact opposite on their miter saws. One day, Murphy's Law will hit them or their unsuspecting viewers without warning.

The tablesaw crosscut sleds should be treated similarly.

A table saw cross cut fence is a rather different case as both pieces of the cut workpiece are being supported past the point at which the saw blade exits the cut.
I have never heard of a case of kickback (I don’t think that it is even a possibility) with anyone using a sled.

The crosscut sled isn't different and it's not about the support on the exit side as a miter saw's fence can also support both the workpiece and the offcut throughout the cut. Kick backs on the miter saws happen not because only one side of the work is supported.

It's all about the stop block that could pinch the offcut and the spinning blade. If the crosscut sled is set up such that the offcut is pinched between the stop block and the blade (e.g. a stop block is clamped on the sled fence on the right side of the blade while the stock is held.on the left side of the blade against the stop block), kick back is not a zero possibility due to blade vibration and the loose piece.

It may be rare but it could happen nevertheless.

See how he moved the stop block away every time he made a cut on the sled (at 1:12 or so):
=1Ng-KUMGNowL5_xA

 

[Packard]

The rule of thumb for crosscutting is to let the offcut end cut loose.

That means on the tablesaw, the sawfence must not be used as a stop, and on the miter saw, the stop should be placed on the side where the workpiece is clamped down.

I've seen some Youtubers doing the exact opposite on their miter saws. One day, Murphy's Law will hit them or their unsuspecting viewers without warning.

The tablesaw crosscut sleds should be treated similarly.

A table saw cross cut fence is a rather different case as both pieces of the cut workpiece are being supported past the point at which the saw blade exits the cut.
I have never heard of a case of kickback (I don’t think that it is even a possibility) with anyone using a sled. You would have to be extremely inventive (not to say idiotic ) to manage to get the blade to catch and even then since there is a fence immediately behind the 2 pieces I’m not at all sure that a kickback can happen.
I would be very interested in anyone who can explain a case where kickback is a possibility

I understand that virtually nothing is foolproof as if you have something that is, there will be some bigger fool to prove you wrong. So I would be delighted for a scenario that proves me wrong and a way for kickbacks on a sled to happen.

I believe, if you used the saw’s fence to meter out the length of the cut instead of the sled’s, and you have the the fence in the default position, that it is entirely possible to get kick-back with a sled.

My saw’s fence allows me to slide it left/right to determine the length of the cut and fore and aft to allow me to avoid trapping the cut piece between the fence and the blade.  By sliding the fence back past the saw blade’s engaging with the stock, you eliminate that possibility.  I can post a photo if that is not clear. 

But repeating my question above, what does kick-back on a track saw look like?  What are the normal causes. I thought  that there was a riving knife on the track saws.  This thread is the first I have come across where kick-back is mentioned in conjunction with a track saw.

 

[Vtshopdog]

Beating a dead horse now:
Consensus is dogs on entry side of cut were primary culprit. 
Plus one for electric feet suggestion for clamp placement.

One input I have is to place a backing dog in hole closest to saw blade.  Looks like maybe you have short and tall Parf dogs?  If you have a full 96mm hole grid, try using one of the short dogs underneath the track nearest saw kerf.  Also, having your support dogs spaced as widely as possible will improve accuracy of your cut angle.  This will not be an issue chopping up semi straight 2x4 from the lumber yard but will be helpful when you're cutting straight, flat machined stock or panels and want as much accuracy as possible.

If you drilled your grid with the Parf system you can get very good results with a track saw.

 

[Crazyraceguy]

Beating a dead horse now:

Yeah, this one kind of took off and I'm late.
It has been covered well.
The main points being push the board into the dogs/fence, from the entry side.
Get those dogs as far apart as practical. (none on the off-cut side)
Clamp between the dogs, if you think it needs clamping.
Do not constrain the off-cut. It will "fall away" as long as nothing can trap it. (this is kind of like the "it's not falling that kills you....it's that sudden stop at the bottom)
Always cut with the concave side of the board up (though ideally start with flat timber)
Be sure you are fully plunged before the teeth touch the wood.
Start with thinner materials, to get more of a feel of what is going on.
Crosscutting a 2x4 is not exactly in a track saw's wheelhouse. Sure, it can do it, but you have a lot of track that is unsupported out there in space. That track can and will flex, in that situation. The saw's own weight and your plunging force are both working against that track staying flat. Ideally, you would want a shorter track and more support under it.

 

[Packard]

Just for the record, a 10” miter saw can be had for $140.00.  Lat year I bought one for $99.00 on sale at Lowes.

(I got tired of carrying my 12” DeWalt up and down the stairs.)

It is not very good, but fine for straight cuts on 2” x 6”, or miter cuts on 2” x 4”.

For very little money this kickback could have been avoided (plus it is light and easily carried).  Plus, it is probably quicker to set up.

 

[onocoffee]

Thanks [member=82497]GreenCheck[/member] for not being too embarrassed to not post this query. The discussion has been informative and instructional.

 

[Cheese]

Beating a dead horse now:

I just love that phrase because I now get to attach the proper emoji.  [big grin]  [dead horse] [dead horse]

Besides, it reminds me of my more rebellious years when I was a part of corporate America.  [smile]

So back to business, I would NEVER EVER constrain the offcut side of the material whether it's wood or metal. Just let the offcut go, it will find it's own equilibrium and it will then certainly not be part of jamming up a saw cut. Gravity does work.  [smile]

In metalworking there's a reason why they call the offcut piece "drop"...as it simply drops to the floor, unrestrained after being cut off from the initial metal stock.

That same setup works for wood products.

 

[Crazyraceguy]

In metalworking there's a reason why they call the offcut piece "drop"...as it simply drops to the floor, unrestrained after being cut off from the initial metal stock.

That same setup works for wood products.

We have always used that term, in the cabinet shop. I've never heard of it being specifically a metalworking thing?
Though I have heard guys refer to it as "off-fall" too.

 

[greg mann]

Just to give the poor horse one last lash: It is not clear how your table is supported underneath but it may be possible that as you made your cut you transferred some your body weight onto the table. If it were able to flex downward that could close the kerf and pinch the blade, causing kickback. If your table is well supported that should not happen but, as I said, I cannot tell how well your table is supported against flex under the cut.

 

[Cheese]

We have always used that term, in the cabinet shop. I've never heard of it being specifically a metalworking thing?
Though I have heard guys refer to it as "off-fall" too.

Now that's very interesting...my professional history is being a product engineer and thus on a daily basis I needed to interface with various craftspeople and be able to speak their language and build a bond with them...that's the quickest way to get things done.  [smile]

Probably 90% of my professional interaction, was with machinists as that was where the items I was responsible for producing came from. I've never heard a metal worker refer to the stuff that falls to the floor as anything other than drop.

Now, I've heard woodworkers refer to this same cutoff using various names & manners but the metalworking folks have always referred to it as drop...just a name assumption norm on my part.  [smile]

 

[Packard]

I wanted to see what kick-back on a track saw looked like.  Google provides some looks.

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.


And do all Festool saws have this feature?

 

[ElectricFeet]

This guy weirdly keeps one hand inside his apron.

He lost use of his arm in a car accident. His journey in woodworking is how the channel started.

And do all Festool saws have this feature?

No. It came out with the TSC 55 ‘K’ model.

 

[Packard]

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.

 

[Crazyraceguy]

How dangerous is kick-back on a track saw.

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

As I see it, the danger is mostly to the track, assuming of course that your hands are nowhere near it.
The saw will somewhat jump up and back toward you, but as you/it lift from the track, the blade is retracting.

And do all Festool saws have this feature?

No, it's only the newer models that no longer have a riving knife.