Overarm guard caused TS kickback?

[Bruce Darrow]

More accurately or more probably, my poor adjustment of an Excalibur guard resulted in kickback today, resulting in 10 stitches to the back of my left thumb. I’ll describe the set-up, the results, post pics of the setup and the two pieces of material being cut and wait for responses re: what I did wrong and how can this be prevented in the future.

The task: cut 5 pieces of 1/8” Dibond (a signmaker’s sheet material – solid plastic core with aluminum faces front and back) down from 12” x 13” - 15” to 12” x 12”. In other words, cut 1 to 3 inches off one end. Single cut, each piece.

Before I turned on the machine, the plastic guard housing was offset left, close to the blade. I centered it (approximately) over the blade. With the fence set at 12”, I began cutting. On the second cut, the 1 1/2 x 12 offcut kicked back and caught my left hand square on the back of my thumb. The workpiece, that between the fence and blade, never moved. The kickback must have occurred after I had cleared the blade with the workpiece, for in the aftermath, there it sat, tight to the fence and several inches past the blade. The offcut sat on the front of the table, where it dropped after hitting my hand. Tomorrow’s pics will make it clear why it kicked back. What is still conjecture at this point is why it got into position to kick back.

I believe that the offcut was riding just inside the left edge of the plastic guard housing, and a small lateral shift of the housing that occurred when the workpiece cleared the blade and guard forced the offcut into the path of the back of the blade. If so, then the gross error was in not making sure that the left edge of the guard housing was on top of the offcut, an adjustment that would need to be checked before each cut. I will confirm this, if true, when I reconstruct the incident tomorrow.

Other considerations:
1. There is no splitter installed. I’m not sure that one would have helped. Perhaps. I’ll take the heat if you all disagree.
2. A sled would probably have been a wiser option, but I have become enamored with the overhead dust/chip collection of the Excalibur, and my sleds don’t allow use of same. Poor excuse, in retrospect. This may have been the gross error.
3. The overhead suction may have contributed to movement of the offcut, but I doubt it. I have seen it move veneer-thin strips and small chunks or knots,
4. The blade was left too high. Again, I doubt this was a major factor.
5. The cuts could also have been made on the SCMS.

I offer all this to warn any similarly ignorant Excalibur users as to the possible danger with this type of cut and to gain feedback so as to prevent it from ever happening again. I am quite aware of kickback causality between fence and blade, and always take care to prevent it. This is the first time I’ve experienced kickback from the left of the blade.

As an aside, I was not positioned to the left of my workpiece, as is generally recommended. Had I been so, I believe I would have suffered torsal or head trauma – Dibond edges are sharp! As it is, I nearly severed the extensor tendon in the thumb, the one that allows the thumb to straighten. I’m in a splint for 2 – 3 weeks while the tendon (presumably) heals.

So fire away folks, and Excalibur users be warned. Pics, and perhaps further enlightenment tomorrow.

Bruce

[Jeff Duncan]

I wonder if the piece somehow managed to find itself at the back of the blade vs the side of the blade? I've had a very long (10'+) off-cut kick back when it teetered on the back of the saw and came back down on the blade....left a nice little hole in my t-shirt;) But I haven't ever had a piece kick from rubbing the side of the blade....I would think it pretty hard to build up any serious momentum from that spot??? Mind you we're talking about the off-cut side where there's not much pressure even if the guard were moving around a bit. Fence side is obviously a different story.

Oh and yes a splitter, or even better a riving knife, would very likely made all the difference in the world. It's position prevents a piece from being pushed into the back of the blade. It would also affect the piece from being pushed into the side if that does turn out to be the case.

good luck, hope your thumb heals well!
JeffD

[ray hampton]

I hope also that your thumb heal okay

[Salem Ganzhorn]

Bruce,
I am very sorry to hear about your accident. The two factors that I notice are: blade height too high and no riving knife. The back of the blade is where kickback starts and riving knives and using a low blade height minimize the exposure of the back of the blade.
Also I have not heard to stand to the left of the blade. Isn't it generally recommended to stand to the right of the blade and out of the line of the blade?
Good luck healing and let us know if you have any additional insight.
Salem

[Peter Aeschliman]

I once experienced kickback using my sawstop PCS with the dust-collecting blade guard in place. To be sure, it's not an overarm style- it connects to the splitter. Similar deal- the offcut (left side of the blade) kicked back after I completed the cut. Like I said, the blade guard attaches to the splitter, so I had the splitter installed.

In my case, the blade guard has "flaps" on either side and has a very narrow profile, presumably so that you can use it for narrow cuts. The problem is that the blade guard effectively pushed the off cut back into the blade.

Luckily I learned my lesson from another kickback I experienced that permanently scarred my forehead (search for the thread I started about a year ago if you want blood and gore!), so I was standing well out of the line of fire. I was actually holding the keeper piece in place, watching the offcut slowly move back into the blade, gritting my teeth, and trying to bump the "stop" switch with my knee. I definitely saw it coming. I now have a dent in the wall.

Anyway, I had a different setup than you are describing, but I wanted to mention it because it's evidence that a blade guard, even with a splitter installed, can cause kickback.

[Chris Kennedy]

I have an Excalibur and I am having trouble envisioning this. It's the lateral movement -- how did that happen? There is some side-to-side play in the scissor arm, but your stock is moving through perpendicular to that. I cannot see how it would impart a force to create a lateral movement. I very roughly ran a small piece of MDF through mine (saw not on) and couldn't get the housing to move left to right.

I think your problem is the splitter or lack thereof. A blade guard will not prevent kickback but I can't see how it would cause it. Originally, I didn't use the stock blade guard/splitter on my saw, and I had it throw a couple of offcuts (once my wife crosscut a 2 by 2 and it threw the offcut and I took it to the chest because I was in the line of fire -- ouch).

Maybe pictures will help, but I'm thinking splitter.

Cheers,

Chris

[John Lifer]

Lack of splitter was/is a major cause of the kickback. As others stated, it would have kept offcut from getting much momentum from the blade. It went around the back and then was lifted and thrown at you. Put it on, or get a low profile that would be under your guard.

[Tim Morton]

Bruce i was thinking about this during the red sox rain delay and we can talk tomorrow...( bruce and i work together, and he was cutting my dibond for me when this happened. )

Could the dust collection from the blade guard have moved the off cut into the blade? We should experiment tomorrow...with blade off.

[mreza Salav]

I have had kick back initiated by the off-cut piece being lifted up by the strong suction at the guard; I was fortunate that the guard did its job in preventing the piece hitting me.
I should say the riving knife was installed properly (on a sawstop) but since the dc outlet was more to the front of the guard the off-cut piece was directed to the front half of the blade.
I think I posted in a thread that too much of a good thing (DC suction) could be a bad thing in some situations...

[Peter Aeschliman]

While I know the back of the blade is more likely to throw the work piece at you, remember that any of the teeth along the circumference can throw the work piece back at you too... the splitter keeps the work piece from twisting and pinching on the blade, but it will do nothing to keep the offcut from being thrown if it touches any other of the teeth on the blade (i.e., the top or front of the blade). As I said earlier, I had kickback with the splitter installed, and mreza also had this happen with his riving knife installed.

Absolutely put a splitter on the saw- I'm not arguing that. And a splitter very well could've prevented this accident (no way to know based on the info provided), but if the blade guard is somehow messing with your offcut piece, a splitter won't guarantee that you won't get kickback. You need to figure out how or if it was caused by the blade guard and address that too.

[Keith Hankins]

Sorry to hear your accident and wishing you a speedy recovery. I will reccomend two of these. they are not cheap, but will address all the issues that led to your accident. Obviously, they are many options out there and ways to deal with it, but I have been using two of these for years now (I had a kickback many years ago and appreciate the danger). These are great for small strips as thin as 3/16. With two I keep one in contact at all times feeding long boards through the blade. It applies equal pressure on the material on the left and right of the blade and keeps things at bay I do use the microjig as a low profile splitter as added safety and its easily removable.

http://www.microjig.com/

[Tim Morton]

UPDATE: It was easy to reproduce the cause of the kick back this morning, and i will let bruce explain further, but the suction of the overhead dust collection hose was strong enough to lift the off cut off the table an into the blade. This was compounded by the fact that the off cut was slightly smaller than the space between the Plexiglas of the blade guard, and the blade. So a teaching moment for sure. There are some unanswered questions, and he will put some pictures up.

Here is the video
View My Video (http://tinypic.com/r/2prsn50/6)

[glenn bradley]

Hope you heal fast and well. My information is pretty useless after the fact but, I do appreciate your sharing. It adds some credence to what I am currently doing and we are always better off when sharing information as opposed to making decisions in a vacuum. I do not use the overarm on cuts that result in small pieces. Small is a relative term based on your DC and your material density but, for me its anything the DC can pick up or move. I use the same logic on the router table and the DP for that matter ;-)

[Ryan Brucks]

Sorry to hear about your injury but thanks for posting this. I was confused about why you thought the guard itself bumped the offcut... doesn't the excalubur ride above the workpiece??

The subject came up in a thread about blade guards a week or so ago. I have done some small experimentation with this myself as I have a powerful 5hp DC that can lift small offcuts. I have DIY guard that rides completely above the piece though... no chance of "bumping" the workpiece with it.

Obviously lighter, smaller pieces will be more easily affected by the suction. The thin sign material you are using is probably fairly light and easily moved by the airstream. A splitter might help in this situation, but I don't think it will 100% avoid it, as the piece can still try to rotate to get closer to the air suction, and then the front corner could still strike the blade.

As Tim mentioned, the most dangerous situation is when the offcut is thin enough to actually fit between the blade and guard side. In addition to hitting the blade, it could somehow bind up inside the guard. Hopefully it just harmlessly shoots behind the blade (i've seen this once), but if it gets stuck somehow, that could get nasty.

Longer and wider pieces are less dangerous since they have enough mass elsewhere to keep them down.

What I found was that when making small offcuts, making sure the blade guard was around 0.5" above the workpiece stopped all instances of the piece being moved by the airstream.

Of course dust collection efficiency suffers, but I think its a good idea when making smaller offcuts. When doing most thing I run the blade guard closer to 0.25" above, or a tiny bit less.

[Peter Aeschliman]

So too much dust collection CAN be a bad thing huh?!? Who would've thought!

So how will you address this? Open another blast gate in the system to reduce suction and/or choke the blade guard blast gate down?

[Van Huskey]

Thanks for sharing! Very important information. Now the question is how to set up a test to determine if suction needs to be reduced on an overhead guard and if so by how much. An initial guess would be if it can lift a piece large (heavy) enough to cause a significant injury then it needs to be reduced...

[Ryan Brucks]

can the excalibur not be set to ride up higher or anything? does it have an ability to fix the height at a certain level, or does it always have to be lifting up by the piece?

I ask since raising the guard is more effective at stopping pieces lifting than reducing airflow. even at low airflow, you'll get some suction with a smaller gap. increasing the gap lets you have the same airflow without picking up the piece.

[Tim Morton]

So too much dust collection CAN be a bad thing huh?!? Who would've thought!

So how will you address this? Open another blast gate in the system to reduce suction and/or choke the blade guard blast gate down?

I suggested that we not use the over head dust collection on small work like this, and he gave me "the look"...like that was not an option. But with a ZCI and dust collection at the saw i think thats worth looking at.

As for raising the guard itself up , and in effect lessening the suction...to me that seems risky. It for sure would help, but i think you want to eliminate or minimize the risk, rather than just reducing it.

[Mike Goetzke]

UPDATE: It was easy to reproduce the cause of the kick back this morning, and i will let bruce explain further, but the suction of the overhead dust collection hose was strong enough to lift the off cut off the table an into the blade. This was compounded by the fact that the off cut was slightly smaller than the space between the Plexiglas of the blade guard, and the blade. So a teaching moment for sure. There are some unanswered questions, and he will put some pictures up.

Here is the video
View My Video (http://tinypic.com/r/2prsn50/6)

This is why when people ask which Shark Guard to get I recommend the one with the 2.5" port versus the 4". With the 4" I have had small cut-offs get sucked in just enough to hit the top of the blade and bounce around like you were making popcorn. I added a gate to the 4" port and solved the problem. I also always use a splitter.

Mike

[mreza Salav]

Here is the no so old thread in which I reported a similar incident (but I wasn't hurt). I was cutting some acrylic 1/4" sheets:

http://www.sawmillcreek.org/showthread.php?186661-Too-much-of-a-good-thing-could-be-a-bad-thing&highlight=

I haven't had the time to fix the problem but my intended solution has been to add a couple of strips running parallel to the blade at the bottom of the guard to the left of the blade;
this way when the guard is on the piece the off-cut pieces will be held down by those strips and yet you don't sacrifice air-flow.
BTW my homemade guard has a 3" hose that merges with the 5" hose of the base to a 6" duct going into a 5HP cyclone.

[Bruce Darrow]

This AM's experimentation and reconstruction of the accident made the whole thing quite clear (or nearly so....) It is certain that it was DC airflow/suction that lifted the offcut up off the table, allowing it to fall onto the spinning blade. POW! Be sure to check out the short video link in Tim Morton's second post.

Neither a riving knife or splitter would have prevented this. Flesh sensing technology would not have prevented this. I do not say either is unnecessary or undesirable. Just saying, doncha know.

Chosen pics are posted below:

238205 This is a reconstruction of the immediate aftermath

238206 The culprit. Note the bloody dent in the right end. Also note that the piece has somehow flipped, with what was the leading edge when it contacted the blade now trailing. It had to have been cartwheeling when it hit me (!)

238207 Note the offcut entirely contained within the guard housing

238208 Another view of same

So the jury is in. Overhead dust collection can be quite hazardous if precautions aren't taken to prevent small offcuts from lifting off the table. In this instance, a right lateral shift of the guard housing so that its left side rested on the offcut would have prevented the accident. The use of a sled, with the whole arm/guard assembly pivoted out of the way, would have prevented the accident. Making the cuts with no DC airflow at all would have prevented the accident. I think each individual operator/shop needs to make the call, depending on the circumstances surrounding the task at hand. The important thing here is that a lot of us have been unaware of this hazard, until now, at least in the case of those who have followed this post.

Now how do we, the enlightened, spread the word to the rest of the woodworking community, before another incident triggers the dreaded lawsuit, with all its undesirable aftermath?

Thanks to all who responded. There are some good questions and suggestions above that I, at least, haven't responded to yet. I'll log on again tonight, when rates-by-the-minute (dial-up orphan - poor me!) are cheaper and try to respond individually.

Be safe!

Bruce

[glenn bradley]

The use of a sled, with the whole arm/guard assembly pivoted out of the way,

That one gets my vote. Thanks for taking the time to go through this so thoroughly. We can try to forsee what is going to occur during an operation but, we can't always see every possibility. The more we share info like this, the more thorough our safety thinking will be. Kudos and heal soon.

[Bruce Darrow]

Salem,

With regards to body placement: All "tutorials" or safety articles I have ever seen recommend placing the body to the left of the blade, keeping it out of the path of kickback from between the fence and blade, which is where most feedback occurs.

[Bruce Darrow]

Keith,

Thanks for the recommendation. I'll look into these and, as I usually use a ZCI, their splitters as well. I've also seen (somewhere/when) where folks make their own removable splitters.

[Bruce Darrow]

Mike,

I'm with you here. I bought the Shark guard for my own saw, after buying the Excalibur for the saw at work, and went for the 2.5 as well. Even with the small port and a 6" port on the cabinet, I have gotten some veneer thin rip offcuts sucked up into it. After yesterday, I'll be rethinking my use of it as well.

[Bruce Darrow]

Mreza,

Very similar story. Sorry now that I missed it the first time around.

[mreza Salav]

I hope your injury heals soon.

I somehow think the danger caused by this situation isn't publicized enough and many people (like you and me) might get caught off-guard.
I think that posting them on these forums helps but the threads may get lost soon and not everybody sees it.

[J.R. Rutter]

I have had this happen to me, fortunately with less pain, but I still have the scar.

I will just throw out here that I have done some cuts in the past where I taped a zero clearance filler into the bottom flat section of the overarm guard. In my case a Biesemeyer. IIRC, it was a piece of MDF. The front of the guard was still open for air flow, but the filler kept little offcuts from getting sucked up.

[Ryan Brucks]

Interesting note on the linked thread for people making their own guard.

Someone mentioned the position of the dust port on the gaurd in relation to the blade could matter. if the port is directly over the blade, or (worse) centered on the opposite side of the blade as the offcut, that will cause a tendency to pull pieces into the blade more. If you can adjust the port so that its centered over the same side as the thin offcut, any "lifting" action would me more straight up or away from the blade. Of course not sure how feasible this is for different guards. For my guard its hard to follow that advice since my guard gets narrower at the bottom than the top... so I don't get much wiggle room either way.

[Ryan Brucks]

some pics of my blade guard. has pieces to surround the riving knife which keeps the guard safely away from the blade should it get bumped. Also reduced the volume of the guard some.

http://worstkind.com/shop/dc/blade_guard_03.jpg


With the design of my guard, those little "baffles" prevent pieces from lifting up very high (probably doesnt help much). More important, they also mean that once a piece has been cut, it's already mostly out of the airstream, with the exception of very short pieces.

Now I cant say how much of a factor it was, but I notice with the excalibur, there's quite a bit of open space behind the blade, with nothing to stop the pieces from lifting up.

I also think its a poor design that the excalibur guard has a large opening at the rear and front only. that means that strong airflow is always going to be channeling right in through the back, especially when cutting a thin piece (ie, sides close to table). Cutting a thicker piece would raise the guard more, and then the opening at the rear would no longe be a large source of intake air, meaning pieces aren't as likely to get sucked up.

Another way to "fix" this (instead of blast gates) would be to put a hole in the guard somewhere with some kind of closeable flap. The idea would be to open this little port when making cuts in thin material, and it would allow the air to come in from other places besides the front and back. I think this would be more effective than simply lowering the airflow with a blastgate. Simple way would be to just make a circle hole, and get a larger circle piece and just use one screw to pivot the flap to open or close it. Looks like the side has lots of room.

or you could just open up the front more and close in the back more.

[Larry Frank]

This has been one of the most informative threads that I have read in a long time. I am sorry about your injury and hope that it heals quickly and completely.

The accident investigation was very good and came up with the root cause. I wish that there was some more on how to prevent this type of accident in the future. If it were me, I would choose not to use the guard when there is any potential for the dust collect system pulling a piece up and into the spinning blade.

[Matt McColley]

Neither a riving knife or splitter would have prevented this

perhaps not a splitter alone.... but what about a splitter with anit-kickback pawls on it?

[Keith Weber]

That blade looks awfully high in those pics!

[Michael Weber]

This has been one of the most informative threads that I have read in a long time. I am sorry about your injury and hope that it heals quickly and completely.
+1. Thanks to the OP. Going to take a close look at my homemade over the blade guard for possible modification.

[Jim Neeley]

Bruce,

I have an overhead planned for the future and have a question. Is your Excalibur connected to your DC system or a shopvac?? I'm aware it has a 4" connection. I ask because the guard / wood / table gaps limit the flow and, if it were a shopvac you could putentially build up a lot of suction and perhaps using a DC (high volume, low suction) would make it safer. On the other hand, if it's already on a DC that's an even bigger issue.

After reading your post I'm liking the sled idea more and more for these small offcuts.

Jim

[mreza Salav]

Bruce,

I have an overhead planned for the future and have a question. Is your Excalibur connected to your DC system or a shopvac?? I'm aware it has a 4" connection. I ask because the guard / wood / table gaps limit the flow and, if it were a shopvac you could putentially build up a lot of suction and perhaps using a DC (high volume, low suction) would make it safer. On the other hand, if it's already on a DC that's an even bigger issue.

After reading your post I'm liking the sled idea more and more for these small offcuts.

Jim

Your question wasn't directed at me but I express my experience:
My guard is connected to my DC (a ClearVue) and as shown in the thread I linked earlier, I used a sled when this happened. The piece being cut was clamped down on one side only
and the off-cut piece wasn't secured.

[Bruce Darrow]

Jim, I'm connected to a 3HP cyclone. 6" drop wyed, with 6" going to the cabinet and 6" reduced to 4" going to the Excalibur. I just installed a 4" gate on the line going to the Excalibur to allow that to be cut off.

[George Beck]

Bruce

I am so very sorry to hear about your accident. It is scary. Actually table saws are scary. I would mention a couple of things that I see and that I would suggest. First of all, I never use a table saw with out a riving knife. Second the blade is much too high. You only want the highest gullet to clear. Third, zero clearance inserts are a real good idea and finally, when I cut small pieces( 1/8 -1/4) and if the cut off doesn't clear the guard, turn the suction on the overhead via a gate.
Years ago I worried about the suction and small pieces so I installed a blower with a small compressor like a scroll saw. The same problem. On small pieces the blower can push the cut off into the blade and BAM. Now when cutting and the cutoff is smaller than the guard so there is no hold down, I simply turn the suction off. I have had this happen with a miter sled when taking off a little amount to size a frame (1/4 or so). The suction picks up the piece and it bangs around inside the hood. No real danger but scares the bejesus out of you.
Heal fast!

George