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Had a near miss today

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Blog entry by Tootles posted 11-29-2012 01:36 PM 3592 reads 0 times favorited 12 comments Add to Favorites Watch

I’ve heard about it, I’ve read about it, I know it can happen, but today is the first time that it has actually happened to me.

Today I needed to rip a piece of Radiata (i.e. Monterey) Pine on the table saw. The piece was 400 mm long x 140 mm wide x 19 mm thick (16” x 5 1/2” by 3/4”). I did all the right things – I used a featherboard and a push stick, I stood off to the side and I checked that there was nobody behind me (school workshop). Then I pushed the piece of wood into the blade. It went in for about 6” and then just stopped. I kept pressure on the wood but realised quickly that it wasn’t going to move any further so I just hit out for the stop button. Once the blade had stopped came the interesting bit, pulling it backwards off the blade. It didn’t want to come and took quite some tugging to get it out. This is what I saw, can you see it too?

The kerf at the top is about half the width of the kerf at the bottom. The wood sprung closed onto the blade. The fact that I didn’t actually experience a kickback is probably just lucky.

Now let me add a bit more information:

  • The saw does have a riving knife, even if it is improperly adjusted and, I think, too thin. The blade was raised enought that the riving knife could have helped except that the cut had not yet progressed far enough for the wood to reach the riving knife.
  • The overhead blade guard was in place.
  • The saw in question has a large (i.e. 15”) blade. This, I think, is what saved my underwear as the cut had not yet progressed far enough for the wood to come into contact with the teeth as they rose out from under the table. If they had, and I reckon they would have on a saw with a smaller blade, I think the blade may have picked the piece of wood up and tossed it.

I can speculate about how far and fast the wood may have been thrown had the kickback occurred, but I have no idea what would have happened to me in the process. I do not believe that I would not have made contact with the blade though. The blade guard and the position of my hand holding the push stick would almost certainly have prevented that.

All the same, I count myself lucky today.

-- I may have lost my marbles, but I still have my love of woodworking



12 comments so far

View camps764's profile

camps764

802 posts in 1083 days


#1 posted 11-29-2012 01:52 PM

I like hearing stories like this…I think stories of people doing all the right things and not getting hurt in bad situations are just as powerful as people doing the wrong things and losing digits.

Glad to hear it turned out ok for you.

I have had pine do this in the past as well. I think you are bang on about the riving knife, it’s important that it is thick enough and adjusted correctly to prevent this. Even seemingly “dry” “small” boards have moisture and a lot of internal force waiting to be released.

This is also a good teaching moment, maybe someone on here can provide some insight on the proper way to adjust a riving knife. You could volunteer to teach the class and use your story to illustrate the importance.

-- Steve. Visit my website http://www.campbellwoodworking.com

View StumpyNubs's profile

StumpyNubs

6259 posts in 1523 days


#2 posted 11-29-2012 02:09 PM

The problem with a lot of riving knives and splitters is that they are thinner than the saw blade. They are supposed to be shimmed so that they are flush with the side of the blade facing the fence. They use this design so that one knife thickness can be adapted to both full kerf and thin kerf blades. That keeps the work piece from drifting away from the fence and against that side of the blade, the most common cause of kickback. The problem is some boards have internal stress that can cause the kerf itself to pinch closed (like yours did) and contact BOTH sides of the blade.

It would be much better if you could get a saw with two easy to swap out riving knives, one for thin kerf, one for full kerf blades. But even if those saws were available, who wants to buy a whole new saw just to solve a riving knife problem?

The answer, I suspect, are those little MJ SteelPro splitters that Woodcraft sells for $40. They go in the zero clearance insert and come in pairs so you can adjust them flush with BOTH sides of the blade. I don’t have a set yet, but I intend on getting one for each of my saws. You might want to look into them too. Just a tip!

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

View David's profile

David

196 posts in 1386 days


#3 posted 11-29-2012 03:03 PM

Glad you are OK.

About a year ago I was ripping a piece of cherry down to size and something happened causing it to kick back and fly literally 45 ft across my basement before hitting the wall. I was also using push sticks and standing off to the side so I was unhurt, but it’s still a good reminder of why you use precautions and don’t just hand feed everything.

-- Perilous to all of us are the devices of an art deeper than we ourselves possess. --Gandalf the Grey http://davidwahl.org/category/woodworking/

View helluvawreck's profile

helluvawreck

15983 posts in 1589 days


#4 posted 11-29-2012 05:15 PM

I had kick back (first and only time) about a year or two ago. It hit a cabinet behind me and knocked a pretty deep gash in the side of the cabinet. The loud noise was almost like a gun going off. I was so thankful that it didn’t hit me and I’m glad that you weren’t hurt either.

helluvawreck aka Charles
http://woodworkingexpo.wordpress.com

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

View Lenny's profile

Lenny

1291 posts in 2250 days


#5 posted 11-29-2012 05:29 PM

Thank you for the post. As someone who has suffered a recent table saw injury (http://lumberjocks.com/Lenny/blog/31947), I am definitely in a “once bitten, twice shy” mode. I haven’t yet returned to table saw use but when I do, it will be with renewed safety-mindedness. Posts like this help.

-- On the eighth day God was back in His woodworking shop! Lenny, East Providence, RI

View Lenny's profile

Lenny

1291 posts in 2250 days


#6 posted 11-29-2012 09:14 PM

I’d like to correct my link.

-- On the eighth day God was back in His woodworking shop! Lenny, East Providence, RI

View Austons_Garage's profile

Austons_Garage

41 posts in 753 days


#7 posted 11-29-2012 09:28 PM

I’m not terribly proud of it but I’ve had numerous kickbacks for all the best reasons. The worst are when you’ve done everything right and the saw is just out to get you. It happens sometimes, risk mitigation is just that, mitigation.
I’m glad you weren’t hurt.
I had a TS toss a 24×31 sheet of plywood at me, and I thought it broke my arm ( and it probably should have) since then I install the splitter obsessively.

View John's profile

John

45 posts in 796 days


#8 posted 11-29-2012 10:44 PM

I have to say, to me that is pretty normal-looking for a partly cut piece of solid wood. If you cut 6” into most boards, shut off the saw, and pull it back the kerf sides won’t be parallel. I know a lot of the time the rising teeth at the back are making some slight contact with the workpiece, and so holding the stock down is as important as keeping it against the fence. I’ve used thicker splitter stock, but then the work does often bind up on the splitter, which means you have to push harder, which is risky because now you’re pushing yourself forcefully toward the blade.

My question would be, what caused the board to stop moving forward? Did the board clamp shut on the spinning blade? I have a hard time imagining how that would simply stop your pushing the stock without going flying or burning up as the rotating blade would cause a ton of friction. Did the leading edge catch on part of the saw? Little edges around the blade insert or on the fence can cause annoying stops like that especially if there’s a little protruding knot or splinter.

Was it a riving knife or splitter? A riving knife should be adjusted so it’s just behind the blade, with very little gap. It travels up and down with the blade, so is always in the right spot. A splitter setup might leave a big gap between the back of the blade and the front of the splitter. That’s always the scary zone, when the leading edge of your work is passing the back of the blade unsupported, and a major advantage of a riving knife.

The safest option is to just use a band saw for rips!

View ~Julie~'s profile

~Julie~

578 posts in 1757 days


#9 posted 11-29-2012 11:20 PM

I’ve had a piece of pine actually close up at the end, with NO visible kerf at all. This is something in the wood and the interior stress certainly can stop a saw, it’s happened to me. Johnnnnn, obviously you have never had this happen, when it does, you will know exactly what this LJ is talking about.

-- ~Julie~ followyourheartwoodworking.blogspot.ca

View David Craig's profile

David Craig

2135 posts in 1832 days


#10 posted 11-30-2012 04:52 AM

Sounds like you had paws on your blade guard. That would be my guess why you didn’t have kickback and the wood was so tough to pull backwards from. I had the same thing happen with a piece of pine. The wood pinched the back of the blade guard but couldn’t pinch the blade. The blade just whirled and made the kerf larger. I was able to just tap in a wedge behind the blade and finish the cut. Reactionary wood can be scary but these stories are great because the safeguards worked like they were supposed to. Instead of getting a board in the gut, you just had to remove the wood from the safety catch. Much happier ending.

-- There is little that is simple when it comes to making a simple box.

View Tootles's profile

Tootles

719 posts in 1225 days


#11 posted 11-30-2012 09:02 AM

Thanks for the comments everyone. I’ll try give some extra information, starting from the top and working down.

As I said, there is a riving knife, not a splitter, on this saw. I think that it is possibly too thin because it is a 1960’s vintage saw which was not designed for a carbide tipped blade. Carbide tipped blades generally have a wider kerf and so a thicker riving knife should be used. The trouble is that, other than having blades sharpened periodically, the saw has not been serviced or maintained for a very long time if some of the other equipment in the workshop is anything to go by. I did get someone in to look at it recently and, between us, we reckon it is the wrong riving knife. Maintenance is now scheduled for January, so it should be fixed then.

The riving knife is set so that there is only a small gap between it and the blade, but it is also set that it does not protrude from the table until the blade has been raised by at least 2”. Too me, that means that it is too low, though it does mean that to have the benefit of the riving knife, I am forced to raise the blade up high – and that is a good practice anyway. This setting should also be fixed when the maintenance is done in January.

The thing about this incident is that the riving knife did not come into play. The cut had simply not progressed that far. The wood had not even reached the teeth at the back of the blade.

Charles, although it was not my experience, I do know what you mean about gashes in cabinets. When I first arrived in this workshop at the beginning of this year, I was shown a hole in the (veneered particle board) side of a work bench that had been caused by a kickback. Given that the saw has a 6hp motor on it, I took notice.

Johnnnnn, perhaps I don’t often make partial cuts like that very often, but it is the first time I have seen that. I agree about holding the wood down and so my preferred “push stick” is in fact a push shoe ebven though it puts my hand slightly forward of the back edge of the wood. I use that whenever I can and only use a European style push stick when the gap between the fence and the blade guard is too small for me to push it through and still hold it successfully. I am particularly careful on that saw to hold the wood down as I have previously experienced it lifting wood that was being ripped.

What caused the wood to stop moving forward? To be honest, I decided that it was better to switch off than to spend any more time than I did trying to work that out. I believe, however, that it was simply that the board clamped shut on the spinning blade based solely on how difficult it was to removed after the saw was stopped, and obviously on the different size of the kerf from start to finish. It was not the clearance insert because there is not one. Nor do I think that the fence played any part in stopping the wood because, on this saw, the fence has been dliberately set to not be parallel to the blade, with a wider gap at the back than at the front. I’ll admit that is not a decision I quite understand, and it does lead for some inaccuracy when ripping, but it is not something that I have changed in my time in the workshop. Hopefully, this too will be sorted out when the machine is maintained in January.

Ripping on the band saw is not a great option in that workshop. The band saw does not have a fence, and we have no jointer to then get a clean edge. The edge cut by the saw is not perfect, but it is generally good enough for most purposes.

David, there are no anti-kickback pawls on the blade guard. The machine was, in fact, designed without a blade guard and one has been retrofitted. This has been done by having a piece of steel come up from the side of the saw table, up over the top, and then down over the blade to support the guard. Yes, it does somewhat limit the size of what we can cut, but it is simply a restriction that we put up with.

I hope this information, long-winded that it is, all adds more to the story. I suppose I should really post some photos of the saw, but that will need to wait until next week.

-- I may have lost my marbles, but I still have my love of woodworking

View Roger's profile

Roger

15051 posts in 1527 days


#12 posted 12-02-2012 04:43 PM

Thnx for relaying this valuable info to us. It is so important for all of us to go about things using the utmost safety. Even then, we have no certainties of things going safely. Glad you didn’t get hurt. Times like this is when a large “easy-off” switch is very helpful for a quick power-off.

-- Roger from KY. Work/Play/Travel Safe. Kentuk55@bellsouth.net

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