better a clamp and a blade than a hand or fingers

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Central (upstate) NY
I was kerfing a slot on a piece of walnut to make a handle. I had made this cut earlier in the day, but on a bigger piece. My work was clamped to the fence using three clamps and some scrap pieces.

I felt a pop in the wood and immediately pushed the saw back. This is when I should have stopped the saw and investigated the situation, though I did verify that the walnut didn't move from it's clamped position. Instead I slowly restarted the cut and the piece of walnut blew apart into two pieces. I lost four teeth from the blade and destroyed a clamp. I don't know where the other half of the walnut is. You can see the saw mark on the half I did find; an identical whole piece is on the far left to show the starting piece.

RAS_mishap_02Apr2010.JPG

I had my left hand completely off the workpiece in order to keep me out of the line of fire. This plan was successful - I have a very minor abrasion from shrapnel (didn't even draw blood). My blade vibrated pretty bad while spinning down. Hopefully this is a blade balance issue and not bearing damage or anything.

The reason this accident happened was operator error - I should not have continued the operation after that first abnormal wood reaction. Having said that, proper engineering controls prevented serious injury - clamping the work to the fence kept my body out of harm's way.

Now I need to find someone who replaces carbide.
 
Kudos on having things set up for safety and for being aware of the line of fire. :thumb:

Looking at the picture, it appears that you weren't using a negative rake blade on your radial arm saw. Could that be a contributing factor to the wood blowing up?
 
I don't think so. If the blade grabbed the work to pull it back, I think that would have happened right when I felt the pop in the wood the first time without a chance to react. I think I just hit some inner tension or internal defect.

I don't feel too shaken, but have decided to be done for the night anyhow. Maybe finding the other piece will shed light on what happened. Tomorrow.

By the way, do you know of any negative rake glue line rip blades?
 
You showed the aftermath but failed to show how it was originally set up for the cut. Yess clamping and stepping aside was a good measure, obviously you knew going in that you were setting up a dangerous operation. Would like to see how you were setting up and what you were trying to do.

I too have been known to stretch the abilities of the saw and had similar reactions, Would be nice to see what you did and add to the list of what NOT to do.
 
You showed the aftermath but failed to show how it was originally set up for the cut. Yess clamping and stepping aside was a good measure, obviously you knew going in that you were setting up a dangerous operation. Would like to see how you were setting up and what you were trying to do.

I too have been known to stretch the abilities of the saw and had similar reactions, Would be nice to see what you did and add to the list of what NOT to do.

You are absolutely correct.

RAS_mishap_02Apr2010_initial_setup.JPG

This is enough to give you an idea what I was doing. The brass was still at my machinist friend's stash and the bag of hardware wasn't on the RAS table.

The blade (the 12" FTG in the original pic) was much, much higher and the piece shown was successfully kerfed using three passes of sequentially lower blade height. I clamped the piece directly to the fence using the middle clamp, and I clamped a piece of wood to either side of the piece for extra stability. Maybe the piece that blew up was just too small to be stable for this cut.

As an aside, would this cut be described as a through-mortise, a groove through the end or is there another word for this cut?

I still feel like an idiot for not ceasing the operation with that one piece of wood when it tried talking to me. At least I made the right safety decision by keeping my hands out of the picture.
 
Woooo dude! Stretching the limits of the clamps and pushing the envelope of safety. First, Resawing puts a tremendous amount of friction and force on the sides of the blade, it is multiplied with each inch of depth. By the time you had the saw blade deeply impelled into the kerf. Count the teeth inclosed in the slot (kerf) multiply that by the torque of the saw. at whatever Rpm and HP rating. KERPOW! how can fibeplastic clamps hold on? How much friction can they apply to that piece to withstand the forces applied through that blade.

You sir, are truely a lucky fellow. A tablesaw in multiple passes can accomplish this with a good fence pusher and finger boards. A Bandsaw properly set up is a better choice, Or a good riptooth handsaw can do a fine job and a lot safer. .
 
Wow. Do it with a handsaw, or run a bigger piece through the planer then cut it for width/height. Those little quick grips aren't qualified to hold anything either. I wouldn't trust the bigger ones to hold those pieces either.

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I don't think so. If the blade grabbed the work to pull it back, I think that would have happened right when I felt the pop in the wood the first time without a chance to react. I think I just hit some inner tension or internal defect.

I don't feel too shaken, but have decided to be done for the night anyhow. Maybe finding the other piece will shed light on what happened. Tomorrow.

By the way, do you know of any negative rake glue line rip blades?

Hi Mark - Mike Jackson, a rep for Leitz had some 30T rip blades with a negative hook....they're pretty well made and very reasonable. Drop him a line and see if he has any left. mjackson@leitztooling.com
 
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