Well, I guess I need to share my misadventure in which I killed my beloved Hitachi C12FDH dual bevel miter saw and its blade.
I was trying to cut off the corners of a 3.5” square in preparation for making a circle out of it. Basically I had a miter saw kickback.
In 20-20 hindsight, here’s what went wrong.
Moral of the story, think it through a little more on unusual cuts. This one cost me $270 and fortunately no one was hurt.
Pictures below show some of the damage. Click on them for enlarged views.
I was trying to cut off the corners of a 3.5” square in preparation for making a circle out of it. Basically I had a miter saw kickback.
In 20-20 hindsight, here’s what went wrong.
- Tried cutting too short a piece. 3-1/2” square
- Plastic HDPE, not wood so it was a little harder.
- Trapped the piece by cutting on the left with the miter angle 45 degrees to the left and a stop block clamped to the saw behind the piece
- Used a hold down stick with a rubber pad to hold the piece, in retrospect this rested on the center of the piece and afforded no resistance to rotation
- Having a positive hook angle blade… it was a small positive hook angle but I incorrectly thought it was a negative hook angle, as a result there was a small force trying to lift the workpiece.
- Failed to recognize the classic table saw kickback formula (nearly square piece about 3.5” square trapped between the rip fence and blade), some lifting forces.
- Cut off the first corner OK.
- Rotated to cut the second corner. I did not realize at this time that the cutoff corner now rested against the fence and presented a much shorter contact area to resist rotation.
- When I pressed my holddown to the piece and turn on the saw, I lowered the blade and there was a huge bang just like a kick-back upon which I released the switch.
- What I figured happened afterwards is that the saw blade bit into the workpiece and put a rotational moment on it that the hold down, centered as it was, did not resist at all. The fact that I cut the outer edge gave it a large moment of force.
- The workpiece actually force itself to rotate 90 degrees as The third corner had a lot of scoring marks and I only was on the second corner.
- The force of the piece turning, but constrained by the blade and the stop block and the fence, put a huge amount of force on the fence and the blade
- The left fence casting upon examination was slightly bent from the force.
- The blade a 12” thin kerf, 96 tooth CMT deflected to the right.
- The blade hit several things, The right fence – made of two pieces, the top part hinged for dual bevel, snapped the casting into two pieces and the blade teeth ate a significant damage into the front edge of the fence.
- The blade also twisted and is between the sides of a steel chute, perhaps ¾ inch wide that forms the sawdust ejection guide.The edge of the blade caught the chute and cut into it about ¾ of an inch, destroying a lot of carbide teeth.The chute is cut and deformed.
- The sudden deceleration of the blade caused a lot of damage to the saw. Aside from the dust chute, the main overarm casting has a 3-4 inch crack that extends through the arbor bearing hole in the casting.
- The bearing thrust holder is cracked.
- The blade is twisted into a pretzel and embedded in the dust chute. Many of the teeth are missing. I was unable to pull the saw blade from the gash in the chute.
Moral of the story, think it through a little more on unusual cuts. This one cost me $270 and fortunately no one was hurt.
Pictures below show some of the damage. Click on them for enlarged views.
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