Miter saw blade coming loose

[Doug B]

Clean the INSIDE of the threads on the arbor

Now, there is one thing I did not try yet...thanks Rich.

When I take it apart again, I'll put it back together again without the blade to see if it will tighten.

My biggest confusion remains...how is there any force being exerted on the left hand threaded screw to begin with? I guarantee you that the screw is getting very tight because the times I have taken it back off it requires considerable pressure to break it loose. I can't figure out what is happening, so I don't know what needs to be done to fix it.

[TDHofstetter]

The screw is there to pinch the two arbor washers towards each other with really significant force. If the screw's bottoming out (whether on the tip of the screw or at the end of the threads), it can't apply that pinching force & the blade can slip between the washers like a brake rotor between brake pads on a car when they're not fully applied.

Here's a quick test. UNPLUG the saw. Push in the arbor shaft lock button. Grab the blade with a leather-gloved hand and try to rotate it, both directions, with the lock button still depressed. You should NOT be able to move the blade significantly as you pull the teeth toward your belt buckle, and any movement you get SHOULD result in a sensation that it's being tightened on the arbor. That's exactly what the motor is doing when you pull the trigger & start cutting wood.

If you push the teeth away from your belt buckle toward the fence, you may feel the blade move, and even loosen as it turns that screw clockwise... as to loosen it. That is exactly what the blade brake is doing when you release the trigger & the motor stops the blade.

If you feel the blade slip as you pull the teeth toward your belt buckle, the problem is still there. The washers aren't pinching the blade enough to lock it in place by virtue of the steel-on-steel friction coefficient. We need to find out why - whether that friction coefficient is compromised by something foreign or the screw is unable to apply enough pinching force on the washers because something's bottoming out too soon. There may possibly even be a miter gear inside the saw's gearbox that's backing out of its press fit, permitting the arbor shaft to extend farther than normal, so the screw fully seats before the blade is fully pinched. Possibly.

These are full-kerf blades, true?

[Doug B]

"These are full-kerf blades, true? "

I still have to fully digest the other part of what you posted Tim, but at least this part I can answer, and it might be relevant to the problem.

I started with a full kerf blade and the next one or two were also full kerf blades....but somewhere along the line I tried out a thin kerf blade. That was what I had on before changing to the new blade. And, returning to an older blade, I now have on a full kerf blade on the saw once again. Now I'm just trying to figure out if that has anything to do with the current problem or not...most recent before the HF blade was a thin kerf, HF was not thin kerf, current one is not thin kerf. Everything has been just fine until I put the new HF full kerf blade on,,,after which everything has seemed to go to H*** in a handbasket.

Somewhere in all this mess lies the real problem...just gotta figure out where...