Scary moment today!

[davidtu]

This is on a BT3100...

I put on a new blade (no, not the rip blade from my other post!) and when I started up the machine, I heard a weird sound of the blade hitting something and I immediately shut down. When I took a look, I found that the blade had hit against the throat plate. I also found that the arbor nut had worked loose! Now that I find scary as heck!

Fortunatley, I turned off the machine in time before anything bad happened either to me or the new blade (Woodworker II, no less!)
Live and learn--but be sure to keep on living!!

[gary]

Wow - close call.

I about wet my pants this weekend too. I was cutting a piece to length with my crosscut sled and the small wedge chaped cutoff decided to wedge itself into kerf in the sled. The blade stopped instantly and the circuit breaker blew. I had to hammer the sled free. No damage to blade or my pants!

[LarryG]

I also found that the arbor nut had worked loose! Now that I find scary as heck!

Forgive me if this sounds condescending or critical, but in the interests of safety (yours, and anyone else who may be reading):

The arbor nut has left hand threads, specifically so that the threads will be opposite to the direction the motor's armature rotates. This means that it cannot possibly "work loose" ... instead, as the motor runs there will be a natural tendency for the nut to TIGHTEN.

What probably happened is that you did not get all the arbor spacers and the large side washers stacked nice and flat against each other when you put on the blade. It's all too easy for one of these to get hung up on the arbor threads, so that the nut will appear to tighten down securely even though there are some gaps in the stack. When power is applied, the stack "jumps" just a bit, which relieves the pressure on the hung-up component in the stack, and now everything is free to flop around.

Glad your little adventure wasn't any worse than it was!

[just4funsies]

You beat me to it, Larry. Those were my exact thoughts when I read the original post. The fact that the blade was just changed cannot be purely coincidence.

[davidtu]

Yes Larry I agree wholeheartedly with your assessment. By worked loose I did mean that the washer had shifted. When I was tightening the nut, I remember thinking it required "extra" wrench travel to get it to snug up but for some reason--probably because I was anxious to see if this blade exhibited a particular problem I was having with another blade (see the rip off thread)--I didn't question it but just kept going until it snugged.

After the mishap, I did have to shift the inner washer to vertical in order to set the blade properly once it had become loose... so I do think that the washer was caught up in the threads... that it required extra wrench travel to snug up because it was just shifting over thread by thread until it finally jammed enough to feel like it was tight. And then when it spun up (and possibly because it also hit the throat plate--perhaps lucky I guess since the noise alerted me right away to the problem) it unjammed and the nut was then loose.

I hate to think that I made two errors in one installation, but I guess I did... the nut and the throat plate! AND I can add two more errors--I ignored a sign that something was off (long tightening time for the nut) and I didn't do my usual habit of lowering the newly installed blade into the housing to see if it spins up OK the first time.

All in all, I guess I was lucky. Many accidents are the cause not of only one mistake, but a nexus of several... certainly had enough going on here to have been much worse, I suspect.

Thanks for your comments.

-david