I have used disposable router bits for some years. This is the type
where the main shaft accepts disposable blades, usually with 2 or 4
cutting edges. These blades are held in by two grub screws.
Recently an associate mentioned that one had shattered whilst in use -
luckily the bits not harming the user or anyone else nearby.
The question is - since in my normal work stance the blade is very
close to my well developed stomach, I feel very much at risk and what
can I do to minimise this perceived risk?
It has been suggested that as a minimum a leather apron should be worn
( I think perhaps two).
Perhaps a bullet-proof vest?
Any suggestions or comments or experiences?
You'll always find someone who's got a story about a router bit flying
out of control. Even a tooth on a saw blade can break loose and fly...
On the other hand, I think your best bet is to double check your
cutters on the router bit each time you use them. Make sure all screws
are tighten properly and everything's fine. Maybe you can take the
habit of starting the bit at the slowest speed just to make sure
everything's well balanced and in good working order.
Aside from that, there's very little you can do to protect yourself
from a potential accident. Powertools are inhenrently dangerous and as
woodworkers, it's a risk we all have to accept or else you quit
woodworking... A leather apron would provide you very little protection
against a flying knife. Don't forget a router bit can spin as fast as
20 000 rpm. Where talking here of a speed in the range of a few
hundreds miles per hour. Bullets travel at a similar speed so if you
get hit by a flying knife at max speed it's like being shot with a .38
caliber. Your leather apron won't do anything...
IMHO, now you're just being silly. I'm not going to do all the math again,
but here's some sources, and their conclusion.
Router bit speed = ~60 mph at the tip for a 1" bit @ 20,000 rpm
From the rec.guns FAQ (http://www.recguns.com/Sources/VIIE8.html )
Muzzle velocity of a 38 special ranges from 1085 to 760 fps, depending on
weight of the bullet. Works out to
(velocity in f/s) f/s * 3600 seconds/hour / 5280 ft/mile = 739 mph to 518
Order of magnitude difference.
Another important measure is the amount of energy delivered. That same FAQ
lists the bullet energy at 156 to 290 ft pounds. For the router bit, I'm
going to pretend the largest fragment would be about the size of the bullet,
but I'm just making that up cuz I'm lazy. Since the wood-working FAQ lists
the kinetic energy as 1/2 * mass * velocity squared, and the only difference
is the velocity of the two projectiles, the amount of energy of the bullet
would be about 100 times greater. That gives the router bit 1.56 to 2.9
foot pounds of energy, which is less than a .177 caliber airgun.
Whew! Guess I shouldn't have taken today off. :) Net effect is I wouldn't
want to get hit with either item, but I'd much rather be hit by the router
bit pieces. Of course, this doesn't take into account the fact that the
router bit pieces are probably rather sharp, rather than "bullet" shaped,
the leather apron would probably be a good idea (can't hurt).
Routers are dangerous, no doubt. But, if it makes you feel any better,
I had a chunk of carbide off a bit fly off and hit my arm. It was a
pretty good cut, but it's not as if it put me in the hospital or
I did stop using cheap bits after that though :)
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