| The piece ricocheted around for a bit... thank you leather apron.
| The sudden imbalance vibrated the router darn near out of my
| hands... like Donal Duck hitting a tree with a stick and getting
| some 'feedback'.
| NO idea why the carbide let go..I didn't hit anything.
I'm glad /you/ weren't damaged.
Y'know, I've always felt silly wheeling my little rolling wall to
shield me from bit fragments when I thought a CNC routing operation
might be even a _little_ risky - and suddenly I don't feel so silly
A dab of Bondo and you'll be back in business... ;-)
DeSoto, Iowa USA
...a little aluminum paint..who'll know, eh? <G>
I agree with the scatter-shield idea. That little scab of carbide was
a bit scary..imagine the whole thing snapping off at the shaft... a
pound of crazed, carbide metal looking for a target at 8,000 RPM.
Maybe I should upgrade to a kevlar apron.. although sopranos do all
get all the good parts in an opera. But yet, I can't imagine any
Viking helmets with any styling to them.
Ducking behind a wall was always comforting during hand grenade
practice, although a nuclear hand grenade may be of some concern.
(After several hundred failed trials, research has since proven that
the average soldier doesn't quite have enough 'arm' to lob one of them
Just to sort of set you mind at ease: I've had a 1/4" roundover bit snap
at the shaft while routing. The bit does *not* go flying all over
creation. It just sort of stops where it is at and falls down. Now, maybe
if you have something with a lot of mass you may get some of the momentum
to translate into motion, but it appears that since the bit is embedded in
the wood, once you take away the energy spinning it, all motion comes to a
stop pretty quickly.
Yikes! I like my sopranos with cleavage, thank-you.
If you're gonna be dumb, you better be tough
Mark & Juanita wrote:
| Just to sort of set you mind at ease: I've had a 1/4" roundover
| bit snap at the shaft while routing. The bit does *not* go flying
| all over creation. It just sort of stops where it is at and falls
| down. Now, maybe if you have something with a lot of mass you may
| get some of the momentum to translate into motion, but it appears
| that since the bit is embedded in the wood, once you take away the
| energy spinning it, all motion comes to a stop pretty quickly.
That's somewhat reassuring - and matches my own experience. I've
managed to break six bits so far - three of 'em in one day! They were
all straight bits, and four were carbide up-spirals. In every instance
the breakage was due to operator error and/or inexperience - and in
each instance the broken-off portion was left sitting at the end of
I also had a 1/2" up-spiral climb down out of the collet. That was a
bit more spectacular, with a shower of sparks and a sudden wrenching
that made the half-ton 'Bot jerk. It gouged the MDF table top, but
only traveled about two inches. I retired both bit and collet (both
were scarred) and became really fussy about making sure that bits and
collets both are clean and oil-free before use.
Still, I can't help but like Rob's Kevlar shop apron idea. :-)
DeSoto, Iowa USA
Two problems with the kevlar idea.
1) Kevlar does not stop sharp edges. Which is why they don't stop knives (or
arrows). And you can be sure that the carbide on a router bit has a sharp
edge on it.
2) Kevlar still allows blunt trauma. If a big chunk of metal/carbide were
to hit you at a high rate of speed, it would be nice if the protection
wasn't flexible. You still end up absorbing the hit, even with kevlar.
If you were going to create a sheild, I would suggest something solid,
either on the tool itself or hanging off the front of you.
I keep getting the image of that classic Clint Eastwood western. He had a
stove door hanging off the front of him underneath a mexican blanket.
I was going to keep away from this as it usually invokes the
academically inclined to argue "the tangenital point of release from a
rotating object" arguement rather than the
that use machines a lot.
I have been using a roundover bit that shed a piece of carbide. It
did not slowly come to a stop. It came immediately to a stop in my
leg. Not having the sectional density to maintain and transfer
energy, it went through the denim and just barely went in my leg. It
was easily removed with the point of my pocket knife, and was only
about 3/16" in my leg. No big deal. But a real reminder about
wearing those safety glasses.
I have a buddy that made (subbed out) small cabinets in his garage
that had a large chunk come off a CMT bit that was mounted in his
router table. He knew how to use it, and had been using the CMT for a
So the chunk of carbide came off his panel profiling "helicopter" bit
and went though the back of his fence and dust collection hose, and
all the way through the sheetrock in the garage wall. The insulation
made a nice save and held the chunk securely after wall penetration.
His router/table reacted so violently that he thought something had
gone wrong with the machine, and didn't get to the bit until he calmed
If it had let go at the end of a cut where the bit cutter had been at
6:30 or 7 o'clock instead of 1 o'clock, his life might be very
different right now.
The good new is that after inspecting the bit and large chip, CMT sent
him a new bit.
As a sidebar, I rarely make any raised panels, but after the
helicopter bit crash the insanity of spinning one of those large bits
seemed to me beyond my comfort level. I bought a vertical bit and it
runs smoother and seems a whole lot safer.
Almost as good for all of us, all you need is Clint's poncho:
It takes a minute to load, but it is worth a look. Especially if you
are a garage worker that might be sharing the "shop" with other family
members. Or like Morris, use a CNC.
"Lee Michaels" wrote:
> I was going to keep away from this as it usually invokes the
> academically inclined to argue "the tangenital point of release from a
> rotating object" arguement rather than the
> WTF-just-happened-I-think-something-whizzed-by-my-frikkin'-leg guys
> that use machines a lot.
In the SFWIW category:
Once spent some time as a vibration research engineer for heavy duty
DC machinery for trucks and buses.
Had a problem with alternators throwing cooling fan blades under
Built a box from 2x4's turned on edge and complete with s viewing
window from "bullet proof" safety glass.
Equipped box with casters and would push it in place surrounding
alternator mounted on test stand, then start increasing alternator RPM
until fan failed.
Several fan blades ended up being driven into the 2x4's during the tests.
Solved the problem and nobody got hurt in the process, but that box
generated it's share of comments.
Lee Michaels wrote:
|| Still, I can't help but like Rob's Kevlar shop apron idea. :-)
| Two problems with the kevlar idea.
| 1) Kevlar does not stop sharp edges. Which is why they don't stop
| knives (or arrows). And you can be sure that the carbide on a
| router bit has a sharp edge on it.
| 2) Kevlar still allows blunt trauma. If a big chunk of
| metal/carbide were to hit you at a high rate of speed, it would be
| nice if the protection wasn't flexible. You still end up absorbing
| the hit, even with kevlar.
Understood - a friend once loaded up a black powder rifle and had me
put a hand-cast lead ball through a cast iron stove lid. There wasn't
any sharp involved, but the softer blunt ball punched its way through
the iron impressively.
| If you were going to create a sheild, I would suggest something
| solid, either on the tool itself or hanging off the front of you.
That's how it's set up in my shop. The 'Bot has 1/4" steel sides, and
I built a rolling wall (2x4 frame to support the plywood "wall", all
on casters) to move between myself and the bit. It's not exactly
armor-plate, but I don't (and won't) use massy bits on that machine.
| I keep getting the image of that classic Clint Eastwood western.
| He had a stove door hanging off the front of him underneath a
| mexican blanket.
Ok for the movies - but my experience with the long rifle and stove
lid leads me to hope that the bad guys had cap guns. :-)
DeSoto, Iowa USA
Which is why they use it to make gloves for woodcarvers? Actually, I
believe the problem with Kevlar and knives, arrows, etc. is that the
design allows those long pointy thingies to push between the woven
material and part it, allowing their passage. Doubt that an errant
piece of carbide would have the mass, trajectory and energy to make it
past. As for blunt trauma... If the whole bit went flying and it you,
that might well be a concern. That little piece that Robatoy "lost"
probably would have hardly been felt against a leather, let alone
True but a guy I know who tested his 2nd Chance vest said the bruising
wasn't all that bad when compared to being shot<g>
Loose Mexican blanket in the shop? Sounds like a definite safety
hazard. Imagine the damage that thing could do if it got caught up in
Morris's bot! The damage from the bowls of salsa and taco chips that
were sitting on it alone could wreak havoc with the shop's occupants.
From the looks of that clean break in the carbide, it looks like it was a
flaw in the carbide tip.
I worked in the carbide industry for 30 yrs and when it's a clean smooth
surface, like your picture, that's an internal flaw in the carbide tip.
Probably a microscopic crack in
the material. If surface of the break was rough, then you would have hit
something to fracture it.
Send it back, they owe you a new one.
Glad you didn't get hurt.
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