Almost a bad facial injury with wood - Math guys help in finding the speed of the outer rim of a log.

July 15, 2019, 08:13 PM

sig229-SAS

I hope all this makes since....

Turning_gal was turning a 9" log on the lathe this afternoon when half of the log split off and hit her face shield with enough force to knock the shield into her face dislodging her glasses, knocking out the plastic insert, breaking the tool handle and dislodging the 1/4" steel tool from the handle.

She was damn lucky the she had her safety gear on but even so she got two open wounds on her arm from the chunk of wood flying by and a significant headache from the impact of the wood to her face shield.

Now the math question: the lathe was running at 800 rpm's ( I know, to fast ) but that was the shaft speed ( 33 mm ) what was the speed of the rim of the 9" log?

All this is a good lesson on tool safety, wear proper gear to protect ourselves from the unknown, in her case she was damn lucky not to have made a trip to the ER.

July 15, 2019, 08:18 PM

a1abdj

377 inches a second, or roughly 21.5 MPH.

July 15, 2019, 08:23 PM

mcrimm

I have a friend who didn’t wear his safety gear. He lost an eye. Say a prayer of gratitude tonight.
Mike

July 15, 2019, 08:33 PM

Turning_gal

[QUOTE]Originally posted by mcrimm:
I have a friend who didn’t wear his safety gear. He lost an eye. Say a prayer of gratitude tonight.

I will, it happened so fast....didn’t get to scream til it was over...never felt the tool leave my hand or the log hit my head until it was all over. BIG lucky safety lesson today...
Big headache, too....

July 15, 2019, 08:49 PM

sigmonkey

About 21 MPH linear and about 32 feet per second angular.

Or the surface was moving about 21 MPH and the broken piece was moving about 32 feet per second.

If you can weigh the piece, we could figure the Pounds per square inch of impact.

July 15, 2019, 08:51 PM

Turning_gal

quote:
Originally posted by Turning_gal:
[QUOTE]Originally posted by mcrimm:
I have a friend who didn’t wear his safety gear. He lost an eye. Say a prayer of gratitude tonight.

It happened so fast....didn’t get to scream til it was over...never felt the tool leave my hand or the log hit my head until it was all over. BIG lucky safety lesson today...
Big headache, too....

July 15, 2019, 08:51 PM

sig229-SAS

quote:
Originally posted by sigmonkey:
About 21 MPH linear and about 32 feet per second angular.

Or the surface was moving about 21 MPH and the broken piece was moving about 32 feet per second.

If you can weigh the piece, we could figure the Pounds per square inch of impact.

---------------------------

It was 15.9oz

July 15, 2019, 09:26 PM

nhtagmember

v = omega * radius where omega is the angular velocity in radians per second

July 15, 2019, 09:56 PM

sig229-SAS

quote:
Originally posted by nhtagmember:
v = omega * radius where omega is the angular velocity in radians per second

--------------

And the answer is?......

July 15, 2019, 10:08 PM

sigmonkey

About 81 Gs at impact for that block of wood.
Or about as much energy as a fastball at 85 MPH.

July 15, 2019, 10:43 PM

LS1 GTO

quote:
Originally posted by sigmonkey:
About 81 Gs at impact for that block of wood.
Or about as much energy as a fastball at 85 MPH.

The math is strong with this one, it is.

July 16, 2019, 07:06 AM

trapper189

15.9oz = 6,956.25 grains at 32f/s into the ballistic energy calculator says 16 ft-lbs of energy. I'm not sure how to turn that into impact force because despite what you may or may not believe, your wife's head is not an immovable object. In other words, force of impact will be greater if the moving object hits a solid concrete wall than if the object hits a 10 foot block of Jello.

July 16, 2019, 07:25 AM

Turning_gal

Or about as much energy as a fastball at 85 MPH.

________________________________________

Ouch....I can picture that.
Thank you for figuring that out.

July 16, 2019, 08:09 AM

trapper189

Well, a baseball weighs 149 grams or 2,299.421 grains and 85mph is 124.667 ft/s. Plugging those numbers into the ballistic energy calculator results in 79 ft-lbs of energy.

Working the ballistic energy calculator backwards finds that the block of wood hit you with the equivelant of a 38mph baseball, or about the speed of a fastball thrown by an 8 year old. Having been hit by a few of those, they hurt to.

July 16, 2019, 09:01 AM

Sig2340

quote:
Originally posted by LS1 GTO:
quote:
Originally posted by sigmonkey:
About 81 Gs at impact for that block of wood.
Or about as much energy as a fastball at 85 MPH.

The math is strong with this one, it is.

His 25 fingers and toes are an advantage.

July 16, 2019, 09:09 AM

vinnybass

I'm thankful it wasn't worse. Good on you for wearing the safety gear.

July 16, 2019, 09:12 AM

lyman

quote:
Originally posted by sig229-SAS:
quote:
Originally posted by nhtagmember:
v = omega * radius where omega is the angular velocity in radians per second

--------------

And the answer is?......

glad she is OK!!

July 16, 2019, 09:19 AM

erj_pilot

Hang on! Let me recheck that math. Hmmmmmmm...

On the serious side, I'm REALLY happy all you got was a minor cut and a headache. Very treatable at home in lieu of what might have been necessary in the ER.

"If you’re a leader, you lead the way. Not just on the easy ones; you take the tough ones too…” – MAJ Richard D. Winters (1918-2011), E Company, 2nd Battalion, 506th Parachute Infantry Regiment, 101st Airborne

"Woe to those who call evil good, and good evil... Therefore, as tongues of fire lick up straw and as dry grass sinks down in the flames, so their roots will decay and their flowers blow away like dust; for they have rejected the law of the Lord Almighty and spurned the word of the Holy One of Israel." - Isaiah 5:20,24

July 16, 2019, 09:35 AM

V-Tail

erj_pilot's post with the blackboard filled with computation reminds me of the story of the physics professor who was showing the class how to deal with a complex calculation.

He took the whole class hour, droning on, as he filled first the front board, then the blackboards on both sides of the room, with equations and notations.

Finally, as the bell rang to signal the end of that class period, he stood back and gestured to the results of his work, saying, "There. Isn't that pregnant with possibility?"

A voice from the back of the class responded, "It ought to be. You've been fucking around with it long enough."

July 16, 2019, 09:53 AM

ensigmatic

quote:
Originally posted by Turning_gal:
... it happened so fast...

It always does.

Had a buddy that was working on restoring an old horse stable. Wood as hard as cast iron. You know how sometimes you go to strike a nail with a hammer and the nail actually takes off in a random direction? Maybe over your shoulder? Well, that happened to him and the nail ended-up embedded in one of his eyes.

I've worn safety glasses or goggles when using a hammer ever since then.

quote:
Originally posted by Turning_gal:
BIG lucky safety lesson today...

If you always wear safety gear than it wasn't luck, but prudent measures. If you're an on-again, off-again safety type: Yeah, that was luck. As in...

Back in the day when there were only lap belts I was in the habit of wearing them sometimes and other times not. Got in an accident, one day, where the lap belt saved me from being launched through the windshield. That was luck. (I've never ridden without restraint in a car, since then.)

Likewise: I'm now in the habit of always donning safety glasses or goggles whenever I'm working with any power or impact tool of any kind. E.g.: Yesterday I wanted to experiment with my rotary hammer and a scaling bit. Got everything in place and "Oh yeah: Safety glasses." Went and put them on, then proceeded.

Glad this worked out well for you!