They don't call them Death Wheels just b'cuz

[Brad Johnson]

Why, yes... yes you should in fact keep the safety guards installed.

Exploding death wheel cuts through polycarbonate and HDPE like the proverbial "hot knife through butter".
https://www.youtube.com/watch?v=KahPvIV2wj8

I had a new one come apart on me once. It was... loud. Luckily I did have the safety guard installed so all I got was minor nicks and scratches.

Brad

[WLJ]

Thought from the title it was going to something alone these lines

[zxcvbob]

Why, yes... yes you should in fact keep the safety guards installed.

Exploding death wheel cuts through polycarbonate and HDPE like the proverbial "hot knife through butter".
https://www.youtube.com/watch?v=KahPvIV2wj8

I had a new one come apart on me once. It was... loud. Luckily I did have the safety guard installed so all I got was minor nicks and scratches.

Brad

Very interesting, and scary.  I can't believe the safety guard would actually stop that; is the guard mainly to make sure some bozo doesn't put on the wrong size disk?  (6 inch disk on a 4" grinder, cuz the 4" spins a lot faster)

ETA: I had the same thought as WLJ before I opened it :D

[Perd Hapley]

What is called a death wheel?

[zxcvbob]

What is called a death wheel?

Portable disk grinder.  (I've never heard it called that before)

[230RN]

I worry about that even with the small thin separating discs on the Dremel tool.

                  

Interesting that a part of it went right through the 10mm plywood, and also that part of the wheel skittered across the whole length of the yard, then hit the fence and still bounced around some more.

Terry

[Hawkmoon]

Exploding death wheel cuts through polycarbonate and HDPE like the proverbial "hot knife through butter".
https://www.youtube.com/watch?v=KahPvIV2wj8

Mildly interesting Youtube channel. Where are they located? Poland? Finland?

[French G.]

Use them all the time. Always manage the plane of explosion so that it doesnt align with your face. If you weren't around for the life of the disc, put a new one on, people seem to think nothing of dropping the tool or hanging it by the disc and then using it.

[bedlamite]

Mildly interesting Youtube channel. Where are they located? Poland? Finland?

Finland.

[zxcvbob]

Now I've started reading about car flywheels exploding (I didn't know that was a thing)  Usually on modified engines using the OEM cast flywheel.

[Hawkmoon]

Now I've started reading about car flywheels exploding (I didn't know that was a thing)  Usually on modified engines using the OEM cast flywheel.

True. I think all race sanctioning bodies required steel bellhousings. A flywheel will slice right through a standard, cast aluminum bellhousing. Since the driver's feet are right in line with the flywheel, it's not something to take lightly.

[bedlamite]

True. I think all race sanctioning bodies required steel bellhousings. A flywheel will slice right through a standard, cast aluminum bellhousing. Since the driver's feet are right in line with the flywheel, it's not something to take lightly.

Not just the flywheel, the driveshaft must be contained too: https://youtu.be/nr4To9xuPT8?list=PLF0UNwsF_jdad3huuNPxYH-xGPjfHw2sm&t=352

[BobR]

True. I think all race sanctioning bodies required steel bellhousings. A flywheel will slice right through a standard, cast aluminum bellhousing. Since the driver's feet are right in line with the flywheel, it's not something to take lightly.

I had a 1966 El Camino I put a L88 427 into, because I ended up at quite a few race tracks when I built it I used a steel bell housing. Not only fly wheels coming apart but you had to worry about all of the clutch components also.


bob

[French G.]

I try to avoid the plane of any spinny bits. I installed a helo engine once, turbine and corresponding shaft i bolted spin at 19.6K and the vibration limit was something like .8ips, which isn't great. Recorded vibes were 10ips, and my hand would go numb from touching the cabin interior structure. I took to being very conscious of where the turbine was. Did all the appropriate troubleshooting and remediation over a day or three, the "experts" on the phone several hundred miles away proclaimed i didn't know what i was doing since i was not an engine guy by trade.

Well, they sent me another motor, went in perfectly, vibes wonderful, one of my best blade tracks ever on a not flown for two years aircraft, and the overhaul facility determined the motor was indeed very much bad. Experts...

[AJ Dual]

Finland.

This is their secondary channel with half a million subscribers where they do side experiments outside of their shop. Their main "Hydraulic Press Channel" where they do experiments crushing and destroying stuff in their machine shop has 2.3 million subscribers.  And their collective number of views is much higher since they're so popular they turn up in people's feeds enough that many don't bother subscribing.

They've upgraded recently, and have partnered with a high speed camera company, and now have a 250,000 fps "bullet time" ring of high speed cameras to catch various kinds of destruction in their shop in 360deg slow-mo.

It's kind of a future shock/cyberpunk thing that a Finn and his girlfriend can become more popular than many television shows, and more viewers than some entire networks even, crushing random crap in his machine shop.  

[Brad Johnson]

What is called a death wheel?

Portable disk grinder.  (I've never heard it called that before)

Google "death wheel grinder pics" for why. Images are disturbing. Consider yourself warned.

Brad

[230RN]

Aircraft spinny bits:

(1) https://www.youtube.com/watch?v=m1U8kII3wwE

(2) Southwest airlines flight 1380

(3) Note the substantial guard ring:
https://www.youtube.com/watch?v=9m7zRLJEIvw

[Boomhauer]

A most appropriate safety video.

https://youtu.be/hq6q2ycIEuM

[MechAg94]

This is their secondary channel with half a million subscribers where they do side experiments outside of their shop. Their main "Hydraulic Press Channel" where they do experiments crushing and destroying stuff in their machine shop has 2.3 million subscribers.  And their collective number of views is much higher since they're so popular they turn up in people's feeds enough that many don't bother subscribing.

They've upgraded recently, and have partnered with a high speed camera company, and now have a 250,000 fps "bullet time" ring of high speed cameras to catch various kinds of destruction in their shop in 360deg slow-mo.

It's kind of a future shock/cyberpunk thing that a Finn and his girlfriend can become more popular than many television shows, and more viewers than some entire networks even, crushing random crap in his machine shop.  

That is impossible.  The TV networks know better what we want to watch.   

[230RN]

So thinking about it, I remember my Pop telling me to step aside a little when starting a bench grinder.  He probably learned that in the Navy.

So thinking about the chunk that went through the plywood, I wondered about how you would calculate the energy the chunk had.  The velocity would depend on the RPM and the chunk's average distance from the center of the axle (to find the "tip speed" at that distance from the center) and the weight by gathering the fragments where possible and weighing them.

Well, by george, by cracky, by gum, then I reckon if you know those two variables in feet per second ("tip" speed) and weight in grains, you could use the regular bullet energy formula.

Seems too simple.  I thought it would be more complicated than that.  Where did I go wrong?

Terry

[dogmush]

Yep: K_e=1/2mv²  Were it me I would probably just stick with M/s and grams, but unit's don't really matter.

Functionally you have a couple of issues though.  First, there's a spin up period to the router, and you don't know where in that RPM ramp up the disc let go, so you don't actually know the RPM.  (for that matter I've found the RPM ratings on the stickers to be more hope than fact).  Then pinning that specific piece back to a position in the 9" disc would be very difficult without some very good high speed footage.  And if you had that you could just measure the velocity on screen ala Mythbusters.

You should be able to pretty easily get a range though.  You can calculate the energy at which the disc won't fail (what it's rated for) and the max possible energy that router could have imbued, and say "it was between x and y Joules".

It's also worth noting that guards and being careful around power tools are a great idea, but the key take away is don't bolt a 6,600 Max RPM disk to a 30,000 Max RPM Router and turn it on. 

[230RN]

Just trying to relate it to "ballistically familiar" units and the usual formula has all the conversion units "built in" in the denominator. Energy in foot-pounds = (V x V X weight in grains) ÷ 450240

V is feet per second.

That 450240 denominator varies slightly with source.  Without re-looking it up, I believe that particular value is from Hatcher's Notebook.

The idea was to figure out how you could get some ball-park numbers.  Note the "average" qualifier. Yes, for precision, a lot better information is necessary, but apparently my guesses and averages and using ballistically familiar methods would work to give you something to compare with a .45 ACP round without going into fig-newtons and other suchlike units in the European manner.  

(I find it necessary to use s more and more lately.)

Terry, 230RN

[zxcvbob]

Yep: K_e=1/2mv²  Were it me I would probably just stick with M/s and grams, but unit's don't really matter.

Functionally you have a couple of issues though.  First, there's a spin up period to the router, and you don't know where in that RPM ramp up the disc let go, so you don't actually know the RPM.  (for that matter I've found the RPM ratings on the stickers to be more hope than fact).  Then pinning that specific piece back to a position in the 9" disc would be very difficult without some very good high speed footage.  And if you had that you could just measure the velocity on screen ala Mythbusters.

You should be able to pretty easily get a range though.  You can calculate the energy at which the disc won't fail (what it's rated for) and the max possible energy that router could have imbued, and say "it was between x and y Joules".

It's also worth noting that guards and being careful around power tools are a great idea, but the key take away is don't bolt a 6,600 Max RPM disk to a 30,000 Max RPM Router and turn it on. 

I believe they calculated the speed from the video, and the disks were spinning just over 14000 rpm when they exploded.  I'm not sure if you want the tip speed or the angular moment of inertia.  (been too long since I took a mechanical engineering course)

[230RN]

"Tip speed" (and the weight of the fragment) will work, bearing in mind that this is not necessarily the actual speed of the outer edge of the wheel, but rather, the average speed of the internal portion of the wheel which is flying out.

Like I said, I was just trying to figure out how you would ball-park some energy numbers to compare with bullet energy.  That plywood penetration and the helmet damage was pretty impressive.

Well, by george, by cracky, by gum, then I reckon if you know those two variables in feet per second ("tip" speed) and weight in grains, you could use the regular bullet energy formula.

Terry