Quote from: i_ron on January 19, 2009, 09:41:44 PM
Thanks Yucca
Ron

That was a good exercise as I had never stopped to figure out the forces involved in such a seemingly simple device as a rotor at speed.

So much so that it scared the shit out of me, to think that that insignificant little lump could weigh a
half a ton and vacate the premises at 400 Km/hour is mind numbing. There would be no stopping it!

Witness the the recent failure of a universal joint on a monster truck in Seattle where a six year old
boy was killed while sitting high up in the stands, hundreds of feet away.

http://www.cbsnews.com/stories/2009/01/17/national/main4731468.shtml

So first thing this AM I got busy and added a further bolt to the cups on my rotor and put in a stop
work order to Thane until his is brought up to a safer standard.

The little #10-32 bolt has a good strength at nearly 2000 lbs but it is like having all your eggs in one
basket were the failure of a 30 cent component could lead to devastation.  I have chosen to add a
1/4 fine thread grade 8 bolt to the cup from the back. This bolt, by it's self, has a tensile (breaking)
strength of 5450 lbs, to get sheer I have taken 57% for 3000 lbs, the two together then have a failure point of 5000 lbs.

If we take half of this... 2500 pounds ... this would indicate a red line speed of 14500 RPM

Or, to be on the safe, conservative side, a maximum working speed of 9500RPM

Are we all in agreement?

Ron

Quote from: i_ron on January 20, 2009, 04:13:28 PM

Are we all in agreement?

Ron

HUMOR

Paypal just notified me that my credit card will expire and to please update...

It came in January but I hadn't looked closely at it...the new expiry date is 11/2012

Do you think somebodies trying to tell me something?   LOL

Ron

@i_ron
Your work is impressive, the new fasteners look and sound much safer!  Yep the numbers are pretty scary, probably even dangerous after ricochet. and I suppose if it threw one it might cause such an imbalance that some more might come off.

The spec for the Ryobi grinder is unloaded speed of 2850RPM with two stones on it. Speeds beyond that on wall current (whilst drawing output coil power) show something good is going on. Speeds close to or beyond 3600RPM (zero slip) on 60Hz input would be plain wierd as you should then be able to unplug the motor without it stopping.

This thread is great stuff, I´m a regular reader and watch all the vids.

Quote from: i_ron on January 20, 2009, 04:13:28 PM
did an edit on my previus message to correct the numbers, R

Quote from: Yucca on January 20, 2009, 06:27:26 PM
@i_ron
Your work is impressive, the new fasteners look and sound much safer!  Yep the numbers are pretty scary, probably even dangerous after ricochet. and I suppose if it threw one it might cause such an imbalance that some more might come off.

The spec for the Ryobi grinder is unloaded speed of 2850RPM with two stones on it. Speeds beyond that on wall current (whilst drawing output coil power) show something good is going on. Speeds close to or beyond 3600RPM (zero slip) on 60Hz input would be plain wierd as you should then be able to unplug the motor without it stopping.

This thread is great stuff, I´m a regular reader and watch all the vids.

Interesting, I didn't know that and was just quoting the name tag RPM, 3600. So the rotor is
easily the equivalent of two stones, adds a whole new meaning to Mr Tee's test. Must send away
for that Tach ...

http://www.dealextreme.com/details.dx/sku.18239

Ron