[Eurisko]

The 2000 ipm disaster

Well, my router is progressing slowly. Finally mounted my Hiwin rails for the X axis. After considerable leveling and alignment, time to test the motion...

I clamped a 4ft. long, 2 in. square solid aluminum bar to the trucks, and was happily running the bar back and forth by hand. I noticed a little stiffness, not too bad, but I wanted to test it under acceleration.

What to use? Haven't mounted a leadscrew yet. Hmmm...

How about an air cylinder? just hold the rod against the bar, give it a quick shot of air. The spring clamp I put at the back of the rail makes a good stop.

Whoosh!

I estimate that the bar was travelling in excess of 2000 ipm when it reached the "stop". The bar continued on, the trucks cleared the rails, and I spent the next 2 hours searching for those damn tiny little chrome steel balls.

2000 ipm is easy. Stopping is hard.

[CarveOne]

Sounds like it could be the YouTube video of the month. Glad no one was watching from the other end.

CarveOne

[Eurisko]

And I'm glad that my son wasn't sitting on the bar when I had my brainstorm.
I sort of used him earlier that day, sitting on the bar for added weight.

Quit worrying.

He's a big kid. 6 feet, 4 inches. The slides performed flawlessly.

[O'Seanski]

Actually, you may be onto something! Stopping is hard, huh? Sounds like you just need the right kind of brake!

I used to watch alot of PBS when I was growing up, and I seem to recall this physics lecture given by this guy at some southern California university. He was explaining electromotive induction, and had a really cool set-up to demonstrate. The lesson was that when a conductor passes through a magnetic field, it's kinetic energy is converted into electrical energy, and subsequently, heat. This copper bar was suspended via two electrical wires. The wires were such that they allowed the bar to swing very accurately through a magnetic circuit.

Well, the guy started the thing swinging. There it swung, hypnotically between the poles of these two deactivated electromagnets. I probably reached a good eight feet high on either side of the cycle. It looked like a pretty hefty bar, too, so there was a decent amount of kinetic energy there.

He said to his class "Keep watching...Try to get a feel for the momentum...Maybe you can detect it slowing down...Ready?" On the next up-swing, there was a 'click', as he activated the magnetic circuit.

The mass of the bar descended, and suddenly, silently, the bar came to an absolute dead stop between the magnets!

The whole class laughed.

If you used an electric setup for breaking, you could probably get it going as fast as you wanted. It might also be energy-efficient, a la "regenerative breaking".

[gandalf1]

If it is now confession time regarding what we should not do at home here is my contribution.
Many years ago I had a Messerschmidt Bubble car and needed to get the starter/generator rotor off the crankshaft. I tried a simple screw puller but that was no good so I thought hydraulics and filled the available space inside the puller with a thick grease and wound the screw in. I must have put a good few hundreds of pounds of pull what with the hydraulic intensification between screw and end of saft but still it did not work. Next great idea was to remake with a smaller rod instead of the screw and try an impact effect. The cavity was filled with grease, the 'piston' inserted and was hit on the end by a big hammer. Still no movement of the rotor but there wasd a loud bang, a cloud of smoke and the 'piston' shot out and went through the wooden wall of the shed. Next I admitted defeat and bought the proper tool. Possibly the impact tool might have worked if I had not left any air in with the grease.
Don't think there is much of a market for 'Diesel' pullers though.
John.

[CarveOne]

And I'm glad that my son wasn't sitting on the bar when I had my brainstorm.
I sort of used him earlier that day, sitting on the bar for added weight.

Quit worrying.

He's a big kid. 6 feet, 4 inches. The slides performed flawlessly.

I was standing at the end of a friend's homebuilt 1" steel tubing framed servo driven cnc laser cutter one day when he did something in Mach3 that caused it to suddenly go full length of travel at a very high speed and slam into the end stops. I had no time to even raise an arm to block anything that might hit me. There was a loud bang as the gantry hit the stops and the whole machine shook. I just stepped to one side of the machine as he looked rather sheepishly at me to see if I was ok. I don't stand at the end anymore. I am jealous of the speeds he gets though.

CarveOne

[neilw20]

I like my linisher. Always polishing and trimming things with it.
Quite often hold a piece of wood almost on the belt as a stop and pop things like washers on and let them lean against the wood.
A little downward pressure with another piece of wood on the article keeps my fingers from becoming shorter.
If anything escapes it just fall off the end onto the floor. I never stand at the eject end.

I had just fabricated a nice high power hold down magnet that need a final trim.

Took off the rough spots at the round rubber roller end all was well.
Now for the final polish.

Piece of wood in place with right hand. Lower magnet with left hand.
All at once, the steel backed deck attracted the magnet, and I discovered I had a rail gun running at 2000 inches per second or 50 M/Sec.

That's 112 MPH or 180KPH which sent the magnet around the shop. It arrived within 3 feet of the departure point and attached to my clamp kit.
2 1/2 hours to find the damn thing. Only clue was enormous dint in the door and the roof, and I had not broken rule #1 below.
Magnet was 30mm Diameter.

Rule No 1. Don't stand in front of the linisher belt
Rule No 2. Make sure it is off when breaking rule #1