"Blow up" a blank!

[ed4copies]

"It happened in an instant"!!

For my last "Sunday at the movies", I was turning a blank between centers, without the brass tube. As I got to the end, the blank "blew up". I decided to leave this in the video.

Then, yesterday my curiosity drove me to watch the original video to try to analyze what happened. So, I did and here is what I learned:

The video is taken at 29 "frames per second". In the first frame of the "blow up", you can see my tool is at the end of the blank, next to a bushing, when the center of the blank blurs (I speculate it is breaking). The next frame it is even "blurryier"!! only in the middle. The next frame two distinct pieces are flying toward the ground. In the FOURTH frame, the blank is completely out of the frame.

So, a pen blank "blows up" in 3/29ths of a second. Just a little over a tenth.

And, it did NOT break where my tool was.

I found this interesting---hope you do too!!

Ed

 

[bobjackson]

Spooky.

 

[D.Oliver]

I think if dedicate yourself and really work at it you could shave a couple of hundreths off of that time!

 

[ed4copies]

My hypothesis is that the blank broke from vibration.

I could easily have created this vibration, as I passed the midpoint of the blank. And I had felt some vibration in previous passes.

I am kind of looking forward to my next "blow up" to compare the vid!!!
(Probably NOT a good frame of mind for turning pens!!!)

 

[GaryMGg]

I think if dedicate yourself and really work at it you could shave a couple of hundreths off of that time!

:biggrin::biggrin::biggrin:

 

[edstreet]

In all honesty it likely started as a fracture and evolved from there.

This does bring up a very valid consideration to. When you are cutting thin fragile stuff like that where on the placement you are cutting matters greatly. If you are cutting close to the head then everything down hill from that is going to ripple. If you are cutting down hill then the head placement will still have some effects but no where near the other option.

To show this in proof of concept put a blank in a chuck and cut on the end and have it out some distance from the chuck. What you will see is ripples in the cuts and vibration chatter. Mandrel or not the same concept applies.

 

[LagniappeRob]

Take up a collection for a GoPro3+ Black - 1280x720p @ 120fps or 858x640@ 240...
I'm sure there are others, but I was looking at one of these so it came to mind.

It would be fun to see... "Jamie wants big boom"