Re: My first ARSG, or a Dangerous Design?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Barton B. Anderson by way of Terry Fritz <teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>

Hi Ken,

All good points. More below:

Tesla list wrote:

>Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><tesla-at-lists.symmetric-dot-net>
>
> > Original poster: "Barton B. Anderson by way of Terry Fritz
><teslalist-at-qwest-dot-net>" <classictesla-at-netzero-dot-com>
> >
> > No, but will cause the tungsten to press into the set screw and into the
> > threaded hole applying a "goodly" amount of pressure to the tungsten.
>There
>
>with say a 4-40 screw on a 1/8" tungsten rod? You are going to get a
>stripped allen wrench before lots of pressure.

Agreed, that's getting small.

> > is no "dig into" the tungsten, but there is definitely pressure. It's nice
>
>This pressure is going to drop if anything slips. The the vibration will go
>up, the collar slides towards the edges of the rod and the forces go up even
>more. Any slippage makes it useless. Add the force of the opposing side
>collar that just creeped away from the center of the motor shaft. Now it's
>working to pull the other side off. Unless you bite into the tungsten rod,
>you are not locking things in place in a secure way.

In the picture for this gap and in my particular disk, the velocity of 
spinning electrodes is applying force of the electrode to the the disk. The 
screw is not required to retain the electrodes outer force away from the 
motor shaft direction. The screw prevents electrode slippage from the 
forces perpendicular to the outer rotational forces. In my case, the 
electrode is centered to the disk and the set screw is centered to the 
electrodes.

Vibration is definitely an area of concern. My disk is well balanced and 
vibration is minimum. Motor choice (wear, bearings, length between 
bearings, rotational speed, etc.) is important for minimum vibration as 
well as disk balancing. However, not all of my gaps have been this well 
tuned. I'm sure others may have some noticeable vibration in their gaps. If 
I had a gap with vibration, I would not use set screws (tungsten or other 
any other material) regardless. Actually, I'd reduce the vibration. How 
depends on the cause.

> > for adjustments to keep the electrode "unscathed". I've used a set screw
> > setup on a G10/tungsten disk for quite sometime now, and have never had a
>
>Which way were the forces acting in this use?

Ah yes, as mentioned above, perpendicular to rotation.

> > set screw (1/4") or electrode  (.375" x 1.25") come loose.
>
>you don't generally use 1/4" set screws on 1/8" or 5/32" rods. It's not hard
>to torque a 1/4" UNC bolt to several thousand pounds. The clamping force of
>tiny set screws is way less.

Agreed.

> > Just don't use screw locking adhesives (Loctite, etc.). Electrodes get
>hot,
> > thus, set screws get hot. This heat causes adhesives to expand and begin
>
>There are set screws with various plastics inserts wedged into a lenghtwise
>slit in the threads. These add a decent amount of friction to keep a loose
>screw from unscrewing itself.

I would personally have fears of melting the plastic. I prefer metal to 
metal contact.

Good points. Take care,
Bart