From: "Richard Schwartz" 
To: 
Reply-To: "Richard Schwartz" 


How much friction is there between the top workpiece and the driving pin?
Could that be binding?   I have just got my machien wroking again, and my
driving pin is a half inch ball.   I made some stick-on drive plates: 2" x
2" brass squares with a copper pipe end cap soldered to the center.   These
stick on to the back of mirror and tool with pitch.   The turntable has a
hole so that the work can be inverted without having to unstick everything.

. . . Richard
(from Redding, California, on the road to Bellingham)
----- Original Message -----
From: "Tom Stokes" 
To: ; "Amateur Telescope Makers"

Sent: Tuesday, March 18, 2003 10:21 AM Subject: ATM Re: [M-O-M] Still
refusing to spin properly............


>
> What strikes me about your tools is that they seem to have an
> excessive height.  This could be causing a very lopsided
> pressure distribution on the face of the tool and preventing
> a smooth operation.
>
> Tom Stokes
> http://home.pacbell.net/tstokes features my mirror grinding machine.
>
>
> ----- Original Message -----
> From: "John Murray" 
> To: "'Mirror Matic'" ;
"Amateur Telescope
> Makers" 
> Sent: Tuesday, March 18, 2003 2:15 AM
> Subject: [M-O-M] Still refusing to spin properly............
>
>
> > G'day Everyone,
> > Well, after a week of experimenting with different turntable and
> > ecentric speeds(30 - 70rpm T/T, 4 - 20rpm Ecc). 3 different tools (2 x
> > 5, 1 x 6.4"), (different sizes and construction) flipping the blank to
> > give a flat surface to start with, casting against the original curved
> > surface etc etc etc. The bloody tools still refuse to spin properly. I
> > believe that the tool on the outside edge is travelling around 1/2 speed
> > relative to the blank instead of virtually no relative speed difference
> > on the outside where the edge of the tool and blank meet. Am I clear
> > there?
> > The toggle has been constructed with 3 pieces of oil impregnated
> > high density vinyl. An inner one, an outer one and a bush which
> > seperates the other 2 pieces. I've lubed this with water, oil and
> > finally graphite powder. There appears to be no slop in the toggle and
> > it rotates with no binding or friction that I can detect. I have tried
> > sweeping the tool across the blank to no avail, also, stationary overarm
> > with around 1/2" of wag again to no avail. The annoying thing is that
> > the first spiral cast tool I made spun beautifully. It just fell apart!
> > The latest tool (5") with 1/8" gaps seperating the 1" tiles
> > (laid horizontal) started the blank going very, very slightly convex
> > with the edge of the tool around 1/8" (no more) overhang from the edge
> > of the blank? That surprised me. Sweeping had no effect on the tools
> > rotation.
> > I'm considering adding a drive to the overarm to drive the tool.
> > Any thoughts or suggestions? Using the newest feature in the link in my
> > signature will show some of the tools that have been used, not all
> > though.
> >
> >
> > Cheers
> >
> > John Murray
> > Whyalla
> > South Australia
> > Our ATM page is at
> > http://astronomy.sa86net.com
> >
> >
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>

--- BBBS/NT v4.00 MP