Re: [ATM] Help me get back to sphere

["Jonathan Bishop" <jonathan_bishop@sbcglobal.net>]

Hi,

Sorry, I keep on saying TOT when I meant MOT below - not that in this case
it should make much different. But that is how I do it.

Jon

----- Original Message -----
From: "Jonathan Bishop" <jonathan_bishop@sbcglobal.net>
To: "The Amateur Telescope Makers List" <atm@atmlist.net>
Sent: Saturday, July 03, 2004 11:30 AM
Subject: Re: [ATM] Help me get back to sphere


> Hi Ken,
>
> Many others have more experience on this than me, but here are my thoughts
> anyway...
>
> You should be able to get back to a sphere by using short TOT center over
> center strokes - provided the lap is hard enough. I suspect that with the
> warmer weather many of us newbies (including myself) are experiencing
> problems with soft pitch laps.
>
> So my advice is to make sure your pitch is not too soft. Maybe try Gugolz
> 73, or boil the pitch you have for an hour or two (outdoors on electric
> pad). Then give it a try. I have not made a Twyman tester (I don't want to
> get that sceintific, yet), but did make sure to get a thermometer so I
knew
> exactly what temperature my garage was. What works for me is to avoid
> temperatures much above 75F, but I guess that depends on the pitch you are
> using.
>
> BTW, I was surprised at how much the temperature was varying without my
> noticing it. I guess we are not very good at estimating temperatures. You
> may want to control that variable at least.
>
> Hope this helps,
>
> Jon Bishop
>
>
> ----- Original Message -----
> From: "Ken Reid" <ken_reid@telus.net>
> To: "Guy Brandenburg" <gfbrandenburg@yahoo.com>; "Rich Ball"
> <ShooterBall@hotmail.com>; "ATM List" <atm@atmlist.net>
> Sent: Saturday, July 03, 2004 12:14 AM
> Subject: Re: [ATM] Help me get back to sphere
>
>
> >
> > ----- Original Message -----
> > From: "Guy Brandenburg" <gfbrandenburg@yahoo.com>
> > To: "Rich Ball" <ShooterBall@hotmail.com>; "ATM List" <atm@atmlist.net>
> > Sent: Thursday, July 01, 2004 7:32 PM
> > Subject: Re: [ATM] Help me get back to sphere
> >
> >
> > > I agree with others that your pitch is too soft. Get
> > > it all off, and then boil it for a while and recast
> > > it. Be sure that it is relatively hard, first. Then
> >
> > Hi All,
> >
> > I've been tempted to ask this question, too, for some time.  My pitch
lap
> > (made with a home made a Silicone II form: 3/4" squares, 5/16" channels)
> has
> > been trimmed once in fifty plus hours. (Gugolz 64 originally:) Only
> recently
> > has it warmed up above 65 F., but it has little affect on getting out of
> > Hyperbola land. (my third trip) It isn't difficult to get a  descent
> > Parabola either. It's just that every stroke suggested  for getting back
> to
> > a sphere digs deeper. Short TOT, Short MOT,  even TOT pabarolizing . I'm
> > chicken to go above 1/3 for turning the edge, again. With the warmer
> > temperature even chordal strokes on the 60% zone have little effect. So
> I'm
> > currently using TOT 1/3 and slowly cutting down the edge. It's a 10" f/6
> > plate glass, by the way. 1.75" thick. I've read Follet's treatise, so I
> > appreciate the edge active, historical implications of pitch lap action.
> > And, I press overnight using wetted Saran wrap between tool and mirror.
> >
> > I've been thinking it's hard pitch. Got to be too hard. Now the thread
is
> > soft pitch is the culprit. This topic 'hyperbola land ' seems to be
> avoided
> > like the plague on the list. Only 1 good reference in the archive. So,
no
> > quick remedy? Simply, a long polish back with 1/3 TOT. Make a Tywann
> tester
> > and avoid all the experimentation? I think once people learn "the way"
> they
> > forget the numerous pitfalls they had to overcome, the details? Could
the
> > tywann tester be a bulwark against this?  Sorry for the rant, I prefer
to
> > shut up.
> >
> > Thanks
> > KR
> >
> >
> >
> >
> > _______________________________________________
> > ATM mailing list http://www.atmlist.net/
>
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