Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Parabolising stroke

  • Please log in to reply
2 replies to this topic

#1 David Dakstar

David Dakstar

    Explorer 1

  • -----
  • topic starter
  • Posts: 59
  • Joined: 03 Mar 2017

Posted 22 May 2022 - 08:03 AM

I am figuring a 20 inch f/4.1 mirror with a sub-diameter 10 inch pitch lap. I want to use a W stroke more.

 

But I am not sure exactly how to do the stroke correctly. I need to deepen the centre and middle zones compared to the outer zone. Should I do a narrower W stroke nearer the centre and a wider one further out? Or keep the stroke the same all the way across the mirror? I have read explanations for the W stroke MOT. But cannot find any for TOT.

 

I am using a powered turntable rotating at around 3 rpm and figuring by hand. I have been using centre over centre strokes with various offsets from the centre, but I think a W stoke should give a smoother surface.



#2 PrestonE

PrestonE

    Mercury-Atlas

  • *****
  • Posts: 2,615
  • Joined: 29 Apr 2005
  • Loc: San Miguel de Allende,Mexico

Posted 22 May 2022 - 09:08 AM

I find it easier with a Powered Turntable to do the Offset

and do say 30 seconds with one length, 45 seconds with another

ect...

 

Easier than trying to keep a W consistent...

 

Though, I actually use the Overarm and change the stroke and time

depending on what I am trying to do.

 

That is How Carl Z does it.

 

Best Regards,

 

Preston


  • Pinbout likes this

#3 Scott E

Scott E

    Explorer 1

  • *****
  • Posts: 88
  • Joined: 12 Jun 2008
  • Loc: New York State

Posted 22 May 2022 - 08:27 PM

The narrower the W and the shorter the strokes, the faster you'll deepen the center. That could lead to a zoney surface but don't worry about that till you're near the end. At that point you'll need to cover the whole mirror pretty evenly. You'll start to get a feel for how your tool works in time. Every tool is different.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics