[Author Prev][Author Next][Thread Prev][Thread Next][Author Index][Thread Index]

Re: [ATM] ?Glued Mirror Cell

Richard,

Thanks for the construction info on the cell, knowing the sequence is very helpful.  I will probably not have the scope up and running until summer, but I will keep you posted.  The cell will be a 6 point, 3 bar type, your design, if I can figure out how to set up PLOP to design the particulars, or conventional, using the Automatic Cell Design, which I can figure out <G>.  I am also toying with the idea of collimation bolts which adjust by screwing in and out of something like long bodied, flat-topped T nuts RTV'd to the bars.  This would simplify the design a little, since you would not need the springs anymore, if tolerances are tight enough.  I did read the patent, having found it from Tom Krajci's pages.  Thanks to you both for the inspiration!

Rod 
  ----- Original Message ----- 
  From: Richard Schwartz 
  To: Jan and Rod Shea 
  Sent: Monday, September 13, 2004 9:13 AM
  Subject: Re: [ATM] ?Glued Mirror Cell



  The picture is really helpful.  I like the penny idea.  I was thinking of something like that, but the penny is easier.  What size/thickness did you make the flotation pivot?  Are you basically wetting the penny with the glue, then mating it with a larger blob on the bottom of the bar that, in my case, would already be glued to the mirror?

  We are talking about two different, but similar items.    I assume that you will have levers or triangles to spread the load to points determined by PLOP.    So there will be PIVOT points between the pennies and the levers, and SUPPORT points between the levers and the glass.   For both of theses I would make them about the size of a penny and about the thickness of two pennies.    

  A good way to assemble the thing is to clean the back of the mirror and both sides of the flotation bar (or triangle) with alchohol.  Carefully mark its position on the back of the mirror with a Sharpie pen.   Then degrease one fingertip with alchohol or acetone, and use that finger to smear a small amount of silicone onto the support points on the glass and the aluminum load spreaders.    Assuming you are using bars as in my 5 point right angle design, place the glass face down on a table.   Stack two pennies inside eacj end of where the bar will go, and place the bar in position.   Now you have a two-penny high gap between the bar and the glass that you fill with silicone.   After you get all of the bars attached to the glass, let the assembly cure overnight.

  To attach the bolts with the pennies on them to the pivot points on the bars, remove the wing nut and one washer from each adjustment bolt.  Stick the bolts through the precise holes in the plywood telescope back.  Then replace the washer and wing nut.    Set this assembly on the table with the pennies facing up.   Degrease and silicone smear the pennies and the pivot points on the bars (not attached to the back of the glass), and find some simple object to support the glass (face up) over the pennies.    The height is not critical because the height of the pennies is adjustable with the wing nuts.   When everything is in position with a gap of about two pennies thickness, lift the glass, and squish the silicone onto the pivot points to create the pivot flexure.  Let this cure overnight before you move it.

  Anyhow, that is what worked for me on a 3/8" x 8" mirror.

  Also, there is a patent on this type of flotation.  You can download it from the patent office, but it is in legalese and is hard to read.  The number is 5877905.

  Good luck with your mirror cell.   I attached a 5" mirror at three points in 1972.   I saw that telescope a couple years ago, and the mirror is still securely attached.   You may want to consider the use of a silicone flexure in your diagonal mount as well.   I am sure you can figure out what to do.   Another good way to do it is the Don Clement way: he uses metal flexures instead of silicone.  His focuser is the best I have ever seen.   Come to think of it, I owe him a visit.   Perhaps in a few weeks I'll go down to Bob May's Saturday workshop (It is half way to Mexico from here) and see Don on the same trip.   For now, I'm getting ready to go to the SETI thing in Mountain View, and I'll make a side trip to Berkeley to take Dominic with me (he's in California now).    Yeah, there are real people behind this text!

  . . . Richard
_______________________________________________
ATM mailing list http://www.atmlist.net/