Class #2
Randolph Center Sky Clock -


  2005-2006 Mirror Making Class & Workshop 'Official Page'.

Class #2 Pics and Info
During Class

Ken Slater's photo taken from here

Fine Grinding

Another good class.  Not much accomplished on my mirror, as far as grinding, but I did finish 40 micron grit.  (Just for reference, that's 0.040 millimeters or 0.0015 inches - about 1/2 the thickness of a strand of hair.)  

About mid-day, I worked with Tom Gorka to create a Plaster of Paris blank for my pitch lap.  The blank is just about exactly the size of my mirror blank. as you can see in the third picture.  As Tom was doing this as a demonstration, most of the help I did was in cleaning up afterward.

Here, you can see Tom mixing the Plaster of Paris.
Click picture to enlarge

Ken Slater's photo taken from here

Here's Tom pouring the plaster mix.
Click picture to enlarge

Ken Slater's photo taken from here

Smoothing it off.  Now just to let it dry for two weeks and then coat the sides and bottom with polyurethane or epoxy to make it waterproof.  
Click picture to enlarge

Again, a very fun class.  As the mirror was holding the plaster as it needed to harden, I couldn't do much more on my mirror, so I spent much of the afternoon talking to various club members.  They are very friendly and knowledgeable.  

Later, in the evening, Ken took me for a tour of the Porter Turret Telescope.  (I'll get some daytime pics next class.)  It's got a Turret much like on top of a military tank, that rotates and holds the mirrors.  It's pretty different, as you can't see the stars while trying to navigate across the sky.

I also looked through a very nice Cassegrain scope, as well as a very nice homemade 6" Newtonian reflector.

It was a good day!

Post Class Here, I'm about half way finished with 12 micron grit.  (A micron is 0.00004 inches, so 12 micron is about 0.00048 inches across.)  

It's about the consistency of baby powder, and I have to put it in a suspension of water and then pour it onto my mirror.  This allows for a fairly uniform 'dispensing' of the grit and water mixture.  As Tom says, grinding with this grit feels about like pushing your mirror through warm butter.  

It's starting to get a polished finish, and can start to produce a reflection on it's own.
Click the image to enlarge.

I'm finished with 5 micron (0.00020 inch) grit now.  This also is similar to baby powder, and must be suspended in water to apply.  Please click on this image to enlarge, as it's amazing the detail you can see in the reflection from my ring.
The next steps Now that I'm done my 5 micron grit, there isn't much I can do to the surface of my mirror before the next class.  5 micron is the smallest 'grinding' grit.  Polishing is done with a 3 micron 'grit' (0.00012")

My plaster 'pitch lap' base has been drying for a couple weeks.  This weekend, I've got to seal the sides (actually I guess it's only one side, really) and the bottom.  The top stays unsealed, so that the pitch can grab hold of it better.  A few coats of polyurethane over the next few days, and it should be well sealed for the next class.
Here's a picture I took of the the Moon and Mars back on November 14th.  Just thought I'd throw it in so you could see it.  The image was taken with an Olympus C-700 digital camera at roughly 10x zoom.  If you click the image to enlarge, you can see that Mars does actually have a round shape, not a pinpoint of light like the stars.
It's sealing time.  The plaster tool has had time to harden, and now it has to be sealed before the next class, when we add the pitch to complete the pitch lap.  I've done two coats of polyurethane on this so far, giving it a light grey color.  I'll probably put on at least two more coats, to really make sure it's sealed well.  It'll need the extra protection since it'll be used for polishing, which requires the same back and forth repetition that the grinding tool endured.
Click the image to enlarge.
While polyurethaning my plaster polishing tool, I decided it would also be a good time to put some on my grinding table to get it all resealed.  It's a good idea to reseal regularly, as resealing captures the old larger grits that I used, and ensures that they can't get out to scratch the surface while polishing.
Click the image to enlarge.
I decided also to re-polyurethane my grinding tool.  Hopefully, I won't need it again, but just in case, I wanted it to also be sealed so that any larger grit ,that might be caught in the nooks and crevices, wouldn't be able to get out in the future.  
Click the image to enlarge.
Next class... Finishing my pitch lap tool, used for polishing.



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Site was last updated on: 01/06/2006