30+inch+TROK+polishing+and+figuring

=__Making of the 30 inch F6 TROK mirror__=


 * __Link to the original web site about making the TROK primary mirror:-__**

http://members.aol.com/DATSCOPE/30inchTROK.html

TROK Ronchi comparison document
Word documents showing polishing and figuring progress

[| TROK Ronchi comparrison document.doc]



TROK Knife edge readings
Spreadsheet files that show the progress of figuring the mirror



Image of the readings taken on the 22022002 is given below. This was the last test completed before aluminising.

TROK Sixtests plots for 22022002




The image below shows the 23 inch polishing lap before the pitch squares are applied. The surface is formed with filler to teh surface of the fine ground mirror. Grease proof paper is put on the mirror to stop the filler sticking to the glass. A thin layer of pitch is then painted on to the surface to seal it to help the pitch squares stick.

The pitch squares ate made in a mould. They are about 12mm thick

The squares are heated with a blow lamp and stick onto the front surface with gaps for the main facets

The lap is then heated in a bath of warm/hot water to soften the pitch. When you can easily stick your nail into the pitch, then it is placed on the mirror that is covered in cerium oxide. Weight is required to enable the tool to conform to the curve of the mirror!!!

The image below shows the tool after a few hours work. Each of the main squares have micro facets cut with a Stanley knife. You can see that the cerium has coloured the pitch squares.

Polihing was done using the machine. Varied strokes were used. Center over center and edge work to blend. Little overhang was used as teh tool was 70% in size. A shine was seen after only an hour. This enabled testing to begin. It showed that the center was high, but recoverable.



A 10 inch lap was used to do most of the figuring. 4 inch and 1 inch laps were used as well.









The test stand was bolted to teh roof of the garage. This allowed teh mirror to lean back in its support and not be totally reliant on the edge (strap) support

Couder and Ronchi testing was used to quantify the mirrors figure. The tester below (made by Steve King) was used. The Couder mask was cut out from thin black plastic. A paper mask was used to aid in cutting out the zones.

The completed mirror after aluminising at Vacuum Coatings is below. Steve is blacking out the bevel.