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  #301  
Old 22-07-2017, 02:42 PM
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sopticals (Stephen)
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Smile Gugolz #55

Quote:
Originally Posted by nobby2 View Post
I have since ordered some Gugolz Pitch #55 from GotGrit.com suitable to my current working temperature of 16C.
Good move. Gugolz #55 is the one I use at working temps around 10C, (I add a small amount of Stockholm tar to it, to modify it to about equivalent to #50 [or slightly lower] for the lower temps I work at). Gugolz is nice to work with. I used resin (rosin?) moderated with pure turps and beeswax way back in the 1960's (loved the smell), it worked ok if one got the balance right with the ingredients for working temperatures.

Stephen.
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  #302  
Old 22-07-2017, 05:38 PM
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nobby2 (Neil)
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Image record as promised from pervious post. I am attempting to polish an 8 inch mirror. I was using Tropical Resin Lap. The first attempts had way to many bubbles. The second attempt with the addition of more Castor Oil was much improved however only lasted one hour before it broke up. Obviously too hard and brittle. I have since ordered some Gugolz Pitch #55 from GotGrit.com suitable for my current working temperature of 16C.
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  #303  
Old 25-07-2017, 04:50 PM
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noodles468 (Jared)
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I recently had a go at the 'tropical' lap myself. My problems were different to yours though Neil, went overboard with the castor oil and now have a lap which is easy to cut channels into, but which I fear is much too soft. Think I will give it a few more goes with the resin to see if I can get it right before I give in and go with pitch.

My lap pictured here, freshly poured (but prior to trimming).
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  #304  
Old 11-08-2017, 07:55 PM
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nobby2 (Neil)
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Mirror polishing

Measuring progress polishing an 8 inch mirror. First picture has curved rough lines with scratches. The second picture is straightening up and looking even with some fine scratches. The target is to create a spherical mirror befor fine turning it into a parabolic mirror.
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  #305  
Old 13-08-2017, 06:49 PM
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Looks like your moving in the right direction Neil. How many LPI is the Ronchi grating? You might want to consider reducing pic size a little. I use "paint" function to size my pics. My camera is a basic Canon A1200 (12.1 Mega Pixel). I do the 20% fix to give nice size pics for the forums.

Stephen.
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  #306  
Old 14-08-2017, 10:07 PM
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nobby2 (Neil)
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Thanks Sopticals for the hint on pic sizes. I am in the figuring stage using 65 lines per inch. I also have 85 and 133 that I may get to. I am working on offsets in front of and behind ROC and comparing with computerised models. Attempting to asses under or over correction. The learning curve is using the correct strokes to improve the shape. Found even 5 or 10 minutes can make a difference at this stage. Have to be very patient.
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  #307  
Old 16-08-2017, 01:55 PM
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nobby2 (Neil)
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Figuring Stage progress

Getting closer to a Parabolic 8" Mirror with the following comparison of the Ronchi calculator 85 grates per inch and a picture taken just using my iPhone. The first two compares inside ROC at -0.2 and the second two at Outside of ROC at 4.0. Pictures low quality
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I set my offsets on the Ronchi calculator at -0.3, -0.2, -0.1, 0.0, 0.1, 0.2, 0.3, 0.4, 0.5. The minus offsets return results from zones closer to the centre of the mirror and the positive numbers results from the outside zones of the mirror.
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  #308  
Old 17-08-2017, 09:50 PM
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nobby2 (Neil)
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Can anyone recommend a mirror coating service in NSW or Australia. Closest to Central Coast NSW would be convenient ?
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  #309  
Old 17-08-2017, 11:02 PM
Saturnine (Jeff)
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Hi Neil
I believe Wayne Sainty of Saintech in Taree does most of the mirror coatings for this area. There was / is a price list in the archives here somewhere along with ph.number and address . Several forum members have used his coating services . Someone else may jump in with a quick link to the post.
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