barkis

Cheers mate, I thought it was an indoor environment. My other thought was, if you're married, then you have a very understanding wife. Mind wouldn't let me near the kitchen. It was bad enough I transported pitch chippings into the house on my person. Trimming the channels after periods of polishing with a trim knife, the little bits flew all over the place, in my hair usually, where some little bit would drop off during the night, and embed itself into the pillowcase. Then the Flak flew I can tell you . The garage can be a cold environment in which to work, but a hard cold lap was a plus in preventing a turned edge, but contact conformity was also difficult, so pressings were frequent through necessity. One had to guard against sleeks too. Good Luck in your forthcoming sessions, I think the mirror is about ready to do your bidding . Ron.

Just where are you doing the work Damian? You seem to be in the house somewhere. The Kitchen maybe? Either there, or you have a very posh Garage/Workshop . Apologies if you've explained this elsewhere in your thread. Ron.

For Sure matey .

Good luck on the run in Damian. I'll be back to join in the celebrations, and I may send you a Pack of Jaffa Cakes, SGL's usual celebratory snack . Best of Luck Matey. Ron.

You're certainly approaching the tape Damian. Carry on the excellent work, and I'll recede from the workplace and let you get to Nirvana. I'll be back to join in the celebrations. I'll send you a pack of Jaffa Cakes, SGL's usual celebratory snack . Best of luck on the Final Approach Matey. Ron.

I don't think King George III would miss the £4,000 he granted for the telescope John. Cheap for the 40 foot monster I would say. Consider the discoveries made with it. I don't think there would be much for William and his Sister Caroline, (Who helped him) to pocket after paying for the materials. It was the largest scope in the World for 50 years. Believed to have helped in the discovery of Saturn's sixth and seventh Moons, Enceladus, and Mimas. Anyway, I think we have hogged Damians thread too much as it is. He must be getting fed up with interruptions :icon_mrgreen:. Ron.

Try to imagine William Herschel figuring that 49" Speculum metal mirror of his, way back when Damian. I think he used a star as his light source, and lugged the mirror in and out of the huge truss to make corrections to the surface as required. Some Job Heh? Carry on yor good work sir, I wish I wasn't so far away from Barnsley, I'd love to pop in to watch progress, and maybe even get a few wets in. You've got me yearning to get back on the grind again you bad lad . Ron.

I would love a big Dob, a 36" f3.5 will do nicely thank you. Housed in a weatherproof Obs, an a simple Alt Az Swing through Fork Mount to gain access to the Zenith. Not too high to climb to the focuser, and no awkward eyepiece positions to annoy me. Just wait for the Cosmos to roll by me nightly through the years, and pour the starlight down to the big collecting eye, and back up to mine. Nice thought. Sorry Damian, I digress in your thread. Ron.

I sold my Texereau book. All I have now are NE Howards Handbook for Telescope Making, and Albert Ingalls Volumes 1, 2, and 3. Old, but crammed with useful stuff. Modern methods have long overtaken them, but one can still home produce good optics from them. Ron. PS. I'm sure Damian won't need to attempt the following . A little humerous drawing from Ingalls book 1.

Eeeek!! Wire Brush?? Tell me you are kidding please . Imagine the myriad scratches a piece of wire could do stuck in the pitch. Ron.

This post isn't to try and offer any advice Damian. I just want to make the point about the incredible attention you are giving this project. Not just your almost running commentary on the work, but to highlight the extreme patience you posses, both in applying yourself to the task in hand, and your willingness to pop on SGL every day to reply to everyone's posts, without an Iota of impatience reflected in your replies. I know each one of us is willing you success, and it will happen. The only equation left is being resolved by you, and that is.. Patience x Time + Thought = Eureka!!! We'll all share in your elation when that moment arrives. Keep pushing those glass molecules up the hill to the edge . Ron.

I always used micro faceting on my laps, whether it was a 12" lap, or a 6". The theory that it is the edges of the lap squares that facilitated the polishing action, means that multi. facets theoretically would speed up the polishing, and also the figuring process. Of course we know that speed is not the factor that is important. Good contact, and at a speed that prevents micro ripple is important. Keep the Faith Damian, you've already got the winning post in sight, you just have to give the mirror a quiet talking to . Ron.

Damian, I'm sure you were under no illusions about the task you embarked upon with this large objective, and John Nichol would certainly have highlighted the difficulties you would encounter. Frustration will always be your companion when you are attempting the figuring process, and when it gets too bad, you should take a break. A 22" f3.7 is a very difficult adversary for anyone to tackle. All of us following your progress are pretty much mesmerised by what you've achieved so far, and certainly willing you passed the winning post. You have the discipline to complete the job, but don't be averse to leaving it to one side for a spell, and get back to it when you feel like it. Have a read of Mel Bartel's Parabolising pages might inspire , they are quite interesting. Best Wishes. Ron. http://www.bbastrodesigns.com/JoyOfMirrorMaking/Parabolizing.html

Have you been using 1/3rd centre over centre strokes Damian? 5 minute periods with cold pressing regularly? You can shorten to 1/4 strokes if it is reluctant to cooperate. I assume your lap is fairly hard, which is good? That is a good way to fix TDE, but you might inherit an Oblate surface in the centre, which is not unusual. That is easy to remedy though. Not trying to teach Grannie to suck eggs matey, and you are winning the battle with that huge lump of glass. You're a braver man the I . Ron.

You'll get there alright, you have achieved enough already to show you have the will to get past the winning post. I look forward to that day . Ron.

Not a brilliant example Damian. But here's a Ronchigram of a paraboloid. Photo by Samuel Borello from NE Howards Telescope Making Book. Not the best photo. you'll see Ron.

Centre oblate is no big worry Damian, it's easir to get rid of a hill, much more difficult to cure a depression careful you stay away from TDE.. Sub. diameter tools can change the surface very quickly, so work slowly, and test regularly. If it takes a long time, so be it, you have to become as one with the task, and if that sounds silly, it isn't Don't be in too big a hurry to judge the surface after a session, what you see shadow wise, will certainly change as time passes. Reserve final appraisals long after polishing sessions. Remember there's no rush. Are you using Rochi gratings, I think you said you were, those shadows indicate such. Perhaps a Foucault tester, although not suitable as a final tester, will give a better insight as to where you are with the surface as it passes through the light cone At the radius of curvature. The knife edge tests can reveal much useful info. Ron.

White Spirit was my friend at times of need. Moves pitch double quick, but can be messy.

I agree completely about that part of mirror creation. My wife used to get quite upset when ever I embarked on that phase. However careful I tried to be, I would inevitably carry pitch chippings into the house, where they would leap off me, and jump onto something prominent, like a duvet, or cushion cover, where they melted instantly, to blend with the material. Sometimes a Pillow case would be infected too. Divorce was almost certain more than once . I used to get a laugh when the late David Sinden, a close friend of John and myself, when he was describing the use of Jewelers Rouge when polishing. He told of carefully removing small amounts from a container, whilst standing in the corner of his workshop, knowing how contaminating the stuff could be. However, just when he thought he had managed to contain it successfully, he would turn around to find it covering almost everything in the vicinity, as though there had been an explosion of it . Right Damian, I think I've interfered enough in your thread, I'll withdraw now, and let you get on with the job in peace. Ill keep an eye on your progress though. Take Care matey. Ron

Damian, why don't you make individual pitch squares, and place them onto a grid drawn on the tool? A little melted pitch on the tool grid squares will stick em on easily, a hot air gun is very useful here too. I used the mirror as a mould for making a full sized lap. I made a collar that fitted around the mirror edge, protruding above the mirror depth sufficiently to accommodate the tool thickness. Grease proof paper was placed over the mirrors surface as a protective layer. I then poured dental cement into the mold. Dental Cement generates some heat whilst it cures, so I placed the mirror in a bath of cold water to minimise the heat transfer to the glass. When the lap tool was fully set, I removed it from the mirror, and cemented a disc of 18mm Plywood to the back of it. I lacquered the lap face with two or three coats to seal it, drew a grid for the pitch squares, not forgetting the channelings. Wallah!, A lap that after warm, and cold pressings, a bit of channel trimming, and job done. Wear on the facets were always uniform, as the surface created matched the curve of the Mirror very well. I made a few extra pitch squares to replace any that need replacing. Caution The lap I made by this method, was for a 14" mirror, yours is a much larger one, so I urge you to think carefully before you proceed, that is if the procedure tempts you. I also had made myself a polishing machine to do the work. All I had to do was keep the lap charged with the Ceriun Oxide squirter bottle . You've come a long way on this job, and the method I adopted may not appeal, and if there is doubt in your mind, I recommend great care, and perhaps even advise you against it. As I said, your Mirror is a great deal larger than the one I did. I would hate myself if anything went wrong with yours using that method. I'm sure your own instincts will guide you best towards the completion of the 22", You seem to have been be well equipped and prepared throughout this project, so I hope you forgive my being perhaps a bit presumptuous in recommending another method. There are many of us following this thread, and really wanting to see a very successful conclusion for you. Great Stuff indeed, you've almost got me fired up to do another one too. . Best Wishes. Ron.

I'm sure any difficulties can be surmounted with Johns guidance Damian. My largest mirror completed was a 14". A self blame disaster with a 16" terminated that effort. However, I always felt a huge satisfaction when a project was finished, be it a 4" or 14". I cannot see you failing at all, you have too much grit. And I think I deliberately intended that pun. Besides, you are a Yorkshireman, and the grit is inherrent .

I would hope that by the time the SGL11 Star Party comes around, this telescope will have been commissioned, and fully operational. I also hope you can find some means of attending said SP, with your creation, as a symbol of what can be achieved by the determined Amateur Telescope Maker. Plus, if the skies permit, there would be queues around the Lucksall Camp Site, of eager beavers waiting for a A look see at some far distant Star Island . Ron.

I got the Sagitta to 9.4mm for your target F of 3.7 Damian, but rarely does one get exactly the hoped for result. It's looking so good though, and I think fist light is on the minds of most of us, but still a ways to go yet, so we'll just have to be patient . Congrats on the fine job you've accomplished thus far though. Ron.

You've done a great job Damian, and you can be mighty proud of this. You are going to finish up with a superb Mirror, no doubt about that. Still a ways to go, but you're under full sail now, and land is in sight. I take my hat off to you, this is going to inspire more people to make their own too. :icon_salut:. Ron.

I made some sub diameter polishers from Dental Cement Damian. It was reasonably cheap from a local dental technicians workshop in the town, so I made a 16" full size polishing lap for a later project, a 16" f3.5. I never did finish that job. It was a thin mirror, and I made the mistake of grinding the back surface with 400 grit to tidy it up. Unfortunately, doing so relieved stresses in the glass that allowed it to badly distort the lovely sphere I had on it. It would have taken fine grinding and re polishing to get it back to a sphere, the position where I always liked to start the figuring process. It disheartened me too much to want to rectify it. It was stupid mistake to make really. Ron.