Physopto

You could drill through the base of the blocks into the paving slab and fit resin anchor bolts. Also s/s bolts between the blocks with large washers plus fibre washers to stop any cracking of the surfaces. What ever you do, do not use hammer action !!!!!! Derek

Dina Rush, Russians make mistakes. Oh Blow! no it was the Americans. Inches and millimetres Derek

Thanks Damian, I did talk to you a good while ago a bit about the process. But what I'm getting at is the even smallest flex due to warping during a polishing episode. It would be impossible to detect by eye. A bit like the mirror glass warming and changing shape during the polishing, as has been said you have to wait to test it, allowing it to cool again? I suppose the pitch is softer anyway and the pressing removes any warp. Your thread brings up some interesting points and discussions. Just hoping you have no more problems and all goes well. Derek

Hi Damian, Correct me if I'm wrong but would dental plaster not be better as it is rigid and not likely to warp. I'm thinking of when you are getting to the finish as it is less likely to cause problems when figuring the mirror. Would it not be more likely to stay the correct shape under a slight misbalance of applied pressure when doing the final work as all wood will flex to some extent ? The amounts of glass you are shifting are very small. Even paper is an abrasive at these miniscule measurements. I'm used to working with measurements down to 10-10 metres, so can appreciate the problems. Derek

One point to note about any alarm box that is accessible is that thieves just use expanding foam to squirt into the alarm box before breaking in, then the alarm is useless. Visible is OK, but have a backup system that is hidden. Use different power supplies for each. i.e. battery driven backup also hidden. Also more than one if at all possible. Flood lights with video recordings as the try to leave. I was told by the police some time ago when a car was damaged in my front path, that the recording has to stand up in court, in other words be extremely obvious that it was the thief ( High Definition). The officer told me most recordings are disputed and they get off with it. Short of nailing them to the ground in the process of the theft it is almost impossible to get a conviction these days. You might even get done for hurting their ears and eyesight if using very loud alarms and very bright flashing lights. (human rights?). Better to make it as unobtrusive/hidden as possible and extremely hard to get into! Life isn't fair to the honest these days. Derek

Looks like he got it a bit hot during the grinding ? Wait until cooled before retest ! OK OK I'm off before the fall out! Derek

Hi Damian, Glad you are now getting somewhere. Hope it works, just take it as a lesson learned. If you don't mess up you don' t learn anything, I should know, it has happened many times to me on other things. So when you build your new grinding / lapping machine for the 36" mirror........................................................ Yes I know, I can hear all the flowery words even now! All the best, Derek

Hi Damian, Good luck, I expect you will be watching that edge very carefully this time. I'm sure you will get it. All the best. Derek

At least you know now from a well respected friend and professional. As with most things that are worth doing in life it is a learning curve. But you have gone this far ! Whatever you decide good luck. Still got the Brasso ! Derek

Well it looks like it is reducing ! Derek

Even one suggestion of giving up is a no starter! You have not struck me as "the giving up sort", so in a nut shell DON'T GIVE UP you aren't that man. We all get bad days when things don't go right. But after a while we see the light. It always happens. I've been there many times over the years, things always get better, you've just got to push through it. Easy to say I know......... Been it, done it, seen it, and all that bull. John will incentivise you during you're visit with him. Working on your own for so long on such a big project must be daunting. But you can do it, just keep repeating that to your self. All the best. Derek

Aye Damian, Give the flat blank to Mike. Mike will probably bring it to me and he'll hold it while I use the grinder. Got a really good diamond plate to finish it off with and a bit Brasso. "Simples" as the Meerkat would say!

Hi Damian, Pity you don't have a walk in fridge then. It would make the final figuring closer to the temp you will be using it at. . Sorry just had to......... Derek

Hi Damian, How long after finishing the work on the glass do you allow for cooling before you take these images? Also do you keep the temperature in the room the same each time for the images and for the polishing? Derek

I hope there is a long que to look through the scope when Damian is finished. Demon Barber and I have got our plans drawn up for the Big Dob Event at the Galloway Star Party. We are finalising the ticket sales! Rope lines are all planned. So Damian is well booked. Derek

Hi Damian, If you are pressing the lap now, does it not take on the shape of the hill in the middle? Or does that not matter as it is relatively small? Derek

Aye Damian, You can see the correlation between the two different methods showing the same centre hill. Very interesting. I'll keep watching. I have just spent the last month and a half digging in the garden to remove an old pond plus about 70 square Metres of grass and replace it with new rolls of turf. As always it is the preparation that takes the time. But rushing either the preparation or the finishing straights can screw things up. So best of luck and be careful you will get there. Derek

How long is a while ? Don't answer it's just a rhetorical question. It's a long job you've set yourself. I think if I had been doing it, by now ( actually a long time ago), I would have fixed up a washing machine motor and table for myself! Hope you conquor the hill soon. Derek

Damian, When are you off to see John? Are you getting rid of the centre hill first? Derek

Well just take your time Damian, I would hate to see you get so close then rush it when getting too excited close to the finish line. All the best Derek

Well to my untrained eye they look as though the edge is reduced. Good to see.

I like the way you say ONLY!! That's a lot of work and every bit gets you that bit closer. I'll keep an eye out Derek

Hi Damian, I am getting withdrawal symptoms, how is the edge coming along. Any pics? No rush Hope the weeks holiday set you up again for the work ahead. Derek

Hello everyone, A while ago I posted a note about Optec and no response to emails. Then a follow up about actually getting in touch with them. It has taken up until today to get the final correct adapter from the USA. The final adapter arrived this morning 22nd May after being posted 15th May. It took 10 days to be made in the USA. Optec's Owner Jef Dickerman and his wife Tina were very pleasant and helpful to deal with. Unfortunately their communication skills are not quite so good at times. One of the first adapters that I received was incorrect, even though I had explained it carefully in the original email for the order. Their numbering system is complex at times as not all parts are on their website nor are there pictures of all the parts. Never the less they tried to help me at all times. At first Jeff identified the incorrect part for adapter I needed, even though he had supplied the bit that was to screw onto it. The part I needed, they did not have,but they pointed me at a web site called "PreciseParts ". So the correct part was eventually ordered by them from that firm. It was specially made for me, and is well worth a look if anyone is struggling to get an adapter over here. Although there have been several problems in the order I am happy with the items received. The rotator is very nicely made and would appear substantial. The initial enquiry was made about the 15th March I think but no answer received.seems very substantial. As soon as I get a chance to use it I will be a happy man (hopefully). I initially emailed Optec about the 15th March, no answer. 1st April I did get an answer after a telephone call to the States. Several emails back and forth order placed 3rd April. Confirmation of order being held by customs from FedEx 9th April. Order delivered April 10/11th (unsure now). Incorrect part found and emails again. Incorrect part sent back to USA cost £ 14.95 insured etc. 5th May received Optec 11th May. Correct part received today and fitted. Derek

There are possibly two methods that can be used to put out a fire without using water. (To not cause damage to equipment). Halon and CO2. Some years ago when at sea as an engineer we had Halon as the fire fighting extinguishing medium. At that time we were informed at the course we attended for these new ships, that Halon was completely safe. We were told that you could walk through an enginroom filled with it to check it had put out the fire. So being a curious person I did a lot of checking upon Halon. At that time there was no internet! It took several months to get the details about Halon. Yes it does put out fires. It is used at a concentration of about 4% in the atmosphere. This is because of cost and is the optimum for fire suppression. But what had not been mentioned on the course was that Halon in the presence of flame produces Phosgene Gas, (Mustard Gas). At that time it was also not known that at concentrations above 4% that it was dangerous to humans even without any flame present. You can die as it is then a poison. It has been mentioned here that the preferred method of fighting a fire in the observatory is CO2. To extinguish a fire with CO2 you will need to flood the area with about 40% of its volume for CO2 to work. To accomplish this you must seal the area to contain the CO2 for several, and possibly even tens of minutes. This is to 1) extinguish the fire. 2) allow the item/s to cool so as not to reignite when air is allowed to re enter the area. It will be very hard to seal an observatory before using CO2! By that time the fire will be beyond your control. If a fire starts and you are there CO2 can be tried if it is caught before it has really got hold. BUT please just ring 999 and get proper help. You only live once. Possessions can be replaced! Derek