Physopto

Over here the original wall ties ( in the distant past ) were just iron/steel bars splayed at the ends. Many houses have had to have them cut out as they rusted and rust is 40 times the size of the steel it replaces. So they found that the bricks were being forced apart and structural damage resulted. The galvanised wall ties replaced the steel ones around the 1910/20s I believe. But theses have also been found to have corrosion problems over the years and just rusted away in the cavities. This meant the inner and outer walls were not tied together and so could either bow apart or cause collapse problems. So now all mortgage providers require that they are replaced with stainless steel replacements. Hot galvanised metal in the past was of much better quality and much heavier deposit than the presently used processes that attempt to save money. Just have a look at barbed wire that has been wetted over the years. You will see the rust.

It was just a suggestion that may be a bit over the top, but it is what I would do to preempt any failure.

Derek

What is holding the roofing felt on the walls? Are they galvanised  nails? If so could I suggest you paint each one with some protective rubber solution. May sound like over doing it but any moisture over a period of time (could be a long time)  will eventually cause corrosion, especially if there is not a good air flow to dry out the moisture. Here in the UK we have found that galvanised ties in our house walls have been the causation of house sales being very expensive. Mortgage companies now ( in the last 20 years ) want them all replaced with stainless steel ties before they will allow the sales to go ahead, simply because of corrosion tie failure. This has happened in properties as young as 10/15 years old. Costs are around £2000 per property. Why take the chance if it can be prevented.

Your build looks really nice. It will be good to see the end result.

Derek

Hey Derek - check this out:

http://greatstuff.dow.com/pestblock/

Looks like just what the doctor ordered - think it would work?

Hi Scorpius,

I think it is the same sort of stuff, the "low expansion" is very important or it may cause bending of structures. You cannot use ordinary expanding foam. it will come down to availability and cost. Soudal stays soft to the touch and you get about 25 litres from a tube. It can be bought in several different forms. One is as in the video you pointed out. But you get less out of a can and it is way more expensive. The other methods require a  foam gun and a cleaner  for the gun. (Use immediately or the gun is very difficult to clean!!!) About £25  here so around $40  over at your end. The guns come in two types. Bayonet and Screw. Initial cost higher because of the guns. But if you use a lot it works out cheaper. You can use the foam for insulation in the cavity between

walls. You are on the right track.

Derek

Hi Damian,

OK, so Mike and I  have cancelled the big event, Grand Opening, ( rope lines, banners  and pay booth) for Galloway this Autumn but are now reorganising for Galloway, Spring next year.  Fees none refundable,     just a slightly later date!    We can talk about your cut, or lack there of, at John's Mirror event 

Derek

Make sure the wireless receiver for the game pad is not shielded by the steel pier. Game pads are prone to interference problems if not in direct line of sight. Also if too close to reflective surfaces, i.e. metal or metalised surfaces. I gave up with my wireless game pad because of problems, it was a Logitech one. I have used that make of mouse for years without any problems but the game pad was useless. You may be better off with a wired version. There are one or two other threads here on SGL that mention problems.

If you have only three sides to your pod I would suggest a heavy curtain between the pod and observatory. It will keep you warmer and light out of the observatory from computer screens. A door and curtain may have been better. Friend here on SGL uses a curtain and it works well.

USB3 can and does cause wireless interference to equipment. It operates on similar frequencies about 2.4 Ghz, plenty of info on the web! So good idea to stick to USB2 for the present methinks.

Looks a great project, watching with interest.

Derek

They won't get stuck on it so it won't hurt them. But they will not like getting covered in the goo. I like mices but not in my gear.

Mices love duct tape

If you did that  you would have to ensure that pieces of gravel could not get jammed between the pier and the wood or you would definitely loose isolation! It would make it difficult to get at the junction boxes as well.

Looking at the pictures again you could just fill all around the gap between the pier concrete and the wood joists for the floor.

You could use silicon sealant in a very thin layer at the pillar to wood and soft foam inside. Soudal make a silicon called Silirub, silly name I know  but decent stuff. They also do a sealant that is over paintable called "Soudal Fix All " but it does not like UV light. No problem underneath but it is not as flexible as silicon.

The alternative is to fit a two piece floating  wood cover fixed to the pillar, so that it overlaps the hole by some amount. with a very small clearance to the bottom of your observatory. It may be difficult as there is very little clearance from your pictures. You could do it in one piece dropped down from the top. I suspect that there is not enough clearance though, so that is why I suggested foam.

One last point is to paint the pillar bottom  with anti- vandal paint, the really gooie type that never dries.

Best of luck in whatever decision you make.

Derek

Hi Scorpius,

You could spiral wind a small wire around the power conduit and earth it using an earthing rod at one end. That would shield the com conduit from any interference.

The gap can be filled with a soft expanding foam. We have some over here manufactured by Soudal called Flexifoam. It does not harden like most gap filling foams but stays soft. It can be used to fill around door frames or behind plasterboard without forcing it apart. It is a good insulator as well. Or you could use silicon filler. I'm not a fan of silicon as it will not bond to itself. So if it goes wrong it cannot be repaired without a lot of work.

By the way Soudal Flexifoam can be used to encase any delicate equipment in a case. You just need to wrap the item in cling film then support it on small blocks underneath the item to allow the foam to get under it in the case. Fill the case with the foam half way, Wait for it to set then trim it flat to the half way mark. Then do the rest with cling film over the first half. Obviously shutting the case lid and awaiting it to expand fully and set. You will end up with a purpose made foam compartment for your gear.

Derek

Hi Damian,

As much as it is nice to read your updates, they are not the be all and end all of your build. We can wait, more important to concentrate on feeling good about your own work on the mirror or the shell of the scope. For your own sake forget us and just take your time. It is not our time, money and effort, it is yours and we are just the interested bystanders. Feeling rushed is probably the worst thing. Just take it easy. I built a model boat a long time ago (nearly 30 years ago). Took me 3 years and £2000+, every time I rushed it went wrong!!!!

Derek

I've not tried my Loadstar for this type of use so far but this opens up possibilities. Excellent read full of information. Thanks to both you and Paul.

Derek

Hi Damian,

Not sure what I'm looking at there. But I you think it is better, good. You need a bit of good luck.

Derek

Just a thought Damian, are you bringing your mirror for us to practice on ?

. .

Mike will bring the car polisher and I will bring the Brasso !

Aye, maybe summit strong enough to hold the Titanic.

Nice!

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