Hello from Sweden

[Lars Berntzon]

Hi, I am Lars. Lives in my own house in Sweden. I'm working as an system administrator in Stockholm. I've been a electronics hobbyist since I was a kid, then I met with computera and was all consumed by that for some decades. Recently I have been exploring my nerdism returning to electronics and among other things dived into guided astrofotographing with an Atmel AVR control box. Im also into aluminium casting and are melting the crashed harddisks from my work (making them kind of hard to read data from) to make things I need. Now I have realized I want to make a better telescope, so I need to melt glass, grind and polish it and finally to aluminize the surface, so I am trying to get a real good vaccum chamber, im thinking of building a diff-pump with my lathe and alu-casting. I will also be doing some welding so a new subproject is making a HHO-welder, and ... For some reason ideas for new projects comes to me much quicker than I can finish them.
I hope to find help and also to share my experiences in this forum.

Regards, Lars

[Jerry]

If you want a good telescope, buy a mirror. They are pretty darn cheap. Check local astronomy clubs, they often have mirror making classes if you really want to do it.

Dont even think of casting the glass. Good mirrors are not your ordinary glass.

Same thing with a diffusion pump, they are available used cheap. A DP is not that easy to build, it is more than a bunch of inverted cups in a heated tube.

[Doug Coulter]

Welcome Lars!

For some reason ideas for new projects comes to me much quicker than I can finish them.

That would describe most of us here, but we do sometimes finish something (look at Jerry's work here for just one example).

Now, we Americans are kind of spoiled as we can get stuff on ebay, junkyards, and suppliers that haven't figured out how to ship things to Sweden (or for that matter, the UK) quite as well as to here, but Jerry is right on this one. And he'd know - he does sputtering and evaporation himself, as well as having done some optics work for a pro outfit - but it didn't involve making his own lenses/mirrors - mainly the mounts and control systems.

I've found it fairly easy to evap aluminum here, but that's only after the vacuum system is done and tight and right - the vacuum is the hard part. I've done some limited sputtering as well, with mixed results - it takes practice to do it homebrew.

One recourse you might take advantage of is that there are a lot of people here who DO have access to good deals on things, and who might, if asked, buy them with your money and get them shipped to you. I've done it for people overseas a few times, with everyone happy at the end (but not real happy with how long things take to get there if you ship with a low-cost service - it just took something like 8 weeks to get an envelope full of preamps to Germany, for example, via mail.

[Lars Berntzon]

Thanks Jerry, I am sure you are right. But I realized after reading your answer is I really do want to make things, for instance make the mirror. In the process I will learn a lot, which is more important than actually finish my projects.The mirror thing is perhaps just a help for me to keep at least wagely focused so I don't diffuse into too many projects. That said, I do WANT a mirror also for my photographing, but again, I realized its not the most important.

Oh, and I confess, I did believe that diff pump is that simple to build . I will still try though, again for the learning process, if I can't make it I want to know why I fail at least.

Doug, you are right. It is hard to get things in Sweden, at least for a descent price. I did look around for a used diff pump, but found none that is shipped to Sweden.

[Jerry]

At least buy a mirror blank and start from there. They have been stress relived and are made from the right kind of glass, usually pyrex or something like zerodur.

[Joe Jarski]

Hi Lars, welcome to the forum. Among other things, I do a little bit of casting too when the need arises.

Here are some some aluminum oil pans that I cast for a friend's Formula Atlantic race car.

Oil Pan.JPG (43.28 KiB) Viewed 7093 times

And a bad picture my crucible furnace made from a 55 gal. drum.

[Doug Coulter]

Lars, do you have a copy of John Strong's "Procedures in Experimental Physics"? It's a gold mine of info on the things you want to do. He covers mirror making, evaporation, diff pump builds...and all that stuff that was "rocket science" when he did it is now fairly easy. He even has plans for mirror tests, how to figure a mirror more accurately than you ground it via non uniform depo of the aluminum, the works. It just sounds like your kind of book. Sadly, I don't have (most of) it online here, but the Scientific American "amateur scientist" has a lot of it. You'd do well to look for a copy (Lindsay publications).

It's not hard to make a diff pump. What's hard is to make a *good* diff pump. In John Strong's day, they used 2 or more in series to get decent vacuums. More modern pumps are multi stage, so you don't need to do that, but this is the result of some very painstaking work to develop the internal "stack" so flow and jet speed and the side gap are all balanced for up to about 3 stages in one column. With that many variables, you could spend half a life working it out on your own - a lot more time and money than making a controller for a cheapo turbo (Pfeiffer TPU-051's go for about $100 on ebay all the time, and need about $20 worth of parts to drive). Any surface work - like sputtering or evap, is positively ruined by the inevitable oil backstreaming unless you want to go with a liquid nitrogen trap (money! - and not just an amount, a rate).