The 22" mapstar mirror

[Glasspusher]

Just to give an alternative take have a look at Mel Bartels's notes....

http://www.bbastrodesigns.com/JoyOfMirrorMaking/Parabolizing.html

​

John

[mapstar]

Mmmm. With the looks of that I would be making a full or near full sized lap and take it back a few steps.

I'll say it again and it will save you a lot of time, You really need to make couder mask and start using Figure XP! You don't need a camera as you will be getting the numbers visually.

Chasing Ronchi curves on large fast mirrors is NOT going to happen. Making a 10" f6 would be fine but not this mirror.

Once you start using Figure XP you will see the light.

I had my first light for the 20" two nights ago and it is totally awesome, it star tests perfectly and the view is amazing! I could view the moon at 700X and the detail was stunning!

I still need to finish a few things on it.

IMG_2121.JPG

Hi Raymond

I will have a go at the mask, foucault tester and XP software and I fully agree that it will teach more about how the figure of the mirror changes than just one test alone.

What you are saying about not needing a camera is right but I really put this thread up to show people what they will see if they have a go at making their own. There isn't that much info from beginners to look at on the Web especially when you are working with basic tooling and making a large fast mirror.

Yes I have not got things right and it may take me a long time to get there but it is all part of the learning process and others hopefully will read the thread and not fall into the same pitfalls.

Onto your Scope pic a bit of a different take with square truss tubes? Any reason for that? Easier to work with perhaps?

Damian

[mapstar]

Just to give an alternative take have a look at Mel Bartels's notes....

http://www.bbastrodesigns.com/JoyOfMirrorMaking/Parabolizing.html

​

John

Nice read and a lot seems to fit with how my mirrors figure is at present.

Thanks for posting the link John

[barkis]

Mel Bartels is highly respected, and has given much to mirror making.

That's a very useful link to lots of good Info, and it's free too.

Got to be good.

[RAC]

Yeah I just think the square trusses are more easy to mount and work with. No other reason.

[mapstar]

Yeah I just think the square trusses are more easy to mount and work with. No other reason.

Ah right that explains it

Looking at the UTA did you go for a wired spider too?

[RAC]

Yep its a wire spider. I've never used one before so thought I'd better try one.

[mapstar]

Hi all just so this is on each page,

John Nichol is hoping to hold another one day seminar if there is sufficient interest.

The previous two editions have been limited to mirror making, this time it will include aspects of telescope making. This is because some people would like to make their own telescope without making their own optics. As a result the day will be about 50% mirror making and 50% telescope making. Details of the day are...

Date: 22nd November 2015

Time: 10am til 4pm.

Location: BIllingham, Teesside. (Easy access from the A19)

The day will feature a talk from SGL's Mapstar (Damian).

More details to follow as the timetable is firmed up.

This is not a profit making event, But There will be a charge for this seminar, sufficient only to cover costs of

the facility, and materials etc. 

If you would like to register an interest in attending the day please send me a PM 

Damian.

[gooseholla]

Hi Damian, Hope the mirror/ telescope is going well. I've registered to come to this day. Cannot wait!

John

 

[Physopto]

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 !

[mapstar]

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 !

I can tell now who's going to be in detention at the end of the day!

I would hope you've already seen it by then

[mapstar]

Hi Damian, Hope the mirror/ telescope is going well. I've registered to come to this day. Cannot wait!

John

Excellent stuff John and we'll finally get to meet.

If the weather is nice I would hope to be calling off after the event to have a viewing session so it may be a long day.

That's if I've managed to finish everything as we both know those scopes take some building.

Damian

[Demon Barber]

Actually,i have just got some 80grit flapper wheel---ought to be enough i recon       

By yer pals know how to land you in it!!

Regards

Mike

[barkis]

I dismantled my large garage workbench today,  and clearing out the junk from the good stuff,  (not much of that I might add),

a lot of paint tins etc. the contents of which  are still usable.

I also found, tucked away at the back, my 16" lap I made from Dental Cement years ago.

The pitch squares have suffered a bit, but the memories flooded back. I got the mirror spherical, but made a foolish, and cardinal error,

I made an effort to clean up the back of the mirror with 400 grit, and when I re tested to see if the surface had changed, I was horrified at the 

funny shapes on there. The mirror blank was only a thin plate glass one, so the clean up had obviously released stresses in the disc.

I abandoned it altogether at that point, I gave myself a telling off for being stupid, then parked the lap in the bench cupboard, and forgot

about it.. 

I will give some thought to making another mirror though, I do have a  15" blank tucked away somewhere.

Ron.

                     

[mapstar]

That's an interesting looking lap Ron thanks for posting.

I've done some more work on the mirror but it's back on hold until I hear back from John again.

I have moved the zone out to within about an inch from the edge although I have no images to post whilst using my mobile.

In the meantime I've been turning more of my attention to the shell build. It's coming on a lot quicker than the glass has but it's more my comfort zone than moving glass molecules about.

I have plenty of pics of the build coming along with a lot more detail than last time so should make for an interesting read.

More work and posts soon I hope

Damian

[Stub Mandrel]

>phew< I was getting nervous...

[mapstar]

Hi all,

It's been a while since an update to the thread and I have been working away trying to bring the blank back to something like. If you all remember I went a little too far with the 10" lap thinking I could pull things back but I reverted to a 6" to work the outer regions.

The mirror looked like this with the last ronchi Image I posted then as I've worked on it 

And as the work progressed 

And finally todays image all taken outside ROC 

Quite a bit of work has gone into bringing it back (about 10 hours) but I'm now at a stage where it looks like a turned edge but it is moving ever so steadily out but from experience tyhe last part is always the hardest to remove. I also have a zone in the centre which I have to work on to bring back.

With a series of images it's much easier to see a change in the shape.

Damian 

[Vicky050373]

As you know I am no expert, but that definitely looks as though it is starting to come together. I can see the difference from the images taken on Saturday. I am so pleased for you

[Physopto]

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

[mapstar]

I've been working the hole out to the edge.

It's steadily getting back to a starting point again, although there will be lots of correction in the mirror and the other images which I've not posted tell a tale too.

I've tried to post similar images to show the change.

Luck maybe a bit short a miracle more like

Damian

Edited September 15, 2015 by mapstar

[Vicky050373]

Luck or miracle - you were due one of them

[Mark62]

Wow what a change. It's looking really good. Looking at what other people have posted of mirrors on you thread I would definitely say that's a big improvement.

Keep up the hard work it's paying off

Mark

[mapstar]

Thanks for the kind comments guys. More work tomorrow on it and hopefully get it back to something like.

Damian

[Stub Mandrel]

I can't take the suspense...

[Soupy]

It's def moving in the right direction buddy, as for the build well that's looking amazing as well... They are in for a treat when you start posting the pics. And just remember... some progress is still progress towards your final goal. Keep at it Damian.