mapstar

Evening all. Lots of work still to do guys but things are changing hopefully in the right direction. A further 7 hours of work today and lots of back and forth working the parabolic curve in which is going to take some doing. Hope to get another couple of hours in before the end of the day so fingers crossed Damian

Cheers all I will update later For now it's a smoothly under corrected mirror Damian

Morning all, The last 3 days have been somewhat of a revelation as I have been working closely with John and plundering his knowledge to bring what has been a troublesome project back on track. Having worked the edge of the mirror with an 8" lap centred on the 75%/70% zone for quite a few hours the Images were indicating an Oblate sphere with what looks like a small centre issue approx 4"-5" in diameter. If you were to think of the shallow crater ontop of a hill analogy this would probably describe it better. A lot of thought went into the next stage of the remedial work and the conclusion was to return to the 10" lap and work with that with the lap centre having an elliptical stroke that went through the 25% zone overlapping the mirror centre. The stroke started and ended with the edge of the lap roughly 1/4" from the edge. This would work the zone but also the surrounding mirror to blend things in. After 3 hours work the mirror centre issue has all but disappeared with just a small amount evident. The mirror is now showing a smoothly under corrected figure ready to make a start on parabolizing again. All in all great progress and extremely satisfying to see something go the way you want it to for once. Again apologies for the lack of ronchi images to go with the posts but I will add these in later as it better shows the surface changes than any of my descriptions. Thanks for reading and more updates soon Damian

Cheers Paul. Hopefully up date everything on Sunday evening. More progress though today and things are looking a lot better.

Hi all, I have been quite busy with the whole project this week so here is a bit of an update. Sorry their are no pictures to add to go with the progress descriptions. The build is well under way and on the mirror front I have had made the trip north again to see John for a little more help and input. The mirror has been worked for a further 16 hours up to now and the results have been a big improvement. The edge has been sorted so that it no longer exhibits any signs of turn. The mirror now shows an Oblate sphere for the outside 75% but still has an issue in the middle which is like a depressed ring zone. Hard to explain but I will upload the photos once I get time. All good progress and I am enthusiastic about what the coming days will bring. Damian

Thanks Rick the build is at least looking good. The mirror will progress lots over the coming couple of weeks. Damian

Not at all Ron, there are lots of sound words in there many of which I should've heeded before attempting my monster. I am my harshest critic and the only person I have to answer to which is probably a big advantage when it comes to the time I have spent on the project. More work soon and I am hoping to progress everything to a successful conclusion Damian

Ron makes some good points in his post many of which I can relate to. It is a difficult task and one of course I cannot say I'm successful at. I hope to one day but it will be a little longer. Thanks for the kind words and advice Ron for all those that I hope will take up the challenge of trying to craft a mirror.

Thanks for reading and commenting. Raymond above has already answered the question you've posed in his above post. I had thought about this in one of the recent posts above why machine polishing doesn't seem to encounter the turned edge problems I have encountered along the way. Because we as humans are very random it is quite easy to subconsciously apply uneven pressure and movement to the lap when trying to polish an edge problem out and make it worse. Experience counts for a lot too and last time my edge problem got to a point where as others noted I was polishing it in as fast as I was removing it. Doing it via a fixed post machine it has constant pressure and path but can make its own problems but turned edge if it is set up right doesn't seem to be one of them. As Raymond says it tends to polish non spherical and can put in zones (bumpy surface) but these are probably easier to deal with than TDE. I've yet to get anywhere near but will keep trying. Damian

I have to admit I've stopped counting. It's been a lot and to hazard a guess would be nearly 300? Scary to think

Thanks Derek. I remember the model boat story and the bits where the wife fitted in. I'll stay focused and hopefully get there but as you say it's only me setting the time scale. Damian

Hi all , I did a couple of hours on the glass again during the weekend working both the edge and the centre to try to smooth things down. The edge is reducing further but from the experience I had last time with this I know the last bit is the hardest to remove. Here's the latest image I have done a lot more work on the shell build which seems to be coming along quite well. More work on the mirror but time is marching on and if I intend getting this sorted for the up coming events I have planned I need to speed things up. Last time I had the turned edge problem I went about trying to chase it with the middle of the lap to the edge which is what I have done this time. The main difference is I have spent more time inside each zone moving ever so slightly out as the kink has. Last time as others have said I was creating the turn as fast as I was trying to remove it by working nearly on top of it. A lot of wasted effort and many thanks to those that were trying to tell me that. It is all experience. Just to theorise (just my thoughts) because of how a person has random motion with stroke, pressure and stance I can see why it is more difficult to remove a turned edge than by a machine which has a set path and pressure so eventually the zone around the edge will polish down and blend in the offending edge. More work soon and I know I've been slow with the updates so I will try to add more Cheers Damian

Hi all, Not much change today I'm afraid and more work planned tomorrow. Also going to continue with the shell build as I need to get that something like. An update with a few images tomorrow afternoon. Damian

Nice addition if not entirely astro related Rich and sorry I've only just picked up on it. Hope all is going well down there and you are enjoying the cycling. If and when my health improves I hope to get back into it myself one day. Scope is progressing albeit slowly but I'm sure you'll be as eager to see it as I am. Damian

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

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

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

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

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

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

Matt You could always make a wooden box to slide down over the top with the Sundial/bird table on top to pretty things up and keep err in doors happy.

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.

Ah right that explains it Looking at the UTA did you go for a wired spider too?

Great thread Matt and an interesting read. Well done hope we get some clear skies so you can show us all those lovely stable images. Damian

Nice read and a lot seems to fit with how my mirrors figure is at present. Thanks for posting the link John