The 22" mapstar mirror

[barkis]

Damian, why don't you make individual pitch squares, and place them onto a grid drawn on the tool?

A little melted pitch on the tool grid squares will stick em on easily, a hot air gun is very useful here too.

I used the mirror as a mould for making a full sized lap. 

I made a collar that fitted around the  mirror edge, protruding above the mirror depth sufficiently to accommodate the tool thickness.

Grease proof paper was placed over the mirrors surface as a protective layer.

I then poured dental cement into the mold. 

Dental Cement generates some heat whilst it cures, so I placed the mirror in a bath of cold water to minimise the heat transfer to the glass.

When the lap tool was fully set, I removed it from the mirror, and cemented  a disc of 18mm Plywood to the back of it.

I lacquered the lap face with two or three coats to seal it, drew a grid for the pitch squares, not forgetting the channelings.

Wallah!, A lap that after warm, and cold pressings, a bit of channel trimming, and job done.

Wear on the facets were always uniform, as the surface created matched the curve of the Mirror very well.

I made a few extra pitch squares to replace any that need replacing.

Caution

                     The lap I made by this method, was for a 14" mirror, yours is a much larger one, so I urge you to

think carefully before you proceed, that is if the procedure tempts you.

I also had made myself a polishing machine to do the work. All I had to do was keep the 

lap charged with the Ceriun Oxide squirter bottle  .

You've come a long way on this job, and the method I adopted may not appeal, and if there is doubt in your mind,

I recommend great care, and perhaps even advise you against it. As I said, your Mirror is a great deal larger than

the one I did.  I would hate myself if anything went wrong with yours using that method.

I'm sure your own instincts will guide you best towards the completion of the 22", You seem to have been be well equipped 

and prepared throughout this project, so I hope you forgive my being perhaps a bit presumptuous in

recommending another method.

There are many of us following this thread, and really wanting to see a very successful conclusion for you.

Great Stuff indeed, you've almost got me fired up to do another one too.     .

Best Wishes.

Ron.

[mapstar]

Hi Ron,

Many thanks for the kind word's and encouragement all of which is gratefully accepted especially when at a low point.

I've managed to cast the lap and although not pretty I'm sure it will work. The lap is 10" in diameter 

I have read of the method you describe before and it is also in Texereau's book or something very similar as I recall. I have tried a couple of methods up to now and thanks for the suggestion on the way you managed to make your's as there is always more than one way to complete the same job some much easier than others. 

Casting lap's is one of my least favourite bit's of mirror making and I'm always apprehensive when it come's to doing one. As far as this bit is concerned I'm not on my own as Rich hate's it too.Finger's crossed I can complete this and show it can be done but a few more knocks to take along the way

Damian

[barkis]

I agree completely about that part of mirror creation.

My wife used to get quite upset when ever I embarked on that phase.

However careful I tried to be, I would inevitably carry pitch chippings into the house, where they would leap  off me, and jump

onto something prominent, like a duvet, or cushion cover, where they melted instantly, to blend with the material.

Sometimes a Pillow case would be infected too. Divorce was almost  certain more than once  .

I used to get a laugh when the late David Sinden, a close friend   of John and myself, when he was describing the use of Jewelers Rouge

when polishing.  He told of carefully removing small amounts from a container, whilst standing in the corner of his workshop,

knowing how contaminating the stuff could be. However, just when he thought he had managed to contain it successfully,

he would turn around to find it covering almost everything in the vicinity, as though there had been an explosion of it  .

Right Damian, I think I've interfered enough in your thread, I'll withdraw now, and let you get on with the job in peace.

Ill keep an eye on your progress though.

Take Care matey.

Ron

[mapstar]

I agree completely about that part of mirror creation.

My wife used to get quite upset when ever I embarked on that phase.

However careful I tried to be, I would inevitably carry pitch chippings into the house, where they would leap  off me, and jump

onto something prominent, like a duvet, or cushion cover, where they melted instantly, to blend with the material.

Sometimes a Pillow case would be infected too. Divorce was almost  certain more than once  .

I used to get a laugh when the late David Sinden, a close friend   of John and myself, when he was describing the use of Jewelers Rouge

when polishing.  He told of carefully removing small amounts from a container, whilst standing in the corner of his workshop,

knowing how contaminating the stuff could be. However, just when he thought he had managed to contain it successfully,

he would turn around to find it covering almost everything in the vicinity, as though there had been an explosion of it  .

Right Damian, I think I've interfered enough in your thread, I'll withdraw now, and let you get on with the job in peace.

Ill keep an eye on your progress though.

Take Care matey.

Ron

Lovely story there Ron and I can quite sympathise with the pitch and rouge get's everywhere analogy. I'm finding it does very quickly.

John has mentioned David quite a few times and recounts very fond memories of him. Please don't think you are interfering as it's a pleasure to read the experience and interest in the subject people have.

Feel free to pop a comment in as I'll always welcome them 

Many thanks 

Damian

P.s. hope you do make another mirror, although I won't be blamed for any divorce proceeding's 

[Physopto]

Hi Damian,

Been reading some of your troubles. Glad it's not me doing it.

Question for you. Can you not spray the Glass with a release oil before the pouring of the pitch? Please don't shoot me down as I know nothing about it.

I have a product called Sabre. It is sold up here in the North East. It is primarily used to clean and polish UPVC window frames. But I use it for al sorts of things. It can be used to clean up oil etc from carpets, Clean Glass and I am sure that it contains some form of Acetone. It will melt car paints. It may be a good way to clean off the residual pitch without damage to the surface. Comes in 5 ltr poly containers I think.

Best regards,

 Derek

[Soupy]

Damian if you are thinking of getting some of Physopto's Magic stuff, I am going Kielder his weekend, and could try to get you some if it's only sold in the north east!

[mapstar]

Hi Damian,

Been reading some of your troubles. Glad it's not me doing it.

Question for you. Can you not spray the Glass with a release oil before the pouring of the pitch? Please don't shoot me down as I know nothing about it.

I have a product called Sabre. It is sold up here in the North East. It is primarily used to clean and polish UPVC window frames. But I use it for al sorts of things. It can be used to clean up oil etc from carpets, Clean Glass and I am sure that it contains some form of Acetone. It will melt car paints. It may be a good way to clean off the residual pitch without damage to the surface. Comes in 5 ltr poly containers I think.

Best regards,

Derek

Thanks for dropping by Derek and I agree it's very tedious at time's and enough to test the patience of a Saint.(although being an imager patience shouldn't be in short supply)

The pitch is poured onto aluminium foil on top of the mirror, so come's off the mirror quite easily unless like mine it goes under the seam in the foil and sticks to the glass itself.

I think the stuff just doesn't like me although the feeling is mutual

Damian

[Physopto]

Thanks for dropping by Derek and I agree it's very tedious at time's and enough to test the patience of a Saint.(although being an imager patience shouldn't be in short supply)

The pitch is poured onto aluminium foil on top of the mirror, so come's off the mirror quite easily unless like mine it goes under the seam in the foil and sticks to the glass itself.

I think the stuff just doesn't like me although the feeling is mutual

Damian

I get it now. Silly me. Yes I've been through similar heart stopping moments. I should be used to the sick feeling but it never diminishes. just out of interest where are you getting the foil? i.e. what size are you using since you mentioned a seem.

Derek

[JamesF]

What's required is some of this: http://www.lakeland.co.uk/70136/Lakeland-Non-stick-Turkey-Foil

James

[mapstar]

What's required is some of this: http://www.lakeland.co.uk/70136/Lakeland-Non-stick-Turkey-Foil

James

Unfortunately I'd run out James so used normal width stuff over lapping it on the mirror. Unfortunately The pitch ran underneath during my bit of a disaster

[nicks90]

and you didnt think to join the bits of foil with some cellotape?

lovely story so far and really enjoying the read.

Edited March 5, 2015 by nicks90

[barkis]

White Spirit was my friend at times of need. Moves pitch double quick, but can be messy.

[mapstar]

and you didnt think to join the bits of foil with some cellotape?

lovely story so far and really enjoying the read.

Thanks Nick glad your enjoying The notes and I'm sure one day you'll get to see the results.

Cellotape is a good suggestion thanks. Unfortunately the pitch being hot make's the glue on the tape melt and let go. I used Gaffer tape in one of my much earlier pours and learn't my lesson there.

White spirit is definitely on the shopping list Ron

[Physopto]

Costco sell wide aluminium foil, it is very thick/heavy and far better than any of the cheap shop bought stuff. Does not rip easily!!. 450mm wide and comes in long rolls. You could do many more mirrors with it ( years of hell sorry  fun), if you can keep it hidden away from the wife.

[Pompey Monkey]

Damian,

You are an inspiration to every fledgling and wannabe mirror-maker out there! I may even be tempted to make my own one day.

Good luck with the figuring process!

[mapstar]

Costco sell wide aluminium foil, it is very thick/heavy and far better than any of the cheap shop bought stuff. Does not rip easily!!. 450mm wide and comes in long rolls. You could do many more mirrors with it ( years of hell sorry  fun), if you can keep it hidden away from the wife.

Ha ha cheers Derek 

I get to spend lot's of time (and money) on it as there isn't a missus Mapstar so the foil would be very safe 

I think I may do one in my next decade on this earth (it's gonna take me ten years to get over this one!!!!) 

Damian,

You are an inspiration to every fledgling and wannabe mirror-maker out there! I may even be tempted to make my own one day.

Good luck with the figuring process!

Cheers Pompey Monkey I'll be carrying on this weekend so look out for update's

Damian

[Physopto]

I'm still very     :Envy:     If I had the time I'd be pulling out my hair as well.

I'm dying to see the outcome. Mike and I talk about your efforts a fair bit!!

Derek

[mapstar]

I hope I can finish it off to everyone's expectations so no pressure!

I've got one of those imaging balaclava's like kenny has to stop hair loss he he

More this weekend as I've been on with other things most of this week. I have picked myself up from the lap incident and optimism is coming back again

Onwards and upwards and thanks for the continued support it's much appreciated.

I'm sure messing about with all those imaging cable's would drive me nuts, I do enough of that at work

:-D

[Soupy]

It's not the cables that gets us mad Damian it's the auto guiding! It's a bit like pitch for imagers, sometimes it's brilliant sometimes it's rubbish but most times it's messy.

[JRM]

Damian,

             Following with interest, I'm on vacation in sunny Florida but head home this weekend, I will soon have to make 

a box to secure glass in as well, on thing though, as Nigel said earlier, using the flat tool as your pitch lap will presents

problems, you lap will be almost 3/8th inches thicker in the center which will make that area of the pitch lap softer compared

to the outer edge, will be hard to keep in full contact if not near impossible, short session and lots of pressing,you should know

by the feel of the lap but test after first round will tell the tale, after the glass  equalizes that is.

not meant as discouragement so please don't take it as such.

Rick M

[mapstar]

Hi all,

Thank you all for the help and advice about the smaller lap . I know this method work's for some so I will as Rick says 'try it and see how things go'. 

Out of interest on this I did do some calculation's on the actual difference in the lap thickness between the edge and middle making a 10" lap. The result is just over 1.8mm between the side and the middle thickness of the lap.

I should imagine that this could be the difference between one side of a lap to the other if anyone's lap does not sit entirely flat whilst making? How many use a spirit level whilst setting up and on the back of the lap when casting? 

I shall see how it perform's over the next few day's and revert to a different method mentioned above if it does not behave.

Damian

[mapstar]

After polishing a second time it was the beginning of February and so I again tested the mirror using the 133 Lines per inch Ronchi screen. I was working inside the radius of curvature

7th feb                                                                                                                                                                                                                 11th feb

15th feb                                                                                                                                                                                                               19th feb

20th feb                                                                                                                                                                                                               21st feb

22nd feb                                                                                                                                                                                                              23rd feb

I had been using the 18" lap to work through the centre with about a 2" overhang. The image's show I have an edge problem (rolled) which I have steadily worked further out but now seem to have come to a standstill. I also began to take image's through the radius of curvature all of which was quite difficult to do as my photography equipment isn't exactly brilliant (note to self there upgrade camera)

 

 

 

These image's were taken on the 23rd of February. The travel is about 30mm from inside ROC to outside ROC in about 5mm increments. After discussing this with John he advised that the edge was the first thing to sort out and the middle could be dealt with later.So I made the smaller 10" lap to work with minimal overhang, the centre of the lap on average 5" from the edge. 

Once I have tidied the lap up and cut the channels I will cold press with lot's of weight and make a start. After about an hour I will then clean and test to see if the edge is getting better and post some more images.

Damian

Edited March 8, 2015 by mapstar

[mapstar]

I forgot to add I also took some foucault images. I had the Knife edge on a slant as I attached it to the tester with blu tac. Think I must've had a big smudge on the mirror too?  I took these on the 13/02

 

 

 

 

And these on the 21/02

Quite difficut to get decent image's and to interpretate as to what's going on but the first set show the edge quite well 

Damian

[Astrobits]

Looks typical of a crater-on-top-of-a-hill. The problem in this situation is to know whether the bottom of the crater is/is not below the required point for the final paraboloid and it is too easy to go too far. Just remember that the centre of the tool does the most work so John is absolutely right - work off centre until the edge is correct, then you can take the centre down to finish.

Nigel

[mapstar]

Looks typical of a crater-on-top-of-a-hill. The problem in this situation is to know whether the bottom of the crater is/is not below the required point for the final paraboloid and it is too easy to go too far. Just remember that the centre of the tool does the most work so John is absolutely right - work off centre until the edge is correct, then you can take the centre down to finish.

Nigel

Thanks Nigel, good to have a second opinion and confirms what John said.

I've just done ten minutes after an initial hour long wet press.

The lap is not quite working so I have warmed it and I'm going to wet press again for an hour with weight on whilst moving it around to stop sticking.

I've taken some test image's before I start so I can compare the progress later once the mirror has cooled.

Damian