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More whipping tomorrow Ooooops I mean working ;-)

No I'm not Derek, although I think I'm into self punishment doing this ha ha

Hi Ron I have been working in the kitchen as you quite rightly point out. The reason being that during the winter the pitch was just too cold to work right in the garage. I've just stayed in the kitchen ever since and there is also much less chance of contamination as my garage is quite a mess and needs a tidy out Damian

Ha Ha yeah I suppose it does

The silicone is going off so it's looking good but the rubber smell is not exactly the best thing in the world!

Afternoon all, Today's efforts have come together after a bit of digging around in the garage for materials. A previous project's left over's yielded some 1/8" (3.175mm) rubber sheet just big enough to cover the table top. So I removed all the clamps (or cleats) and with an 8mm hole punch marked out and cut 4 holes in the rubber for the bolt's to go back through.I also removed the excess wood on the clamps (cleats) so that the slurry could flow around the back. Once it was bolted back down I trimmed it with a Stanley Knife I then went low tech low cost approach and just run some packing tape around the edge leaving approx 8-10mm above which I ran a wedge of silicone up against on top of the rubber. Fingers crossed tomorrow morning I will have the first polishing session once the silicone has gone off, and determine then where as Derek suggested I can put the drain hole . Hopefully things will be a lot less messy Damian

I think I may have some somewhere

The grinder I may have to give a miss as tIe risk of contamination with the grinding disk is there although small. I've had a thought about facing the flag with something like a sheet of pvc or rubber? something similar must be 600mm2 or bigger I could just run a bead of silicone around the outside then? Less chance of picking up something off the flag when moving the mirror to clean.

Cheers for the questions Nick and no question is daft as it maybe something obvious I've overlooked At this stage there is no difference in temperature to the touch but it will have raised slightly after polishing. If you handle the mirror, then where your hands have been it will expand causing high spot problems when you polish, and I'm sure some Texereau Know it all will be along soon to point it out! It's one thing I wanted to eliminate before progressing further but there is a piece of anti fatigue matting between the mirror and table so it would in fact thermally insulate it from the table surface. You can see the matt in the back ground against the radiator

I'd thought of something similar Derek with the bonding although it was going to be silicone as I had it in stock drilling the flag again to allow the slurry drainage was another thought (great minds and all that). Plastic would be better as metal anywhere near the glass at this stage fills me with dread. Upvc with a stanley is probably an option and I've just remembered I've got some square drain pipe somewhere

Evening viewers Work has been at a stop for the last couple of days due to the unfortunate interference of my job Today I managed to get back to it though and decided to change something I've not been happy with for a while and that is the work table I use. The top is made out of a piece of kitchen worktop and is what I've been using from day #1 to grind then polish on. Anyway this was looking rather worse for wear and with all the best intentions about sealing it the chip board had swollen especially where the three clamps were mounted through to stop movement of the mirror. I had a thought about this and decided that I would find a 600mm2 flat flag stone from the local DIY store and change it for that. So I scoured the rack and came up with one Once home it was out with the toys to do a bit of modding. I drilled it through in 6 places then countersunk the screws. I sealed these with silicone. I then grabbed a bit of american hard maple from a previous project and made some new clamps mounting these with M6 countersunk bolts right through the flag. Because of the shape of the flag I put 4 stop blocks/clamps on which actually give a loose fit so not to pinch the mirror. To finish off I then rounded the corners of the flag with a diamond disc. All in an hour. Once the piece of foam matt is back on it's ready to polish again although I may add some form of channel around the side to stop all the slurry running everywhere as it did with the old one. I'm still thinking on this though?. Damian

After a bit of downtime I have nore work today and maybe an update later on progress. Damian

Cheers Ron I'll hold you to the Jaffa's Damian

And to also add John the history lesson is free too so the £4000 goes a long way I don't mind interruptions so carry on guys it breaks up what has turned into an edge rectifying thread Damian

Thank you Ron, a very encouraging comment and thank fully he got it finished using the ultimate star test. Bet he was as happy as I'll be once I get my shaving mirror complete You could also have a few wets if you could wrestle the lap away from me although I think after 5 mins we'd be having a cup of tea and you'd be reminiscing about your own mirror making exploits and acquaintances. I've done three hours today and maybe a little change to the edge Inside ROC Outside ROC Not much to report and the battle continue's maybe tomorrow. A well deserved beer now and some relaxing to think of strategies for tomorrow Keep watching Damian

Not as much as some do Ron, but at least it's helpful digression

Wondered what all those beers and clouds we've shared were all about

Thanks for the comments Guys I think the thread may need a little more humour Ron and had a little chuckle as I'm sure the pic could be turned to represent the edge problem I have. I too have the Texereau book and there are some interesting and relevant points and technique's in it. As you state though Ron some of it woefully out dated and it made me really laugh a bit on page 13 stating that an 8" can be fully exploited on a simple alt az mount weighing 40lb or less where as a 20" would need a more substantial mount weighing 2 tons . I'm sure there are quite a few dob owners on here that will feel mighty strong knowing that's how much their moving everytime. Soupy I hope you were using the term expert very loosely there especially seeing as I'm about as far as M31 away from that Derek I've seen the John Dobson video and to be quite frank for someone held with such esteem in the astronomy community it is quite shockingly rough Battle has recommenced with the edge so an update later guys. Back to the lap Damian

Yeah your right guys it will be nice to see a change for the better. Tomorrow will tell as I've plenty of work planned

Hiya RickI'm using the 133LPI grating as I don't have an 85. I do take measurement image's closer to radius of curvature although post the same image's just for comparison. It would be nice to see it clearer but there's an edge problem so no two ways about it I need to get rid of it through one tactic or the other. I'll do more work tomorrow and see how I go. There is a lot of glass to remove to parabolise it so was hoping that a bit of deepening would take glass off lowering the overall surface down to the edge. I think it's too far away to do that as yet so will carry on with probably a mix of what I've been doing before as it seemed to be working albeit very slowly which is no worry so long as I get there. Just patience and time and I'll get it sorted although time is drawing in Damian

A small update today as I managed an hour yesterday and today will be taken up by work. I returned to working on the edge but could see no difference in the images apart from I'd started to create a hill in the middle again. My mind wasn't fully on the task yesterday so I decided to call it a day and hoover the grass! The edge showed no improvement as can be seen Inside ROC Outside ROC I'm going to attempt more edge work tomorrow and after 2 hours test again. If the edge does not improve then I may need different tactics Damian

More work today and yesterday to the tune of 5 hours with the W type parabolising stroke It's amazing the amount of thought's that are provoked in people reading this and I had a pleasant chat over the phone earlier about the thread, progress and Ideas on what can cause edge problems. Ajohn also mentions a few things above and must have needed a stiff drink after re-reading the 13 pages again. Mind you I also think my caller probably needed one too Here are the image's Inside ROC Outside ROC Over all there is still a hill in the middle which is good and I think a slight change to the edge although the stroke gives this minimal work. More tomorrow fingers crossed and see how things progress Damian

Hi Cath. Thanks for the compliment and question. As you say the internet has lot's of info on the various testing methods that can be employed. The Ronchi is simple to set up and use I can only talk about the set up and experience I have at present. My set up consists of the following Ronchi Screen 133Lpi Camera tripod Linear translation stage LED and power source Ply frame to hold everything Small camera set on night mode A frame to hold the mirror with a sling and a wedge for adjusting the mirror focal plane (to line it up with the light source) The Ronchi screen I use actually came from the USA (http://www.ronchiscreens.com/screens.php) I bought the large screen and bought 2 the 133Lpi and 250Lpi although I only use the 133Lpi. The small screen would be o.k. I paid around £35 for both including the postage The linear translation (XY) stage is something to accurately adjust the travel in and out from the mirror. Like the one I have with the 25mm travel micrometer at the back (just an X stage) Fleabay £30 Or a micro scope XY mount about £20 Mirror frame (under Foucault knife edge test) you can see the mirror just hanging in the sling this was before the re-grind and re-polish. Lot's of problems here, It had an under polished centre, lots of finger prints around the edge as well as a hill turned down edge and just generally very poor shape You need some way of mounting these to the tripod, and then the screen and the light source to the stage for travel. In the photo I used some ply to hold the screen in front of both the LED and the camera. This is a moving light source tester as the LED travels with the screen and the camera. The LED shines through the screen and is reflected back off the mirror back through the screen to the camera lens. Light source and camera lens are as close as possible The mirror has a radius of curvature worked out roughly the depth of the curve by a spherometer so you should know this but it can be determined by getting the reflection of the led in the mirror and steadily working your way backwards till the LED image in the mirror fills the whole mirror. Looking through the camera you should be able to see the fully illuminated mirror and the lines on it. The lines alter as you move inside and outside the radius of curvature and you can use free software ROnWin20 written by John D Upton to produce matched Ronchi image's of your test mirror by entering the mirror details. The Ronchi is just a variation of the Foucault Knife edge test. It represents multiple Knife edge's as far as I believe. Phew hope that's correct, but there are plenty of much better explanations on the web. Not many talk about how to set up for some strange reason and about the moving and fixed light sources Damian

I had about an hour's more work yesterday on the mirror, but hoping for quite a bit today and see how things progress. I managed to take a few Ronchi Images of the mirror before I made a start. Inside ROC Outside ROC Time will tell if I'm going the right way. Damian

Hiya Nick, Depend's on how deep a scratch is but I very much doubt it as even though I may be taking a lot of glass off (in polishing terms) it's a small amount. Fingers crossed though as mine are very light. I have another couple of hours planned this aft so I shall take some image's later on of the progress Damian