These finer grits are very fast indeed - for the first time, I brought home supplies of two separate grades, and if I can find time to work over the next two weeks I should be able to complete grinding and begin polishing next time I go to the class!

It was an interesting class this last Saturday.  Not only did I confirm that the #400 grit had left me with an apparently flawless pit-free surface, but there were a few new faces:  a woman (who's name I did not catch) had brought her son along, together with some of his friends.  They're working on a six inch reflector, similar to mine, and are taking turns at grinding.  If they can keep it up, and are able to master the technique quickly enough, then the four of them could easily overtake me and have a working telescope before long.

My mirror has now had about an hour's work under #500 carborundum grit.  The change from #400 is minimal - it feels and sounds the same, although when I place the mirror on top of the tool at the beginning of a new wet, the slurry flows much more easily, and for a few seconds there is practically no friction.  If I place the mirror and let go, it immediately slides away towards the edge.  At the end of the hour, I noticed a few good-sized pits, and a few little constellations of tiny shallow indentations with softer, rounded edges - perhaps a grouping of micro-bubbles?  More work is needed.  Still, I'm working at such a fine scale now that getting to the next stage involves removing a really tiny amount of glass which doesn't take long at all.  Once i'm done here (hopefully only another hour's work), I'll do a few wets with #800, and then have a beer because I'll be ready for Part Two:  Making a pitch lap, and polishing.  I'm told that this is the first great test of patience.  Well bring it on, I can take it!

Meanwhile, I've been putting some thought into the physical construction of the telescope itself.  The assumption has always been that it'll have a cardboard tube, an a bog-standard dobsonian mount.  However, I've got an ancient german-style equatorial mount sitting in a box under my bed which might just be up to the task.  And since I've only ever used equatorials, I don't find them complicated or tricky to set up at all.  Alternatively, I'll build the standard dob mount, on a wedge.  Since I'm relatively close to the equator, though, that means inclining the whole assembly at a shade under 60 degrees from the horizontal - probably quite unstable.  Still, these are just ideas.  I'll think about them more seriously as I get closer to having a working telescope.

I had a lucky break this evening, in that my wife has taken the kids to her sister's place leaving me with a sleeping baby and time to grind glass.  I spread newspaper out on the kitchen table, laid out my kit and started grinding with #400 carborundum.  After a little less than an hour, I dried off the mirror and set it up on the latest makeshift testing station.  Our dining room table is a round four-seater with a very clever mechanism that allows the two halfs of the circular top to slide apart so that an extra rectangular section can fold out, turning it into a 6 seater.  But if I just slide the two halfs apart a few centimeters, and grip an upwards shining torch between my knees, I can place my mirror over the gap to inspect it for pits.  Using a reversed 40mm eyepice as a loupe, I studied the surface for about 15 minutes before resigning myself to the seemingly impossible:  No pits anywhere on that surface.  Not a single one, apart from the general roughness left by the current grade.  I attempted to photograph the surface through the eyepiece, but the surface is so uniform that I can't even be sure if the images are in focus.  Yay, I think?

Anyway, I've attached the photos (Comments?  Send them to the usual place!), and now have to wait a whole week before I return to the class for a supply of the next grade of grit.  Also, WOW, this fine stuff works fast.  It won't be long before I'm spending more time cleaning and inspecting than actually grinding!

At last, I've got grit under my fingernails and fingers that can no longer operate a capacitive touch-screen phone (Seriously.  3 hours of exposure to silicon carbide, ground glass and a detergent-glycerin-water mixture have done something weird to my fingers so that my phone no longer thinks they're human.  ooooh.....), and as a bonus I moved on to the next finer grade of abrasive!

So I arrived at the class this afternoon, dodged a thunderstorm getting my mirror making kit from the car to the workshop, and ran into an immediate problem:  I didn't know which cannister of abrasive to open.  See, I keep all the sponges, salt-shakers and grit containers from each stage of grinding because even though it's cheap stuff, it still costs time and money to replace.  To avoid cross-contamination between different grades of grit, each set is neatly sealed into a labelled ziplock bag.  No doubt in the movie of my life, they'll replace that lot with an elegant system of machined and polished stainless steel cannisters (because Hollywood knows of no other way for technology to be packaged), but I like it for being cheap, simple and effective.  Except that at some point I forgot to label two of them, leaving me uncertain which contained #220 grit, and which contained #320.  Getting them mixed up would be a disaster, since using #220 grit on a #320 ground surface means going back a stage.  And what with the baby and all, that particular stage took me about 8 months.  So I sighed, dumped the abrasive from both packs into a flowerbed, washed both packs, and fetched a clean supply of #320 grit.  An hour's grinding later, I showed my mirror to one of the class Elders, who advised that the fresh pits appearing on each wet were likely not a result of subsurface fracturing, but simply being dug by larger than expected particles in my grit supply.  There's a margin of error in the filtering and packaging process, not to mention the risks taken every time we decant from the manufacturers original packaging into smaller cannisters.  He suggested that I do a few wets at #400, and if the progress doesn't look good then simply return to #320 for a few more hours.

So I did that, but I'll share a secret:  the little sabbatical I took has left me a lot less perfectionist and finnicky than before.  It's been 8 months, I need to see progress NOW.  Psychologically speaking, if it turns out that I'm not actually ready for #400, I will likely not admit it to myself.  Ah the impetuousness of youth...

I'm still finding my feet in the new year, and haven't really regained mastery of my time since the baby was born, so I'm not sure how much work I'll be doing at home between now and completion, but at least I've resumed work and am glad that at no point since this time last year have I forgotten about the project or contemplated giving it up.  It's just a matter of time, now, before I have a happy little 6" Newtonian all of my own!

Hello?  Anybody still reading this thing?  If you've given up on me and my project, I couldn't blame you.  Things have been pretty silent for a long time now, for reasons I've gone into in more than enough details previously.  However, over the coming week I'll be unpacking my mirror, reclaiming my bucket and spray bottle from the housekeeper's cleaning cupboard, and preparing to pay a visit to the ATM class this saturday.  Meanwhile, I'm hoping to put in a few more hours (and finish my stash of #320 grit) to get that mirror free of pits and subsurface fractures.  Watch this space!

I haven't been to class in a very long time.  So long that I couldn't say if it was even still running!  Fortunately, they made an appearance on the Afrikaans language magazine show Pasella, to a national audience, which confirms that they've continued operating as normal, even while I languish at home (and at work, and in exam halls, and...).  If you'd like to see some of the faces who've done their part to instruct and motivate me, watch the segment below:

I just realised that I haven't touched my mirror in almost two months.  Ouch.  I'll spare you the excuses (nothing much has changed except for the fact that the new baby has severe reflux, which is harmless but does make all baby-related tasks that much slower.  Refluxy babies vomit a lot, and very easily.  Any one feeding might have to be repeated three times and take over an hour.  This is frustrating, and has knock-on effects.  Oh, that bit about sparing you the excuses?  I was lying).

Anyway, the project has not ended.  It's just... sleeping.  The mirror is still nice and spherical, with a pretty #320 grit surface still showing a bit of sub-surface fracturing, but once I wear that lot down it won't be long till we're ready for polishing!  And that's when I start the next big lesson.

I managed to complete and submit the assignment this morning, leaving me free to keep my promise.  Not a whole lot got done - only three wets and a whole lot of getting to know my mirror again under a bright light.  I'm doing something that never occurred to me before:  Find pits, mark them with a permanent marker, then photograph the mirror.  Do a few wets, then repeat, and compare photographs.  Much easier to keep track of which pits are persistent, and which are new.  

Anyway, those three wets actually gave measurable progress:  One persistent pit is gone, apparently a slew of new shallow pits have appeared (assuming I didn't simply miss them last time around).  So I'd guess there's still some subsurface fracturing to eliminate.  One interesting point, though, regarding the enormous pit I've been watching for some time:  This pit was so big that it was diagnosed at the class as a bubble.  But as I worked, it gradually lost its round shape to reveal a jagged bottom.  Shortly before I packed up for the sabbatical, it had worn down into two small adjacent pits.  Only one of those are now left.  As small as this one tiny detail is, it gives me more satisfaction than everything else combined!

Although on second thought, I'd say the papery smooth overall finish is way better.  Almost sensual, if you ignore the pits dotting it!

Time flies when you're having kids.  In the last entry, I promised to wait no more than a single month before unpacking my mirror and resuming grinding.  I now see that I have only two days left, and am not ready!  But I haven't been lazy.  In that time, my wife has had a baby, my plumbing has sprung multiple leaks (and in a separate incident, had the geyser burst) leading to my landlord's cut-rate plumbers tearing open half the walls in my home trying to find the leak.  I've studied for, and written, three exams, and I have worked on reports for my astronomy course (final one is now three weeks overdue, but only a few hours from completion), and the observatory sessions for that course begin next week.  I've been cooking, cleaning, feeding, washing, making emergency trips to doctors and pharmacies, and on top of all that my leave ended and I'm back at work full time.  

I've been busy, is what I'm trying to say.

Still, no excuses.  Depending on when I manage to submit that final assignment, I will either push glass tonight, or tomorrow.  You can hold me to that.

As I anticipated a month ago already, I'm packing away my still-incomplete mirror to get on with the demands of Real Life^TM.  My wife is expecting to deliver our third child in a little over a week, I am about to start exams, and my employer will have me travelling.  I gather many ATM projects have died this way - they get put aside for a while, to be resumed on some future date that never comes.

The good news is that this will not happen.  I will not let more than one month pass before putting glass to glass again.  Any longer than that and my telescope will turn into one of those multiple-year projects.  If I'm going to master this stuff, I need to complete a LOT of telescopes before I get old!

Late in the evening of 9 May, I spent about an hour and a half working on the mirror, with maybe 45 minutes actual grinding.  Two wets with #320 carbo, tool on top, 1/3 diametral strokes, very light pressure.  Rinse and dry the mirror, inspect, do another two wets.  The giant megapit near the centre is visibly reducing (I can see the irregular bottom now - it looks like two overlapping pits.  Eventually they'll separate into two small pits, and shortly afterwards vanish completely), but a lot of brand new pits are appearing.  I reckon this is good news, and I will continue for as long as necessary to try eliminate subsurface fracturing from previous grits.  I suspect that I've learned more about grinding technique from dealing with the subsurface fracturing than any other experience so far.  We'll see if what I've learned is actually right on my next mirror!

I think that I am nearing the end with this grit, but am determined not to rush it.  The real factor now is my inability to find more than an hour each week to work, rather than the speed at which glass is being removed.  When I started I was hoping to be done in time for ScopeX, and I think that if I had no other projects running then I could easily have achieved that.  Still... I have a more realistic understanding of my time now.  This telescope will be built by Christmas, right in the middle of the rainy season, so first light might only be in 2012, but that's okay.  I've got more than enough going on to distract me if I start to feel impatient!