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moving into the finer grits

crashtestdummy

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After waiting a week for a first class royal mail delivery my new bevelling tool arrived and an hour was spent doing what is likely the last bevel I will need to do on the mirror unless I have to go back to 80 at a later stage.One thing you don't realise before grinding a big mirror is how many bevelling stones you need.Ive been through atleast 6 or 7 by now, a few early ones snapped but my technique is much better now :)

cleaning off that 80 grit ready for 220

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heard back from john who said that I should do an hour with the 220grit and a 2" overlap then pencil test to check for good contact.The first pencil test wasn't that good so I did another hour and tested again with slower more deliberate strokes.Bingo,much much better contact now and the pits from the 80 grit were disappearing fast.1 more hour has been done with the 220 grit and two further pencil tests which look perfect and I think there are 2 small pits left from the 80 grit so I will probably do another 30-60 minutes with the 220 grit to make sure its perfect then move on to 400 grit which will probably take a similar 3 hours or so to do.600 alu oxide to finish then its time to make a pitch lap and then many hours polishing.Cant wait!!!

getting good contact

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good grid waiting grinding.not a pencil but still qualifies :)

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pretty much perfect contact now.this is 3 or 4 times round the table

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finished curve.not 100% sure if it looks exactly like a sphere or not but I will find out eventually

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Think that's if until next Tuesday now and then I need some 600 grit ordered.I move house on the 26th so likely I will end up with a couple of week inactivity as I will have nowhere to grind so will try and make my ronchi tester

upto now ive done 73 hours on the mirror and im upto 12h 15 minutes with the tile tool.the time is adding up,and its been 6 months since I started <gulp> admittedly I only do a few hours a week so ive not hammered it.

clear skies Rich

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Looking real good Rich, easiest way to determine shape is to sharpy test first wet with new grit,it tells you

alot about how things are progressing,sharpie marks will disappear faster with each smaller grit sizes as you

go through them, but in reality the next grit size after 220 should be your last sharpie test. Its real hard to

get those tile out of contact once full contact is made unless your doing something totally wrong.

but then again you are doing a F 3.3 or so, a whole different animal in itself.

73 hours so far, man your arms must be soar, nice report.

btw.. hope to start polishing the 20" this week or next, more likely the latter but things are warming up.

Rick

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My mirror has pretty much settled at F3.5 from my initial 3.6 aim.I did 10 minutes tonight with 400grit and the pencil test shows great contact so I think it's getting there well now.It's amazing how smooth the grinding strokes get with finer grits and how much much more the tile tool sticks.the pitch lap is you goibg ti take some pushing around!!

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