Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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I've ground thru 500 and I am making my way thru the AoX grits.....
I was just wondering mark, how long (approx) should it take @ 25M and 15M. I spent about 30 minutes and 1/2 a pound @ 25M and now I am on to 15M and plan to do the same.
The surface seems to be ground evenly (judging by pits from the center to the edge).
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2316
Loc: salem, OR
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A half pound?! I mix all grits from 220 on with water, and 25 micron makes a dilute slurry at about 10:1 or 15:1, of which I'd use maybe half a liter at most, so that's like 50g perhaps. The 25 and 12 last almost forever due to how far they spread.
Working time is about right though, the finer grits require progressively less time. I'll give 30 minutes to 25, 15-20 to 12.
Best,
Mark
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3401
Loc: Northeast
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"A half pound?! "
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Same here, half a pound!!! Hate to see your floor! 
I think my progression, I used 220, then went to 25 micron, think I used about half what you did, over 3x the interval. Reason for doing it that way, I could see the difference quite a bit better when thoroughly done. Then switching to 12 as final grit, about an hour and a half for good measure. (maybe 4 oz total) I went 60, 120, 220, 25m, and 12m.
The finer you go, the more particles for any given volume. Just a little squirt of 12 goes a long way. If most is just squashing out, then it's wasted. At least that's the way I look at it.
M.
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So many projects, so little time!
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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It is roughly half a pound... Probably 1/3 if I really weighed it.
What I've been doing is running a water drip sprinkling on the grit with a shaker as I go.
I've finished thru 15M,for 9M I will mix it into a slurry to avoid any chance of sleaking.
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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I've finished fine grinding.... Only managed to get 2 very small scratches near the edge (which I mirror clip will completely cover) and one sleak about an inch long near the edge. It may possibly polish out but I think I am just going to live with it.
I've cast the 15" polishing tool. This time I did something a little different....
I added acryl 60 (1 Quart) to the hydrostone mix to add strength and water resistance to the hydrostone.
I need some advice.....
My environment (a garage) is going to be about 60 degrees (a little less at times), despite my efforts otherwise.
I have gugolz 64 pitch and was wondering if anyone has any recommendations on whether I should soften it up with some mineral spirits? I would rather have it a bit too hard than too soft (TDE).
Thanks...
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2316
Loc: salem, OR
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My recommendation is Aculap standard grade. Polishing out the quartz is fairly brutal and the microenvironment on the surface will be / should be warm. The only problem I have with that combo is in very hot weather when I get too much pitch flow.
How thick is the polisher tool? Hydrostone is a bit squirrely for making polishers and I don't use it for that, as it changes shape too easily.
Best,
Mark
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3401
Loc: Northeast
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If you're working with 64, I would definitely -NOT- thin that pitch, and particularly not with mineral spirits! It should be adequate as is. I polished a 6" F/13, and a 6" F/4.5 both with relatively hard, used #73 in a 60 degree cellar this last week, and they came out fine. Very smooth, no edge, and I'll say adequately (!) accurate. The polisher was cut more like one used for a flat; few, and very shallow grooves. I was suprised how well it worked with the fast mirror!(new technique)
M.
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So many projects, so little time!
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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My polisher tool is 2" thick and weighs more than the mirror  . With the acryl 60, I would think the flexural strength should be plenty good - also the acryl 60 make the plaster more water resistant. I also plan to seal it up with polyurethane as well.
As it is I guess I won't mess with the pitch. I've been out of the game too long to make a subjective determination if the pitch is tempered correctly. I will go with the straight gugolz 64 and accept my destiny .
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2316
Loc: salem, OR
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The polisher should be plenty thick enough then.
I've used G64 a lot in polishing out by machine, I like the Acculap better because (a) it lasts better (b) recycles endlessly (c) it doesn't suddenly go south on the machine like I've seen the current formula of G64 do.
Mark mentioned faceting and I use large facets with narrow channels near the end, just enough to hold some thin slurry.
Best,
Mark
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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I did consider acculap but I've used G64 in the past and liked it alot (light years better than "burgondy" pitch).
Large facets, how large? I was going to do 1" square facets. Not sure if I can visualize what you mean by narrow channels near the end.
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2316
Loc: salem, OR
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See pic (that's a 12" polisher) - around 2" facets. The faceting pattern is deliberately non-periodic. The facets can be smaller if you like.
If you start out with wide channels and polish a long time they close up to become narrow, and/or close completely. As you're completing the polishing out it's better to have narrow channels as the smoothness benefits.
Best,
Mark
Edited by mark cowan (11/05/09 12:12 AM)
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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Poured and channelled the 15" pitch lap and I am having a little bit of trouble.
Basically the lap is not contacting over the surface of the mirror. I figured I would solve the problem "hot" pressing the lap to the mirror. I have tried 2 hot pressings both about 15 minutes long with about 75 pounds of weight on top.
The lap is slowing coming into shape but the better the contact is, the harder it is to get off! My last pressing took *ALL* of my strength (and weight) to free it. I am using about 5-1 mixure of cerium/water with a few drops of dawn for the "release" agent.
I am afraid to press longer as the tool may become permanetly stuck.
The other odd thing is the surface of the lap is pretty "tacky". i.e. it feels like a giant piece of scotch tape (same feel of tackyness). Again, it has been awhile for me making mirrors but I don't remember my laps ever being that tacky. I am sure this tacky/sticky ness is a big part of the reason it is do damn hard to take the lap off.
So any suggestions for a better release agent? Pressing tips?
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Mike I. Jones
Carpal Tunnel
Reged: 07/02/06
Posts: 1673
Loc: Fort Worth TX
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Try cutting a clean common white polyethylene trash bag down one side, open up the trash bag, wet the lap, and just lay the trash bag across the lap or mirror before pressing. The lap won't stick to the polyethylene, but it will come into perfect contact through it. Saran wrap also works but it's not usually wide enough for your 20". Keep the trash bag clean between pressings.
Also, before trash bag pressing, take a razor blade and make 3 or 4 scratches in each of the big facets to break them up into smaller subfacets. That will let the lap flow into contact better, and reduce the drag and tendency to chatter or zone.
Mike
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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Duh, I should of thought of that  ... This is exactly what I did when I cast my tile tool.
That seems to be the trick, after several hot/cold pressings and rechannelling I am nearly getting full contact with the lap. I guess I need to find a better technique pouring the lap to get good contact from the start.
Quote:
Try cutting a clean common white polyethylene trash bag down one side, open up the trash bag, wet the lap, and just lay the trash bag across the lap or mirror before pressing. The lap won't stick to the polyethylene, but it will come into perfect contact through it. Saran wrap also works but it's not usually wide enough for your 20". Keep the trash bag clean between pressings.
Also, before trash bag pressing, take a razor blade and make 3 or 4 scratches in each of the big facets to break them up into smaller subfacets. That will let the lap flow into contact better, and reduce the drag and tendency to chatter or zone.
Mike
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Mark Harry
Post Laureate
Reged: 09/05/05
Posts: 3401
Loc: Northeast
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Sounds like you're having trouble with contact. What kind of base are you using for the pitch- flat, or curved to match the mirror?
Mark
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So many projects, so little time!
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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It is curved. I cast hydrostone directly on the surface of the mirror.
I am slowing getting there.... After many hot pressings and channelings the lap is mostly in contact. I just have one more cycle to go thru (hopefully).
Man... this sucks, I must of did something wrong in pouring the pitch, inital pressing or something. 
Quote:
Sounds like you're having trouble with contact. What kind of base are you using for the pitch- flat, or curved to match the mirror?
Mark
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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Finally I got the lap in good contact with the mirror and polishing has begun. I have about 2 hours in now and I already have a "flash" polish on the glass.
One thing I noted was after about 2 hours the lap just seemed to be skating on the surface. And indeed I was wasn't getting much action. So I took the tool off and brushed the surface of the pitch with a brass brush to "deglaze" it and wow what a difference that made in the lap action.
Not that this is a new idea or anything (many people do it) I was rather amazed what a difference it made.
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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Wondering if I can get some expert advice here...
I am little concerned that my pitch is too hard. During my 1st polishing session I was getting great contact. So I stopped for a few days (lap was stored on its "back") and went to resume.
I cold pressed the lap for 30 minutes on some wedding tool (micro faceting) with 50 pounds of weight on it (the tool weighs around 25 so 75 total). After all of that I was not getting good contact at all. The wedding tool barely left a mark on the pitch, you could see it but it was not very pronounced.
The room enviroment is about 57 degrees and I did add a few drops (3 or 4) of olive oil to the pitch when I was melting it. I heated the pitch very slow and it never came anywhere near boiling.
So I am going to press it for another 30 minutes to see if the contact improves.
Any thoughts?
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2316
Loc: salem, OR
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Do some hot (or warm) pressing. Hot pressing on quartz is almost a gimme, as you can do it very quickly (30 secs or so with the lap treated with hot tap water and a wire brush) and you get good contact immediately - with no penalty for deformation on the glass. It's what I do day to day and it works great.
Note this is only for polishing out!
Best,
Mark
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Brian Engel
member
Reged: 08/25/09
Posts: 95
Loc: Cincinnati,Oh
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After another 30 minutes the contact is better and after polishing for 3 hours it is decent.
My gauge for good contact is that the lap is spinning somewhat fast and constant(no stops and starts). I would expect that as the surface gets smoother the friction gets less, therefor the lap will spin slower and slower?
I have about 7 hours total polishing time and still needs a lot more. I am going to put it up on the test bench to see what kind of mess I have....
Quote:
Do some hot (or warm) pressing. Hot pressing on quartz is almost a gimme, as you can do it very quickly (30 secs or so with the lap treated with hot tap water and a wire brush) and you get good contact immediately - with no penalty for deformation on the glass. It's what I do day to day and it works great.
Note this is only for polishing out!
Best,
Mark
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