From: Guy Brandenburg 
To: Scott Ewart 
CC:  atm{at}shore.net
Reply-To: Guy Brandenburg 


FWIW, in our workshop we make a slurry for the really fine abrasives like
500 and such. You might want to try it. One 'wet' of the really fine
abrasives can last a really long time.

On the other hand, it sounds like you may have a problem with grit or
water-source contamination if you are chasing new holes around. In other
words, it may be the case that your water supply is introducing small grit
particles that are larger than your 500 grit abrasive, and that your holes
are coming from that. You could try using filtered or bottled water for a
while to see if that solves the problem. Or, if that does not solve it, you
could try elutriating your 500-grit abrasive itself - that means to dump
the abrasive into some water in a large, clean stoppered container, shake
it up very thoroughly, let the larger particles settle out for a little
while, then decant and use the remainder.

Guy Brandenburg
NCA MMW at CCCC

Scott Ewart wrote:
>
> ----- Original Message -----
> From: "Gerald Boutin" 
> To: 
> Sent: Saturday, June 21, 2003 2:45 PM
> Subject: ATM Grinding Efficiency
>
> |
> | For 500 grit, I am doing wets of about 7 to 8 minutes of grinding 1/3
> | COC, no additional pressure and about one stroke per second. I generally
> | alternate the disks with each new wet. I am pretty sure that one of my
> | earlier errors was having reduced the amount of grit between grit sizes
> | too much. I started SiC 500 grit using 1/8 tsp of grit per wet. I am now
> | using closer to 1/4 tsp per wet. However, progress still seems much
> | slower than it should be, or I would like it to be.
>
>     Using too much grit can slow you down quite a bit.  You want just one
> layer of particles.  Otherwise, you're just grinding grit against grit, and
> the glass just rolls along.  This goes for any stage of grinding, but in
> fine-grinding, the actual amount you need seems so small.  You're better off
> just sprinkling a little at a time from a shaker - just a dusting, then add
> more every minute or two as the sound quiets down.  If there isn't enough,
> they'll start to stick.  For 80 grit, the right amount lasts only seconds,
> then add a little more.
>
>
> |
> | Likewise, how do I judge how much water is about right? I am generally
> | going for enough water to get more or less a thin slurry about the
> | consistency of milk. While grinding, I add a few drops of water if I
> | notice that I no longer see water receding as the top blank uncovers the
> | lower blank. (I may not have worded this last bit correctly, hopefully
> | it conveys some meaningful info.)
>
> It can be a bit thicker than milk.
>
>
> |
> | I have tried doing the last session of 5 wets using the concave blank on
> | the bottom as it seems to me that the other way around isn't going to
> | work the top of the convex blank where the pit is. Unfortunately, this
> | is taking the ROC farther away from my intended target, rather than
> | nearer. Worst of all, I could not see any noticeable reduction in the
> | pit size.
> |
>
> You may just have to go back one grit size.  It may save time in the long
> run.
>
> Scott
>
>
>

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