Sunday, March 29, 2015

150329 TimC on isolating problem causing scratches

Tim C  8:17 AM (2 hours ago) to Jerry, Mike, Richard, Tim, me, Tom:
   Of course I am very sensitive to this. Let's check Tuesday. I am so sorry to hear of these scratches. I am very confused by all of these scratches. It seems to me we have (as a group) never had so many show up in finishing stages. Coincidence? I am not sure. It only takes one grain of grit to do the damage. The question is, " where is the likely source of this contamination?" How does one try to isolate the source?
As I have told many of you, in the dental lab, when we have a problem ( not necessarily this kind of problem, but similar) we try to list all the components in the production to the point of the problem, then one at a time change a component till the problem ceases.
With the problem at hand, if it cannot be fixed, the problem occurred late in the polishing/ figuring stage. To me, it calls for looking at :
A. The environment the problem occurred
B. The cerium oxide and container it is in
C. The surface you are working on
D. The pitch / pitch lap
E. Cleaning and storage materials and containers
Are there more I have not listed?
If it were me, and boy it has been, I think I would group the pitch and cerium into one group. Otherwise changing just one perpetuates the problem mercilessly, while replacing both and fixing the problem still isolates the cause greatly. I do have a question here though. That is, is it really necessary to change these out now? Can Mike go back to 500 then come forward with the same materials, especially the cerium, as it did no damage for a long time? Is the pitch now contaminated or is it just a matter of cleaning the lap carefully?
If it is likely that this was a random piece of grit that has now been expelled from the working environment, it is just a matter of being careful with work surfaces and all materials.
Again Mike, I am so sorry to hear this and I'm obviously sympathetic. As you know, I am going to go back a sixth time to regrind the donated mirror. I'm going to complete another 8" I have simultaneously. I want to know more of if one piece of Pyrex can be different from another. I still want to know if the cause that persists with this one mirror can come from the blank and not all the other standard components. I did change out all of the others and the scratches persisted. If my methods hold up it seems the problem point to the Pyrex. As Jerry suggests this may be highly unlikely. So that leaves me. Because I work in a very abrasive environment everyday, I may be the source. I may be bringing in contaminants under my fingernails, on my clothes ( which I change before each workshop) or hair.
One last component is possible. Randy, from Astrosystems told me he had to put a plastic sheeting above the work area he was in. The acoustic ceiling tiles were a source of contamination for them. As many in the workshop have commented in the past, "it's too bad we do not have a dedicated place we can keep our projects and even a dedicated clean room to polish."

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