Greetings all, We are scheduling a workshop for this week, Tuesday, May 20th. Bill, please have the East gate open for us? Thanks Bill. Please remember all, 2 cars only across the bridge. You may drop off heavier equipment at Broder and go park back in the lot. At the end of the evening we can help transport your equipment back to your car. I had the incident happen again where something created a scratch in the mirror I am working on. I am saddened, frustrated and fascinated all at the same time. I would like your help with this. I've never had this happen before and I have decided to the right thing here and track down what is causing this to recur. Here is a pretty obscure image:
I did feel the edge grab this time. The brighter blip in the photo is a sub surface bubble. My first impression is that this is the tiles at the edge of my tool that are breaking off. There is no chip at the edge of the mirror although the bevel has gotten much smaller. Rather than grossly rubbing the edges with a sharpening stone, I will take these to work and use my dental hand piece with a diamond disc to soften the edges and create a new bevel. In our dental lab we deal with different alloys that have specs like Brinell Hardness or Vickers Hardness. In the workshop I think it will benefit our knowledge base if we can specify the hardness of Pyrex and the tools we use. In this case it is sheet tile purchased from the local tile shops. They come in sheets that are tied together with a webbing I think is rubber or nylon. Would it be better to have a softer tool material in case of fracturing or would that matter? Once a small chip of tile releases onto the surface of the mirror, it tumbles and my theory is it gouges the surface. I am not sure if a softer tile would leave the mirror untouched. Anyway, enough of this for now. Christopher cut a round of plywood for me to create a pitch lap on. Thank you Christopher (cool picture you drew on it). I covered this with epoxy. It turns out we can get the better epoxy from Home Improvement Center. I tried Home Depot and OSH. They both dropped carrying Devcon materials. They carry Loctite but in an 8-9 ounce package it is inferior. In fact at OSH I talked with an employee who agrees. Too bad customers and employees can't influence purchasing department heads. Too bad cost trumps quality these days. We may pour a lap- I will check with Tom. We will continue with projects and I believe we will be looking at a Schmidt-Cassegrain this week and trying to clean or plan cleaning the optics. Please let us know if you will need testers and racks this week. Possibly much going on. You may come a little early if you want. I think Bill and the Museum is okay with that. Please, no sooner than 6:30 though, I think that is the time we okayed. I will put out an email if it is not. Thanks all! The workshop is going great. We had 10 last week. Let's keep going and please remember, let's leave Broder better than we found it. T
> From: Jerry > Date: May 19, 2014 at 9:22:40 AM PDT
ReplyDelete> To: Tim > Subject: Re: Workshop
> This the perfect thing to put on our SBAU website, in the forum area. Paul has done such a good job setting up the template we should shift some of our communication and discussion threads to that venue. If you want.
> As for what caused your unfall. It's hard to pin these things down. My guess is the most likely reason is chips breaking off of the edge of a tile on your tool. Not the edge of the tool but a tile edge interior to your tool. To find it you'll need to examine the entire perimeter of each tile with a low power microscope. To avoid it you'll need to bevel the edge of each tile or use beveled tiles from the beginning. I think it's best, for this reason, to use a solid tool over a tile tool when ever feasible. Smaller mirrors up to ten inches, I always use a solid tool. Over 12.5 this is not feasible for cost and weight reasons. At 12.5, use a solid tool if possible.
> I noticed last week that on your tool the tiles are worn down to the epoxy filet between tile. When a chip breaks off of a tile the epoxy filet may be holding it in place and preventing it from safely falling into the space between tiles.