TDE question

I'm attempting to figure a 10" mirror that is suffering from a very small (1-3mm) turned down edge. A google search on the subject has led me to try the tool on top with short strokes (my strokes are about 2" long). However, this has not had a noticible effect on the defect and my wrists and hands are getting quite sore (I tend to use a lot of pressure.) I have noticed that the center of my mirror is getting higher and higher, which I guess is a good thing cuz it means I'm removing glass, but it there something I should change so that the glass removal is 1/2" from the edge rather than 3" from the center?

thanks,
Jeremy

Don't use so much pressure this means less control and can in my opinion cause tde.

Also how soft/hard is your pitch. you want good contact good pressing slow smooth 1/4 stroke with little sideways movement should fix it.

It will raise the centre like you say and turn the edge up dropping .7 area down but you can fix that later.

another method is simply trim the edge of the tool by a couple of mm and press then nice slow even 1/3 strokes. this should keep you closer to a sphere.
rd
Make sure you are not overdoing the length of the stroke which is the usual cause. get someone to look at the length from opposite you.

Don't give up you could also simply mask it. Good luck with the glass pushing remember slow even strokes less pressure.

My tool is about 1" smaller than my mirror, so I rarely bother to trim it. Even with the pitch overhanging the tool, the lap is still about 1/2" smaller than the mirror. The 2" strokes I described are the largest I'm doing. Most strokes are closer to 1-1.5", and at this stage of my work the strokes are faily slow and controlled. Therefore, as I work my way around the mirror, the outer 5mm on the sides of the mirror barely gets touched. Should I add some sideways movement to change this (Phil seems to say no, Norm says yes, is there a tiebreaking opinion?)

Norm, you seem to be suggesting a small "W" stroke with pressure on the edges as they overhang. This seems like it would make matters worse. Or, are to talking about mirror on top?

Thanks again,

Jeremy

Jeremy, if you’re dealing with a sphere with a TDE, then there are two approaches you can take.

The first is to work at the COC of the main mirror and plane the whole thing down to the level of the extreme edge. That’s I think what your currently doing, but that’s a lot of glass to remove, so it’s gonna be slow.

The second approach is to move the knife away from the mirror, until the edge and center now appear to be at the same level. Now the bulk of the glass to remove is concentrated at the outer zones, up to but not including the edge. I think the zig-zag stroke with accentuated pressure (not too much) towards the edge of the tool that Norman described works this way. Should be faster, but it will be more difficult to maintain a sphere and you may have to do some additional correcting later.

Either way is OK, it’s just going to take some time. And yes, it is important to get the edge right first, then go after the rest of the figure.

Good luck!

DS