At your temperature range I would choose Gugolz 55 but at least for now getting a sphere you seem to be doing good with the Gugolz 64.
As well as can be seen in a single Ronchi, your pretty good sphere, only slightly oblate looks smooth. If your lap is thick enough it would not be unreasonable to press the current lap to fill in the beveled area and bring it into good contact, retrim the channels and continue working fix the edge. If I'm right about the lap size causing the TDE, it will not take long for it to get very good with the lap equal to the mirror's diameter. In most cases while working to remove the tde, the cause of the tde remains active, so the fix can take a long time. When you have removed the cause of the tde, it will go away quickly.
For figuring the f:2.6 I'm sure Gugolz 55 will do better. And maybe you intend to use sub diameter laps for that too.
My tools are usually the same diameter as the mirror and trimming the edge of the lap vertically leaves the surface of the lap equal to the mirror diameter. Frequently as the work continues, the lap bulges at the edge and curls slightly around the mirrors edge while pressing. After pressing I will stroke mirror a series of short strokes forward back left right and the edge of the mirror shaves the curl off, leaving the surface of the lap a mm or two larger than the mirror diameter. Without lifting the mirror off of the lap (or lap off of the mirror) I wipe the pitch chips off the edge of the mirror and lap with my finger, and continue work as normal.
I have been assured by some of those who have not done this method of dressing the laps edge that letting the pitch curl around the edge and shaving it off with the edge of the mirror will turn the edge down, and the chips will scratch the mirror. Neither has ever happened to me.
Pitch chips will not fit between lap surface and mirror unless you separate the mirror and lap. If you do that and chips get between them, pitch will not scratch the mirror. I have only rarely had pitch chips get between mirror and lap and it is easy enough to make a stroke taking the edge of the mirror past the chip and the next strokes push it into a channel or off the edge. Sure... if you have chips between lap and mirror and you can't take care of it by stroking the edge of the mirror past it, stop and clean the chips off. Just describing how to handle chips makes it seem to be a much bigger problem than it is. I have only done this method with Gugolz pitch and it does have a different fracturing nature than some other types of pitch. I think it would work ok with most other pitch types, but I can't be sure.
Edited by dogbiscuit, 18 July 2019 - 08:25 PM.