Making a 33 cm f4.8 mirror on the Mirror-o-Matic 9: Parabolizing 2: Parabolizing
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- เผยแพร่เมื่อ 21 ส.ค. 2024
- In this video the parabolization of the mirror from start to end is covered. Testing is done with the Foucault test at first, but in the end stages the Bath interferometer is used instead. The Bath interferometer is also used to test the finished mirror
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You make it look easy. Great mirror.
If you don't have a moving pole, how would you parabolize? By hand? Nice work btw.
Hello Jan!
Now, when it’s a little cooler, I’m preparing to parabolize a 16-inch mirror. So I'm carefully studying your example of parabolization.
Based on the formulas you provided below, I wrote a small software that calculates the overhead and maximum offset.
But there are several questions.
When figuring about 10:51 for a 160mm tool I get a maximum overhead of 19mm and a maximum offset of 37mm.
How do you get a set of overhands and offsets?
Thanks! Oleg
Oleg, I calculate the maximum overhang and offset with those formulae. Sometimes I deviate from those numbers, depending on the actual figure of the mirror; its a matter of excperience. Then I start at offset 0 (or sometimes 5 or 10) and then decide how many offset positions I want to use. Most of the time this will be 5 or 6, sometimes 7 in the beginning of parabolizing and sometimes 4 at the end stages, when less parabolization is needed. I also decide beforehand about the number of overhang positions. Most of the time I do 5 or 6, sometimes 7-8 at the early parabolization stages, sometimes 3-5 at the end stages. Most of the time I diminish the overhang 3 mm at a time, sometimes, closer to the end 4 mm or, when I only use a few overhang/offset positions in the end stage, even 5 mm. I hope this helps.
@@janvangastel6763 Thanks for the detailed answer. I'll try to apply it to my mirror with an optical diameter of 406 mm. For the edge zone we have a 240 mm tool. According to calculations, the maximum offset is 68 mm and the overhead is 72 mm. Using your tips, we will choose 7 times at the beginning of parabolization.
Will have Offset: 0, 10, 19, 29, 39, 49, 58, 68 mm and OVH 72, 69, 66, 63, 60, 57, 54, 51 mm.
Time spent in each overhang position similar to video 10, 5.5, 4, 3.5, 3, 3, 3, 3 minutes.
In your opinion, is this the correct calculation and time for the initial stage of figuration?
Thanks!
@@oleggerashchenko2201 Yes, I think this is correct. But it is always important to check after a session, if the result is as it is meant to be. Sometimes, especially in the beginning, the edge zone will lag behind. And if that's the case it will be necessary to adapt the progression accordingly.
看起来很棒❤
I polish by machine, never by hand. Just look at the video. I don't know what you mean by 'a moving pole'.
Hi, one question. Could you please tell me how you clean off the machine when required? As the rotating disc of the machine seems to be taken off in the cleaning process.
The rotating disc can easily be taken off, including the drive shaft. And also the drip pan can be easily taken off the machine. Takes only a few minutes. I clean the machine every time when I have finished the grinding phase of a mirror, to be sure there's no grit left that might scratch the mirror surface when polishing and parabolizing. I place everything I want to clean in my garden and use a hose to clean it, after having removed most of the grit-glass mud, so that I do not pollute my garden.
Hi sir! Greetings of the day!
Si I have a doubt.
If the KE reading of a particular zone is higher than the ideal reading for that zone as calculated in figure xp,, the zone is higher than ideal or lower than ideal? I mean how do I interpret if the zone is raised or shallow?
If a reading is higher then ideal - above the 100% in the M-L plot in figure xp - then that zone is overcorrected, so too deep.
@@janvangastel6763 thank you sir for the reply. 🙏
What concentration of сerox do you use? He is almost invisible in the video. Thank you!
I use a concentration of about 1:100 when parabolizing. When polishing about 1:50.
@@janvangastel6763 Thanks for the answer! In other words, for 100 ml of water you should take about 1 gram of cerox. Did I understand correctly? Does this affect smoothness???
@@oleggerashchenko2201 It does affect smoothness a little.
Jan how do you determine overhang and offset.Can you describe or indicate where to read?
Overhang=(LD*ssf-(MD/2-ZR), in which LD=lap diameter, ssf=sweet spot factor (for instance 0.20 or 0.25; is part of tool diameter you want to get past the outer target zone radius), ZR=outer zone radius of target zone. Max offset: ZR-X-0.5*LD. X=10-20 mm, depending on the width of the target zone. That's how I do it. Not necessarily the only way to do it.
I do not want to be cheeky. But I can not understand your calculations.
Can you give me your calculations as an example for zone 6 if possible?
And do you consider them 0.20-0.25 (%) in percent? What is MD-main diameter.
OK, forgot to write down the meaning of MD: mirror diameter (corrected now in original post). Exampel zone 6. Zone 6 is the outer zone of the mirror in this video, with diameter 329 mm. The lap I used = about 60% of that diameter: 200 mm. So MD=329, LD=200 mm. ZR=~165 mm (half of mirror diameter, because it is the outer zone. I used a ssf (sweet spot factor) of 0.30 (I always do for the outer zone). So overhang is: 200*0.3-(329/2-165)= ~60 mm, meaning that the tool will move past the edge of the mirror 60 mm on both sides of the mirror.
Thanks for your help. Continue to post videos. I hope if I have questions I can turn to you.
How much does this lens cost to buy?
I don't know. I don't make mirrors commercially.
You might want to include some narration on your videos.
I tried, at the start. But it took me to much time, so I added some text.
Hi does anyone know what the software is that Jan is using?
Hi Dawid,
I assume you mean mirror testing sofware. I use FigureXP for Foucault testing and later on, when I use the Bath interferometer for testing, I use DFTFringe.
Jan.