Making a 33 cm f/4.8 mirror on the Mirror-o-Matic 6: polishing the surface with a pitch lap

After 'super fine' grinding, I moved on to polishing the mirror surface, with cerium oxide. I also tested with Ronchi and Foucault tester for sphericity and quality of the mirror's edge. No hooks on the end of the Ronchi lines and bright diffraction bands on both sides of the Foucault image: so no TDE

[@johncondoleobat]

That’s a lost art of conventional polishing they want too do in now on c n c good job nice test !

[@janvangastel6763]

Yes, it is perfectly possible to use glass used for windows (it's named float glass). It needs to be thick enough though, so not thinner then other kinds of glass used for mirror making.

[@satyajitbhadraroy7723]

What is the thickness of this glass?

[@janvangastel6763]

@@satyajitbhadraroy7723 25 millimeters.

[@AliKhan-1966]

Nice

[@tompolk7588]

Thanks for posting these videos! Does the AL polisher tool have a radius or flat surface before pitch lap?Are the Ronchi images inside or outside of ROC? Looking forward to your figuring videos.

[@janvangastel6763]

Hi Tom,
I have AL tools ranging from 100 - 250 millimeters (every 10 mm). Up to 150 mm I left the surface flat, for larger tools I added a radius made of 2-component epoxy. I think the radii range from ~f/5 - ~f/7. I made them on a mirror I was working on when using the tool for the first time. The Ronchi's are outside of ROC

[@shaunsprogress]

My ears! how would you go about parabolising this sphere after?

[@janvangastel6763]

This is how I parabolized this mirror: th-cam.com/video/LCi0BDmLSL0/w-d-xo.html

[@mohammedasif6322]

Can we use plain glass like used for windows to make telescope mirror?

[@nikosorf4250]

as long as it's not tempered glass and is thick enough it should be fine

[@hpktech7736]

hi sir good

[@tikitak9190]

Вращение электро-приводом верхнего диска ускорит процесс?!

[@speedx5803]

Nice job, beautful mirror! did you do any manual correction or you just finish the poslishing all in the powered turn table? I'm working on my first mirror and find that turn table poslihing like you show here always ends up with a lower center cave.

[@janvangastel6763]

I never correct by hand during polishing. The only thing I do by hand is removing astigmatism if necessary.
I also have a central hole sometimes after polishing, but I don't care, as long as it is not deeper then it will be after parabolizing. In the early stages of parabolizing, the hole vanishes. Only for an f/7 mirror of longer it can be a problem and should be removed before parabolizing. I do that - on the machine - with a 75% tool, center over center stroke, with 15% overhang.

[@speedx5803]

@@janvangastel6763 When removing the central hole your way, will the curve change? notice you do it with 75% tool and 15% overhang, does the magic also work here that will keep the curve not changed? I'm asking because my goal is to make a optic spherical mirror. BTW, thank you very much for the quick reply, it is very helpful answer!

[@oleggerashchenko2201]

Total length of stroke is 4 cm ( or 2 cm ) via excenter ? This critical??? Thanks!

[@janvangastel6763]

No, stroke length is 2 cm. This is not critical at all. Might also be 3 cm or something like that.

[@yobb89]

don't you want a parabolic figure when making a fast mirror ? , if so how do you flaten the outside edge of the mirror and how do you work out how much ?

[@janvangastel6763]

Yes, after polishing the mirror needs to be parabolized. I have also a video about how I do that.

[@sssskkkk3240]

Please jan i need one 😕

[@PeterK6502]

The visible zones are likely similar in size to your used pitch square size.

[@janvangastel6763]

Yes, that's is right.

[@metingokbulut837]

🇹🇷🇹🇷🇹🇷💯💯💯👍👍👍

[@materialsluckpr3384]

what ceriumoxide you are working ? white or red ?

[@janvangastel6763]

Red.

[@janvangastel6763]

No, I can't. I don't make mirrors commercially.

[@sssskkkk3240]

Hi jan
Can you sell me one?