Hogging the Curve on a 20" Quartz Telescope Mirror

[JustWonderingHowToDo]

I have a few questions:

Does it matter if you use aluminiumoxide or siliciumcarbide for an abrasive?

Wat grain size should you start out with. The books I have start at #80. Wouldn't things go faster if you used a lower number ( 60, 36 , 24)?

[aalavandhaann]

Hello Gordon,

I have a question. The tool that you use for hogging, will that used for rough and fine grinding too? or should we change the tool after hogging? I have made a machine based on your fixed post grinding design. I am yet to start my grinding coz i have this doubt. Please clarify guru ji.

Thanks & Regards,

Ashok Srinivasan.

[foreilly1958]

Gordon, How is the twenty inch coming along?

[tabhorian]

I hear you breathing heavy. My god that must have killed you. I have got to get a machine, thats all there is to it.

[zi6film]

Hi Gordon, take a look at my videos on mirror hogging , i use diamond blades so no grit less cost and faster too !!

[webcamhilversum]

Thanks for the info Gordon. I'm looking forward to any future video's on polishing and parabolizing the mirror using the machine. Beginning this year I bought a LOH HLP-300 grinder / polisher. Anyway, your video's gave me a lot of new ideas!

[GordonWaite]

@webcamhilversum Congrats on the grinder! What is your size capacity? Did you get a two-spindle model? You're in it for the long haul now! Enjoy... Gordon

[webcamhilversum]

Yes, it is the machine with two spindles. Specifications say it is design for a diameter of 30 cm (12"). However, the pans are 45cm in diameter so I modified the holders for the use with 40cm (16") mirrors. No problem at all, it is an incredibly solid machine. Good luck with selling your mirrors. I had the same idea when I bought the machine, so may be we will be competition soon ;-)).

[webcamhilversum]

What a great series of videos on mirror grinding! I have a question: what is the green material you use underneath your mirror? I'm wondering because I'm still looking for the ideal material to put underneath the mirror to avoid astigmatism in thin mirrors.

[GordonWaite]

The green material is a piece of high-quality outdoor carpeting, or artificial turf. The turf is quite dense, and the individual strands are all 1/2" tall, so it has a very flat and level surface. I've been using this stuff for many years, and it makes a great backing for both grinding and polishing. You can usually order smallish pieces at a carpet store, although it's a little expensive in small quantities. You might find a sample, though, for less. Avoid cheap stuff, though. Thanks!