Building a fixed post mirror grinding machine

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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#21

Post by Kanadalainen »


Update summary: Lots of work to get to this point.

Things I need to probably change or fix: My gearing of the DC motor. I will need a slow speed for polishing (5 rpm), and faster speeds for hogging out and fine grinding (15- 30 rpm), so likely need to think about adding a gear reduction.

Fixing the aluminum turntable to the wooden turntable base.

Building wedges to locate the mirror on the turntable.
Last edited by Kanadalainen on Mon Aug 19, 2019 12:33 pm, edited 1 time in total.
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#22

Post by Kanadalainen »


Update: I located the centre of the aluminum turntable this morning.

In the bottom image, you can see the intersection of drawn lines marking centre. Not too exciting I guess, but hey.... progress!
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IMG_3387.JPG
IMG_0868.JPG
IMG_0287.JPG
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#23

Post by Kanadalainen »


In this image I have put together a gear reduction stage for my DC motor.

On the bottom is a 6 inch pulley bolted to a 5/8" shaft, held by two pillow blocks. The keyed shaft was kind of pricey... 25 bucks, and needed a lot of polishing with coarse sandpaper to get to fit the pillow blocks. This took me a couple of hours to get everything square and turning properly.

Edit: I can't get this photo to load, so I will show an image of the final product, when I put it together this evening!
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#24

Post by Kanadalainen »


Update August 19, 2019

This evening I wrestled with the gear reduction drive. The idea is to get to a final reduction of somewhere near 8:1 - which would be best suited to the small DC motor that I'm running.

I built this, and took it apart in different iterations about 6 times before finally getting it to work properly.


Its not terribly attractive, but that's OK. :lol:

The idea is to use two small 5/8" pillow blocks holding a common drive shaft with differential pulleys on either end. I wanted the final drive to be adjustable, so I stacked a couple of pulleys, including a 1 and 1/2" as well as a 3' pulley. Seems simple, but to make everything work together (including the placement of the motor to achieve decent belt tension was not trivial.

Anyway - here's what it looks like.
Attachments
IMG_2438.JPG
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#25

Post by Kanadalainen »


Penultimate assembly:

Almost ready to use this thing. I put it all together and adjusted belt tension so nothing was under too much lateral stress when I tightened down all the bolts.

The best part is I think its going to actually work!!!

I'm going to order a 10" blank and some grinding grit plus tool-making materials from "got grit" in Florida.

Here are some pics of the penultimate version. (I still have to screw down the aluminum top to the wooden base, and determine whether I need to add casters for stability under the turntable. Also I will need to fabricate some wedges to hold the mirror blank in place).
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Gear reduction spindle arrangement
Gear reduction spindle arrangement
Final belt drive - about 4.5:1
Final belt drive - about 4.5:1
drilled out oak square that captures the main spindle and locks it
drilled out oak square that captures the main spindle and locks it
Top aluminum block under main pulley - locates the spindle and keeps everything orthogonal.
Top aluminum block under main pulley - locates the spindle and keeps everything orthogonal.
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#26

Post by Kanadalainen »


And a nice drum roll please?

<<crickets chirping, a sparrow yawns>>

The penultimate product, a nearly functional mirror grinding machine.

Here is a youtube link:






Enjoy!
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#27

Post by Kanadalainen »


It kind of reminds me of the old Chaplin film Modern Times.



I still need to finish the turntable, and get serious about my Foucault test rig.

Thanks for reading to the bottom. :)

Ian
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
EAGLE 5
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Re: Building a fixed post mirror grinding machine

#28

Post by EAGLE 5 »


Any updates on the machine, are you planning on doing mirror this winter?
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yobbo89 Australia
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Re: Building a fixed post mirror grinding machine

#29

Post by yobbo89 »


big glass!
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#30

Post by Kanadalainen »


EAGLE 5 wrote: Sun Oct 13, 2019 3:51 am Any updates on the machine, are you planning on doing mirror this winter?
I am. :)

I will "skill up" by first grinding one or two 8 " mirrors. These will likely be in the range of f5 or f6, and in so doing will learn how to hog out the glass, then rough grind and figure it with Foucault tests and bath interferometer data.

Thanks for asking. :)

Ian
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Kanadalainen
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Re: Building a fixed post mirror grinding machine

#31

Post by Kanadalainen »


yobbo89 wrote: Sun Oct 13, 2019 6:29 ambig glass!

The goal is to make a 20" mirror. Ambitious, but possible I think. I would hog it to roughly f3.5 or f4, and figuring it from a sphere to an accurate parabola will be the difficult part.

The eyepieces currently made now allow for the use of very fast mirrors. Such a large, fast mirror would limit FOV, unless you bring in a very wide angle EP (100* 21 mm ethos or equivalent).
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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PatWilc Canada
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Re: Building a fixed post mirror grinding machine

#32

Post by PatWilc »


How has your mirror grinding been going? Great machine I am thinking of trying to build one. I am hand grinding a 16" F6 right now but it is going slow with a lot of hiccups along the way.
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