Re: [ATM] []Hogging 10"F5 Plate glass

["Khail Rosenberg" <mikhail.rosenberg@rosenbergtelescopes.com>]

I recommend using Dental stone next time.. quite cheap and very effective
dont even need to use epoxy on it, and dries in minutes..

plus if you live up north you can put the dental stone under your blankets
after you make it... it gets quite hot (after you mix it with water)



On 1/22/08, Mitch_Bisnauth@cknainc.com <Mitch_Bisnauth@cknainc.com> wrote:
>
> The blank is a Newport 10" and it took about 12hrs total time over the
> past w/end - which is long base on what I've read.  I think I overdid it
> because the cavity now matches the full ROC template but with 3 pits about
> 0.5mm directly on the edge along with some localized low zones in the 2/3D
> zone - (I started experimenting with stroke types and zones to get some
> 'feel' for what happens and to get the 2/3D area and edge to catch up with
> the center - there is some 'overshoot' maybe by about 2 wets).  So some
> work remains which fortunately is required so as to mate the full tool.
>
> 1 teaspoon/wet of 80grit was used initially for about 1hr of grinding but
> reduced that to 1/2/wet - I felt the initial wets with 1tsp were too long
> because about 3-5min each wet was "playing in the mud" trying to capture
> the grit without adding too much water on the flat surface,  whilst with
> 1/2tsp the grit died just as the mud showed up and the wets were about
> 5-10min depending on the area and strokes.  (Dry grit and 1 spritz with
> walmart spray bottle). Hogging strokes were initially to-fro across the
> center with the stroke length varying from full diameter to about the
> diameter of the hog - however the center ran away so I targetted the 2/3
> zone with 'chordal' strokes - (I thinks the edge pits came during this
> stroke), after about halfway through hogging I started to 'blend' at the
> end of the wet using the mud and a 0.5D circular stroke so that the edge
> of the hog just crossed the center and overlapped the edge of the blank on
> each circle, (not sure what that stroke is called..).  I was frugal with
> the grit - there is more than 1/4lb remaining to do the bed-in of the full
> tool, (started with 1lb of 80grit), grit was distributed directly to where
> I felt grinding was needed.  I rinsed the blank completely clean after
> each wet and toothbrushed the hog.  I did not wipe off the surface water
> after each rinse and in the later 4hr stage I did not add any water to the
> blank for a wet - there was sufficinent pooled on the surface to start the
> wet.
>
> The hog and the tool are from the same materials because I decided to test
> the tool materials using the hog,  - 1" tile seems unavailable in TN
> without buying about $100 worth - but 'Hobby Lobby' has 3/4" unglazed,
> (both glass and 'ceramic'), (I used the 'ceramic' version @$9.99 w/o tax
> for about 130 squares - enough for both hog and tool), 20lb "Drystone"
> came from Plaster.com for $25 delivered.  The plaster was 'retarded' by
> increasing the water from its recommended max of 20% to 25% and using cold
> water from the fridge (Per the literature on the entire plaster casting
> method - both of those are no-no as the lower water temp increases mixing
> viscosity and the excess water impacts strength - however I felt Drystone
> 16,000 psi sufficient to take these adulterations).  Drystone has a
> positive expansion which combined with its strength and delivered cost
> made it my choice.  I thought the positive expansion will tend to 'push'
> the tiles to the blank as curing took place and improve mate of the tiles
> to the blank - but in retrospect with the generated cavity and the mass of
> the tool I doubt that there was any benefit from that - it seems that the
> real benefits are its cost and strength.
>
> The hog is a 3.5" steel ring about 1/16" thk that was filled with Drystone
> and 8 tiles - I tried it with and w/o channels - (no new info ...the
> channelled version held the grit better, I couldn't tell if I was cutting
> better), however the channels were not surrounding each tile - they were
> gouged with a Dremel diamond drill ~ 1/16" to 1/8" wide and no more than
> 1/8" deep- at any open space on the hog face.  I'm inclined to say that if
> the tile arrangement has to be hand-assembled from individual tiles as I
> did there seems to be little benefit trying to space the tiles to allow
> channeling completely around each tile and there is/may be some benefit in
> having a more 'cleanable' channel arrangment.  The full tool is built on
> this info and I intend to use it with and without channels  - the tiles
> are layed in rings so I can put 2 ring channels with some central
> depressions to check with/without channels.
>
> On the hog I had a few bubble-pockets at some tile edges from trapped air
> so when doing the the full tool I poured the slurry in 2 'pours' - the
> first with enough slurry to just cover the entire tile arrangement and
> gave entire blank+tool the usual vibrate to evacuate any trapped bubbles,
> the second pour just completed the fill - no trapped bubbles on the tool.
> The tool cure temp maxed out at about 100F (roasting thermometer) and the
> tool seemed fine this morning - I stuck it in the oven this morning for a
> warm up.
>
> This is old info for many on the list - but it may fill the gaps for other
> newbies who are trying to do a mirror without easy access to a club/help.
> Most of what I did was from info through this list - thank you everyone.
> (Bob May, Mike Lockwood, Thomas Moulton "grind more, worry less"....
>
> MitchB
>
>
>
> Dave and Connie <dmatt@frontiernet.net>
> Sent by: atm-bounces@atmlist.net
> 01/21/2008 08:32 PM
>
> To
> "Bob May" <rmay@nethere.com>, <atm@atmlist.net>
> cc
>
> Subject
> Re: [ATM] Started Hogging
>
>
>
>
>
>
> At 09:04 PM 1/21/2008, Bob May wrote:
>
> >A bit complex and complicated but usable.  I assume that you're
> >doing something in the 15" range for that depth.  You're final
> >depth for the first hogging is a good one as you will be wanting
> >to not go too far and mess up by having to remove a lot from the
> >edges.  I usually go about that far myself with the iron tool.
> >This allows me to constantly decrease the ROC as I go through the
> >coarse grits and keep the center from getting unground relative
> >to the edges.
>
> Actually it is going to be a 10" f6 (I hope).  The Stellafane calculator
> gives me .105 as a depth so I figured that .090 would be a good target
> leaving me .015 to get the tiles to seat and remove the 60 grit damage. At
>
> this point I am done with the 60 grit.  The job took 4-6 ounces total
> (quartz blank).
>
> I was going to go with the pipe cap but found that I really couldn't get a
>
> hold on it.  I stopped programming 10 years ago from carpal and tendonitis
>
> on both sides.  The nerves are permanantly damaged.  The taller tool was
> to
> allow a good grab and I found that the nuts helped the cutting action.  If
>
> I was to make another I would pobably just glue the nuts in place.  That
> would give more projection, more even distribution, and a better bond.  I
> was down to the cement in places by the time I finished.
>
> I am a bit disappointed with the cement tool at this point.  The top has
> gone concave as it cured.  The whole point of casting it on the mirror was
>
> for it to be convex and save the edges of the tiles.  I'll give it another
>
> day or two to move around curing and see where it ends up.
>
> The epoxy is pretty much trash for me as I will only need a little for
> future boat repairs and I have about 1/2 gallon.
>
> Dave
>
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