Mirror Lab Activities...

Going to work at the Steward Observatory Mirror Lab every day, sometimes it seems progress is slow, but at the same time there is always something going on!  While doing the same thing every day would soon get boring, fortunately tasks change with time and it rarely gets old.

Case in point is what the casting lab is up to. 

They can produce mirror substrates a lot faster than we can polish them, and they are preparing to cast another mirror late in the Summer, likely in August.  As a result, mold production is in full swing.  They've recently replaced the old CNC mill they wore out with 15 years of machining, and after getting used to the new machine, have been hard at work.  It is an entertaining 8 minutes or so to watch the machine turn a raw block of alumina silicate into a mold core, complete with tool changes.  It even cuts off the core with the right height and angle.  It takes something in excess of 1600 cores to make an 8.4 meter mirror - fortunately because of symmetry. that many individual programs are not needed to machine each of the cores!  At left, one of the non-hexagonal cores are being machined - the cloud of particles are headed for the dust collector towards the left.  At right, John removes the finished core and prepares to load a new blank.

There is, of course, quality control - many of the cores are

checked coming out of the CNC to make sure tolerances are met in the machining process.  At left here, Phil is using "smurf glue", so named because of its blue color, to help fill small voids at the base of the cores.  In the casting process, higher hydrostatic pressure at the bottom of the mold can inject molten glass into these voids which might cause issues in the glass blank after the mold is removed.  The smurf glue seems to seal the bottom edge well enough to solve the issues we had on one mirror blank.  At right, some of the raw blanks await machining in the mill.

After machining and sealing, the cores await installation.  Since

the non-hex cores are hardest to machine and last to get installed around the outside, there are a few hundred cores on a large number of storage shelves.  The picture at left shows some of the more normal hex cores, queued up for placement in the mold.  We were told at our Monday organizational meeting that over 25% of the cores have been installed after about a month of effort.  Since much of that effort was in the outer cores, they are actually over half done with core machining.  As of this morning, the picture at right showed the present mold progress - actually a panorama of 3 frames.  Fast progress is being made, but much work remains for the August firing date.  After finishing the mold, there is a pre-fire, complete mold inspection, and 20 tons of glass inspection and loading.  Last I heard they were on schedule!