Its been a long time since my last update,partly due to hectic schedules with the new job and a week away on the isle of wight for a training course but mainly due to my inability to make a pitch lap first time!!
After finishing off with the 600 and having a nice scratch free surface that shows up reflections much better, it was time to get on with the bit I had been dreading-casting a pitch lap.
I gathered all the bits I needed for this-a 17" wooden disc for the lap(to save weight over a plaster disc),2kg of the softest guggoltz pitch,baking foil(largest size I could find,the camping stove and a cheap £3.50 pan from asda :)
melting the pitch is a job to take your time with but even at 30 minutes to melt it down is way too quick according to others but about the slowest I could do it with my stove.Getting the pitch out of the card containers is a good challenge in avoiding contamination.i used a brick softly to crack the pitch inside the card and then emptied it out into the pan.this takes a good 10 minutes with 2kg.
making sure your blank is clean and warm(I dunked mine for 20 mins in warm water),dry it fully and cover fully in baking foil(reflective side up).
the first mistake I made was to pour the pitch too runny which meant it went slightly under the join of the foil but it was still useable
as sson as it started to thicken slightly I put my wooden disc on top and pressed down to get the air bubbles out and to keep the shape.i then added a 10kg weight to pres it down and left it to set.
to cut a very long story short,i didn't wait long enough to remove the lap from the blank and as soon as I started cutting the channels the lap splintered a lot and I ended up breaking the pitch off and starting again.and I repeated this process again another two times until I got to the lap I have now.
my current lap still isn't perfect,it has some splintered bits and a few imperfections and the channels need deepening but it does polish ok if a little sluggish
unfortunately after 30 mins of polishing I picked up a slight scratch so ive ended up going back to 400 and 600 grit to get rid of this scratch before I start polishing again.even with 30 mins polishing its amazing how much more reflective the blank is!!!
hoipefully be back to polishing next week and can see about testing if my blank is a decent sphere or not :)
getting there slowly but surely!!