Well we've digressed somewhat but parting off has been flogged and flogged not just now but several times earlier and sadly - got nowhere really.
So let's deal with Three similar problems and attempt to find WORKABLE answers?
The First is 'your window weight in cast iron'. i agree with every word and suggest that you nget rid of the sand-- from where your German battleship settled in the sand in 1917 in Scapa Flo.
First heat it up red hot- perhaps on the barbecue and leave it overnight to get rid of the hardened 'skin' with some of the sand attached/embedded.
Then dunk it in what you can get- battery acid, drain cleaner or vinegar, the remain of the pickle jar or any cheap acid-- even your vomit. I jest not- all will work
Then hitting the right angle from a perhaps 6 inch grinder. Let's say that you want a 7 degree angle?
Multiply the 6 inches by 7 degrees and multiply it by a secret constant of 0.0088. and you get 0.369 and call it thousands of an inch. The nearest usable figure is 0.333" or a third of an inch. If you build up a wooden/plywood 'grinding table' to be that third of an inch from the centre of the wheel--- you have a grinding angle of 7 Degrees. It's taken me longer to type it than do it. It's what the 'greats' tell you but put it oion a list to hide how simple it all is
And now - between phoning a 'girl friend' and accepting an offer to quaff a whole bottle of Scotch with a mate- I hit trouble with a cheap and not very nice 4 jaw SC chuck which I finally wanted to use.
Everytime she walks she wobbles--- moving pictures. So what to do? Well, Martin Cleeve,authour of Screwcutting in the Lathe and Professor Dennis H Chaddock author and designer of the Quorn tool and cutter grinder came up wit a solution without buying a GripTru chuck. So far, I stripped the chuck off the Myford backplate and did a facing cut of the plate including the register-- and put it together. The wobble was gone but the jaes were a gnat's cock out. So far so good- a man on a motor bike would never see it.
But these two worthies got closer to 'concentricity' so my next job-- assuming that I will be sober tomorrow, is to remove a bit of the register on the backplate so that the chuck with its 4 bolts could move if altered. So I'm going to overbore the holes in the chuck-- so that a chuck is just tight enough o be clocked to run true- with the judicious application of a hammer.
OK if the jaws are still out a bit, I did mention the use of va Bosch POF 45 wood router.
As they say, meanwhile back on the ranch. Hope this all helps
Norman