Here is an MS Word file I have on lapping mould from GBO members posted in the past:
Lapping molds
Posted by Billy Marr
Mon, Oct 23, 2000 at 12:54
In another forum I read a way to lap molds that is
different from what we have discussed.
First you need a bullet that has been cast in that
mold.
Second cut off the portion that you do not want to
lap.
Third drill a small pilot hole in the bullet and
insert a small wood screw.
Fourth coat with valve lapping compound fine will
work.
Fifth insert in mold hold mold in hand excerting
enough pressure to let bullet spin but still lap keep
putting pressure until bullet spins freely.
Sixth cast a few and messure repeat as needed.
I tried it this weekend it works great.
Posted by Leadpot
Will.
You can lap a mould but you must be careful with a aluminium mould if that is what you have, when you lap, for it don't take to much to go to far.
This is how I do it. I drill a hole in base of a cast bullet were the sprue was cut that fell from the mould you want to lap. I use a 1/2" or 9/16" #7 or 8 sheet metal hex head screw and screw it in the base of the bullet. Next I use premium buffing compound, like dico it comes in a stick. I scratch a little off the stick on to a glass plate and mix it with a little cutting oil till it is a smooth past next I roll that bullet in the compound just hard enough so some inpregnates into the lead a little then put that bullet back in the mould and just roll it with your finger a little to settle it in and get the mould coated with the compound re coat the bullet again if you need to and put it back into the mould and close the blocks.
Now you can use a nut driver and spin that bullet in the closed mould till it gets a little loose then use a drill with a driver and spin that bullet in the mould. but you want to take car you don't slip off the base of the screw or you might damage the cavity base edge.
The compound I use is dico E5 emery for cutting and SCR to polish.
Or you can use pumice or rotten stone and oil. I use this for lapping barrels with a lead core. you can get this in paint stores.
Remember if your blocks are aluminium they lap fast. I hope this will help you.
I have used this method for out of round moulds and taking some tool marks out.
Kurt
