Lapping a Lyman mold

[Todd S]

I have been trying to lap a steel mold and I'm having a heck of a time. I have done four 6 cavity Lee molds with no problems. The steel mold though, is another story. It takes sometimes 6 or 7 hard whacks with a wood handle on the hinge to drop the boolits. This is a second hand mold that required some attention when I recieved it. There was a slight amount of surface rust on the inside. I scraped it with a wooden chopstick and removed it. When the boolits drop, they look pretty good. Now for the problem. I am just trying to polish the cavities. I was trying to use both car polish and comet. The boolit would get wedged in the mold cavity and would not move. When I pulled the boolit out, it had little wings on it from the cavity edge. One of them actually had the screw drive all the way through the boolit and touch the bottom of the cavity. It just left a very small dot. How do you guys get the mold lapped without the boolit seizing?

[Wally]

Make a "plug" out of 0000 steel wool that fits tight in the bullet cavity...attach the end to a power drill. Coat the steel wool with a polishing compound..I use Red Automobile rubbing compound. Spin inside the closed bullet mold cavity... I had a severe sticking problem with a Lyman 452460 and this cured it.

[Mal Paso]

Arrowhead lapidary supply sells small quantities Diamond Paste. 600 grit if you just want to polish. 320 grit for enlarging. Grind the tip off the screw.

[462]

Fine grit valve grinding compound, found in your local auto parts store.

Read this sticky:http://castboolits.gunloads.com/showthread.php?55260-Kroil-in-a-boolit-mold A controversial topic, to be sure, but one never knows if it'll work till one tries it.

[GP100man]

I take lappin compound & spread it out with my finger ,then roll the boolit in it while press down with a peice of flat bar.

I spin these by hand .

[TMSCU]

I use 320 grit Clover lapping compound on a plug of steel wool to start. Change to 600-800 grit to polish. Instead of using a screw I use a small short dowel with a split cut in it to grab onto the steel wool. Put the dowel with the steel wool in an electric hand drill and spin it inside the cavity on slow speed. Check progress often...

[longbow]

Here's another vote for valve lapping compound. It doesn't take a lot to open up aluminum but the iron moulds can be a bit of work.

I use a light wipe of valve lapping compound (mine says 425 which seems like odd grit size but it all I could get locally) all over the boolit then close it in the mould with very light closing pressure and turn SLOWLY with electric drill/screw or even better to start is to cast through a nut so the boolit is turned by the nut then turn with a wrench or socket by hand.

If you are just polishing then you aren't removing much metal and fine compound is better though my 425 works well. Even so it is best to open the mould and clean off the mating mould faces regularly so the mould closes fully and is evenly lapped otherwise the cavities will go oval.

After you turn the lap a few times it will shed some lead then you can close the mould completely and get even lapping.

Also, look here:

http://www.castpics.net/subsite2/MoldMods/MoldLapping1.pdf

and here:

http://www.castpics.net/subsite2/MoldMods/How%20to%20Hone%20Out%20a%20Mould.pdf

Good instructions.

Longbow