Lapping TL mold .002 ?

[ghh3rd]

I was hoping to scare up a Ranch Dog Lee TLC432-265-RF mold, but I guess that will be a tough order to fill since they aren't making them any more. Course, if someone has one they don't mind parting with, I'd be willing to talk...

I found that I can get a TLC430-265-RF, a Lee undersized 'second'. I was thinking of trying to lap it from .430 to .432. If I screw it up, all I've lost is $20 & shipping.

Is it possible to lap a TL mold an extra .002 without affecting the lube grooves too much?

Thanks,


Randy

[longbow]

Absolutely!

I have lapped several moulds. 0.001" to 0.002" is pretty easy if you are careful. Going much more takes more care.

There is a tendency for the cavities to go oval with more metal removed at the seam. I think possibly some is due to chip removal at the sharp edges but also due to lapping compound and lead bits building up on the mould faces holding the blocks slightly apart.

I recently opened up my Lyman 314299 from 0.312" to 0.316". I had started some time ago but found the cavities were going oval ~ wider at the seams. I stopped when I had 0.315" at the seam and about 0.313" at 90 degrees to the seam and Beagled it. so boolits were near round.

Recently I had to lap an undersize mould out almost 0.004" so went very carefully and cleaned the mould faces often then spun the lapping boolit by hand with no more compound on it ~ just what was embedded. I got very round cavities.

It worked so well I went back to the 314299 and used the same technique to finish it. It is now 0.316" body and 0.305" nose and as round as the original cherry cut cavities at about 0.001" out of round at the seam.

Aluminum moulds lap very quickly so I would advise spinning the boolit by hand, not with an electric drill if you are doing aluminum. Iron takes longer so maybe roughing with a drill then finish by hand. That is how I did my iron moulds when removing more than 0.002".

I think even with tumble lube grooves 0.002" is quite doable.

Longbow

[mooman76]

I agree it should be quite doable. Some take and after lapping out .001 make a fresh cast to continue with to help keep it round. With luck the mould may come out .001 large to start with and then you have less to go.

[semtav]

I just lapped my Lyman 410663 about .001 and have the same oval problem. I read somewhere a method to avoid that problem. Mainly caused by getting compound in the parting seams.
I'm going to try it to see if I can get it back round.

[longbow]

semtav:

Just lap a bit then clean up the mould faces and don't add any more compound to the lapping boolit ~ use it almost dry as there is still lapping compound embedded in it. That is how I did it.

Some use dry grit and roll the lapping boolit between steel plates to embed lapping compound into it then use it like a bur.

Yes, the major problem is lapping compound and bits getting between the mould faces. Turn the boolit a bit then open and clean the mould faces, turn, clean, turn, clean then clean up the mould faces and cavities, return the "dry" lapping boolit and turn a little more.

When the lapping boolit becomes loose use another or recast if you are taking out more than a thou or two.

I just lapped a 6 cavity mould and didn't want the large cavities to get much larger, just rounder. I started with a boolit from the smallest cavity, lapped the smallest (end cavities) and worked towards the largest cavities. Of course more material was taken out of the smallest cavities due to tighter fit. I had to lap and clean then change cavities frequently but in the end I managed to get them all pretty round (mould blocks were offset about 0.0015" so 0.003" overall) and very close in diameter.

The boolits are now a good fit to my gun and shoot well.

These cavities were offset and uneven sizes by close to 0.004" at the extreme dimensions.

If you have only lapped out 0.001" you can't have much oval to the cavities. I bet a little careful lapping and frequent cleaning of mould faces will get your cavities round.

There is a good article on mould lapping here: http://www.castpics.net/ under mould references/mould lapping

Longbow

[Buckshot]

..........Be carefull! It'll surely be educational in any respect. When lapping a mould the first things to be affected is sharp positive (sticking out) corners, edges and fragile detail. It's just simple mechanics, and if there is one thing a Lee type TL mould cavity is full of it's sharp positive corners and edges.

..............Buckshot

[Wayne S]

Buckshot,Longbow,etal,
What are you useing for lapping compound ? I just came apon a Saeco # 307 in an 8 cavity mold. The sample bullets I got with it were .307 x .311, and I'ld like to get it to throw round ..310-.311
Any suggestions ? anyone want a winter project :lol: