enlarge mold

i just got 2 ea. 6 cav lee 45 colt 200 gr molds. i like to size .453. they both are a little small. i would like to lap them .001+ bigger. i was thinking about getting the molds going good then cut the spru and leave the bullets in the blocks. sit the block on a drill press and drill a small hole in to the bullets but not all the way. then put in a drywall screw and cut off the head. take out the bullets and chuck up #1 in a drill . use tooth pase at a slow speed.. close the mold around the bullet and repeat as needed. how is that? i have never laped a mold but see it is a common thing to do. by consern is getting the hole centered. has any one done this to this same mold? how did it work? would a ww cast or lion type cast bullet be better?

That will be a lot of work you will have an hard time controlling.
I would not use toothpaste. The sodium bicarbonate, or pumice, they use as an abrasive is awful mild.
If it were me, I wouldn't have gotten a six holer in the first place, however, that is what you have to work with.
I would cast through some nuts. Leave the sprue intact, and eject the castings. To these, I would use instead lapping compound. The lead swallows up a lot of grit so I did not have an issue with cutting too much. I would turn the nuts with a wrench while closing the mold.
Final sizeing is an issue here.
I would save several cast boolitts for the final sizeing. You want even.
Going slowly, and measureing your progress, you can open them up.
Good luck.

686,

I've used the method you've described and it worked.

Center the hole as best you can, but don't worry if it's not exact. If you let the mould wobble around with the drill, everything will be fine. Go slow.

As docone31 said, cast up a bunch of lapping boolits, check the size often, and use a fine grit lapping compound.

I did it over the course of a few days, lapping a bit, casting new boolits and letting them sit overnight to cool, measuring, and repeating the process until I got the size I wanted.

You know what to do and will get the results you want.

I use the small self drilling hex head screws once it drills deep enough to hit the threads does a great job.

The simplest, safest way IMO is to mount your drill bit in a tap wrench and turn it by hand. It's virtually impossible to drill too deep and it really doesn't take long. Run a short #6 hex head screw in with a drill and a socket. Don't worry about bottoming the head, when it stops going in you're good to go.
Pouring through a nut is also good but I found it easier to center the nut over the cavity if you use a big nut - easier to see into it before you pour.

You are wanting a larger cavity. Why would you use toothpaste? It prevents cavities.

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You are wanting a larger cavity. Why would you use toothpaste? It prevents cavities.

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I was trying to gather info on increasing boolit size, and.... well let's just say carpetman has the same type of humor as me :-)

I just lapped out a 6 cavity mould that was very much out of round and different size cavities.

Also, the mould halves were offset by about 0.0015" so the range of boolit sizes went from 0.430" to 0.434" with 0.002" to 0.003" out of round at the seam and at 90 degrees to the seam.

I usually use a wood screw and drill to spin the lapping bullets but that is also normally when I have lapped iron moulds. This one is aluminum so I used the method docone31 describes to make sure I did not over do it.

I managed to round out the cavities pretty well and match them all for size. Here is my method:

- I cast several boolits with nuts over the cavities and run the lead up into and over the nut
- I lubricated the boolits with oil then turned by hand using a box end wrench in the smallest cavity while closing the mould by hand. This allowed the sharp edges at the seam to shave of lead. I opened the mould regularly to clean out chips then carried on until there were no chips.
- then the shaved boolit fits the tightest spot of the smallest cavity
- I used that boolit to lap the smallest cavity first with valve lapping compound, again opening and cleaning out lapping compound and sludge until the boolit turned easily and freely
- after lapping the smallest cavity(s) I moved up to the next size and repeated using the same boolit
- repeat until all are done
- cast and measure
- I needed to repeat this about 3 times using a new boolit each time
- To finish I used the same boolit already embedded with lapping compound (but no new compound added) in all cavities, lubricated with WD40 and turned it until it turned freely

All cavities are now oversize at 0.434" to 0.435" but quite round. The smallest cavities were brought up by about 0.004" but the largest cavities were just rounded out without much increase in size using this method.

One of the dangers of lapping is that cavities tend to go oval I think due to lapping compound and sludge holding the mould faces apart. The cavities seem to open up more at the seams. Regular cleaning and then further lapping will help avoid that as does finishing with an embedded lap using only a lubricant but no more lapping compound.

If all you wanted to do is polish the cavities, toothpaste or other very fine abrasive (Bon Ami) would work fine but to remove metal I think you are better off using valve lapping compound.

Nothing really new there, just my advice. Take it slow and easy, it will not take long to lap out 0.001" and it is unlikely you will get an oval cavity just taking out 0.001". In fact taking out 0.001" is pretty easy so I guess I am rambling a little with this long post!

Longbow

How and where do you apply the abrasive?
Just to the top of the lands by rolling or do you get it in the lube grooves too? (thinking about it now, you probably have to)
Do you put the abrasive on a dry bullet or have some type oil or sticky on it?
thanks

Clover Compound comes suspended in grease - it's a thin paste. Smear a light coat on the boolit. You may as well coat the whole thing.

I'm liking this already. got the bottom band to a nice symmetrical .4105. The other bands aren't quite as good, and I left the top band alone, so I'll see how that works before I do any more. (Lyman 410663 Snover)

Any good recommendations on prepping the mold for casting after honing?

I cleaned it with solvent and acetone, but do I need to do more?

As I have many Lyman moulds, I have gotten good at this. As has been said, drill hole in boolit, insert screw shank minus head, fine valve lapping compound, electric drill, clean, cast, repeat if necessary.

I have one thing to add from my experience: In the interest of keeping the moulds round, we want the blocks completely closed from the beginning. I accomplish this by taking a file and making three equally spaced flat spots from meplat to base (like land engravings, but I turn the file on edge and cut some out of the grooves, too). Put a thin stripe of compound on the filed spots, place the lap in one of the mould halves carefully so that either a stripe is exactly perpendicular to that half or the opposite half, NOT aligned with the part line, and close the blocks completely and tightly. It may be difficult to get the boolit to start turning, but once you do you can be assured that no compound got between the blocks. The vent lines will fill up with it, and when opened the mould must be cleaned before repeating, but it gives excellent concentricity.

Semtav, Hot water, detergent, toothbrush, scrub it 30 seconds after you're sure it's cleaner than it needs to be. Brake cleaner works, too, just make sure you don't get it hot before it evaporates or you could easily be severely poisoned.

Gear

Thanks gearnasher. that might really be handy if you're trying to get one or to bands resized.

I want to try this on a Lee 310gr gas check mold on which the gas check shank is already a bit oversized (hard to seat the checks), but the boolits are only dropping at 430. I suppose that grinding the gas check shank off of the boolits before using them to lap the mold would keep the shank from enlarging. But, what about the lube and crimp grooves -- how can you keep them from getting deeper?

Thanks,

Randy

Would technique to achieve this result be similar to what is needed to alter gas check mold to plain base? If it is, doesn't one of our members/sponsors offer this service - lathesmith or buckshot?