Lapping a lyman mold

[sharpshooter79]

Howdy Folks,
I have a Lyman 358429 mould that cast bullets at 357 size. I was going to try to lap it with some valve lap compound, and read the above sticky but was having trouble understanding it. Anybody here lapped a mold before and how did you do it? I have the article from castpics. Anybody ever tried the way described in that article? thanks!

[MtGun44]

Most valve lapping compount is way too coarse. You want about 400 grit or 600 grit
or even finer. Have not read the castpix method.

Most use a screw in the base of a boolit cast from that cavity as a driver and spin by
hand or with a drill. Some have reported embedding ONLY in the bands, wiping excess
and being able to control where the lapping occurrs. I have not tried this, just reporting
what I have heard.

Pay most attention to those that have actually done it. Only commenting to save you from
damage with too coarse a grit.

Bill

[462]

I've lapped a couple Lyman moulds, but prefer beagling (sticky here, or Castpics) as it is reversible. I used the screw-in-the-base method, rather than the pour-lead-through-a-nut method.

If you decide to lap, go slow, cast new boolits and measure often. I waited overnight before measuring the new boolits. Lapping iron moulds is a lengthy process --at least for me -- beagling is quick and easy.

If you decide to beagle, shoot me a PM.

[zomby woof]

When I've lapped in the past, I always get the compound between the blocks. Plus some compound always migrated into the GC part of the mold. With my last sticky mold, i tried something different. Take a mold half, place a boolit into it and apply some compound (I used 800). take a file with teeth on the side. Use the side of the file and apply pressure to the boolit and rotate it back and forth. Make sure the file doesn't touch the mold, only the boolit. I did a light lapping and the boolits fall right out.

[nanuk]

there are a few really good articles on lapping moulds

I think the one by OldFeller is really good.

read about it Here! (http://castboolits.gunloads.com/showthread.php?t=3172)

[DLCTEX]

In my experience valve grinding compound in the fine grit works well on an iron mould. It takes some aggressive work to open the iron ones. I have a Lyman mould that had to be lapped and beagled both to get it to where I wanted. By rolling the boolit between two steel plates to embed the grit you can enlarge the bands and leave the grooves and nose alone. You may want to finish by polishing with Comet or such to insure good boolit release.

[rintinglen]

I opened up a Lyman 357-446 by using fine Clovers 600 grit, a #8 bolt and tons o' elbow grease. I first drilled the base of the boolit to accept the bolt while the castings were still in the mold. I used two aluminum plates to drive the polishing compound into the bands. I carefully wiped the excess from the grooves and the nose using a folded patch soaked in solvent. Then I inserted the boolit back in the mold, screwed the bolt into the hole and turned the boolit using the bolt and a 1/4 inch drive ratchet. When the boolit turned freely, I cleaned the mold, discraded the used castings and the repeated the process twice more. I then cleaned the mold, cast up some more boolits, and repeated the entire process. This gave me .3585 boolits that worked better than the original .357+ diameter ones. It took all afternoon to do so.

[GaryN]

I tried it. It is a lot of work. I just send them to Eric now(Hollowpointmold.com). He is fast. Does a great job. Is reasonably priced. And I didn't have to do it.

[Boolseye]

Recently did a 6-cav Lee. Worked great. Here's the thread:
http://castboolits.gunloads.com/showthread.php?t=134379
It worked very well. I did come to the conclusion that using a drywall screw in the boolits and turning them by hand with a screwdriver worked best. You close the mold as much as you can and still turn the boolit (too tight and you'll screw the screw deeper into the boolit, expandng it), and eventually the mold will close completely around the boolit and it will turn easily in the cavity. At that point you can clean up, cast another boolit for polishing (I use comet) or for further lapping with compound. keep the compound off of the mold faces throughout the process. As with all such projects, preparation is key. I cast and measured all boolits before starting, diameter at the seam and 90º off the seam, and recorded everything. Go slow and don't force anything, and you'll be fine. It will take longer with iron molds.

[longbow]

I have lapped several moulds of iron and aluminum with good success. As mentioned, you have to open and clean grit off the faces regularly or the mould cavities will become oval.

You haven't said how much you want to lap out. If only a thou or two that is quite easy and won't take long. If more than 0.002" it can be tedious especially with iron mould blocks.

I use valve lapping compound that is about 400 grit (I think it says 426 on the can).

If only lapping out 0.001" I would cast through the nut per instructions here:

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

If removing much more than 0.001" I would use the screw method, drill the boolit base, wind in screw then use an electric drill to start the lapping process. Once close to required size I would hand turn the rest of the way.

As mentioned above, Beagling is quick and easy and suitable for up to about 0.003" enlargement. It does produce slightly oval boolits but they are symmetrical and sizing should make the driving bands cylindrical again. If shot as cast, as long as they are slightly larger than groove diameter at the small dimension they should seal and shoot fine.

Beagling info here:

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

While Beagling certainly works, if I have no use for the original as cast boolit diameter I would lap the mould to cast the diameter I want. That is just me.

If you decide to lap:

- make sure you know what needs to be done (search this site for lapping, read and ask questions)
- work slowly
- clean mould faces OFTEN so they close on the lapping bullet and you get even lapping
- check the diameter OFTEN by casting new boolits and mic'ing them then lap as required

With iron moulds I find I get good finish with the valve lapping compound but with aluminum moulds, I find it leaves a slightly rough surface so a final polishing with finer compound might be best.

If it is a multi-cavity mould I would measure bullets from all cavities and use the smallest (if there is a difference) in all cavities, starting in it's cavity and moving along. When the lapping boolit gets easy (easier) to turn it is time to recast and measure.

Lapping is not terribly difficult, just time consuming and not one of those jobs you want to rush. Again, go slow, clean often and measure often.

Some recommend pure or soft lead lapping boolits. I usually use ACWW or range scrap.

The link Boolseye posted is a good one.

Good luck.

Longbow

[kweidner]

I did the screw method for a 429421. opened it a little over .004. Took forever. I worked on it on and off for a week. Attainable but slow. Think of it as part of the fun of casting.

[sharpshooter79]

Howdy Folks,
Thanks for the replies. Sorry it took so long to get back to ya'll. I tried the pour through the nut method, it didn't open it enough and I ended up twisting the nut off so I will try the screw method this time. Thanks for the help!

[GP100man]

sharpshooter , your trying to rush it & have too much compound on the lappin boolit if it`s grabbin that good .

I like embedding the compound & it only takes a small amount to do the lappin.

I do a finishing polish with comet cleanser.

[Mal Paso]

If you hate cutting with a dull saw, Diamond Powder. Arrowhead Lapidary Supply will sell small quantities reasonably. I like 325 grit but they have everything.

[sharpshooter79]

Hey GP100 man,
Thanks for the heads up, I will rethink how I do my lapping. I assume you were lapping a steel mold too?

Mal Paso, thanks for the info!

[runfiverun]

cast and let the boolits harden or water drop them and wait a day or so.
i opened a 4 cavity 429667 it took me most of a week going from 428 to 430.
i used my 4/6 alloy, to help get things moving along.
i would also get the mold up to temp before lapping it.
i finished it off with some whitening toothpaste to get everything smooth and shiney..
it is one of my favorite molds to cast with now,

[GP100man]

Yep , comet will do on the aluminum or a real fine grade of compound .

The diamond dust is really the way togo but just have`nt ordered it to have it when I need it .