lapping a mould

[augercreek]

The reason I ask is that it's very hard to find a .323- .325 mould in 80-120 gr weights so I'm thinking of buying a smaller dia. mould and lapping to a larger dia. What type of compound would you use?

[toallmy]

A lot would depend on the material the mold was cut from and how much you intend to enlarge the cavity .
Aluminum will grind out very easily , iron takes a lot more , brass is pretty soft also .
There is a lot of good helpful information in the archives .
Tell us more if you can .

[SvenLindquist]

Buy a NECO bore lapping kit. It comes with all the grits you will need. Take your time and change the lap (boolit) often,

[augercreek]

Thanks much

[country gent]

For what you want to do clover compound silicon carbide in oil base in grits from 240 to 600 ( 240, 320,400,600).
Cast several good bullets from the mould. ( visual full fill out sharp corners and form) weight dosnt matter. Drill base for a stem A piece of 1/8" key stock 1 1/2" long glued in the hole works well, ANd allows a small tap handle to be used.
Once epoxy is cured impregnate a bullet with 240 grn grit by applying a small amount on a steel plate and rolling bullet thru it between s plates. Carefully insert in cavity and close blocks around .
Use a back and forth tapping motion ( 1/4 turn back and forth) working 3-4 times and rotate 1/4 turn repeating thru 2-3 full rotations. Check progress visually. and move to next grit.
Having a pit of alloy hot and ready is a big help. when you want to check size clean mould pre heat in pot and cast 4-5 good bullets let cool and measure. repeat as indicated. A little light oil added occasionally helps keep the compound sharp and cutting better.

A comfortable work area, a light vise to hold the blocks closed, rags brushes and solvents. A hot pot of lead and ladle.
Working by hand slow and carefully you will have a very round true bullet when done. It is a very precision process.
Keep in mind when lapping in a hole or bore .001 removed equals .002 on actual size of part.
Keep compound and other build ups from between blocks.
A final polish with simichrome or toothpaste as a compound will give a very fine polish. to the cavity.

[country gent]

You can grade your own compound if needed using 2 clean clear glass bowls. Fill one about 3/4 full with a light oil ( not critical) grinding dust from your pedestal grinder is sprinkled on this oils surface. AT 15mins carefully pour of from the sediment this is normally to coarse for use. stir oils sediment mix and let set another 15 mins and pour into first cleaned bowl. this sediment is a coarse compound. continue this thru and you will get finer and finer grits as you go. You need to pour carefully so to not disturb the settled grits as you go. But in this way you can make your own lapping compounds. The full procedure is given in older Machinists Handbooks.

[RED BEAR]

Unless someone knows something i don't you can probably have mold made for what all that lapping compound cost. As someone who used to lap parts i would fo with aluminum for sure and if you have very much to take out ( more than a couple thousands ) then good luck. I will also say cast bullets as hard as possible and change them often.

[jsizemore]

Page 4 of the catalog on this site might get you what you want. Tom can cut them to whatever diameter you want with the alloy of your choice.

http://accuratemolds.com/index.php

[Good Cheer]

Clover compound mentioned above works great, very aggressive.
Also, you can selectively change the bands with lapping (not just the whole thing at once) but you're talking a shorter boolit so that probably doesn't matter. 8mm though, trying to find a light weight to modify is gonna be difficult in itself.

Side note about abrasive grits...
You can take a small household type box fan and slowly sprinkle dusty fine sand in front of it. You'll get a sand drift effect with the finer blowing the further. Before very long in will be segregated by particle size. The technique can be useful depending upon what you need it for and what you have to work with.
Some of the best was the silty stuff the crawdads brought up in the yard where we lived in SE Texas. It dulled mower blades so well I knew it had to work for other jobs too.
:-P

[EDG]

Just get a new mold made by one of the custom guys. Their prices are pretty reasonable and you get what you want. Reworking an existing mold might get you a chunk of scrap.




The reason I ask is that it's very hard to find a .323- .325 mould in 80-120 gr weights so I'm thinking of buying a smaller dia. mould and lapping to a larger dia. What type of compound would you use?

[Kraschenbirn]

'Nother alternative: 1) Find yourself a Lee 324-175-1R and cast a few boolits from your preferred alloy. 2) Wrap a piece of coarse emery paper around a piece of lathe (or similar) and begin filing down the base of a boolit, weighing occasionally, until you get down to the weight you want. 3) Repeat #2 on another boolit and check that the OAL is the same (or close). 4) Have someone mill the top of your mold down so that it drops the same length boolits as Step (3).

I think I've got some of those 324-175s 'as cast' and, if I do, I'll cut down one or two this afternoon and see how they weigh out.

Bill

[Kraschenbirn]

237534

Above is the Lee 324-175 cut down to eliminate the gas check shank and bottom lube groove...'bout as much as practical to leave an adequate drive band. From #2 alloy and sized to .325, this one weighs 130 gr. right on the nose. Not quite in the range you're looking for but I looked around a little and didn't find anything much lighter available. (Accurate lists a 120 FN and NOE has a 133 gr RNFP in stock)

Bill

[gwpercle]

Steel : 1.)automotive valve grinding compound ( Clover) #280 , # 600 finish with # 1200.

Aluminum: 1.) automotive paint rubbing compound , followed with
2.) auto paint polishing compound.

Aluminum is soft so be careful...rough grits can cut fast .

[augercreek]

237534

Above is the Lee 324-175 cut down to eliminate the gas check shank and bottom lube groove...'bout as much as practical to leave an adequate drive band. From #2 alloy and sized to .325, this one weighs 130 gr. right on the nose. Not quite in the range you're looking for but I looked around a little and didn't find anything much lighter available. (Accurate lists a 120 FN and NOE has a 133 gr RNFP in stock)

Bill

I like your idea! This week I got a Lyman mould 323470 never used on bay 165 gr. Lovern design. I like all the lube grooves in these. I haven't cast any yet but thinking ahead could a person take a cast and reinsert it into the mould part way and shave off part so you'd get a shorter bullet?

[longbow]

Lapping works but in my experience trying to lap more than about 0.003" out of a mould is not only work it is hard to do and keep the cavity(s) round and with sharp edges on driving bands.

There's some good info here:

http://castpics.net/dpl/index.php/the-library/moulds/23-modifying-molds

There are several articles on lapping. I'd recommend hand lapping, not using an electric drill especially with an aluminum mould. Aluminum moulds cut quite quickly. Iron moulds take longer and are more work but same problems in keeping cavities round. You have to remove the lap and clean the mould halves frequently or you will find that grit gets between the mould halves separating them and you get oval boolits.

To remove a thou or two is pretty easy but going much past 0.003" not so much.

If you are only looking for 0.002" to 0.004" you might try Beagling or maybe lap some then Beagle.

If you want to modify a mould as you've suggested with a filler try Erik at Hollow Point Molds:

http://www.hollowpointmold.com

He can make you a spacer (I think) or enlarge driving bands.

Alternately go to Accurate Molds and Tom will make you what you want.

Longbow

[longbow]

Paper patching is another route though a skill set in itself. It should get you where you want to be though with a stock mould.

[country gent]

When lapping a hole you get 2 for 1 for every .001 removed on a side you get .002 on dia of the casting since it removes stock around the entire hole or cavity. Lapping is a very accurate way of finishing a hole to size and finish. Using the right abrasive and grit helps a lot, to coarse and finish suffers and its hard to maintain size. to fine and its a long process with alit of lap wear. You can lapp and maintain sharp corners but it takes frequent lap changes and careful work. Working the lapp in a 1/4 turn back and forth motion 3-5 times and rotate 1/4 turn thru a couple rotations makes a very round centered cavity. Rotating with a drill motor or drill press the lapp may walk to one side or the other. A drop of light oil goes along ways to keeping the compound cutting and the best finish. As you work the lapp the compound will break down ( how it stays sharp) and cut finer as you go. You lapping is only as accurate as your lapp you want good bullets cast to do this. Actually impregnating the lapp with compound is preferred over just wiping it on. To impregnate the lapp wipe a small amount of compound on a steel plate lay the lapp on it and with another plate roll the bullet thru it with medium pressure back and forth the full circumference. Thus pushes the grit into the surface locking it in place.
Over the counter materials auto rubbing compound's, tooth pastes, are very fine and don't break down well but can give very fine finishes. Comet, Mon ami, abrasive scrubbing powders are very coarse and not well graded. Valve grinding compounds if fine enough will work for roughing. The actual lapping compounds are ideal well graded break down as needed and easy to work with. Ive tried polish lapping with JB bore cleaner and never seen much change in size or finish. Diamond compound's work well cut and finish good but are expensive.
As above you can grade you own compound with light oil and a couple bowls not hard but time consuming.

[Boolseye]

I have lapped a few moulds, and success depends on working very slowly and carefully. It is a lot of painstaking work. It can be done, of course. There are threads that can be found in this forum that will lead you to thorough articles and posts written on the topic. The first moulds I lapped was a six cavity Lee tl452-230-2R, opened it up about .002” using valve grinding compound and comet paste. (A paste made from comet cleanser and water). Later I bought some clover lapping compounds too. If you rush, you’ll just trash your mould. You need to cast some perfect boolits and drill a hole as centered as you can in the base, then screw in a Sheetrock screw or equivalent but not too far-it will cause the diameter to increase. Then you apply some lapping compound and slowly work it in the cavity. Go slow and clean up the mold faces periodically, after a bit cast more boolits and see where you’re at. I use a power drill but very slow. Be cautious if things start to bind up, stop and take stock. If you drive the screw in too far it will come out the tip and you’ll have a nice little bump at the top of that boolit for the rest of eternity (I have just such a situation on a .40 cal mould I lapped. Dead center, anyway!). I will add some resources if I find them. There were a few articles and threads I referred to when I was doing this. If at all possible just beagle it or buy a mould that’s the right size. If you lap, it tough but ultimately satisfying. The other thing I did was keep careful track of my progress, before and after (see photos of notes .40 cal mould). Measure original diameter and have an idea of how far you wish to take it.
https://uploads.tapatalk-cdn.com/20190309/f5b98921b85deee8437f38120cb59ac2.jpghttps://uploads.tapatalk-cdn.com/20190309/a76cbeaa2de65a7945e2f16cbb6cd00d.jpg

[RED BEAR]

Cutting down the lee mold is the way i would go if your not going to have one made. I have cut down several its not hard. I am retired and no longer have access to machinery. Just take off the spruce plate remember left hand thread use a very rough file or wood rasp with mold in vice to get close to where you want then switch to finer file and measure often to keep flat you can mark high spots with marker when you get here you want i used a razor knife to score the top to vent gas. Only took an hour or so to do one. I also drilled through the spruce screw and used drill.to cut half cicrle and put a spacer and used a standard screw to go all the way through to hold the spruce plate.

[augercreek]

Lots of info here guys and thanks for all the input.

[Boolseye]

Just reading through again, Kraschinbern’s suggestion makes a lot of sense. For $20 and a couple hours of work you’d have your boolit. I also like Red Bear’s suggestions, I’m tempted to try it myself. I have that mould but rarely use it in favor of the Karabiner.


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[Conditor22]

I have a mold that had been shaved to make it lighter, it was a mess, I'm still working with it to make it shoot good.

You change the profile of a boolit the odds are really good that it won't shoot well. (unless you get lucky). Boolits are designed/engineered to shoot straight. Nose to drive band weight size and a bunch of stuff thats way over my head.

I've honed out/Leemented several molds to even out the cavities (mostly Lyman 4 cavity molds that the factory messed up on and I got for a song). Like previously mentioned, I wouldn't go over 4 thou.

You can increase the boolit diameter by PC'ing but there again I wouldn't go over 4-5 thou. YMMV

[Boolseye]

Kraschenbirn, how does that cut-down Mauser boolit shoot? I’m guessing you keep it in the 1000-1200 fps range.


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[Kraschenbirn]

Kraschenbirn, how does that cut-down Mauser boolit shoot? I’m guessing you keep it in the 1000-1200 fps range.


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Never tried shooting it. The boolit in the pic was a 'one-off' experiment to see it milling down a Lee 324-175 would work to produce something in the weight range the OP was looking for. I just cut down a couple of 'as-cast' with a razor saw and squared up the bases on a belt sander. Btw, my two samples weighed within 1 grain of each other.

Bill