Lapping an aluminum mould

H

Hog Buster

New member
I’ve got one of those Lee aluminum moulds for my 45/70 that casts bullets out of round and .001 or so too small. Even though it’s new I started to pitch it, but with time on my hands have considered lapping it. I’ve lapped many steel moulds and had success, but never an aluminum one.

So my question is lapping done just like a steel one, or is this thing just cheap unworkable junk and should I have known better than to buy it?

By the way I’ve always used linotype slugs, cast in the mould to be lapped, because they seemed to give me better driving band edges and lasted longer.
 
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I've had problems trying to do anything abrasive to aluminum because the removed particles tend to cake on the abrasive and cause scratches.

The only time I've had luck was when I did it under running water to keep the particles from building up. The water flushed them away and kept them from becoming a problem.
 
We call it Lee-menting, and it's fairly common among advanced casters.

Most thread a bolt into the base of the bullet, coat the bullet with some type of mild abrasive and spin the bullet slowly in the mold. Over at the Cast Boolits form there are lots of threads about lapping aluminum molds.

Here's a link to one such discussion. This one has pics and is one guy's take on the process.

So my question is lapping done just like a steel one, or is this thing just cheap unworkable junk and should I have known better than to buy it?
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No, I've got a bunch on my bench and I like them better than steel molds. They're just different from steel molds and must be treated differently. I've never had a problem with an aluminum mold rusting, but I have had steel molds rust.

So, the question might be, are all those steel molds just cheap junk and should I have known better than to buy them?
 
JohnKSa

Good point, I hadn’t thought about that.

Paw Paw

Yeah Dennis, another good point. CRS must have gotten me I should have thought of Cast Boolits right off. I’ll take a look. I’ve done it to steel moulds many times, but never to aluminum ones..... I gau-ran-tee if I pass a bad time wid dat mould over the bayou it goes dare.

I've used a couple of them in the past, but I'm a bit heavy handed and they just didn't last. I've got steel ones that are 50 years old and still casting.


Ok, Dennis I just checked out Cast Boolits and it's pretty much the same way I do steel moulds. Thanks for the info, I'll give it a try.... Gene
 
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One of the uses WD-40 is actually pretty darn good for is a drilling and tapping fluid for aluminum.You may find it usefull.
 
Hibc & GP100man

Thanks for the info. I’ve always used mineral oil or some packaged coolant/lubricant in the past when cutting, milling or drilling aluminum. My problem has always been finding a suitable grit to mix with it for lapping. One that would cut enough anyway.

As far as using powdered cleanser it’s OK for cleaning a rusty mold but not really strong enough to lap with.

Over the years I’ve tried many products from auto paint rubbing compounds to valve grinding compound. Clover valve grinding compound probably worked the best for lapping steel moulds, but I thought it may be a bit harsh for aluminum.

I’ve never tried to lap an aluminum mold so was just looking for info. As cheap as they are the reality is that it may be a waste of time.
 
The main thing is to avoid using any abrasive with aluminum that tends to embed. Silicone carbide is too sharp, like little shards of glass, but harder, and they will permanently surface the mold with abrasive. Usually a rounder particle is desired. Garnet is often chosen for bronze and brass, so I assume it would work with aluminum. Another approach is to use an abrasive that breaks down as it works the metal. JB Bore compound for example. I know that sounds too mild, but this is soft aluminum and will cut fast.

This outfit sells Garnet lapping compound. Their site has a lot of practical tips. Call them to double-check on the most appropriate compound to use with aluminum.

All that said, Lee bores their mold cavities with a lathe, so the cavities should be perfectly round unless some crud got between the block halves when they were bored. They should have a 2 year warranty, so I would return it to Lee with a couple of the bullets. I expect they'll just replace it. If you think they gauged it too small, mention that, too.
 
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I don't understand why you are complaing about the "cheap" Lee molds? Just because you need to lap one? :rolleyes:
It sounds like you've had to lap quite a few of those "top quality" steel molds, though. :confused:
Like the previous poster said, go check out CastBoolits. Lee-menting is explained in great detail.

I've had probably as good results with my Lee molds as my Lyman/RCBS. Any of the molds can be slightly out of round, large, small... whatever.
My opinion of Lee's molds is that they are inexpensive... not cheap.
Take care of them, don't bang em around, drop em on the floor, use em as a hammer... They just require a slightly different approach. But, you won't find em all rusty after sitting on the shelf for a couple months (or years).
 
If you take two measurements, 90deg apart, is one measurement larger than the other, and is one measurement larger than spec, while the other is smaller?
I used to think my Lee molds cast bullets out of round,too. My sizer and caliper measurements showed them to be oblong,which seemed to confirm things.
Then I started water dropping right out of the mold into a bucket with a soft bottom, and mysteriously the quickly cooled bullets from the same mold were no longer out of round.
I suspect many of the issue with lee molds being "out of round" are just folks having trouble keeping the Lee molds from casting too hot, and bullets having extra time to sag out of round as they cool.

Water dropping might be worth a shot to see if that gets rid of your out of round problems before you lap the mold.
 
I really appreciate you guys trying to help, but after over 50 years of reloading and casting I know when a mould is out of round, or casts bullets out of specs. I’ve altered quite a few in my time, just not any aluminum ones. Hence the reason for posting.

As far as Lee products go, they’re cheaply made therefore they are cheap to buy, but have no enduring merit, except cost. While this great for Lee, i.e. repeat sales, I’d rather have something with a future. That’s not to say they don’t have some useful products, they do, but most are just short lived throw-aways.

Wow, I can’t believe all this discourse about a 20 buck product. I’m now sorry that I posted the question.

Thanks again, but the above is my opinion and I’m sticking to it.
 
no problem with me... you're entitled to your opinion.

It just doesn't quite gee-haw with the thousands of folks that have been using those cheap Lee molds for 20+ years with no issues.

But, like I said, everyone has their own opinion, and I appreciate hearing yours. Doesn't mean I agree with it, but I can enjoy good discussions without feeling the need to "convert" someone... or to be converted, for that matter.
now, let's go get a beer....
 
I know when a mould is out of round, or casts bullets out of specs.
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I'd give Lee a call instead of fooling with a mould that far out of spec. Even if the 2 year warranty is done, they'll still probably fix you up. Plus you'll do a service to everyone else by nudging them to improve their QA by pointing out a fault.

All the Lee molds I have are fine... certainly not out of spec enough to cause any kind of concern. But I've heard of other people at our club who've bought lemons from them, and Lee was really on the ball in fixing things up for them.
 
Thanks again, got the problem solved, new Lyman on the way. Now if I can only find the right powder and charge for my (newly purchased) Model 94 .375 Winchester, before it rains again.......
 
+1 on the comet cleanser for lapping aluminum,,, also recommend using a harder alloy to cast your lapping slugs from for best results . Linotype works well as do heat treated wheel weight bullets or wheel weight lead cut 50/50 with hard lead shot ( magnum ) to bump up the antimony content. Remeber you want to remove matierial from the mould rather that from the bullet. Cast a half dozen or so of the lappers and switch them frequently. I have done this on a couple of cranky steel moulds to drop bullets easier as well, Polishes them up real nice.
 
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