Aluminum Galling

[358156 hp]

I have a modified LBT mould that was converted from the LBT sprue plate design to an NEI style aluminum plate. I bought it cheap, and it's being a pain. The sprue plate galls in the pivot area, leaving scratches & gouges around the pivot bolt. A similar mould with a steel sprue plate doesn't have this issue by the way. I've cleaned it up once, & lapped both areas smooth again on my trusty chunk of 2/4 in. glass with 800 grit & light oil, lubed it with some left over Bull Plate and it immediately galled again as soon as it got hot. This time it won't go back together until I'm confident it will work. I briefly considered a lubricant like LBT mould lube, or a high temp antiseize, but I'd prefer a dry lube. My real concern is that I may need to have the plate anodized so that I have dissimilar contact surfaces. Since the mould has been modified for the big sprue plate I don't believe an LBT sprueplate is the answer. The meathead who modified it also milled the LBT venting from the top surface of the mould. Those of you familiar with LBT moulds know that the sprueplate & mould venting were developed to work together as a system. Any suggestions on how to proceed?

 

[Jeff H]

As for a dry "lube," I've used welders' soapstones - marking stones, on the bottom of sprue plate with very good results. I scrub the bottom of the sprue plate with the stone to create the dust and then blow off the excess. Occasionally, it needs a light wipe across a rag to remove any loose dust. I remove all but the lightest trace of the stone on the plate. This method has often worked where using "sprue plate lube" (synthetic 2-cycle oil) hasn't quite done the job.

I do not know the composition of these marking stones and for all I know, they may contain the worst thing in the world to put down your bore, but I've seen no ill effect in thousands of bullets passing through bores so far.

 

[JWFilips]

If I'm casting well with an AL mould I always have a tendency to gall it! Sometimes I don't even know until the next time I pick it up.
A real PITA! Buggs the heck out of me The only cure I found is have a nice big cast bullet by your pot to "erase" the lead oxide fowling from the sprew plate!

 

[Ben]

How tight is your sprue bolt that holds down the sprue plate ?
If it is excessively tight, it will gall and no lube that I've ever used will stop the galling.
I like for my plates to swing by the own weight when I turn the mold over.

 

[358156 hp]

Both times the sprue plate was noticeably under fairly light spring tension, but no enough for it to move freely under its own weight. It pretty well approximated the plate tension of a factory sprue plate on an LBT mould. That said, this amount of tension may be too much for this mould with the rather large NEI style aluminum plate. NEI aluminum plates are/were also hard anodized originally. From what I've seen of other moulds from this guys estate I can see he was a really big NEI fanboy.

 

[Ben]

I think my 1st try at resolving this would be to reduce the sprue plate pressure on the top of the mould blocks.

Ben

 

[358156 hp]

Thank you, Ben. It's not normally in my nature to try the simplest, most sensible solution first. I'll put it back together tomorrow (with lubrication again) and try out your suggestions.

Much appreciated! Happy New Year!

 

[Ben]

Let us know how it works out for you.

Ben

 

[Ian]

As for a dry "lube," I've used welders' soapstones - marking stones, on the bottom of sprue plate with very good results. I scrub the bottom of the sprue plate with the stone to create the dust and then blow off the excess.

Well don't I feel dumb. In 25 years that's the first I've heard of using soapstone, and the idea sounds absolutely brilliant.

I was going to suggest hitting Brad up to re-cut the vent lines on his mill and make a drill rod insert for the pivot bolt that sits about .002" proud of the blocks so the metal around the hole won't gall.

 

[freebullet]

I beat the crap out of the lee molds, I just sand the top flat & cast more.

 

[fiver]

soapstone works OKAY lead doesn't stick to it but it is grabby, I use it on my shot maker to roll the drips into round shot, other wise it just slides down the plate.
antisieze will fill up those grooves you already have and keep the plate moving.
the carrier oil will burn off and leave the metal behind.

 

[358156 hp]

Well don't I feel dumb. In 25 years that's the first I've heard of using soapstone, and the idea sounds absolutely brilliant.

I was going to suggest hitting Brad up to re-cut the vent lines on his mill and make a drill rod insert for the pivot bolt that sits about .002" proud of the blocks so the metal around the hole won't gall.

Funny you mention that. I looked a little closer at the sprue plate last night. Veral uses a bushing in his sprue plates , and it too is a part of the system. When the thick aluminum plate was installed, the installer used the bushing as well, but didn't take into account that since the new plate is thicker than the bushing depth, the bushing can't perform its original task, which is to provide a supported pivot point for the plate, and to eliminate binding from overtightening the sprue bolt itself. This all didn't come together until Ian mentioned .002 for clearance. This whole mess may stem from everything we've been discussing here (intolerance stacking?). Similar soft metals with a lack of clearance, too much spring tension for the application, and a lack of lubrication. I could lap the sprue plate to allow use of the original bushing with .002 protrusion, plus use a softer spring (belleville washer). This is a lot of effort for a $50.00 mould, but it is winter, and it's getting too cold to play outdoors.

 

[Brad]

How thick is the new plate? I can make a bushing. I think.

 

[Jeff H]

Well don't I feel dumb. In 25 years that's the first I've heard of using soapstone, and the idea sounds absolutely brilliant.................

I certainly can't claim the brilliance, as someone else, somewhere else must have done it before. I fell into it while trying various softer-than-mild steel/iron materials to clean off lead flecks from the bottom of sprue plates/mould tops. Didn't work for that but it helped a lot in mitigating the accumulation to begin with. Everything I've learned has come the hard way or dumb luck - and some reading in recent years, but a lot of the reading yielded a poor ratio of good:worthless.

 

[CZ93X62]

I follow Ben's recipe for sprue plate tensioning, and turn the sprue plates with a gloved hand. This has been easy on the aluminum mould blocks by all makers.

 

[358156 hp]

How thick is the new plate? I can make a bushing. I think.

I have the bushing. The plate was drilled for it, and it was stuck in place, but the plate is thicker than the height of the bushing.I think I should be able to lap the plate on my big hunk o glass to match the bushing, then I'll try taking an additional .002 off the plate, leaving the bushing with that .002 protrusion. From that point I can either dress the plate a little more, or shorten the bushing a touch the same way if needed to fine tune things.

 

[358156 hp]

I follow Ben's recipe for sprue plate tensioning, and turn the sprue plates with a gloved hand. This has been easy on the aluminum mould blocks by all makers.

I normally tension my plates just enough to allow me to turn the mould sideways if needed without the plate swinging freely. Normally, a light touch is all that's required to move the plate. This particular mould had a lot more tension than that, and I didn't catch it until Ben made his suggestion. Then I felt silly...