Sprue plate adjustment?

[Mike W1]

Been fooling around for some time now trying different things to improve my cast bullets. Working with one mold only, a Lyman DC 452374. Have tried spring (belleville?), wave and split washers and cannot see any advantage of one over the others. Made an aluminum sprue plate to compare with the stock steel one. When set correctly the only advantage I see is the aluminum one might let you increase the casting pace a bit but my cooling fan seems to do the job just fine with the steel plate so at least for this mold the advantage if any is moot.

The best thing I've done so far is remove the sprue plate stop pin and install a button head socket screw in it's place. Have weighed a lot of bullets on this adventure and that screw has taken the percentage of bullets falling in the ± 1 grain of average to around 97-100% out of the front cavity now.

Now upon further casting efforts and fiddling with tension on the sprue plate I wonder if there's a better way to adjust that tension. I know the accepted method of setting tension is that the plate JUST swing freely but that does leave a lot of room for error. I'm getting satisfactory results in any given session but cannot necessarily duplicate those results next session unless I DON'T readjust the tension. And there are times that the screw holding the sprue plate pivot pin comes loose and you lose the adjustment.

Somebody earlier posted a couple pictures of the spring setup that LBT uses and I'm wondering if something like that could be adapted here and forego the spring washer entirely. Not being a machinist I'm guessing it would require a slot milled on the back of the mold. And that's assuming Mr. Smith would sell some of those springs. Any thoughts on this?

 

[fiver]

do you have a set screw for that pivot screw?
I'm assuming yes, if so does the screw have a flat spot for the set screw to rest against or something that will take the shape of the threads to keep it from moving.

if your contemplating a spring under the plate I would re-think that a little bit.
a spring will allow the plate to lift up when you break the sprue off the bullet.
the magma molds for the machines use a spring and a bolt that goes clear through the mold.
you can of course adjust them to lie flat.
[they use a stop on the machine for closing them to the same place each time and rely on friction to hold them there.]
anyway they use a spring so that the plate will pivot up and away from the mold so it doesn't trap the bullet in the away cavity.

 

[Mike W1]

In that mold there is of course a set screw but on a Lyman pivot screw the lower part is without threads and that's where the set screw engages, not on the threaded portion. One could put a flat there of course but that's an option I'm not real comfortable with. May resort to a lead shot in there or maybe fine copper wire up in the threaded port.

A spring like I'm thinking about would go over the sprue plate, not under it. Wouldn't be that much different than the washer used now. From what I gathered with the way the LBT works if you did want adjustment you'd move the spring either up/down in the slot.

 

[Kevin Stenberg]

Wouldn't the heat take the temper out of the spring?

 

[fiver]

I think you'd need about 3 times the amount of heat a mold plate see's to de-temper a spring.
I'm sure the heat cool cycling would weaken it over time but it isn't being compressed over and over like a valve spring.

 

[Rally Hess]

I'd like the mod to the Lyman mould you've done, but would prefer it was in the opposite corner from the sprue plate screw. I'm found using the NOE moulds it tells me when I'm getting lead smear on the mould. Usually from trying to open it too soon, and some stays with the sprue plate in the cutting side of the fill holes. When I close the mould it has to go under the stop screw and the smear makes it harder to close. I have really also come to appreciate the ability to adjust the tension when closed.

 

[popper]

belleville washers have a specific purpose - and a perfect use under the sprue bolt. Wave washers will eventually wear a groove in the surfaces although they do have more even presure. What typically happens is the surfaces under the washer are not cleaned and lead/lube eventually pushed the plate up. Allows those scrapes on the mould top. The weigth of the plate/sprue should hold it down, not spring pressure. The washer is there to reduce junk buildup under the plate pivot - NOT to keep it flat.

 

[Mike W1]

belleville washers have a specific purpose - and a perfect use under the sprue bolt. Wave washers will eventually wear a groove in the surfaces although they do have more even presure. What typically happens is the surfaces under the washer are not cleaned and lead/lube eventually pushed the plate up. Allows those scrapes on the mould top. The weigth of the plate/sprue should hold it down, not spring pressure. The washer is there to reduce junk buildup under the plate pivot - NOT to keep it flat.

I'm gonna have to mull that over a long time before I get to agreeing with it all. Seems to me if it's so then you could just let the sprue plate swing freely without a washer at all. Combined with the improvement I see in consistency out of my front cavity WITH the button head screw installed kind of kills the idea to me so far. And I'm also wondering what's getting under the washer that you're talking about which sits on top of the sprue plate.

 

[popper]

I did find that dental floss is good for cleaning the pivot bolt under the plate. Plate should swing pretty free when the mould is hot. Uneven expansion of the plate and mould make a perfect contact impossible. Astm has a fastener handbook that gives proper usage of washers.