Breaking top of mold?

[TexasGrunt]

I often read the advise of breaking the top of the mold to help round out the bases of the boolits.

However I can't picture in my mind how this is done. Before I start messing with/up a mold could someone please be kind enough to provide a visual example of what I'm supposed to do?


Thanks.

[toallmy]

Are you trying to help venting , or the out side edge ?

[gwpercle]

That is in reference to upper outside edge of the mould block. Where the sprue plate swings over .
Smooth the upper block edge and underside of the sprue plate and its leading edge. Sometimes these edges are left rough or with burrs ( think Lee mould) and need some TLC to keep the mould top surface from getting scraped by the sprue plate swing back and forth.

The cavities should be left alone unless there is a tiny burr that needs removal. But by and large the cavities will not require any breaking of the edges.
Gary

[Beagle333]

If you do break the edge..... do it very gradually, a little at a time and test often. It's a fine line between adding some venting, and adding whiskers to the base of every boolit.

[.22-10-45]

I use a hard Arkansas stone & under magnification..just want to break sharp top edge..with blocks together and holding edgewise up to light you should only see a very tiny V where blocks meet.

[popper]

I just drag the BACK of an exacto blade lightly over the edge, working from the cavity out. Accurate moulds. Makes a very tiny vent line.

[country gent]

For a simple tool to polish these edges a pop cycle stick ( can be purchased at krogers or grocery stores by the hundred cheap). cut une end square to sides and lightly sand flat. I use double faced tape and a layer of it half way down and folded over to half way up. Trim edges to sides of stick and then peel cover layer off and a piece of 600 grit wet dry paper or finer. Once this is made you have a light flat polishing stick for use. ( I mark the grit on the exposed wood handle). Slowly work around edges at 45* on the top edges of the blocks. Start with just a visible bright line to break the edges. You can even use these to polish the sprue plate if necessary. I have these sticks made from 220 grit up to 1000 grit. A fine stone can be used here also but they normally are heavier, coarser, and harder to control. If you want to really polish slow and controlled the wood stick with Flitz or diamond compound imbedded works well.

[gwpercle]

Just remember , aluminum is very soft and doesn't require much to smooth an edge or surface.
I like to use a hard flat Arkansas whet stone to work on them , it takes very little off at a time.
Somewhere on the site is a sticky about prepping Lee moulds , the same instructions can be used on any mould.
Keep flat surfaces flat, you don't want any dips in a block top or in the underside of a sprue plate
Gary

[longbow]

I've done a few moulds with good success. It seems the newer CNC cut moulds are just a bit too precise (is it possible?).

I use a diamond hone to just remove the sharp edge where the mould blocks meet making an extremely small double bevel of about 45 degrees each side. Emphasis on extremely small! We are talking a few thou here so don't go taking a coarse file and make a stroke or two! Very fine stone or hone and SLOW, removing only the very sharp corners at the top of the blocks.

As mentioned aluminum cuts very fast as does brass but even iron will succumb to a file.

Longbow

[54bore]

I just drag the BACK of an exacto blade lightly over the edge, working from the cavity out. Accurate moulds. Makes a very tiny vent line.

I have 4 accurate molds now, are you talking about doing this to the Aluminum molds? I have 2 Iron molds and 2 Aluminum from Accurate, I wouldn't think the back of an exacto knife would do much to an Iron mold? I have never heard of this method before? The last 2 I've gotten are aluminum, i am absolutely sold on his Molds!!

[TexasGrunt]

Thanks for the help everyone. I have it figured out and it really helped with my Lyman 358242 that was driving me nuts.

[TomAM]

I use a whet stone on the top edges to create a small V groove on all my molds.