Vent lines and mold makers

[lastborn]

Ok, I'm either going to show my ignorance or learn something.{which I do on a regular basis} I have read many threads here on having a mold that won't fill out no mater how much tinkering and or cleaning you do to it or what alloy you try. I have also read several threads where people are just about ready to throw the said mold in the trash and as a last ditch effort grab either a hacksaw or a file and open up or cut more or deeper vent lines and all of the sudden they have a GREAT or favorite new mold. NOW here is my question. Why do the mold makers cut deeper vent lines when the mold is made? Maybe, let's say twice as deep. I know if they are too deep you would get fining. Long post but I would really like to know why they are not cut deeper. Do all the mold makers cut the same depth vent lines? Can you order a mold with deeper vent lines? Is this a dumb question?
Thanks

[shotman]

First no question is dumb second the vent lines are for the slow guys that do it by hand. if you use a bottom "drippy" you dont need vent lines
I know some will say they are needed but they are for looks and a pain to keep clean
Use Kroil and you dont need the lines and if you have them they will stay clean

[Bret4207]

Well, this "slow guy" has several old Ideals with NO vent lines and I can cast near perfect boolits with them and a ladle. So that shoots shotmans theory down.

I don't know the answer. I know if the mould is up to temp (hot enough) venting seems to be less of an issue. It doesn't take much venting to cast a good boolit. Too much is as bad as not enough though.

[old turtle]

I have molds with and without vent lines. It might have to do with the surface of the mating surface of the blocks, or how tightly the sprue plate is on the top. It may be like airline fares, no one really understands. If I were to have a mold with no vent lines and everything else fails I would try the vent lines. I agree Bret4207 that too deep can be a real problem. Existing vent lines usually only need cleaned. But then what do I know, unfortunately not much.

[HORNET]

It's fairly easy to get vent lines too deep and end up with 'finning' or spikes down the vent lines. A better approach would be to make much wider but shallow vents. IIRC, Victory Molds used this approach and relieved most of the actual face of one block about .001", leaving a few 'pads' as standoffs to maintain the correct spacing. This requires much more precise machining and is probably not as cost effective in high volume commercial applications. If you make sure that there aren't any burrs turned into the existing vents and blocking them, most molds work fine. Some will need a little added attention or revised casting technique.

[cajun shooter]

It all has to do with the style of the pour. If the alloy is forced in with ladle or bottom pour then vent lines are not needed. I have a DC Lachmiller 358156GC that has very smooth block walls with no vent lines that drops perfect bullets when used with my RCBS.

[GLL]

Ladle cast in a VERY old IDEAL 454190 ! :) :)

Jerry

http://www.fototime.com/720B35FD551CEF8/orig.jpg

[montana_charlie]

Ladle cast in a VERY old IDEAL 454190 !
Are you saying the picture proves that vent lines are unnecessary for good bullets?

...or...

Are you blaming the lack of venting for the round corners on the bands?

CM

[GLL]

CM:

All of my unvented moulds tend to produce the same rounding defect on the bands even when pressure poured with a ladle !

Jerry

http://www.fototime.com/E574E14FBE964F2/standard.jpg

http://www.fototime.com/04DCFAB757B5561/standard.jpg

[onondaga]

The vent lines are small because their primary function is to allow only air out while alloy goes in. A good swirling pour into the funnel gate of the sprue plate is more important for cavity fill than vents. Keep your flow length from ladle spout or bottom pour nozzle no less than 1/8 and no more than 1/4 inch in length and don't pour into the center of the funnel gate hole. Pour half the width of the stream off the center of the funnel gate hole. This asymmetry in flow into the hole causes a swirl of the flow into the cavity and helps casting quality. Pouring straight in can cause lots of problems because of turbulence and can even block oversize vents. Bulls-eyes are great on paper targets but don't help at all when pouring into a funnel gate hole.

The rounded edges discussed above are extremely minimal if they are really not true to the mold cut. If there is an error it is thermal and most likely related to low temp of pour, low temp of mold or low temp of flow due to excessive stream length or some combination.

Retired Precious Metal Casting Analyst (really)