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Author Topic: Q for Mould Makers on Vent Grooves  (Read 584 times)

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Offline cooper

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Q for Mould Makers on Vent Grooves
« on: October 06, 2003, 05:12:10 AM »
I galled-up the top of one of my bullet moulds (NEI meehanite), so my brother put it on the mill and fixed it by taking about .003" off the top.  He also resurfaced the bottom of the sprue plate.  He left both surfaces very smooth., and now it doesn't vent well.  I have a hard time getting filled-out bases. Sometimes the base of the bullet does not fill out at all - the bullet base is rounded and is short of the top of the moud by .01" or so.

It's obvious that the base of the mould is air-tight and is not venting.  My brother said he would put it back on the mill and put some shallow grooves on the top of the mould, but he lives 2000 miles away and I'd have to mail it to him.  Is there another way to vent the top?

Would it be OK to put in a few fine grooves with a file?  If I do send it to him to mill-in some vent grooves, how deep should the grooves be? And about how many would I need?
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Offline kenjuudo

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Q for Mould Makers on Vent Grooves
« Reply #1 on: October 06, 2003, 06:37:36 AM »
cooper- I would check to see if the sprue plate is free enough to swing on it's own weight and is not too tight. A SMALL chambfer on the top inside edge of the mold blocks is usually enogh to vent properly. Nothing radical, just a few strokes with a very fine file or stone.
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Offline Duffy

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Q for Mould Makers on Vent Grooves
« Reply #2 on: October 06, 2003, 08:53:31 PM »
You could probably put a piece of 60-80 grit sandpaper on a piece of glass and give the sprue plate a couple of strokes. That should give you enough vent lines to help.

Ryan
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Offline Cat Whisperer

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Q for Mould Makers on Vent Grooves
« Reply #3 on: October 11, 2003, 02:49:38 AM »
Although your premice of the sprue plate sealing makes sense, I wonder.  I agree that if one changes only one thing it probably caused the observed effect.  But - your timing in filling the mould may also have changed.

A slightly loose sprue plate should vent well.  Moulds with no vent lines often vent well.

Check your mould temperature as well as your alloy temperature.  If either is a little cool you may have problems filling out.  Also, a little (2%) more tin may help.
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Offline Orygun Mark

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Q for Mould Makers on Vent Grooves
« Reply #4 on: October 16, 2003, 07:33:06 PM »
cooper,
   I carefully bevel the top of the moulds slightly to get bases to fill out. Remove very little metal and hold the file at 45 deg or less. Do this from the edge of the cavity out.  This has worked on every mould I have done it on.  Orygun
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