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Originally Posted by hawnjigs
"Sagacious", are you just drilling a larger hole down the middle of the Do-it gates and leaving the tapered ends intact?
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I always try to cover all the bases in my reply, but sometimes I miss a few. Let me back up and explain a little better:
Yes, the hole is enlarged slightly. The tapered end is intact, just smoothed slightly by the countersinking bit. The goal is to true-up and smooth-up the gate, not to remove a lot of material. Less is more here.
I enlarge the gate about 1/32" on a 1oz jig mold, and about 1/32" to 1/16" on a 3 or 4oz mold. For a smaller gate, I'd probably suggest a smaller increase in the gate aperture, such as the 1 or 2 hundredths increase I use for a small pistol bullet mold. You just want to true-it-up so that the gate is perfectly round and smooth. That has worked well for me, and just a small increase in the gate opening seems to make a disproportionate difference in pouring speed and smoothness.
I haven't tried-- and wouldn't recommend-- opening the gate on a mold that drops very small jigs. If your mold is cnc milled, I'd suggest against trying to "improve" it by opening the gate.
I'm not really sure if it's a simple increase in the aperture that makes the difference. I suspect it's also (mainly?) that the gate is made perfectly round, and now the tapered part of the gate is very smooth. The lead just swirls down into the mold very quickly, much more so than you'd expect from just an increase in diameter of a couple hundredths (1/32" is 3 hundredths). Precision pour placement became no longer required-- the lead swirls right in.
I think it has more to do with what you noticed: That a small burr or eccentricity can cause a flow disruption in a high-density fluid (molten metal) that's great enough to affect how the metal flows into, and fills, the mold. That's just my guess and working theory.......... where's Vodkaman when you need him lol?
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Can drilling the Do-it gates larger cause any pitting problems due to a widened sprue break?
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Good question. The sprue is only about 1/32" wider, which is (I'm guessing) perhaps within the tolerances you'd find in a production run. If a clean sprue break is critical, you may wish to test this technique with a old mold-- and your lead, pouring technique, and equipment-- before you commit more heavily.
These techniques have worked very well for me. If you're not careful, you could probably do more harm than good, so measure twice and drill once.
Be careful not to drill into the cavity walls!! If you have a mold that's giving you pour hassles anyway, I'd measure the gates, get a drill bit 1/32" larger, a 45* countersinking bit in the right diameter, and give it a go.
Hope this helps, good luck!
