What Can Deduce from this Picture - Other than the fact that I need to make a bigger injector...

Vodkaman and I were having a discussion about how different molds fill, and coincidentally the next day I finished this mold. My biggest injector will not fill this mold, but it is a great example of how this style mold fills. I shot it three times to make sure the physical results were the same.

Yes its a 21 cavity bottom inject style mold.

Anyway: Are there any useful conclusions you can draw from this picture?

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© June 2011

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10 Comments

Why bottom fill and not top fill? Wouldn't it make sense to let gravity help you along the way?

I haven't thought through all the details, but I seem to get more perfect baits with bottom fill molds. Well, I do when I have a big enough injector to fill the mold. One thing I think happens is that the air gets pushed out the top easier like pushing air out of a syinge. There are no air bubbles trying to float back up through the flowing plastic like a top fill or side fill mold.

I think gravity does help, by allowing the lighter material (air) to float on the heavier material. I also think that the plastic pushes up more uniformly seeking a level rather than falling haphazardly into the cavity.

There are some other things that seem to work as well. So far all of the molds I have made like this seem to laminate better. I have not tried to laminate this one yet. This mold is intended for heavy salt baits, and I have foudn that salted plastic is a little harder to laminate. If you have shot laminates you know the plastics need to have almost exactly the same viscosity when injected.

Also, except for one where I went with a really tiny sprue I never have to top off the sprue. Just shoot it and move on to the next mold.

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Long about the time I see that is when I use bad words.

Nah. I have to be honest. I did the math before I shot it and pretty much knew it wasn't going to fill. The cavities themselves take a little over 5 ounces of plastic. Add the sprue and I knew my 6 oz injector wasn't up to the task. I have some aluminum tube and aluminum rod suitable in the shop. I'll make a bigger injector this week.

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After reading your explanation that makes perfect sense. Thanks for elaborating for me.

I could be wrong about why it works, but the results are pretty consistent.

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what if you made the injection in the middle and had the baits off each side? also if you have dual injectors, you could just suck up the same plastic into both and that would give you enought plastic to make it through the whole mold.

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what if you made the injection in the middle and had the baits off each side? also if you have dual injectors, you could just suck up the same plastic into both and that would give you enought plastic to make it through the whole mold.

Yep, I thought about the dual injectors since I have them. Kind of a pain to get them both into a pyrex cup during testing though. LOL. I either have to have two cups or fire up the Presto Pot which requires more plastic to pickup well.

I will post a picture of two identical bait molds vented and cut almost the same per cavity. One is single line bottom inject like this one, and one is injected in the middle with baits off to each side. Both are 32 cavities. (Very small baits) The bottom injection cavity one makes 32 perfect baits almost every time. The middle to the sides one makes 1 - 10 baits that does not fill perfectly every single time. Good enough to fish with, but not perfect. The bottom inject is still not a cure all. Mega bubbles and poor mixing and suspension of salt still creates bad baits, but it does seem to work better. Also THICK baits are tough no matter what, and thick seems to be relative.

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I know I still haven't posted pictures of that other mold to demostrate the differences, but I have discovered or rather confirmed something else that helps with mold making to produce better baits.

1. No matter the style the larger the individual cavity ports the better.

2. The straighter the individual port enters the cavity the better.

3. The closer to the main sprue the better.

This allows the bait to draw plastic from the main sprue instead of air from the vents when it cools. Narrow, longer individual ports tend to freeze off before the bait does forcing it to draw air when it cools.

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