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squigster

Need Help With Mold/venting

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Hi Guys,

I am having a problem with a mold I have had for a while. It was designed as a one piece mold but my brother is a machinist and I decided to see if he could make it a two piece by adding a plate to it therefore making it a two piece. The problem is that the bait is getting voids in it.

he added vents on the tails and the baits has a vold from the sprue to about 1" down the body in the center of the body.

I figured air was being trapped so I drilled a hole in the top half and repoured now I have two voids, one where it was originally and another right behind the hole I drilled. I dont want to keep experimenting and drilling holes in it and was wandering if someone could possibly shed some light on what may be happening. My first suspicion is the sprue isn't deep enough but that's just a guess. Thanks in Advance. Attached are some pics.

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I am not a machinist or an expert on this topic. It took me a while to figure out from your pics where your plastic flow was. Can he machine another plate from the top? Half the injection port on each side of the mold? If so the venting should be good but you will have to treat it as a hand pour mold topping it off after injection as it cools. It looks like venting is not the problem. The lack of sprue is.

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I think the bubble occurs when you start the pour/injection. The bubble forms behind the inlet and moves rearwards during the pour.

To test this theory, try starting the pour ultra slowly, once the nose is filled, you can speed up.

If this is the case, rounding the underside of the pour spout might work, removing the sharp corner which is causing the bubble. But this is going to make more work trimming the sprue of course.

Dave

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Thanks Guys. I tried adding plastic to the top after pouring but it never gets sucked down. He took the mold yesterday and is going to machine the sprue into a cone shape and make it larger. I hope that solves the problem. I will let you now the results.

Thanks,

Jim

Edited by squigster
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Problem solved! He added a vent to the nose and made a cone "sprue" the depth of the top plate and it sucks the plastic down and it works great! No more air pocket! Thanks for all you opinions! I do appreciate it!

Edited by squigster
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