Skirted Chub Grub

[SBuck88]

Guys, I just got the 3" skirted chub grub and every time I shoot it, I get a bubble from the sprue going into the bait.  Is there a way to fix this, or is it a mold issue?  When I cut the sprue off, there's a hole that leads to the actual bubble in the bait.
Thanks

[andrewlamberson]

Make sure you keep adding plastic to the sprue until the bait is completely cooled. As the plastic cools it pulls plastic from the runner and sprue and if there is no plastic....it pulls air.

I make a LOT of those baits and don't have a problem with air...but I keep the sprue full!

Andy

[ctom]

You need to keep topping off the injection port with hot plastic until it no longer draws plastic into the sprue hole. This is common in molds with a large capacity. You can also keep pressure on the injector after it stops for ten seconds or so and then  keep topping off the port. On the larger capacity molds you could try injecting a hair slower and with slightly cooler plastic. Also, a cold mold will shoot different than a hot one so expect some changes as the old heats up. If things start to go poorly try clamping a cold mold on each side as you inject the one you want in the center of the sandwich. The outside molds will act as a heat sink in a way to draw the unneeded heat away from your working mold.

[SBuck88]

Thanks guys, I will top off.  I have been keeping pressure, but didn't top off after.  I'll test tonight and get back to you.

[SBuck88]

Make sure you keep adding plastic to the sprue until the bait is completely cooled. As the plastic cools it pulls plastic from the runner and sprue and if there is no plastic....it pulls air.

I make a LOT of those baits and don't have a problem with air...but I keep the sprue full!

Andy

It helped but it seems there's still a small bubble just beyond the sprue.

[andrewlamberson]

Take your plastic to 350 degrees the first time ...and then inject at 330 and see if that helps. You might need to rub a little worm oil on the spline if the the legs are not filling all the way.

The lower injection temperature should help minimize shrinkage which is drawing material from the sprue. If you are shooting this mold really hot (360+) then the plastic may be shrinking faster than you can refill the sprue (are you getting a tiny hole in the center of the sprue?).

I don't hold any pressure on this mold, but I do immediately top off the sprue and keep it full

[SBuck88]

Thanks andrewlamberson for the tips.  It's working perfectly now.  I think I know how I was getting the bubble.  I was holding pressure for so long that when I topped off, the bubble was already sealed in.  After doing what you said...no pressure and topping off,  there's no bubbles now!  Thanks!


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