Voids In Baits, And Other Newbie Questions.

[Ed_White]

Hi all, I am trying to make my version of a very effective sand eel look-alike for this fall, stripers eat these things like candy. The trouble I'm having is incomplete baits, voids or bubbles here and there. Here's the model I made to start with:

 

6" long, made from a piece of cedar and epoxied.

 

The bait carries a weight on the hook like a Storm shad, I made a bondo mold to hold a jig hook and pour the lead, I was pretty happy when it worked OK.

 

Made a bondo mold from the cedar model, looks like this....

 

 

Epoxied the cavity after I drilled it for some dowels to make the eye sockets. Started having bubble trouble on the first few squirts, so I tried a small vent from the top of the paddletail, thinking that the air in the cavity needed somewhere to go. Really just wound up squirting extra plastic all over the place.....this was when I injected with the mold in this position (flat) on the bench. Didn't help much so I epoxied up the vent opening and tried injecting with the mold standing on end. Not bad, but still have the voids.

 

Here's a pic with the hook in place in the mold;

 

 

So, with the hook/weight in place I'm shooting the plastic past the weight....should I be filling the mold from the other end? Molds are fairly easy to do once you have a good model, I've made 3 so far, bondo, bondo glass, and PoP. The bondo is giving the best results so far, so I want to make one more mold to try to eliminate the voids.

 

Here's a few that turned out, they're rough, but will fish, they swim fine. I'd really like to fine-tune my process to get full baits more often, I'm not having much trouble making models or molds, or heating/mixing the plastic, but the bubbles are getting me PO'ed.

 

 

One beginner question, when you fill the mold, your squirting plastic into a mold which is full of air.......where's the air go? I've seen YouTube videos of guys injecting multicavity molds with no vents, they just fill until the injector stops, then pull back and fill the sprue, and wind up with full baits......

 

If anyone sees something wonky in my process, or if I'm doing something really dumb, let me know, I'm a big boy, I can take it.

 

Thanks,

Ed

[bluetickhound]

I can't offer any advice but I gotta say.... If you are a nOOb, I can't wait to see what kind of work you'll turn out when you get the hang of this!! I'm thoroughly impressed with your molds and craftsmanship....

[carolinamike]

Ed, right off the bat I can see that you need more venting to let the air out. Definatly a couple of vents at the tail, a couple mid-ways, and then a couple up towards the head. Venting only has to be on one side of the mold. Also, inject the plastic slowly to give the air time to work out, anytime you get an air bubble and your sure there is no air in your injector then most of the time its a venting problem.

[Ed_White]

Cool Mike, thanks for the advice, will try it and report back......

[Frank]

I see one problem with the weight as it will cool plastic and roll bubbles around itself and down the bait. Two way of fixing that. One heat the hook and lead so it does not cool as fast. But will take longer to demold. Two make a new mold that fills from the bottom and pushes the air up and out. Maybe fill from just behind the weight so it does not do the same thing as before. I had a mold made before with the same issue and heating the insert solved it but demold time was off the time chart. Frank

[Ed_White]

Thanks Frank, I wondered about heating the weight too, I think I'll try that, as well as a few more vents, before I make the next mold. I'm just making baits for me, so waiting to demold is not an issue, but I may make multiple molds just to keep things moving.

[JSC]

I'm with Frank  ...  The Weighted hook is soaking up the heat  ...  and like Mike said it looks like it needs some vneting   ... Belly injecting might be the solution as well as a preheat of the weighted hook  ... let us see the solution when you get it worked out.

[Ed_White]

You guys know your stuff, a few thin vents and a heated weight cured almost all of the voids, I'm getting full baits and that makes me happy.....now, to redesign a mold to inject into. This current mold was originally setup to stand on end and squirt down into it, with the vents I need to lay it down flat on the bench. Anyone want to share some basic mold design ideas? Location of fill, vents, etc.?

[Lonestarbaitcompany]

I've made molds that inject from the top with the main mold flat side down, you can pretty well fill them from any point you want on a bait that big but you will want extra space for plastic to go into to account for shrinkage. The only other factor I take into account is when I cut the spruce off I want the bait to look right.

One a side note on 2 piece pop molds I know the air will leak out between the halfs. I usually don't need venting with them.

[JMS Julio]

Hopefully someone can help me out. I purchased an aluminum cnc 4 bait craw mold but no matter how many times i shoot it the baits come out with a pretty big dent in the body cavity. i have tried shooting the plastisol at all diffrent temp ranges from 300 - 360 degrees. shot it fast shot it slow, heated injector heated molds but still same problem. also its not always the same bait with the void. sometimes its the top right bait other times the bottom left and so on and so on. but only occurs with this mold, driving me nuts. any suggestions. Thanks   

[bluetickhound]

Are you keeping the sprue filled as the bait cools in the mold?

[carolinamike]

JMS, hold pressure on your mold for a few seconds, this should help. Also are you using a hard, medium, or soft formula of plastic? Keep in mind the harder the formula the less the material will shrink. Also the thicker the bait the more shrinkage will occur.

[JMS Julio]

Using Calhoun medium from bear baits. Already tried keeping pressure on injector as per chuck at lakeside molds whom I bought the mold from. And I am also keeping the sprue filled as it cools bluetickhound. shot a bunch more this afternoon, But same thing. pretty much tapped out on what to try.

[mark poulson]

I shoot at 330-340 degrees and get no shrinkage/dents.  For me, the hotter the plastic, the more it shrinks/dents.

[carolinamike]

Mark I think he said he tried from 300 to 360 but you're absolutley right, the lower the temperature the less shrinkage you will get. You want the plastic to be just hot enough to fill the cavities.

 

JMS, try blocking off the last cavity, that could help the situation. If you could post a picture of the mold, it may be a gate issue. The gates may need to be enlarged or they could be too long which would cause the plastic to freeze off which would not allow you to hold pressure on the bait. The shorter the sprew to the cavity of the bait, the better the mold will shoot.

[Frank]

Mark I think he said he tried from 300 to 360 but you're absolutley right, the lower the temperature the less shrinkage you will get. You want the plastic to be just hot enough to fill the cavities.

 

JMS, try blocking off the last cavity, that could help the situation. If you could post a picture of the mold, it may be a gate issue. The gates may need to be enlarged or they could be too long which would cause the plastic to freeze off which would not allow you to hold pressure on the bait. The shorter the sprew to the cavity of the bait, the better the mold will shoot.

Sounds like a gate issue to me too. This is probably not real good advice but it may help. Take a round file and enlarge the point where the sprue enters the bait. This is the gate and without seeing the mold I may be way off but don't think I am to far off. Not to much though. It should not effect the bait at all. Frank

[JMS Julio]

 

 

[JMS Julio]

Here is a picture of the mold. I am all ears fellas.

[bluetickhound]

I'm with Frank on this after seeing the picture. It also looks like a good ways to get to the bottom two baits.... If you decide to open the gates just be careful. You can always go back and hone out a little more but once done, you can't put it back...

[bluntt]

JMS I have the same exact mold and have poured a ton of baits through it.. NO problems whatsoever.. I even shoot laminates with it. I pour it hot and leave it standing up to cool.I have had zero problems with shrinkage and bubbles but again i leave the mold standing up to to cool.  I use MF plastics 5.0 plastisol and their 464 plastic which is half salt water half regular plastic and it pours great for me. I have also remelted zoom, reaction innovations and powerbait and repoured through this mold with no problems. Hope this helps.

[JMS Julio]

Ripped open a couple packs of zoom and shot them with the same results. Out of ideas.

[Frank]

Ripped open a couple packs of zoom and shot them with the same results. Out of ideas.

What does this statement mean? Are you using remelts to judge a mold or new plastic? Remelts can be all over the place. Frank

[smallmouthaholic]

You make be sucking air w/ your injector. Change the rubber "O" ring and withdrawl the plastic into the injector slower.Make sure the interior of your injector is clean by removing the end and cleaning out all the minute pieces that by-pass the "O" ring. Lubricate the interior of you injector w/ Pam cooking spray for ultra-smooth operation and remove excess before drawing up your plastic.You should also remove the tip of the injector ,push the plunger down so the interior "O" ring on the plunger is exposed and wipe off the "O" ring that can accumulate plastic.

 

You can also carefully drill out the existing diameter( inside the tip) to reduce the long,narrow interior induction column but-don't go past the inside taper of the tip( last 1/2'' of the tip) or you'll end up drilling out the side of the tip.This is best performed on a drill press w/ vise grips to hold the tip securely. You will have to gradually enlarge the induction hole w/ graduated drill bit sizes.Apply oil to keep your bit cool..

 

edited for additional content

Edited August 15, 2013 by smallmouthaholic

[mark poulson]

Before you alter anything, contact bluntt, post #20 in this thread, and see how he pours the same mold successfully.  

There may be a combination of plastic/temperature/injecting method that he uses that you can adopt without having to alter your mold at all.

 

I also used a drill press to alter an aluminum mold, but that was a lead mold that I altered to accept larger hooks.

I used a relatively low speed, put a stop so the bit couldn't go too deep, and then, once the bit was down in the area I wanted to alter, I locked it at that depth and used the bit like a mill to remove material slowly until the bigger hook eyes would fit.

Once I had the setup it was repeatable for all the cavities on both halves of the mold.

While I'm pretty sure you can use JB Weld to restore any material you've "over-removed", I can't swear to that, so proceed with caution.

 

I agree with Frank about the sprue connection.

Looking at your mold, the only bottleneck I see is right where the sprue meets the cavity.  I'd be tempted to open that up a little, even though it would mean a less cosmetically pleasing cutoff.  I don't think it would affect the bait.

[JMS Julio]

Frank the comment on the zoom plastic was in reference to post #20 from Bluntt who advised he has also shot zoom re melts through his mold which is the same mold and has not had any problems. I had a couple packs of zoom worms so i figured what the hell and gave it a try. But ended up with the same results. I am going to attempt to enlarge the bottleneck of the mold where the sprue meets the body cavity and see if this helps as per the advise. Again thanks for the ideas guys. I Really appreciate it.