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Swimbait Mold Venting

mold vents

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#1 FLYguy

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Posted 04 July 2012 - 09:38 AM

I have a prototype swimbait that I am having scanned and an injection mold made for it. Two cavity and two piece mold. Any tips or suggestions on how much and where it needs to be vented?
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#2 J lure

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Posted 04 July 2012 - 10:08 AM

Can I ask how are you going about scanning it? Is it the mold maker doing it or you using a seperate source? Also once scanned does it put it into autocad or another program?

#3 MonteSS

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Posted 04 July 2012 - 11:02 AM

Consider having it sit belly down in the mold rather than on its side so you can do laminates.

...Bill

#4 MonteSS

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Posted 04 July 2012 - 11:14 AM

Consider having it sit belly down in the mold rather than on its side so you can do laminates.

...Bill


That should have been 3+ color laminates.

...Bill

#5 Bob La Londe

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Posted 04 July 2012 - 11:31 AM

Some people have said a mold needs to be vented every 1/4", but I have found that some do not need that. Any mold with larger details and ridges should be vented on every detail so a ridge, fin tip, flap, leg, claw, etc can not trap air. The vent does not need to be large. I have done some with vents only .002-.003 on one side of the plate with decent results. On long smooth features like the back of a swimbait I might only vent every 1/2". Always vent at any points extreme distances from the injection point.

#6 toadfrog

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Posted 04 July 2012 - 03:08 PM

This is a little off the subject but wouldn't it be better to shot from the thinnest portion of the bait While the liquid is piping hot letting the flow go forward to the heavt parts . This could possibly prevent the need of but one or two vents thus reducing machinning .

#7 Bob La Londe

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Posted 04 July 2012 - 07:08 PM

The thick part of the bait will shrink the most during cooling, and cool the slowest. I you inject through a thin part it is likely to freeze off cutting off the flow of plastic into the still shrinking larger part.
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#8 toadfrog

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Posted 05 July 2012 - 05:37 AM

I was curious about that because I have injected hard polypropelene before and the molds were made to shoot thin stuff first . Different product all together I know . But I had to scratch my head and wonder. Inquiring minds have to know.

#9 Bob La Londe

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Posted 05 July 2012 - 09:06 AM

"Hard" and semi hard plastics are a whole different animal. I've seen semi automated blow molding machines in operation and the production time is incredibly short compared to plastisol. I almost think every plastic is its own learning process. I wish I had the time and the money to work with more things like that.

#10 FLYguy

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Posted 14 July 2012 - 03:35 PM

Long time getting back to this I know. Bob I am having the moldmaker scan it with laser technology. I was using another source for my scans previously and the formatting of the cad system was cumbersome to the machining folks and they said they would rather do it their self rather than convert the files to something they could use. There are a lot of programs out there so I am having all of my files saved in PARASOLID which is a nuetral file and freindly to most CNC machining folks. I am having it machined belly down so I can laminate it. My previous foray with the mold was with the swimbait laying on its side and kept getting shrinkage dimples in the same spot on all of the baits. I added several vents, tried harder plastic, narrowed the sprue, changed the sprue entry to the cavity, played with mold temperature on preheat, different plastic temerature thinking cooler might be better, shot with topping the sprue off, shot with holding the pressure on for as much as one minute, and finally gave up on it. It would only shoot a good bait on one side about every fourth time. The first mold had the sprue feeding the cavities to two sides. My new one will feed the cavities all off of the same side of the sprue which I think should make a difference. Its a 5.5 inch bait with hook slot and slit belly and the body at the thickest part from back to belly is 24mm, thickness side to side at the thickest part is 22mm. This is about all I can think of as far as information goes. Any suggestions on the amount of venting I would need? Are there any suggestions on the Rheology side of the equation that could make the flow break up and shoot better?This is a lmited deal so I am using a hand injector. Also could use some tips on painting one if you have any, its pretty tedious and I would like to shorten the time with some templates or something so I could spray instead of putting dots on it to make a trout pattern in several colors

#11 Bob La Londe

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Posted 15 July 2012 - 12:02 PM

If you have a hard master you might be able to make a half clam shell by heating a plastic sheet in the oven and then vacuum form it. There are some folks on Ebay selling some stuff like that, but I have not really looked into it. Then you could cut your pattern into your clam shell. Make a bunch of both halves and you might be able to go quite fast. Let your creative juices flow.

#12 FLYguy

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Posted 15 July 2012 - 01:32 PM

I think your last post was off subject and someone is probably looking for some of your quit wise advise on another post. I would appreciate any insight you may have to my issues with my soft plastic swimbait mold though.

#13 Bob La Londe

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Posted 16 July 2012 - 10:37 AM

Also could use some tips on painting one if you have any, its pretty tedious and I would like to shorten the time with some templates or something so I could spray instead of putting dots on it to make a trout pattern in several colors


So you do not think making a clamshell type template for PAINTING your baits has anything to do with PAINTING?

Or did you just not understand how making a form fitting template for PAINTING would help with accurate repeatable PAINTING?

Sorry, I failed so dismally at helping you with an idea for making a good template for PAINTING in my suggestion that, you could make a very accurate and form holding template for PAINTING.


Whhizzzzzzzzzz.......!

I would appreciate any insight you may have to my issues with my soft plastic swimbait mold though.


I'm sure you mold will be wonderful, and you don't need any more help with it. Certainly nothing I could offer.


For anybody who thought my suggestion for making a bait holding template to accurately position the bait within the template for repeatable and accurate PAINTING had some merit and did have some relationship to PAINTING a bait: Some types of plastics clean up very easily with very mild cleaners or solvents so they may be useable for a very long time. You could make each half with a long "handle" section or even possibley make them as folding clamshells. Drop the bait in, paint it set it aside, and do the next one. If you made a bunch of them yoiu could go very fast. With some skill with an air brush you could possibley do two or three colors with a single template depending on the patterns.

Edited by Bob La Londe, 16 July 2012 - 10:47 AM.


#14 carolinamike

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Posted 16 July 2012 - 12:56 PM

FLYguy, dimples in a plastic bait has nothing to do with venting. The dimples are caused by plastic shrinkage, the softer the plastic the more shrinkage you get. A medium hard to a hard formula plastic will take care of your dimpling problem. Keep in mind that the thicker the bait the more shrinkage will occur. A good example is the Z company lizard, almost all of them have a shrinkage dimple in the belly. Venting will not stop dimpling, venting is done to prevent air in capsulation also the more venting you have the faster you can fill the mold. I'm currently dealing with the same problem for a company that has a thick swim bait but they want it produced in a super soft plastic, and truthfully i dont know if its going to work or not. So far its not looking good with the prototype, i'll know more when the production mold comes in. As far as dimpling goes, a harder plastic should solve your problem.

#15 FLYguy

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Posted 16 July 2012 - 01:41 PM

First off let me apologize for missing the context of the clamshell template for a painting template. I honestly was looking for plastic shrinkage advice and threw the painting question is as side bar, and yes whhhizzzzzz........ is an accurate analogy. I tried to be polite when I responded and hope I didnt come off as disrespectfull the artists who inhabit this board. I personally take mild issue to such things so again, my appologies.
Thanks carolinamike for you insight, I will try a straight saltwater formula and see if it holds action when it swims. Much obliged