plaster of paris moulds

[jfc32440]

hi all just wondering if anyone can help me with a few queries I have ,im making a few moulds of some plastics I have just wondering if
(1) How big does the vent have to be in my moulds (making ribbed worms 5" and 6")
(2)can I inject into these moulds as  I would prefer this than hand pouring

moulds will be made out of plaster of paris all help would be greatly appreciated

                                                                                              james

[jl3140]

I'm not really sure how big the vents have to be exactly, it depends a lot on the mold. Usually I just scratch out parts (similar ton aluminum mold) with a nail after it's dried for twenty four hours. My guess is the vents won't have to be that big.

Yes you can inject them, but be EXTREMELY careful. I wouldn't recommend doing this at all, however it CAN be done. I've broken several molds when I tried to inject them, but I've never broken a mold just hand pouring it.

On a side note, make sure to seal the mold where the plastic will be at; I believe you can use 1 part of elmers glue to 1 part of water but I've never tried that. I always use mod podge, I think you can get this at walmart if you want to use it.

Josh

[jfc32440]

thanks josh for the info now just one more little question ,how do I know how much plastic to mix and if I half fill a worm and need to make up more plastic how long do I have before they wont bond together ?

[jl3140]

Well normally(for aluminum injection molds) if you run out of plastic the baits will not form correctly in my experience due to the fact that the vents are at the end of the molds. With a hand pour mold, you shouldn't have this same problem but I could be wrong.

However if you were to try to make two color baits make sure the second color is hotter than normal to make the two colors bond.

But as soon as possible is the best answer to your question.

Hopefully that helps

[Basstaic]

I am a little confused here.  I have made hand pour molds out of plaster of paris, but have never heard of making an injection mold out of it.  How do you create a plaster of paris injection mold?

[jl3140]

I am a little confused here.  I have made hand pour molds out of plaster of paris, but have never heard of making an injection mold out of it.  How do you create a plaster of paris injection mold?

The exact same way you make a two piece handpour mold but with thicker mold halves; however, I don't recommend making an injection mold because they are not safe at all.

[jfc32440]

Well guys made my first ever 2 sided mould today ,turned out ok just wondering where i put the vents ? Is it at the opposite end of the pour holes and how big do they need to be?

[jl3140]

On the opposite ends of the pour holes, how big they need to be really depends on what temperature you pour plastic at. If the plastic is really thin when you pour, the vents don't need to be very big. You will have to experiment on the size of the vents

[Mantase]

If you are injecting the plaster molds you most likely don't need any vents at all. The air will escape between the two halfs of the mold. When you hand pour the same mold you will need vents. I have made several molds this way with no problems.

[brandx112679]

 Never had a problem injecting a water putty mold, they are basically the same thing as plaster of paris.   Your going to have to make sure it is dry, I use 2 ton epoxy to seal it with. but I'm sure elmers would work fine.

[Chuckleberry FIN]

The only problem I have with POP molds is when I drop them.  Not quite as durable as those aluminum ones.

And yes, my POP molds are  2 piece, "injectable" POP molds. There are videos that show how to make them.         

As far as air vents.  I usually scratch out one at the tail of a worm and then another near the head.   Seems to help my baits with air pockets.  I scratch them out with the tip of the blade of a knife.  I start with scratching a small vent.  But if it doesn't work, you can always make your vents a little deeper.  But if you have made them too big at the start, .... you get the idea.   Hard to make them smaller again....LOL     

Elmers Glue and water in about a 50/50 mixture works fine for me as a sealant.  Elmers Glue (wood glue or plain white) both work.   I usually apply 4 or 5 coats.   

Good luck.

[Mantase]

If you still have questions on the molds, check out my videos just look for the link in my  sign and go to the videos sections.

[sim]

YOu should fix your signature - remove the 'quotes' from around your website name and add a : between http and the first / - otherwise the link is broken and no one can see your stuff -

http://lonestarbaitco.com/

[BareKnuckleJigs]

Been thinking about some RTV but that stuff is expensive, in a way.  Wondering if Urethane Rubber may be suitable...and looks like some of it may be alot cheaper than RTV.

[Mantase]

Thanks sim, I didn't realize it was broken. Should be working now.