Tech questions. re: heating, pouring and POP moulds.

[slipperybits]

Greetings from Australia

Have been doing a great deal of reading in the DIY SP section of this forum and while educating myself I have collected the various tools and materials I need to start pouring my own plastics. Before I begin my first pour there are a few things I would like to clarify and am hoping some of the more experienced pourers will offer some assistance.

• Are there any considerations when using a hot plate? Most people seem to use a microwave, however I would have thought a hot plate would offer better temp control and eliminate the need to zap the plastic in between pours. What temp setting should I use with a hot-plate? Is there a greater risk of burning the plastic?
  
• In various pouring techs, I have read that it is important when pouring to not allow the plastic to touch the sides of the mould (I presume to prevent the plastic cooling before it reaches the bottom of the cavity.) However, when using a reservoir, how is this possible?
  The pour hole I have made to use in my molds (made from the screw-on nozzle on a silicon gun) is around 6mm at the bottom and around 15mm at the top; I would have to be VERY accurate with my pouring to prevent any plastic touching the sides of the reservoir at the bottom. Have I misunderstood something?
  
• There seems to be a number of different opinions re: when to vent a mould. I.e. yes where tales taper quite thin or there are undercuts (curly-tails grubs and paddletails). No with straight worm patterns. I have included pics of a couple of patterns and wondered whether people thought I should be venting the tails or not.
  

Atomic Paddletails

Squidgie Flick Baits

• How would people recommend I set up a mould for laminated baits when using the patterns above? A pour hole in the dorsal side of the bait would not allow gravity to fill the cavity as well as a hole at the head – pouring to the tail. Would I need to incorporate more vents when pouring laminates?
  As I am just beginning I will probably stick to vertical pour, single colors. But I am curious how laminates are done and would like to experiment down the track. Any links to pics of laminate molds on this site people know of?
  
  
• The mould line on the paddletails is along the lateral line of the bait. When I make my 2-part moulds, is it better to lie the bait belly down in the POP or flat on its side?
  
• I have read a wide range of opinions on curing POP. E.g. longer curing periods = better strength, heat can cause POP to become more brittle, POP will never fully cure if simply dried at room temp in the house. Is it necessary to use some sort drying box? Would a fan forced oven on lowest setting generate too much heat?
  
• What sort of thickness should I aim for with my mould halves to create enough strength and durability in the POP?
  
  
• Would a polystyrene box be a suitable vessel for pouring the POP mould into? Should I coat it with Vaseline or seal it with Elmer’s first?
  

Aplogies for the barrage of questions. Sometimes the more reading you do, the more questions you develop and I've done a LOT of reading. Appreciate any advice/giudance I recieve.

Cheers in advance,

Jim.

Edited August 9, 2009 by slipperybits

[longhorn]

Jim,

Welcome. Here's my on some of your questions.

hot plate will work fine but will scorch easily...I'd make a little stand to keep the pan off the burner a couple inches which will help.

I would make one-piece open molds of both the baits pictured. They will come out great and will allow you to easily pour laminates and are way faster to produce. The flick bait looks like it has a flat top already.

I cure my POP in the oven at 325 for an hour or so per inch thickness

I think any POP mold should be at least 1 1/2 " thick

I use a flexible box such as rubbermaid...no coating necessary and the flex will allow the release.

hope this helps.

[Richard Prager]

Longhorn pretty much sums it up. You will be able to do a lot more with open pour molds. I use the microwave but that's just a matter of preference.

[slipperybits]

Thanks for the detailed response Longhorn. I hadn't considered open, one-piece molds for these baits, but if you think they would work well, i will give them a go.

Would that mean i need to glue the tops of the baits down to my mould vessell, as shown in this forum with senkos and worm patterns.

OR can i simply sink the baits belly down in the POP as it begins to cure?

I think it may be difficult to glue them down as they are not completely flat, particularly the tail area...

Regarding the use of a hot plate - what temp setting is recommended to cook the MF SS?

Jim.

[longhorn]

You can use the sink down method make sure your POP is thin enough and sink the baits right away after you get most of the bubbles to the top. You will have to stay with the mold and keep pushing the baits back down because they will float. Keep doing this until they stop floating.

If the baits have a flat side I prefer to use double-sided tape instead of glue

I don't use a thermometer...I think around 325 but not sure...you'll just have to get some experience with your setup. You won't be able to set your burner on 325 and set the pan of plastic on it till it gets to temp...you'll have to watch closely and stir a lot and remove the pan from the burner at times to keep from scorching. You'll soon get a feel for it.

An alternative to gluing down is the pin down method where you put a thin sheet of vinyl or plastic over cork board and use straight pins to stick the masters down...then put the mold box (with no bottom) around the baits....seal with masking tape to keep the POP in and pour the POP over the masters.

[Husky]

You might want to try this method for VERY INEXPENSIVE RTV molds. I've been more than pleased with the results!

[slipperybits]

Thanks again longhorn. Hadn't heard of the pin-down method before. I assume since you desrcibed both 'sink down' and 'tape/pin down' methods, I could use either with these baits. Sorry to harp on the same topic, but is there an advantage to one over the other. Which would people recommend for the baits pictured?

Hi again Husky, glad you made an appearance. Yes I have considered your RTV method, however I would not even attempt to try and build a hard copy of my baits out of wood or clay. Much easier and more accurate to use the soft bait masters i already have. Though I havn't checked that thread for a while so there might be changes to the tech I'm not aware of. Will have a look later (at work now)...

Also, I already have all the materials and POP ready to go, so I would like to have a try at making the POP moulds.

Cheers,

Jim

[longhorn]

If the master has a flat top I use the tape down...if not I use the pin down. I would use the pin down on the shad. You only need one good cavity of each bait. With that you can make overpours and make some good multi-cavity molds which are identical to the master.

[Vodkaman]

Should you ever attempt a 2 piece mold (they use US spelling here lol). The 'not touching the sides' reference, is not so much to do with the cooling, but the pour hole is likely to block before the pour is completed, leaving you a large bubble or void just behing the neck.

The reservoir (funnel) is to allow you to over fill. The plastic shrinks when cooling and will draw Some of the over pour into the mold.

Venting will be required at the extremities. One for each point of a forked tail, one for each leg on creature molds, one at the tip of the paddle tail. When you start the pour, it is very possible for the plastic to trap air in front of the flow, a vent allows this air to vent out, thus not spoiling the casting.

For difficult pours, read up on injection and vacuum methods, to complete the options available to you.

Dave

[slipperybits]

Hmmm... in the words of Early Cuyler, I just had to 'educationalise' myself in a new concept - overpours. Just located your thread on 'Simple POP production moulds' Very useful Longhorn, thanks.

Vodkaman - are you Aussie too? Thanks for clearing that up for me - makes perfect sense.

Just on the double sided tape for sticking down baits. I know there are a number of different styles available - i.e. widths, thicknesses and materials. Is there a preferred type / brand for this purpose?

Thanks again.

[longhorn]

I use Scotch brand in 1/2" Permanent because that's what Walmart has.

[Joe S.]

As far as the hotplate goes, you will have to adjust it accordingly until you figure out where you can keep it at, mine has low, medium, and high, and I keep it between low and medium.

I can leave a pan on the burner and it keeps it pourable without burning the plastic. I use two burners, I have one I use for a large volume pot (Candle wax pitcher) I usually put 2-3 cups of plastic in that and crank that burner up to High then keep an eye on it and stir as it begins to cook, once the plastic starts changing I turn it down to medium so it has some time to cool down before burning the plastic but it is still cooking it and continue to stir.

I use the second burner for my pouring pans, that is the one I keep between low and medium, I never really put more than half a cup of plastic in a pouring pan, most of my recipes are based on either half or quarter cup. So I will pour the clear plastic into the pouring pan then add my colors/glitter scent etc. Stirr that all up and then dump alot of that inrto another pan so I have two on that burner.

It is easier to pour with 1/4 cup or less of plastic in the pan especially for smaller baits, I leave the other pan on the burner while pouring with the other, once I'm empty on the one I was just pouring with I grab the other one and transfer plastic back into the one I was just using and leave that one on the burner, and pour with the other, rotating them each time there empty, once there both empty I refill one of them 1/2 way with clear plastic and mix my ingredients again. And repeat the process

When removing the clear plastic from ther larger picture on the other burner I have to adjust that temp control to compensate for less plastic in the pot each time I refill the pouring pans.