2 piece sickle tail question

[borderbasser]

I recently made a 2 piece copy of a 10in power worm out of plaster. I figured out that you have to pour the tail first and then put the mold together. However, when I tried this, I couldn't get the mold together fast enough to get the body to fuse to the tail very well. This method sure seems like a big pain in the A#$. Is there another way? I have read the thread about using a bucket and a shop vac to create a vac cum chamber, but that seems like an even bigger pain. Has anyone experimented with creating a positive pressure environment in the mold..ie pressurizing the mold to force the plastic into the tail. Here is my idea. Drill a tiny hole near the tip of the tail and scribe a fine line from the tip to the hole to allow the air to escape. Then, pour enough plastic in the mold, that in theory, when the plastic is forced up in the tail the static height of the plastic in the body will be above that of the tip of the tail (if you don't do this, when you remove the source of the pressure, the plastic will U-tube back down until the height is equalized between the body and tail). Once the plastic has been forced into the tail, finish pouring the bait. The only question is what is the source of pressure? I'm sure it would only have to be a few pounds and very little volume. I thought that one of those things that parents use to suck the buggers out of a baby's nose(nose bulb) might work. Just stick it inside the tapered pour hole until it makes a pretty good seal, and squeeze. The only problem I can foresee, is a flashing problem, but I think if you seal the edges of the mold with tape, this might remedy that problem. Anyway, what do you guys think? Anyone ever tried this or something similar with any success?

Thanks fellas.

PS: I have only posted a few times, but would just like to say that this is the best, most informative, and friendly forum I have ever been on. Thanks for all the help!

[jigmeister]

BorderBasser , I was the one who posted the idea about using a vacuum chamber made from a 5 gal bucket a couple of years back. It will either take vacuum or pressure to completely fill a two piece mold such as you describe. I came up with the process to make a copy of a "Madman" craw ( 2 piece mold with insert for hollow center) . It was about the hardest mold making experiment I had ever attempted . The vacuum method allowed me to completely fill the mold through stratigic placement of venting. I also tried using an automotive siphon gun (used for filling /extracting fluids form transmissions and rear ends) . Its like a big metal syringe of something like 20 oz. it has a threaded hole in one end for the hose fitting . I changed the original plastic hose bard fitting to a brass one . Heat your plastic ,put the hose barb fitting in and pull the handle back filling it up with hot plastic . Push the handle forward with the hose barb facing up till hot plastic just runs out to purge any air . Now place the hose barb into the sprue hole in the end of the mold(s) and inject the plastic. You should strive to expell all the hot plastic while hot to minimize clean up . Both ends unthread and come off for clean up.

Either way you go its a pain to pour a 2 piece mold without expensive injection molding equipment but it is possible...........Jigmeister

[saint308]

Here is a question along the same lines. How do you go about pouring a laminate with a 2 piece? I am pondering a try with a stick bait mold, but not sure the best way to go about it. I have read that you pour about a third of one side of the mold and let it sit for 15 secs. Then you put the mold together, and pour normally. Is this the best way? I am concerned the plastic will not fuse together. Thanks. Saint.

[jm]

A good source of experimental amounts of vacuum is an old refrigeration compressor. The oval ones will develop an extremely deep vacuum, sufficient to boil water at room temperature, but almost any of them will work. Get one out of an old refrigerator after the freon has been removed. Be sure to restrict the flow with a pinched line or a valve or it will blow out all the oil.

Another good source of lab vacuum is an old piston type vacuum pump used for the old bucket milkers. Usually they are about 1/4 to 1/2 horsepower, belt driven, and provide a pretty good volume and a reasonably deep vacuum.

I am experimenting with vacuum as a method to remove the air from the "plaster" to make molds. It seems to work quite well. I think that if I combine vacuum with vibration, I should get a pretty bubble free mud quickly.

jm