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Molding plastic
Weaponeer Forums : Casting

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  whiteing

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Posted: November 23 2008 at 12:01pm | IP Logged Quote whiteing

http://lindsaybks.com/dgjp/djgbk/injatt/index.html

http://lindsaybks.com/dgjp/djgbk/inject/index.html

http://lindsaybks.com/dgjp/djgbk/vacf/index.html

http://lindsaybks.com/dgjp/djgbk/index.html

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  midmichigun

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Posted: November 23 2008 at 10:08pm | IP Logged Quote midmichigun

Ladies and Gentlemen,

As suggested by several board members, casting a mold, melting in some wax... and doing great things... is a good idea.

Here is where I am at. I am using the Silicone rubber mold that was used to cast the ar15 epoxy lowers that you all have seen. My mother had several pounds of Canning Paraffin Wax that was "donated" to the cause. Whats nice is the low melt point of this compound. So I set the oven and melted some wax into the mold. Problem points will be where the buttstock screws into receiver, and the VERY thin magazine well. My first cast didn't turn out very well, here are the high points so far:

1. Wax kept leaking out of my mold. Look at the photos and see where the mold lines lie. What I was doing was filling the mold, while it was in the oven, and continued heating. This was to insure that wax was melted everywhere, and to try and minimize bubbles and thin areas (if mold was cold). Everything was done on a cookie sheet BTW. Well, I ended up taking the mold out of the oven and poured small amounts until the leaks stopped (wax had cooled and plugged its leaks. The wax in the glass measuring cup I was using kept liquid for a long period of time. I also applied some gentle pressure with a few 30rd boxes of 7.62x39 ammo to help squeeze the parts together.

2. I left the mold with the wax at RT (room temp) for over half an hour. I felt the mold and it was still very warm. Therefore I took it outside for over 40minutes. I gently pried open the mold after this time (well over an hour after oven removal the outside fell cold). I found a pretty "spongy" mess. ie, the mold was still to warm.

If the paraffin has poor working properties, I may have to move up to Bees Wax. While this is the "bee's knees" for mechanical properties (in my opinion), it is harder for people to get. I have a quantity from my honey bees, so supply isn't a problem. At RT, bees wax (cleaned and refined) is fairly hard. Remember the goal is to be able to pull it out of a mold! So any strange corners can be a hazard for wax.

The wax seems to melt well at 150F. However, some sites recommend specialty waxes for the Lost Wax Method of casting, due to paraffins brittleness at RT. They also warn of using bees wax, since its not as hard (or brittle) as paraffin at RT. Brittleness is an issue with a mold with a complex shape. Some bending can be corrected/ fixed. But if the wax shatters (brittleness) then it obviously won't come out in one piece. Remember it is Michigan, so my outside temps will be alot lower.

I have two goals here on making a wax casting. One will involve the Metal Casting thread. However, an accurate cast may help me make a different hard mold for plastic work.

I would hate to chop up my mold, but I am debating doing some work and removing the threaded buttstock portion of the lower. That way I have a solid wax connection that can be worked/ modified in either the wax/ metal or plastic stage of the casting. Also the mag well may be worked on so the walls are initially thicker so I can pull out of the mold. I can always clean it up later with a little mill/ file work.

Doing some shopping, I went to my old standby hardware store. I was looking at electric water heater elements/ thermostats. I haven't used these in awhile, however, you can set up an element/ thermostat for melting plastics. While it would be difficult to use a water heater element, it is a starting point. I have a quantity of 400watt band heaters that would love to fit on an iron pipe. I may incorporate a water heater thermostat/ relay and a few band heaters to come up with a plastic injection system.

Sounds like dcorb has his stuff wired together and is moving forward... I just don't have the time guys.. However, I will post any contributions I can make. Thats what forums are for!

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  bbphotova

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Posted: November 23 2008 at 10:57pm | IP Logged Quote bbphotova

Not sure if it adds to the discussion or not, but it may help to not worry about forming the plastic to super exact tolerances by utilizing an insert of some kind, similar to Glocks or Kimber's Ultra Ten II.  Could add stiffness and durability that the plastic or epoxy wouldn't have.

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  gundoctor

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Posted: November 24 2008 at 1:44am | IP Logged Quote gundoctor

There are some special waxes for investment casting--made to work well and burn completely out of the dipped investments.   Most casters will probably want you to use a specific wax based on my very limited experience. You might yellow page a local investment casting facility--maybe they will sell you a pound or two.

Wow, a real tool and die moldmaker is around.  We need you around here in both the casting and stamping threads.
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  midmichigun

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Posted: November 24 2008 at 10:39am | IP Logged Quote midmichigun

gundoctor,

Agreed on the casting waxes. However, I wanted to try what common people have in their house or farm before trying the "real" stuff.

As someone pointed out, with the bad economy, suddenly people want to help you (so they can make money). However, my background is that not many people up here are/ were friendly towards the hobby/ Right of gun building. One day I may start a thread, but I don't want to make it a Rant about my adventures. Hence my try at doing as much as possible at home on my equipment. I have been counseled by many "experts" about NOT building: ak's, ar's, fnfal's, 1919's etc due to cost and difficulty.

Yes, lets have as many people (tool and die) step in as possble with their backgrounds and experiences. Its the only way this thread will grow, since its a "one-off" of traditional home build.

Anyway, I tried my last attempt on using common wax this morning. My mold was hard enough that to just open it, caused the wax casting to crack up. So onless you have very simple shapes to cast, paraffin wax will not work.

However, it has some attributes if you wish to try your hand at it.

1. It is was easy to clean out of my mold

2. Low melting temp

3. Very cheap.

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  midmichigun

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Posted: December 04 2008 at 12:02am | IP Logged Quote midmichigun

Ladies and Gentlemen,

Here goes more posting.... Please find attached a nifty photo. I cast an AK pistol grip in half. This was your typical Romy grip. As per 922r, we have to have several US made parts. Hence the push to "Make" your own. This is also an easy "casting plastic" idea. After cutting the grip in half, I did a liberal coat of cooking spray used to release muffins and bread from their molds. I formed the box and starting filling in with plaster. I made the mix more "sloppy" to make sure I didn't have problems with air capture. I also used COLD water to slow crystal growth of the plaster.

The next photo shows the SET of plaster molds that I made. Essentually, I cast both sides of each half. This way i have several options. I can make a hollow cast pistol grip (without using soft mold compound). I can also make a solid pistol grip. That way if I find that my chosen material is to weak, I can make a solid cast.

After one side was hardened, I took the part out of the mold to clean, and make sure I could remove it. I then relubed EVERYTHING, including the fresh plaster. This was to insure that the two plasters would not adhere to each other. Notice I used a penny as a locator to insure both halves line up.

Here is an intermediate photo when I was casting half of the grip. Notice the detail present!

Well, when I get back, I can start casting in plastic, rubber or metal, my US 922r compliance parts. I believe that US grips cost between... uumm... $10.00- $20.00. Using the same technology, I can cast a "unique" grip that is custom fit to my hand. I would simple do the above process, but with a hardening clay.

If you look at the first photo, I have built up a clay dam to keep the plaster in one place and to prevent it locking the grip in place.



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  dcorb

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Posted: December 04 2008 at 6:11am | IP Logged Quote dcorb

I was going to edit the above post to remove the blank lines but it seems I lost the ability to edit posts.

 

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  dcorb

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Posted: December 04 2008 at 6:15am | IP Logged Quote dcorb

Very cool on the making of the Romie grip mold!

I would like to try doing this sometime soon. I have a nice wood grip which I would like to copy. One thing I do not want to slice it in half so I guess I would need to use more plastic making it.

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  midmichigun

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Posted: December 04 2008 at 9:03am | IP Logged Quote midmichigun

dcorb,

If you go with the pliable rubber molds, then you can do wonders. Remember when working with "hard" molds you have to think of "line of sight". When looking at a part, typically, what you don't see, won't remove itself easily or at all (overhangs with complex curves). Flexible molds rock in this regard since you can pull out your part and the rubber gives.

The plaster was just another way of casting a part. I hear about kevlar, fiberglass.... plaster is simple, and cheap, just add water. However, its not as durable. Its just another media that we can use to cast objects.

Part of this casting, is the cost benefit of how MANY do you want to make of a part? 1, 2..... 10,000?

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  Inabadhood

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Posted: December 05 2008 at 1:37pm | IP Logged Quote Inabadhood

Great progress!  Looks good! 
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  midmichigun

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Posted: December 09 2008 at 12:08am | IP Logged Quote midmichigun

Ladies and Gentlemen,

I stole this link from J Dillinger on an ammo thread. If you follow down, you will see a plastic grip/ trigger guard. I believe the price was 3/$50.00 or $25.00each.

http://www.classicarms.us/

While technically not one of US casting, thought it would help keep the thread alive and spawn some thoughts.

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  gundoctor

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Posted: December 09 2008 at 2:01am | IP Logged Quote gundoctor

Here is how to cast your pistol grip in one piece.

Making the mold


Build a frame that will hold the grip  approximately 6" sq would work.

roll out some modeling clay about 3/8thick and line the bottom of the frame.

place the grip on the clay.  (make sure the grip is coated with release agent)

build up clay to the "parting line", or 1/2 way up the grip.   Carefully with a exacto, scrapers, etc make the clay stop at the "parting line".  An even neater way to do this is to roll out some clay to 1/2 thickness of the grip and then trim the grip shape out.   Our course, you will have some "fine work" where the clay joins the grip.

I suggest you put a few "keys" in the clay.  This is something that will align the mold halves.  Something like some pins.

Pour your mold resin over the grip 1/2 embedded in the clay and let cure.

Flip over and remove the clay.   You may need to remove the grip to clean it up, but the clay will brush out of details easily.

Spray the grip and cured 1/2 mold with mold release.  Then pour the other 1/2 of the mold.

Of course, you will need to leave a means to get resin into the mold and possibly some little sprue places for air to escape.
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  dcorb

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Posted: December 10 2008 at 1:56pm | IP Logged Quote dcorb

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  dcorb

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Posted: December 11 2008 at 8:54am | IP Logged Quote dcorb

While surfing around I discovered these grips at Lichtenberg Research:

http://www.lichtenbergresearch.com/parts/vz58pistolgrip/vz58 pistolgrip.html

Sounds like he is hand making them.

Pistol grip cast from hard Poly Urethane. The original composite grip was used as a pattern. These are hand made and are not injection molded like an AK grip. Each one is unique and they are strong and solid. They have been grit blasted and coated with Satin Deft Clear Wood Finish can be used as is or sanded and/or painted as desired. We could have purchased a new single stack receiver for less than we have invested in this process. We own only one mold and our production rate is only one part per day. E-mail us for availability before ordering. The mold was a big investment and its life expectancy is unknown. Once mold wears out or breaks a business decision will be made weather to buy another mold or discontinue this product.

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  midmichigun

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Posted: December 11 2008 at 9:02am | IP Logged Quote midmichigun

dcorb,

Excellent posts! I look forward to getting back. It should be nice and warm in Michigan this time of year! I was thinking about molding up some ice grips for the AK, "guaranteed to fit your hand in 15minutes. May need towel for installation. "

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Posted: December 11 2008 at 9:15am | IP Logged Quote dcorb

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Posted: December 11 2008 at 11:39am | IP Logged Quote weaponeer

a video on Making a Kydex Knife Sheath.  the same could be done for other parts as well.

http://www.youtube.com/watch?v=3lczZWgN4Kg

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  Inabadhood

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Posted: December 11 2008 at 12:00pm | IP Logged Quote Inabadhood

Good Info!
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  dcorb

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Posted: December 13 2008 at 6:13pm | IP Logged Quote dcorb

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Posted: December 13 2008 at 6:31pm | IP Logged Quote dcorb

This looks it might be fun:

Knead-a-Mold

http://www.townsendatelier.com/store/knead_a_mold.php

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