Hello, all,
Didn't know exactly where this post would belong, but I was curious as to if anyone had any experiences attempting to re-melt similar type plastics for the purpose of machining it, and what works best? Assume I know nothing and I'm about to ask dumb questions, and make rediculous suggestions.

obviously, compatible plastics would need to be collected... if, say, I collected a pile of ABS junk, ground it all up into little bits, put it in a metal shoebox - sized container sprayed with mold release and put it int the powdercoat oven at like 300deg, would I get a nice slab of ABS to machine goodies out of?

Polycarb?

anything that DOESN'T work? I would think I would avoid PVC as it gets a bit stinky when it melts...

Hello, all,
Didn't know exactly where this post would belong, but I was curious as to if anyone had any experiences attempting to re-melt similar type plastics for the purpose of machining it, and what works best? Assume I know nothing and I'm about to ask dumb questions, and make rediculous suggestions.

obviously, compatible plastics would need to be collected... if, say, I collected a pile of ABS junk, ground it all up into little bits, put it in a metal shoebox - sized container sprayed with mold release and put it int the powdercoat oven at like 300deg, would I get a nice slab of ABS to machine goodies out of?

Polycarb?

anything that DOESN'T work? I would think I would avoid PVC as it gets a bit stinky when it melts...

THERE IS SUBSTANTIAL RISK IN MELTING/HEATING PLASTICS [ =POLYMERS ]
WITHOUT A FUME HOOD AND WITHOUT KNOWING EXACTLY WHAT IS IN THE PLASTICS.
IT IS NOT RECOMMENDED FOR THE REASONS LISTED BELOW AND SOME THAT DON'T
COME TO MIND:

1. There are two classes of polymers: thermoplastic and thermosetting.
The former will soften when heated; the latter will never soften, just
decompose, when heated. Bakelite is an example of the latter.

2. Some polymers produce toxic gases when heated. For example, vinyl
chloride produces HCl gas when heated.

3. Plastics are not pure materials; they are formulated products. Some
of the chemicals used to give the plastics their desired mechanical and
physical properties also form toxic vapors when heated. An example are the
common phthalate plasticizers.

4. Some polymers "unzip" when heated evolving monomer vapors. Acrylates
polymers are notorious for this. Acrylate monomers are toxic.

A safer route would be to use water dispensable gums [ e.g. algenates ]
like dentists use to form a denture. These harden and can be used to form
models from plaster of Paris, or self-reacting styrene formulations
available at hobby stores. Even in this case adequate ventilation is
necessary because styrene vapor is also toxic.

My purpose was to use things that would otherwise be trash and make it into something I can practice on the CNC with... and test up fit of parts made with a program before wasting a $100 block of aluminum on it... even if I lose some of the ideal mechanical properties of the material by remelting it. I also expect a techni-color spotty browinish mix of colors. no biggie to me for this purpose.

Sounds like my primary safety concern is the production of noxous gasses. Thus PVC's are out. The oven is vented and out in the garage - not in the living space. It's the oven I use for powercoating, so no food would be cooked in it, no concern there. Lets assume I put a big ol' box fan next to the oven and blow any escaping gasses out the open garage door. And I keep my distance for the most part. And wear a gas mask. Noxous funes should be minimized to levels generally encountered while cleaning the bathrooms.

Is there anything I can tell from the recycling codes on plastic parts that would tell me if it will be thermosetting or thermoplastic? Is this something I can google?

is there anytype of material that I could grind up and use without much worry of decomposition? From a mechanical properties point of view I would like to use polycarbonate. If I get a bunch of broken plexiglass for free, would it be ok to just melt down and machine on?

What I do Is go to the local Plastic distributor and they have a lot of scraps that they sell by the pound (1.00)

Sounds like my primary safety concern is the production of noxous gasses. Thus PVC's are out. The oven is vented and out in the garage - not in the living space.

The EPA would really get angry with you! :p They usually don't take well to venting toxic gasses to the outside with no concern for where they go...

A lot of the guys on here use scrap wood to proto parts before doing the final design in Alum. Seems like a better option to me. :cool:

Look at the Machinable Wax.

You can easily machine Machinable Wax without the need for costly and messy coolants or lubricants, because MACHINABLE WAX is "self-lubricating", "non-abrasive" and it will not fuse when machined at high-end spindle rpm's and feed rates.
Unlike wood or plastic, MACHINABLE WAX will not "gum up" on tool bits. Sharp edges can be maintained, accurate threads can be cut and thin wall sections maintained with the quality of surface finish capable of being produced by your cutting tools and machine. MACHINABLE WAX is not cellular, grainy, or abrasive so "voids" in machined surfaces (common with plastics and wood) and "tool wear" are negligible. Machinable Wax will also machine "within designated tolerances" to provide you with a dimensionally accurate prototype that can be assembled for checking.

You can also "saved" the chips, re-melt and reuse the wax!

Look at the Machinable Wax.

You can easily machine Machinable Wax without the need for costly and messy coolants or lubricants, because MACHINABLE WAX is "self-lubricating", "non-abrasive" and it will not fuse when machined at high-end spindle rpm's and feed rates.
Unlike wood or plastic, MACHINABLE WAX will not "gum up" on tool bits. Sharp edges can be maintained, accurate threads can be cut and thin wall sections maintained with the quality of surface finish capable of being produced by your cutting tools and machine. MACHINABLE WAX is not cellular, grainy, or abrasive so "voids" in machined surfaces (common with plastics and wood) and "tool wear" are negligible. Machinable Wax will also machine "within designated tolerances" to provide you with a dimensionally accurate prototype that can be assembled for checking.

You can also "saved" the chips, re-melt and reuse the wax!

Sounds like that's what I need to get ahold of. And it can be reused until it's too full of dirt to hold together, I suppose?

Where's the best place to get some of this stuff?

Here is a couple of links:
http://www.freemansupply.com/index.htm
http://www.flexbar.com/PDF/20_21.pdf

That Machineable Wax is some cool ****!

Check out their video: HERE (http://www.freemansupply.com/video/products/machwaxqt300.htm)

Hi,

I was wondering if the plastics are best melted in a vacuumn?

Is it heat or oxygen which causes the plastic to degrade, excepting the thermosetting plastics that is.

Thanks
scwTech

Hi,
Wouldn't melting the plastic in a vacuumn eliminate the problems with vapors and chemical reaction with the air?
Thanks,
scwTech

Actually no because to maintain a vacuum you would have to pump on it, i.e. pump out all the nasties through your vacuum pump.

The way in which many thermo plastic materials are recycled into the solid brownish/greyish/mottled lengths that are used to build deck material or park benchs is by heat and pressure. The plastics are shredded or ground and then mixed in a screw extruder which heats and mixes them together. The pressure has two functions; it causes the plastics to fuse together at a temperature well below their melting point or depolymerization temperature and it raises the temperature at which they start to depolymerize and outgas.

There is a home made injection molding book available from Lindsey Technical Books. It is here ( http://www.lindsaybks.com/dgjp/djgbk/inject/index.html ) I have a copy and it has been a project I have wanted to do for a long time. If you stick to the cautions in this book you should be ok. This was written by the brother of the guy who started the charcoal fired aluminum foundry craze.

Look at the Machinable Wax.

You can easily machine Machinable Wax without the need for costly and messy coolants or lubricants, because MACHINABLE WAX is "self-lubricating", "non-abrasive" and it will not fuse when machined at high-end spindle rpm's and feed rates.
Unlike wood or plastic, MACHINABLE WAX will not "gum up" on tool bits. Sharp edges can be maintained, accurate threads can be cut and thin wall sections maintained with the quality of surface finish capable of being produced by your cutting tools and machine. MACHINABLE WAX is not cellular, grainy, or abrasive so "voids" in machined surfaces (common with plastics and wood) and "tool wear" are negligible. Machinable Wax will also machine "within designated tolerances" to provide you with a dimensionally accurate prototype that can be assembled for checking.

You can also "saved" the chips, re-melt and reuse the wax!

You also might want to consider BEESWAX. (made by honey bees). It has almost all the properties above. It does not have any toxic properties, has a low melting point, (melt on kitchen range) and is available on e-bay for about three dollars a pound. Lower prices in quantity. Also, numerous vendors to choose from.

Jerry

Thanks Geof, makes total sense,
I'm going to get this book which SpookyDad refers to, sounds like what I'm interested in.
scwTech

I just went to that link and noticed this comment part way down the page:
"Surprisingly, recycled 2 liter soda jugs produce very hard, durable moldings. Polyethylene milk bottles produce a softer, waxier type of moldings."

This is really quite interesting. Milk bottles are made from pure polyethylene, medium to high density I think. Pop bottles are made from several different plastics in layers. One layer is for strength because they have to hold against the pressure of carbonation, the inner layer has to be something that does not add any flavor to the contents and I think the outer layer is formulated either for abrasion resistance or to take printing. There might be other layers as well.

When a pop bottle is melted and mixed together as would happen doing small scale injection molding what you get is a plastic alloy; a mixture of different plastics. Alloys, whether steel or plastic, are nearly always stronger or stiffer than the individual components in pure form and that is probably what is being observed here.

Excuse me rambling, fifteen years ago I had a part time position in a local College of Industrial Design teaching a course on Properties of Materials. This was the kind of thing I would discuss with my students to make the course more relevant and less theoretical.

You can also make your own machinable wax. It sounds strange, and I will be doing a full writeup on how I make it to machine foundry patterns soon. But basically you melt ordinary parrafin-quite hot, not a double boiler- and stir strips of polyethelene plastic in until they disolve. This can then be cast into sheets and is a good machining product. It looks like about 25 percent poly is about right

...But basically you melt ordinary parrafin-quite hot, not a double boiler- and stir strips of polyethelene plastic in until they disolve. This can then be cast into sheets and is a good machining product. It looks like about 25 percent poly is about right

I would assume you are using low density polyethylene or maybe medium density such as milk bottle material? I cannot imagine it working with UHMW polyethylene.

This is quite interesting because all you are doing is creating a hydrocarbon solvent, the liquid wax, which is capable of dissolving a longer chain hydrocarbon. Chemically it is no different to dissolving paraffin wax in a low melting point solvent. In fact it is entirely equivalent to high wax diesel fuel.

I would say caution is the order of the day because the hot mixture would be capable of creating horrendous burns; even through clothing. But with correctly set up equipment and protective gear quite doable.

Here is an idea, which is probably already lurking in your mind, prepare this hot mixture and then devise a way to vacuum impregnate low density MDF. I can imagine having the MDF in a shallow bath with a vacuum being pulled from below. You flood the top surface with the molten wax/PE mix, possible after preheating the MDF, and then shut off the vacuum pump. The resulting material could be quite durable and very machinable. A drawback would be that it would probably be impossible to paint but the wax mixture could be dyed almost any color.

geoff,

the idea of a hot-wax, poly mix causing horrendous burns just made me shudder!

another material people use for prototyping aluminum parts is RENboard\RENshape.. I am not sure of the cost, but i beleive it is high..

Another interesting material might be those 4x4" 'plastic-wood' deck posts at home depot... i keep looking at them for something else and deciding 'no...' but they may be similar to the RENboard...

I have the lindsay press, gingery book. it is a neat little thing, and inexpensive(at $15)... there is a bit of info in there about grinding and melting plastics... probably exactly what you want to know...

however, my involvement in IJ part design has made one thing clear - thick sheets of plastic must be molded under great pressure to obtain good properties. i am not certain melting a high or medium density plastic and pouring it into a mold will give you good results at all. air bubbles, sink marks, etc...

i think the hot-wax and poly idea sounds very interesting. i have always wondered if there was a DIY approahc to machinable wax... this is so obvious... if i didnt have ~10 blocks of the wax, i would be very curious if this works out...

good luck!

I wonder if the commercially available machinable wax is actually made by that process. The only difference between paraffin waxes of different melting points is the length of the carbon chain in the molecules; if you remember your chemistry from high school, methane (natural gas) is one carbon, propane (liquified petroleum gas, lpg) is three, butane is four, octane eight, etc etc. If my memory serves me correctly, kerosene is a mixture of between around 18 and 24, baby oil in the 30's or so, vaseline more than that, waxes going up into the hundreds or maybe even thousands and then the polyethylenes going into the hundreds of thousands and into the millions; it is a continuum.

Someday I might get around to trying to make some DIY machinable wax and I will also try my impregnated mdf idea.

I've used those poly soda bottles for years for air pressure reserve for r/c aircraft landing gear.
What I'm looking at is using the recycled stuff for making molds of it for composite fuselages and perhaps hollow molding wings.
Now it might be interesting to mold a fuse using old soda bottles as well for a durable knock about sort of slope glider.
Seems as though the paraffin/poly mix might make a good self releasing mold.
Now I'm rambling.
Thanks again for the wisdom!
scwTech

http://cgi.ebay.com/Plastic-Injection-Molding-Machine-NRK-Plasticor-Junior_W0QQitemZ7620727013QQcategoryZ20789QQrdZ1QQcmdZViewItem
a small home plastic mold machine,

and use legos,

its all you need, serious.

the d-m-e jiffy shot is good with pellets, once you purge the nasty-smelly-probably costly blue junk out of it. I took some pics which I will be posting soon of the complete teardown of mine.

The EPA would really get angry with you! :p They usually don't take well to venting toxic gasses to the outside with no concern for where they go...

A lot of the guys on here use scrap wood to proto parts before doing the final design in Alum. Seems like a better option to me. :cool:

I've been wondering about this sort of thing lately. Is there is a good way for a hobbyist to handle toxic gasses that is environmentally responsible? Venting is easy enough wether you are doing chemistry or whatever, but how is one supposed to detoxify or otherwise safely contain unfriendly gasses?

-Drachasor

Drachasor,

ask anyone who smokes cigarettes, probably causes more cancer than ALL the hobbyists could cause even if they tried. If you're concerned about toxic waste, then just ask the guys that dump spent waste rods and barrels in Utah; that will eventually seep into the ground and into our water.

do the math.

Here is an idea, which is probably already lurking in your mind, prepare this hot mixture and then devise a way to vacuum impregnate low density MDF. I can imagine having the MDF in a shallow bath with a vacuum being pulled from below. You flood the top surface with the molten wax/PE mix, possible after preheating the MDF, and then shut off the vacuum pump. The resulting material could be quite durable and very machinable. A drawback would be that it would probably be impossible to paint but the wax mixture could be dyed almost any color.


@Geof

Here is how to do it
1 put MDF into a pot

2 cover with liquid (GRP resin is an option)

3 put on the lid and draw vacuum. Here the porus MDF is evacuated of air.

4 admit air. Now the evacuated MDF will suck in the liquid

5 lift it out for to dry/set and do another

6 machine a nicenameplate


It works :)

Something I've wondered for a while. Will a standard welding PAPR respirator protect your from toxic vapours/fumes released when melting quantities of plastic?

I took 460 grams of paraffin and heated it to melt. I then slowly added about 115 grams of cleaned and cut up milk jugs. All I got was some gooey polyethylene. I then increased the temperature and the paraffin smoked but the polyethylene only remained clear. WHen I poured the mixture into a mold, It looked as if only the paraffin poured into the mold and the Polyethylene remained in the melting pot. What did I do wrong?

Doug

graemeian,
Thanks for experimenting and saving me the mess. I will be watching to see what develops with this. Machinable wax from FreemanSupply is quoting at $260_US for 40lbs (2"x24"x24"). So, I would like to see a DIY M_wax formula that works. http://www.freemansupply.com/MachinableWax.htm

This link is for an interesting project and toward the end of the page he does some DIY machinable wax with paraffin and polyethylene powder ??? http://www.submarineboat.com/sub/helm.html#Fly-By-Wire


UPDATE:
DIY M_Wax: http://www.cnczone.com/forums/showthread.php?threadid=26351

Guys, I put in one of the posts about making you r own machinable wax. I have been experimenting and have tried the stuff they sell for making candles harder. It dosn't seem to be as good. The best formula still seems to be 1 part polyetheline sheet to 3 or 4 parts paraffin by weight. Use fairly thin sheet so it will disolve. I thinkl the problem with the milk jugs is they are too thick. they sould eventually disolve but the whole time the paraffin is smoking and outgassing(I feel like it coats the inside of my nose) I usually use some of the candle colorant,I hae a nice purple now. Now if I can just figure out a good way to get sheets. I currently pour onto a plywood sheet and then machine it flat to the thickness I want but this leads to a lot of waste. I am thinking of trying to "roll" the wax just before it gets really solid. Any Ideas?
Dave

Guys, I put in one of the posts about making you r own machinable wax. I have been experimenting and have tried the stuff they sell for making candles harder. It dosn't seem to be as good. The best formula still seems to be 1 part polyetheline sheet to 3 or 4 parts paraffin by weight. Use fairly thin sheet so it will disolve. I thinkl the problem with the milk jugs is they are too thick. they sould eventually disolve but the whole time the paraffin is smoking and outgassing(I feel like it coats the inside of my nose) I usually use some of the candle colorant,I hae a nice purple now. Now if I can just figure out a good way to get sheets. I currently pour onto a plywood sheet and then machine it flat to the thickness I want but this leads to a lot of waste. I am thinking of trying to "roll" the wax just before it gets really solid. Any Ideas?
Dave

i have used a releasing agent in a old cookie sheet to get flat sheets i simply coat the inside of one sheet and the bottom of another pour the hot wax in the bottom and place the other on top with some bricks added for weight it presses down and leaves a sheet of machinable wax, you can control the thickness by how much wax you use , just my way might work for you

Last night I experimented with making my own Machinist wax. Worked out fairly well. However I have not yet tried to machine it. I tried three different materials: hot glue, PE and HDPE. Of the three the PE mix worked the best, with the hot glue and PE mix working the second best. The HDPE worked ok but I don't think it would be suitable for use as a wax casting core after machining as the melt temperature is above 200 F.

What I did was checked the MSDS sheets on all the materials first to see what their flamability was. None of them have a flash point below about 400 F (450 F I think). And none of them have an Auto ignition point below @800 F.

I bought the wax from a craft store (in granulated form) and the PE was bought in sheet form from Sears as a painters drop cloth. It was about a dollar for half a pound of the drop cloth and it was only 1 mil thick so it disolved fairly easily. I then heated the wax to 300 F as recommended, and the PE dissolved ok. I tried the hot glue and HDPE on various batches and ended up taking the wax to almost 480 F (with no incident). I adivse extreme caution with this. I was working with only a few ounces of wax as a trial and found that increasing the temperature does not much change the solubility of HDPE or Hot glue. Both of which acted similarly in the mix, they globbed up and only part of them dissolved. I suspect what happens is the shorter polymer chains dissolve and the longer ones are left behind, as when I fished them out the resulting plastic was fairly brittle compared to the initial plastic. In any case the results were interesting, I'm thinking about casting a few round bars and having them tested locally to see what the properties are like. The PE definatly works and if i had to do it again I'd order bulk wax granuals and then order the PE in granular form. Though the method I used is probably the cheapest. I also added blue die just to make it look like the real machinist wax (that I have seen). Hope this helps.

As a last note I tried variations of the ratios... 4 parts wax to 1 part PE seems to give a nice material.

I have made a pneumatic injection molder and , I am using plastic bottles and such to familarize myself with different tyes of plastics.

My big question is, what is an easy way to grind up plastic bottles into small pieces to feed into the injection molder?

I cant seem to find any info on this. Does anyone have any advise or direction to point me.

I dont want to buy bulk material yet, since I am still experimenting.

Thanks!