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Questions about working with plastics.

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Triode

Active Member
For building robots around the size of an RC car or a desktop computer, I am trying to learn what kinds of plastic would be practical to work with at home. And which methods people here find easiest. Using legos, wood and cardboard are getting old and I can't weld in my apartment.

I want to build things like RC tanks, little robotic arms, maybe a robo router that uses a dremil tool, but that last one will be later, for now I want to learn plastic working for small stuff. There is a lot of information online, almost too much to tell whats good for my applications. I've read about plastic welding, but most of the reccomended equipment is in the $300 which is more than I want to spend for now, however cheaper welders are usually not reccomended, and glues are reputed to be pretty weak.

So, what kind of plastic is good to work with? I'll be cutting it, bending it, and either gluing or welding it. Right now I don't intend to do any forming or moulding. It seems that a lot are pretty easy to bend and cut (though that can be a problem with some) but which kind can be fused well, and how would be my first question.

directing me to links to usefull tutorials is welcome, im not asking to be fed the whole thing, but some direction is much appriciated.
 

Hero999

Banned
What about vacuum forming?

I used to do it at school and it's supposed to be easy to make your own vacuum forming machine.
 

Triode

Active Member
I've read a few how-tos on that, it looks interesting, and if i really get into plastic working I may try it, but for now I'm just wanting to do housings, chassis, frames and the like. But if you have any advice about forming or moulding, or any reccomendable tutorials, those are welcome here as well.
 
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Chippie

Member
HIPS....High Impact Plastic is generally used for modelling..its cheap and can be vac formed..and is available in various thinknesses, oh and can be joined with MEK( Methyl EthyleKetone) solvent adhesive(just dont go sniffing it... :) )
 
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HarveyH42

Banned
Acetone can be used to bond plastic to plastic, and its fairly strong. Styrofoam dissolved in acetone to a paste consistency, works good to fill in gaps, and add strength. Plus its easy to find, and cheap.
 

Triode

Active Member
I've heard of bonding plastics with solvents, but I don't think it works on all of them. When I was working with that hybrid racer team we tried to use some solvent to bond what I think was a type of acrylic, and the bonds ended up being very week even with 3 days of curing. One of the things I'm hoping to find out is which plastics weld well, and which ones can be bonded with certain solvents or glues.

Thanks for mentioning the High impact polystyrene. Id seen so many types of plastic mentioned that didn't stand out. But from what I've read about so far it sounds good to work with. It should be bendable and from what I've found it can be fused with solvents or glues and can be welded. It also is said to cut fairly cleanly. So I'm going to read about it more, but it's looking like it could be what I want.
BTW, here's a document I found about available ways to bond polystyrene, its short and to the point
 
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kchriste

New Member
Forum Supporter
Have you looked at shapelock mouldable plastic?
 
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kchriste

New Member
Forum Supporter
No. But I've noticed it on several robot sites lately. Don't know how well it works with things that get hot due to the low melting point, but I'm sure it has it's uses.
 

arhi

Member
For building robots around the size of an RC car or a desktop computer, I am trying to learn what kinds of plastic would be practical to work with at home. And which methods people here find easiest.
I use RapMan made by Bits From Bytes as it is perfect for making robot parts. You design parts in 3d cad program and print them in 3d using RapMan :D. RapMan uses different plastic filaments, most popular and one of easiest to work with is ABS. The parts printed are very strong. I also use HDPE and PP as those are easier to obtain here, but if you do not need high temperature stability you can use PLA filament that is even easier to work with then ABS.

You can see some pictures of the printed objects:
my picasa album
some printing examples

RapMan uses electronics that is based on PIC and firmware written in C that is going to be open source. It reads the G-CODE file from the SD/MMC card and prints the object extruding plastic filament layer by layer
 

jpanhalt

Well-Known Member
Most Helpful Member
Interesting subject. Here is my experience from a few years. Remember with adhesives, surface prep is extremely important. With solvent welding, be sure to get the solvent recommended for the plastic you are using. Other solvents may seem to work (e.g., pure chloroform or methylene chloride), but will result in poor welds.

TEFLON(ptfe) -- mechanical fasteners (watch out for cold flow); adhesives after chemical surface etching; cannot be solvent bonded; never tried welding.
NYLONS --use mechanical fasteners (strongest) or adhesive; cannot be solvent welded; some claim to be able to weld it, but I have had poor luck doing that.
ACRYLICS -- mechanical; works poorly with common adhesives; can be solvent welded, but tends to craze later; never tried heat welding; good for vacuum forming.
POLYCARBONATE -- similar to acrylics, but even more difficult to bond.
POLYESTERS -- adhesives and heat forming.
EPOXY FIBERGLASS -- usually cast before polymerization, but can be heat formed; takes epoxy and cyanoacrylic adhesives well.
DELRIN -- no experience other than mechanical fasteners; might be weldable.
POLYURETHANE -- mechanical; it is heat weldable.
POLYSTYRENE --solvent or heat welds fine; thermal forming.
ABS --almost any method works; heat welding and solvent welding are good.
POLYOLEFINS (e.g., polypropylene) -- heat welding; cannot be solvent welded; mechanical fasteners; if the surface is properly etched, adhesives will work, but heat welding is preferred.
POLYSULFIDES--I have limited experience bonding them; have used cyanoacrylic adhesives and contact (Pliobond) adhesives.
PVC/CPVC (polyvinylchloride) -- even easier than ABS to work with; solvent welding and adhesives (particularly 2-part acrylics) work well.
COROPLAST -- like PVC (it is a high density PVC); I have used 2-part acrylic adhesives; never tried solvent welding; this material comes in nice sheets like a plastic version of corrugated cardboard.

Other information: go to McMaster.com and search on "bonding plastics." There are specialized adhesives for bonding almost anything. Unfortunately, the preparation and cost is often not practical for individuals.

John
 

Triode

Active Member
Thanks jpanhalt, thats the kind of information I was looking for. From your description, since I am planning on making frames, apendages and housings out of bent sheets, it sounds like Polystyrene, ABS or PVC would be what I want. But I am still unsure about the best bonding method, it has to be reasonably strong, but also affordable, I thought solvents were a faily cheap option, but you mention them being costly. I know that a temperature controlled plastic welder can be fairly expensive. I'm also going to have to look into the cost of the plastic sheets themselves. Though there is actually an industrial plastic supplier with a will-call where people can buy smaller quantities fairly near where I live, so buying it shouldent be too hard. But as you suggest I'll look up the bonding agents and see what they seem to cost. Aren't there some that can be bonded with regular solvents, such as acetone, with a bit of the base plastic dissolved in it?
 

jpanhalt

Well-Known Member
Most Helpful Member
PVC is the same material that is used for plastic pipe. Yes, MEK and acetone will soften it and may work. I would still use the solvent that is sold for it. This is solvent welding and is quite strong. I use PVC and CPVC rods, sheet, and pipe for all sort of projects. PVC does not support weight very well.

Polystyrene is what was/is used widely in scale model airplanes, tanks, etc. Most hobby shops will have a water-thin and a thickened version of "adhesive" for plastic models. Both actually produce a solvent weld too, are quite strong, and I suspect they will work for both polystyrene and PVC. However, I have never used it for PVC, because the stuff sold specifically for PVC and CPVC works so well and is inexpensive.

ABS -- This is a bit more difficult to solvent weld or to make adhere with an adhesive, but is still quite easy compared to the really difficult plastics. It is stronger than PVC for supporting weight. An adhesive/welding solvent made from chips of ABS dissolved in methyl ethyl ketone (MEK) is even recommended for repairing interior parts of some full scale aircraft. Acetone will probably work, but MEK is less volatile and a little easier to work with.

For your siding and boxes, you may want to take a closer look at Coroplast. It is extremely durable and the corrugation gives it a special look you will learn to love. It is available in various colors; white is most common. It is getting used more and more in consumer markets. I have seen garment storage boxes made from it at home stores. I use duct tape (really) or gaffers tape (very similar) to hold my boxes together. A two-part flexible adhesive will also work. I use an acrylic, as mentioned above, but it would be worth trying a polyurethane ( e.g., Gorilla glue) available in home stores. It is so impermeable to water that you will need to mist one surface first before assembly. As for price, it is really cheap. I pay about $8 per 4X8 ft sheet at an industrial supply for packaging. Craft stores sell it for several times that amount per sq ft, but it is still relatively cheap compared to ABS.

John
 
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Triode

Active Member
It sounds like for my purposes using either PVC or polystrene for the parts requiring more strenth, such as the sides of an arm, or the chassis of a car, and Coroplast for larger parts and ones that would be curved, like body panels. So the solvent for Polystyrene and PVC is inexpensive? That makes sense, I just though earlier you said that the preperation costs were high, I wasn't sure what you meant by that.
 

arhi

Member
Triode .. you can also think about plexyglass (ACRYLICS). It is light and "strong", very good for base / holders, it can withstand much more heat then PVC/ABS..

Now, it is more brittle then PVC/ABS but IMHO much better. You can easily get the "plates" of different thickness (1mm - 20mm with 1mm step is available in shop near me for example in tables up to 2m x 6m).

Bonding acrylic is
- nuts & bolts :) - this is my preference way of bonding acrylic as it can be disassembled quickly and easy
- liquid acrylic - this is 2 component glue, one part is honey like mass and the other is powder that solidify it. You can both use liquid acrylic as a glue to weld/glue two pieces of acrylic or you can pour that into a mould to get a piece you want. After it sets (few hours but depends on the hardener) it becomes just like any other acrylic so very hard. 1Kg of liquid acrylic in local store is ~10US$ so I'd not say the price should be the problem, and I recon it should be cheaper in USA then in this god forsaken land.

Working with acrylic is very easy, sands nice, you can cut it using dremel disks or with a saw... you cannot use the nibbler for the holes (it will break) and you have to pay attention when drilling holes as you cannot drill big holes from the first go .. you have to drill small holes first - also you need lot of rpm :) but dremel should handle it with no problem.

of course acrylic being available in transparent + many (semi transparent to transparent) colors is additional bonus :D
 

Hero999

Banned
A bit off topic but beware that mixing polystyrene with petrol makes napalm which is very dangerous if ignited.:D
 

Mr RB

Well-Known Member
It sounds like for my purposes using either PVC or polystrene for the parts requiring more strenth, such as the sides of an arm, or the chassis of a car, and Coroplast for larger parts and ones that would be curved, like body panels. So the solvent for Polystyrene and PVC is inexpensive? That makes sense, I just though earlier you said that the preperation costs were high, I wasn't sure what you meant by that.
Sounds like you need vacuforming, look up "DIY vacuforming press" or similar. That will make your body panels, and maybe chassis parts too since once the thin sheet is formed into curved/bucket type shapes it gets very strong.
 

arhi

Member
hero, we agreed not to give terrorist tips on the forum :D :D :D

Mr RB, not sure how feasible vacuforming press is for "home builders" as I did not see any vacuforming press you can use in house, you really need a real workshop area for that.
On top of that - in order to vacuform he need to make a mold first .. it can get fairly expensive at the end ...
 

Triode

Active Member
I've read about vacuforming, but for now I'm just planning on making frames and housings by cutting plastic sheets into shapes, bending them in places, then welding them via some method. I will also drill holes in it and use bolts in places, but almost all plastics allow for that. I'm trying to keep this practical and fairly cheap. I don't have a huge amount of room or a garage, so vaccuforming isn't a good option for me, and right now I don't think its necesary to make the kinds of things I'm thinking of. Likewise, while I would like to make a CNC cutter some time, that also requires a good amount of space and resources. I'm limited not just by room, but that in an apartment you cant do work that makes a lot of noise, makes a big mess, emits a lot of fumes, or uses flame and gas. If I could do that stuff I'd just get some angle iron, a chop saw and a welder and make whatever I like :) So thats the reason that for now I'm thinking some plastic housings that are simply cut, bent and fused with heat or solvent, would be a nice quiet relativly clean way to build some things, that I could do on the craft table next to my workbench.
 

arhi

Member
planning on making frames and housings by cutting plastic sheets into shapes, bending them in places, then welding them via some method. I will also drill holes in it and use bolts in places, but almost all plastics allow for that.
Check what is the easiest plastic to get near you. You can find sheets of plastic, different thickness in many stores ... the most common is PP, HDPE and Acrylics. PP is cheapest, HDPE is stronger then PP and more resistant to high temperatures, Acrylics is lighter and stronger the PP and HDPE but is very brittle so not as easy to work with as PP & HDPE. ABS is great for extruding but for working with sheets, I advice PP or HDPE or Acrylic depending on what you need. You can mix them of course.

I'm trying to keep this practical and fairly cheap. I don't have a huge amount of room or a garage
That's why I mentioned RapMan:


video:
YouTube - About the RepMan

does not take too much space, no fumes, no gas, no vapours ... you can see on this guy video how big it is and how it works ... the only problem is price .. if you want to get a full kit it will set you back some 700GBP ... if you make it yourself, you can go much cheaper (~300E)
 
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