A pox on acrylic.
A few months back I bought a laser cut acrylic plate for prototypes. Well it was easy to bolt things to it, but a piece snapped off with little strain. Acrylic it seems is brittle and prone to breaking, but it also seems to take well to glue, perhaps it is a wash.
Comments
I prefer PVC and can find many sizes and shapes in the scrap bin at a local plastics supplier.
@
Ok, that's actually one word but it's more dramatic that way! :0)
edit: W9GFO beat me to the punch.......
-Phil
You can perform a simple test to verify if you have cast or extruded. Light a piece on fire - if it drips little fireballs then it is extruded. If it just burns and crackles it is cast.
Also, cast generally has paper backing and extruded generally has plastic baking. Don't know if that is always the case though.
+1, as long as you stay clear of extruded plywood, which is similarly brittle.
-MattG
-MattG
http://www.terasic.com.tw/cgi-bin/page/archive.pl?No=593
An alternative to acrylic is fiberglass reinforced plastic, which is more durable and resists breakage. It's not as fun cutting and drilling it, and requires eye and face mask protection. I use a material that accepts printed full color images, which are then routed out (or vice versa, routed then printed). The process is similar to how they colorize surf boards. The 0.090" thickness is pretty good for smaller robots. Larger bots will need thicker plastic, or two plys.
I'm not sure how well FRP laser cuts, not having a laser cutter (boo hoo). It easily withstands 400 degrees, so I imagine it takes a lot of watts to pierce it. Probably better to waterjet it. I don't have one of those, either.
-- Gordon
-- Gordon
BTW, G10 cuts wonderfully on a CNC mill using a router bit designed for printed circuit boards.
My absolute favorite material to laser cut is acetal copolymer (like Delrin). It cuts very cleanly and even smells nice as the laser is slicing through it. But it's not as stiff as acrylic, plywood, or reinforced plastics. So it's less suitable for larger structures.
-Phil
Go easy sniffing those melting delrin fumes, pal. I've had a few whiffs of burning delrin (go figure!) and it burns eyes and lungs.
From http://www.ifa.hawaii.edu/instr-shop/MSDS/Delrin.pdf :
Heating PTFE above 300 degrees C may liberate a fine particulate
fume. Inhalation may produce polymer fume fever, a temporary
flu-like condition with fever, chills, nausea, shortness of
breath, chest tightness, muscle or joint ache, and sometimes cough
and elevated white blood cell count. The symptoms are often
delayed 4 to 24 hours after exposure. These signs are generally
temporary, lasting 24-48 hours and resolve without further
complications. However, some individuals with repeated episodes
of polymer fume fever have reported persistent pulmonary effects.
Protection against polymer fume fever should also provide
protection against any potential chronic effects.
It probably isn't the same. The stuff I'm talking about is what they use for shower and bath tub liners. I don't think it's as dense. Often has a "gel" gloss (sometimes matte) coating. One side may be smooth, and you can see the fiberglass bits embedded into the plastic, and the other side may be smooth or rippled. They also may use it for walls in public bathrooms as a substitute for ceramic tile.
I don't like to router fiberglass because the dust contains little itty-bitty pieces of glass ... though I guess that small it's back to being sand.
-- Gordon
I use a water based sanding sealer that takes all of about 20 minutes to dry. I also use Deft clear wood finish in spray can that dries even faster.
Are you sure its Delrin? Delrin is absolutely the nastiest thing I have ever cut with my laser. Oh it cuts nicely but if I don't leave the fan running and the lid closed for a couple minutes to evacuate all of the fumes the slightest whiff of it burns the eyes and is sharply painful to the nasal passages.
-Phil
Say what you will, I'm homopolymerphobic.
I know this is an old post but I wonder why you didn't recommend expanded PVC (ePVC)? I know you use it with some of your kits and based on things you've said about ePVC, I decided to try it myself. I really like the stuff.
It does dent easily but I think it's plenty sturdy for most hobby robots. I'm using ePVC (aka foamed PVC) on a treaded robot I'm attempting to make (I know you've already seen this Gordon).
It took a long time to cut out all those parts so I'm postponing future work until I get my CNC router up and running. The CNC router is taking a while since I'm stubbornly trying to program the controller myself.
But even without a router, the ePVC is really easy to cut. The parts shown above were shaped with a Dremel, belt sander and X-Acto knife. I think ePVC is a lot easier to use than other plastics.
BTW, I have a Magician robot. It's still in pieces (one more piece than the original kit). One of the pieces broke within the first few minutes of beginning to assemble the robot. I think I prefer paper backed foam board over acrylic for building robots.
Edit: Just in case any of you don't already know this, don't cut ePVC (or any other PVC) with a laser (not that I have laser cutter but I've read this warning a bunch of time from reliable sources).
humans (HCL, Cl2, and so forth). The reason acrylic is so popular is because it laser cuts extremely well and doesn't clog up filters.
It you want tough then polycarbonate is a good choice, but it doesn't laser cut well at all (I've seen recommendations to cut only
1mm sheet or thinner) It also has traces of chlorine due to the manufacturing process so proper ventilation is mandatory.
So if you are able to mill, go for polycarbonate, otherwise acrylic / laser plywood. Acrylic can be machined with care, you have
to avoid overheating it and melting it as well as avoiding mechanic overload. Delrin is great, but expensive and available in
a more limited colour range.
I mention PVC from time to time, but don't want to be a broken record about it. Sometimes people have a reason for using acrylic, such as intending to laser cut it. Suggesting PVC for users of laser cutters isn't being a good citizen!
One thing often overlooked with expanded PVC is its weight. Polycarbonate, masonite, and other materials are quite dense. They're strong to be sure, but not all small robots require it. You get more play time with a lighter robot. It's a nice solution for lighter robots that don't require their structural strength from the plastic material alone.
I'm impressed with what you were able to do with hand cutting. Those mortise and tenon joints look clever. You'll enjoy doing them with your CNC, though be prepared for some trial and error to get everything to fit. Be sure to get a 1/16" 2- or 4-flute end mill for anything with a tight inside radius. My standard tool bit is 1/8" 2-flute. It's more coarse, but with medium to darker colors, it means the sharf from the plastic is in larger bits. You will rue the day you started cutting light-color PVC with a small diameter 4-flute bit. The dust is finer than sawdust, and definitely not as pleasant.
Thanks, I learned how to make careful cuts by hand from the Ron Czapala School of Carely Cutting Front Panels by Hand.
Thanks for the advice. I don't think I have a 1/16" end mill (not with the right sized shaft anyway). I'll order a couple of those.
I'll need to think about what to do about the dust. I know the stuff can get everywhere from my experience of shaping a lot of pieces on a belt sander.
A little vaccum attachment that gors around the bottom of the router is best. I wish I had that, actually, but my CNC is fairly small, and there's not much room. So instead I hold the nozzle from the ShopVac right at the cutting bit. It gets 95% of the dust.
I also recommend a face mask.
Up until recently Home Depot carried some very nice 1/8" MDF. Very light colored and laser cut really well - the edge was light brown. Now I am in a bit of a bind trying to find a substitute...
Their new Shadow chassis looks nice. Their gearmotors are also redesigned with an extended motor shaft which can be used for a motor encoder. But IMO it's a shame they stuck with the same 1:48 gear ratio which makes an encoder necessary. Two steps forward, one step back.