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Working with Lexan
Last season, our team used Lexan (polycarbonate) to shield the electronics from damage. We found it easy to cut, bend, de-bur, and generally pretty good stuff! But it's a pain to drill!!!!!!!!!!!!! Especially when trying to drill large holes in it to remove weight. We tryed a hole saw with poor results and regular twist drills were problematic as they get past 3/4". Any suggestions? :ahh:
Phil Paspalas Head Coach - Team 1676 The Pascack Pioneers 2005 NJ Rookie All-Stars |
Re: Working with Lexan
try lubricating the drill bit with dish soap, it generally produces good results
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go pick up a set of step drills and use them they will make life alot easier! I suppose it is possile to just use 5 different bits in and step up through them but a step drill will be alot faster and a sharp one will go through lexan like a hot knife through butter! in '04 I personally drilled almost 6000 3/4" holes in sheets of lexan for our bot (we didn't use them as they were still too heavy and if we drilled anymore holes we wouldn't have a side panel lol!!)seriously though get a set and go at it its faster then you think and quite easy!
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The problem with working with lexan and any other plastics is that they tend to melt before the bit actually chips away at the material. An easy solution for cutting plastics is to turn the drill bit or hole saw slower, this makes less heat and there is less of a likely hood of melting. Alot of lubrication on the bit and material will help as well.
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So, in your opinion, would lexan or another polycarb be a good choice for the outer shell as well? Some of us think we might want to try and do something like that, because it would make the visibility requirements on the controller and ball bin a lot easier, and would make good protection. We're a rookie team, though, and since we don't have any experience in how rough things might actually get, or how much the polycarb would cost...
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load bearing or going to take hits 1/8" or larger non load bearing plates for numbers and such 1/8" or smaller. The uses of lexan in FIRST basically come down to how flexible you can accept during use because even with the forces involved in robot collisions i have seen very little polycarbonate break. So the thicker it is the less flexibility you have and vice versa....Plexiglas is another story all together. |
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Good luck on your rookie year and feel free to post up if you have questions about anything. ~Kirk |
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not true anymore..the restrictions on acrylic and plexi were lifted last year. |
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For safety reasons, I would never allow plexiglass on a robot. Polycarb only. IMHO, FIRST is making a mistake in allowing plexi...
The "step" drill referred to above is usually called an omni-bit. Omni-bit may be a trade name but any hardware store will know what you are looking for. It drills through polycarb like butter. |
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I agree whole heartly with you i think they did this because sometimes teams only have access to specific materials and plexi is still more common and cheaper then lexan/polycarbonate. |
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~Kirk |
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Alright, awesome. Thanks for the advice, did I mention you guys are the best? lol... I'll be showing up now and again, count on it
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White or frosted transparent: Acrylic (plexiglas) Blue frosted: polycarbonate From what I recall, polycarbonate has a "blueness index". The higher the number, the more blue tint it has. Since 1963, when Dan Fox at GE invented LEXAN, this "blueness index" has gotten lower and lower. Andy B. |
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You have peaked my interest... I know that you can order "optical quality" polycarb which, as I recall, is very clear. We have some at the school. I'll check tomorrow evening and see just how blue it is. Mike |
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I would use a sheet metal brake rather than pliers and, whichever method you use, please wear safety glasses! Mike |
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~Kirk |
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I am sure that every single person who is reading this note owns some "optical quality" polycarbonate. This style of polycarb is extruded in a clean room and the molten plastic is pushed through a filter. Who can guess where this "optical quality" polycarbonate is used by everyone? (15 years ago, I was a co-op engineer at GE Plastics. The Mt. Vernon, Indiana plant extruded 1,000,000 lbs. of the stuff PER DAY back then. I can still recall the sweet smell of Methylene Chloride.) Andy B. |
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*ding*
Is it the 40 amp fuse block? *buzz* (see reply below) |
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oh, heck, I'll give the answer... it's a compact disc. CD manufacturers seemed to be the most concerned about optical quality. Andy B. |
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Wow... thats new. Though it does make a lot of sense, now that I think about it...
Does anyone have an idea for where a good place is to get this stuff? Lexan, other polycarb, or plexi even, though I know some of you dissaprove of it |
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Your local Home Depot may also carry Lexan, I know ours does.
JT 229 |
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Many teams will not have access to these methods, but:
Lexan (polycarbonate) is easily cut using a water-jet. Plexiglas (acrylic) will probably shatter if you try to water-jet it. Conversely, Plexiglas (acrylic) is easy to laser-cut, although it does create a stink. Lexan (polycarbonate) should not be laser-cut because its fumes are toxic. My team has one sponsor with a water-jet machine and another with a laser-cutting machine. We found out about the differences above through some trial and error. |
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We have used polycarbonate in our electronics enclosure for the last 3 years and have never had a problem with it. We used 1/4" thick for a base to hold our electronics down and 1/8" thick for doors. To stop melting polycarbonate, slow down your hole saw. When drilling "lightning" holes in polycarbonate use more smaller diameter holes as it will keep other robots from finding the hole and hitting your electronics. |
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We've used Lexan for just about everything at one time or another. The best way for cutting/drilling holes that we've found is to use WD-40 as a lubricant.
Have someone spray it onto the bit while you are cutting/drilling. You have to keep the bit cool. Once the Lexan starts to melt, it grabs the drill right out of your hands. Been there, done that. Ouch. Also, If you have any plans on screwing into the stuff, we've found that drywall screws work very well. You have to drill a pilot hole and use lithium grease (or some other lubricant) on the screws. If you are using a drill to drive the screws, be sure to set the torque limit down to about 6. You will shear the screws and they are not fun to get out after that. |
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Another thing about poly carb is that if you are planning on using any kind of loctite DON'T. We made the mistake and the poly carb actually developed hairline cracks leading out from the center of the hole.
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I didn't see it specifically addressed anywhere in this thread (except in the Andy Baker "blue" index), but all polycarbonate is not the same. We have found a huge difference in Lexan brand versus other generic polycarbonates and the name brand is worth the price difference in terms of machinability and strength.
We love the stuff - it absorbs energy like crazy during the "rigors of competition". The self-tapping drywall screws work very well if you follow the instructions Warren gave for pilot hole and Lithium grease; using .375 thick Lexan you can mount into the edge and it makes a nice butt joint. And the loctite issue Kirk mentioned - been there and done that too. It causes some sort of thermal reaction while curing that shatters the lexan from the inside. |
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a. There are only a handful of places where polycarbonate resin is made. This is done in chemical plants, with huge capital costs and very big environmental considerations. Polycarbonate resin looks somewhat like white grape nuts, but a bit smaller. b. Resin is sold to extruders or compounders. Some extruders make sheet, some make plastic pellets. Sheet is cut and sold to end users. Plastic pellets are sold to molders. Compounders mix other things with resin to make co-polymers or other special applications. They may mix in other materials (fiberglass, micah, other plastics, etc.) or they may filter it to make specialty grade products. Like anything else, resins are tested and graded. The best resin sells for a higher price. Lower grade resin sells to lower prices, of course. Some companies focus on the high grade stuff while others sell cheaper grade material. These companies usually list the mechanical properties of their materials, like this for LEXAN 101R. You can compare other polycarbonates by looking at elongation, hardness, fatigue, and other ratings. Andy B. |
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What are you drilling with? You using an actual drill or have you tried a milling machine perhaps?
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is acrylic easy to mill? anything i should be careful of?
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You just have to have skill to work with acrylic. HAHA
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A good suggestion for electronics and lexan is to mount the actual electronics (Victors, Controller, etc.) on a plank of wood (lighter), and just cover it with a sheet of Lexan. The electronics are still protected and you don't have to worry about drilling lots of holes in the Lexan.
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If you are working with acrylic every time you try to drill it, bend it, or screw into it you are risking it cracking if not shattering. Acrylic was not allowed for use on FIRST robots for a while because of this. Personally I don't know why they changed the rule. Acrylic can be dangerous if you do not know what you are doing. Because of this we do not allow it on any of out robots or even in the shop. If you can help it just stay away from the stuff. You guys will be much happier with the results you get from working with polycarb. Kirk |
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