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

try lubricating the drill bit with dish soap, it generally produces good results

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!

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.

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…

As a rule of thumb about lexan/polycarbonate:
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.

Poly Carb is great for protective panels. If you have supports under it you can go as thin as 1/16" which is what we usually use. Poly Carb is very good for resisting puncture and will not crack. One warning MAKE SURE YOU GET POLY CARB most stores will sell acrylic as poly carbonate. Acrylic is not only not allowed in first but is breaks like glass when it is impacted or bent.

Good luck on your rookie year and feel free to post up if you have questions about anything.

~Kirk

not true anymore…the restrictions on acrylic and plexi were lifted last year.

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.

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.

For those teams that don’t know how to tell the difference between the two, the best way to tell is take a pair of pliers and try to bend a corner. If it bends like a piece of soft aluminum its polycarbonate if it cracks or breaks its acrylic.

~Kirk

There is nothing like Brute Force Testing to come to a very quick answer. :eek:

Other wise its pretty hard to tell them apart if the wraping has been removed.

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

Yet another way (and probably the easiest) is to look at the edge of the sheet of plastic.

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.

Andy,

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

Kirk, et al,

I would use a sheet metal brake rather than pliers and, whichever method you use, please wear safety glasses!

Mike

When doing any type of drilling in Lexan, it is best to leave the protective paper coating on (both?) sides. This prevents most cracking, and allows a cleaner cut/hole to be made.

Of course you should always wear safety glasses. :smiley: I was just trying to give them a quick and dirty method to tell the difference. We have been at multiple regionals where we needed some poly carb but we have been given acrylic.

~Kirk

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.