pic: Team 3688 Lexan Line Bender 12 volt



It’s about 17 inches clip-to-clip.

The 20-gauge nichrome wire was sourced on eBay.

The circuit should be fused for 20 amps.

The one we made was modeled after this one:

This is cool, especially with the construction video. Thanks for sharing! I actually need something similar to this for work… you may have helped me save a good chunk of my project budget :smiley:

Can you post a few lines on how you use it?

How do you hold the plastic in place? Do you use a form/guide to give it the curve you want?

Sure!

First, though, a note about heat: The nichrome wire should glow orange-red when it’s hot enough. If it doesn’t get there, then either the voltage is too low or the wire (a resistor) is too long for the available voltage (ohm’s law).

OK: the acrylic/plexiglass/lexan is placed over the wire channel, as shown in the photo. For a sharp, consistent bend, (and for small pieces) it’s sometimes helpful to place a piece of wood on the half that will not move during the bend.

Depending on thickness, it can take a half minute or more to get hot enough to bend. You’ll know. If you try too soon, you’ll get an uneven and unpredictable bend; if you wait too long, the plastic will bubble and get thin, decreasing its strength.

When ready: if working alone, disconnect the power supply and quickly fold the hinged half up to the desired angle. Hold it there until the plastic has cooled and regained strength. If not working alone, then you can take a bit more time making the bend and then have someone disconnect the power while you hold the bend.

Pretty simple, really. Still, it’s a good idea to practice on some scrap pieces first.

BTW, this thread had it’s origin in “Uses of Lexan”: https://www.chiefdelphi.com/forums/showthread.php?t=150980

As mentioned in the mother thread, this video served as our inspiration:

I just noticed that in the comments accompanying it, the author posted a video of it being used:

Acrylic and Polycarbonate (Lexan) are two very different materials, and bend in very different ways. For acrylic, this technique works very well. However, acrylic is brittle and prone to cracking, and I cannot think of any application where it would be suitable in an FRC robot.

Polycarbonate on the other hand is very resilient. We simply bend it on a sheet metal brake, cold, just as you would metal, and it comes out great. You just have to overbend to compensate for the spring back.

We do something similar although we actually heat a line first and then bend with our brake. It makes a perfect bend every time. We use one of these http://www.delviesplastics.com/p/Stripheater.html but you can obviously just build something like 3688 did.

Excellent! We’ll bring a sheet metal brake with us to our next competition :slight_smile:

Thanks for the help!

We don’t have the resources for a sheet metal bender… But this bender cost us very little and serves us well. Being portable doesn’t hurt either.

Also, we use our acrylic supply to test our ideas before using the precious lexan.

Once you understand the difference between acrylic and lexan, why do you let any acrylic within a mile of your build site? It can only end in tears.

I’ve heard of teams prototyping with lasercut acrylic because polycarbonate absorbs infrared radiation and can be a pain to cut. Acrylic is usually cheaper and just as easy to find.

If you’ve got a laser cutter, plywood cuts great and is way cheaper than acrylic. And it’s lighter and more resilient, so you can make your whole robot out of it. :wink:

The lexan bender is really cool though.

It’s only for prototyping shapes and never gets stressed or used in a competition. We use it because we have it.

Still useful for non-contact display items. Example - laser cutting team awards. Less uses but certainly still viable as a material.

Nice job on the bender, OP.

I’ve had success bending Polycarb using a vice and a pencil torch. It takes a careful, steady touch to get the material melted without bubbles and I haven’t yet found it to be a good project to hand off to the students. Making a bender instead will make a nice little project for newer students.

On Acrylic, I agree: avoid structural applications. But we’ve found through some industry expertise that the optical qualities of Cast Acrylic are far superior to Lexan/Makrolon/polycarb. We edge-light an etched panel of cast acrylic and it’s typically the best-looking part of our robot.

I’m applying my safety hat here from work… How hot does that wire get when powered? Also, should there be a cover over it to prevent accidental contact? Burns Hurt.

EXACTLY.

It gets really hot. I suppose 1500F or so. We require that each student who uses any apparatus or tool have proper training as well as mentor supervision. Moreover, we are a small, rural school and most kids here still have a lot of common sense.

But you raise a good point. I’ll put a warning label on it.

Usually, cracks, not tears. Thanks for sharing!