Polishing optics milled from acrylic

acrylic-optics-finish-testing

[Ben Krasnow] milled some lenses out of cast acrylic and needed a way to get an optical finish on the tool-marked surface. He tested several acrylic finishing methods to achieve a crystal clear finish. The tests were done using flat chunks. A regiment of sandpaper, from coarse to fine, was used as the first stage of the operation. From there [Ben] sought out the best finishing step, starting with hand polishing tests, flame polishing, and methylene chloride vapor polishing (which is something along the lines of acetone vapor polishing for 3D printed ABS parts).

Flame polishing and vapor polishing are not really exact sciences… at least in the tests he performed. It was difficult to know exactly how long to expose the acrylic. Too short or too long resulted in poor clarity. Watch his video to get a look at all results. We’d say the the easiest way to make milled acrylic clear without achieving an optical finish is to flame polish it as it doesn’t really require that you sand it ahead of time. But [Ben's] tests prove that you can’t beat hand polishing with 600 then 2000 grit sandpaper before finishing up with a liquid plastic polish.

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Bending materials with a simple hot wire forming tool

bending-with-a-hot-wire-former

Regular reader [RoadWarrior222] has watched as we’ve featured several projects that show how to bend acrylic. But so far he hasn’t seen us cover his favorite technique developed by [Dale A. Heatherington] which uses a hot wire forming tool to make precise bends. The tool is simple to use plus it’s cheap and easy to build. It’s a great choice if you don’t have a heat gun, and it may be possible to make cleaner bends than other techniques.

The business end of the bending tool is the red-hot Nichrome wire running through the aluminum channel. That channel is used to protect the MDF and act as a spacer so that the wire doesn’t touch the acrylic. On the near side the wire is anchored with a screw, but on the far end it is kept taught by including a spring. The wire heats up as it is connected to a 12V battery, but since the heating is cause by the wire’s resistance it will only get red-hot in between the alligator clips providing power. To make sure your bends will be perpendicular to the edge of the acrylic there’s an aluminum guide strip on one side of the MDF platform.

You can salvage Nichrome wire from an old hair dryer. If you have any left over it’s great for other projects like building a CNC hot-wire cutter.

Acrylic enclosures use integrated clips to do away with fasteners

acrylic-clip-lock-enclosures

Here’s a design that lets you make acrylic enclosures without using fasteners. The red outline in the diagram above is a bit hard to make out. But look closely and you’ll realize that there is very little material which has been removed to form the clip. This uses the rigidity/flexibility of the material to form a spring that will hold a couple of pieces tightly together.

In a links post last year we looked at [Patrick Fenner's] fantastic analysis of the strength of using kerf-bending to form several sides of a case out of one piece of material. He’s used that same analytic expertise to take a look into this design. He even suggests that making the cut on the hook-side a bit deeper will help improve the resilience of the part. If you have a laser cutter on hand and want to give this a try he’s posted the plans on Thingiverse.

Airsoft turret has turn, tilt, and auto-feed to keep those BBs flying

airsoft-turret-with-laser-cut-parts

Yet another project that proves you need to acquire a laser cutter. This Airsoft turret rotates, tilts, and includes a hopper for ammo.

All of the pieces were cut from acrylic. The base includes a bracket which keeps the large rotating gear level by sandwiching it between the layers. That and the tilt mechanism are pretty straight forward. The module responsible for loading the BBs is pretty neat though. It uses a gear with round teeth the same diameter as the ammo. Once a BB is picked up it is forced upward into the tubing that feeds the gun. Get the full picture from the demo video after the break.

The one thing [The Liquider] is wondering about is how to provide feedback for the tilt and rotate functions. We can’t think of an easier way than to use simple rotary encoders. The Arduino Mega he wishes to use as a driver will have no problem interfacing with reflectance sensors and the acrylic makes it simple to mount this type of black and white encoder wheel.

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Heating, bending, and gluing to make acrylic enclosures

acrylic-enclosures-heating-bending-gluing

You can do a lot with acrylic and few tools. If you’re just starting out we’d suggest taking a look at [Michael Colombo's] guide to heating, bending, and gluing to create custom acrylic enclosures. Chances are you already have most of what you need. The one tool you might be lacking is a heat gun.

The process starts with math. Before cutting the acrylic down to size you need to calculate how much you need. Next [Michael] demonstrates his cutting technique using a Dremel and a cut-off wheel. We prefer to clamp along the cut line, score many times with a razor knife, and snap the stuff. But you can also send it through a table saw if you have the right blade.

The bending technique he uses starts by clamping boards on either side of the bend. The acrylic left sticking out is pushed with a scrap board while the bend is heated with the heat gun. Once all of the corners were made in one piece the sides were glued in place. This last step can be tricky. The acrylic glue is made to work with perfect seams, so make sure your cuts are clean and the bent pieces line up.

The process was documented in the clip found after the jump. If you’re looking for a more targeted heat source check out this dedicated acrylic bender.

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Stocker monitors the markets

stocker-monitors-the-market

If you can’t help but spend the day checking in on your stock prices this ambient device can help you cope. It monitors how the trading is going and illuminates an LED as feedback. Here the Apple stock is trading up so the light is green. The video after the break shows other stocks trading down, causing it to switch to red.

An Arduino interfaces with the custom application via USB. For now it looks like the two colors are all it’s capable of but we think there’s a lot more potential. Some creative coding could use factors like how much the stock has moved, trading volume, volatility, or a plethora of other data to give feedback. We could see a spectrum of colors (like on a temperature map) used to improve the level of feedback. And if the market really tanks there’s always the ability to add flashing!

The diffuser for the project is quite interesting to us. [Ali Reza Kohani] made it from a leftover scrap of acrylic. The bubbled surface was created with a heat gun before bending the sheet into an arc.

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One method of fabricating translucent faceplates

laser-cut-translucent-panel-covers

Enclosures are the bane of electronics engineers (or so says [Dave Jones] of the EEVblog and The Amp Hour). But fabricating a case that looks great has been getting easier lately. [Eric Forkosh] produced this professional-looking translucent face plate with a minimum of effort. He found a way to use a laser cutter to etch icons in acrylic.

Admittedly, this is not very involved. But just look at the quality he achieved. The secret to his success (aside from having a quality laser cutter on hand) is to use high-temperature spray paint. The acrylic is coated in paint and allowed to dry before heading to the laser cutter. By using the rasterize setting under low power he kills two birds with one stone; the paint is etched away while the acrylic is left a little bit rough to act as a diffuser for LEDs behind the panel. [Eric] cautions against using regular spray paint. In his write up he shows off the unsightly results of doing so.

This makes a great addition to some of the case options out there. One that we have been keeping our eye on is the Sick of Beige initiative being spearheaded by [Ian Lesnet].

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