Laser Marbling in Smoke

This Instructable will allow you to view a frame by frame strobe of changing fluid smoke swirls using a laser and a hand powered construction.

Skill: Beginner

Time: 1 weekend

Estimate Entertainment Value: 15 minutes, once a year.

Safety: Possible blindness. possible felony.

You are probably familiar with a laser beam. In a foggy area, these are solid and unbroken beams of light because the particles in the air have had time to mix well. When the particles have not complete mixed, like the smoke of a campfire, a laser strobe can reveal slices of swirling smoke. You can do it without any work by using your hand to shake a laser over smoke. Though, waving your hand is imprecise and can get tiring, so this project will use rotary motion of a mirror to strobe a laser through smoke. The results are better than the attached photo, I guarantee it.

This is a worthwhile instructable for the following reasons. It shows you a new visual experience and explains how to do it with basic tools and inexpensive materials. The assembly steps are designed for beginners, but may require some debugging and re-cut parts. A high school student should have the skill, judgement, and budget to complete this project, though the final product will be entertaining for all ages.

CAUTION: A high powered laser is required, so while this project is relatively easy to complete, it requires judgment in order to avoid loss of eye sight and broken laws. The laser I suggest is 40x more powerful than a "laser pointer". It requires pointing the beam up from a campfire, so precautions must be taken to avoid hitting an air craft.

Overview: $15 Lego, $10 laser, $10 mirrors, $5 wood, $30 drill, $20 drill bit set, $10 saw, $5 screws, $1 campfire, $50 protective laser glasses = $156 starting with nothing.

I am considering offering a $20 kit for the Legos, mirrors, screws, and shipping. This will be available until June 2020.

The last step in this Instructable is a buying guide.

Minimum Components

Laser Protective Glasses - Must protect against 532 nm laser

Laser - High power green laser. I purchased mine on eBay. My laser is "< 250 mW". Lower power may work, but I have not tested this

5x Mirrors - ~1/2" x 2" Adhesive mirror. Width should be smaller than 0.62 inches

1x Construction wood - 1 x 4. The actual wood will be 3/4" x 3 1/2" and 8' long. Try to find a piece in the discount pile.

20-40x Wood screws - 2 inches

### Lego Parts ### (Buying tips at the end)

9x Technic, Brick 1 x 4 with Holes

2x Technic, Brick 1 x 6 with Holes

2x Technic, Brick 1 x 8 with Holes

3+ Technic, Axle 4

2+ Technic, Axle 6

10x Technic, Axle 8

3x Technic, Gear 12 Tooth Double Bevel

1x Technic, Gear 20 Tooth Double Bevel

1x Technic, Gear 36 Tooth Double Bevel

10x Technic, Pin with Friction Ridges Lengthwise WITH Center Slots

10x Technic, Axle Connector 2L (Ridged with x Hole x Orientation)

1x Technic, Liftarm 1 x 2 Thick with Pin Hole and Axle Hole

3x Technic Bush

5x Brick 2 x 2
2x Brick, Round 2 x 2 with Axle Hole

2x Plate 1 x 4

1x Plate 1 x 8

8x Plate 2 x 4

Tools:

Drill

Drill bit set - At a minimum, you need a bit sized to drill a pilot hole for your wood screws. Optional features require bit sizes ranging between 1/8" to 1/2"

Hand Saw

Setting:

Campfire

Sky free from airplane flight paths, or find a way to shield the sky from the laser.

While sitting at a campfire, I would like to be able to see the particles in the swirling smoke. The core concept is a laser beam shining off a rotating mirror. To make the design compact, the axis of the laser and the final mirror are in parallel, with an angled stationary mirror reflecting the beam to the final mirror. The rotating mirror is geared so that one rotation of a crank outputs 20 mirror rotations.

There are three general steps to this instructable.

1. Assemble the Lego gearbox
2. Cut the component supports
3. Secure component supports to backbone.

The final design is based on these requirements.

Requirements:

• Sweep laser in a plane. Non-planer sweeps resemble a double exposure. It is difficult to focus on the smoke patterns at a single location.
• Hand-powered. This project is meant to be entertaining. Including a tactile sense heightens the experience.
• Speed of sweep should be roughly 20 rotations per second.
• *Heat resistant. When used roughly 2 feet above a flame, the device should not warp or catch fire.
• Powered at a comfortable distance. The user should not be uncomfortably hot or smokey when using the device.
• Simple design. A high school student with limited wood working knowledge should be able to construct this. Number of required tools should be minimal. Total cost assuming no owned tools is less than $200.
• Compact. The device should be easy to hold while operating. The operator should not get tired by holding it.

Conclusions:

• Mirrors allow for rapid movement changes since they are lightweight.
• Mirrors also allow for a compact design. The angle of the beam can be redirected as needed.
• Using Legos for a gearbox assures functional beveled gears. Legos in general are great for rapid prototyping. I have changed gearbox designs at least six times in this project.
• Wood cuts should be straight. This allows for using a hand saw.

• Simple materials using a single piece of hardwood will serve as the backbone and supports for the components. The wood is also more lightweight than plastic or metal for the skill level required.

• Using the existing square edge of the hardwood as the support's joining side reduces the need for skilled sawing.

*Not yet addressed

Follow the PDF to assemble the gearbox and 4 mirror axle piece.

Correction: The axle through the large gear should go through the center of the gear rather than offset.

The long axle is just a series of 8 unit axles and connectors.

The gears transform one rotation of the crank into (36/12) * (20/12) = 5 rotations of the output axle. Additionally, there are 4 mirrors on the end of the output axle. This results in 20 laser strobes per rotation of the crank. This is accomplished by dividing the strobe sweep into smaller parts. With 2 mirrors, the laser strobes 180 degrees. 4 mirrors strobe the laser 90 degrees. I think this is still too wide and would prefer 45 degree sweeps, which would require an 8 faced rotating mirror. This is not practical for this iteration of the project.

You may notice that the output axle is on a lower level than the crank. This is foreshadowing a future design that is a more compact final product. There may me some other Lego design choices that may not make sense, but will make it easier if you decide to upgrade to my future design.

The basic structure of this build is a 1x4 backbone with supports to vertically align each component.

You will not need to worry about cutting perfectly straight for all but one of the cuts. You will be using the existing flat edge of the 1x4 as the required straight edge that connects to the backbone.

When cutting the supports, it is easier to work with each piece if make the needed detailed cuts before cutting the piece off from the stock material. An example of this is when cutting the laser support, you should cut out the “V” feature before cutting the piece off of the 1x4. This is because it is a lot easier to control a larger piece of wood when sawing and drilling on it.

In this step, you will be cutting two supports from a square of stock material.

Start by marking the reference axis as shown in the first photo. This will help keep measurement directions consistent across parts. Measure 5/8” out from both sides and draw a straight line. Mark the midpoint of the part which will be roughly 1 5/8” from the end of the part. This line will intersect the first drawn line at the midpoint oint of the part. Mark the length of the part, where you will cut the material from the stock, BUT don’t cut yet. Use this mea.

There two offset steps below because the crank and the output axle are offset by 1 level.

On the first support piece, take a 1 x 4 technic brick with three holes and align the center hole on the line drawn at 5/8”. Make sure the holes on either side are centered on this line as well. Now take a pen/pencil and mark the holes. If you can not reach the center of the holes, mark the center of the hold on the bottom of the brick, then remove the brick and continue the line, making a perpendicular with the 5/8” line.

On the second support piece take two 1 x 4 technic bricks and stack them. As with the step above, align the three holes of the bottom brick with the line at 5/8”. Mark the center of the top thee holes.

On both support pieces, drill through the center hole with roughly a 9/32” drill bit. This is for the axle. Drill the holes on either side with exactly a 3/16” drill bit. This is for the friction pins. You do not need to drill through for the pins, but it is fine if you do.

Test that the gear box connects with the supports. Turn the crank, there should be no added resistance due to the drilled hole.

You will be cutting two separate supports for the laser. They will be identical.

Mark your axis. One of the existing flat edges of the stock material should be the bottom of the support.

Draw a bounding line at 3 2/8” that will Indicate the boundary of your square support. Measure roughly 1/2” + from the height of the gearbox support so that the laser has plenty of room to pass over the gearbox. It should be about 2 1/8” from the bottom. Mark a line at this distance. Mark another perpendicular line 1 5/8” from the side. The intersection marks the vertex of the “V” shape that you will be cutting. Draw a line from the “V” vertex to the corners of the final support piece.

Use the hand saw to cut the “V”. Now cut the support piece off at the 3 2/8” line.

Repeat this step for a second laser support piece.

Note:You can make laser closer to the gearbox in order to reduce space, but if you are a beginner, it is an easier process if you don’t have to worry about this source of misalignment.

This is the most difficult step. It may require several attempt.

There is a single mirror support piece, but for convenience, you will cut a second square to help with alignment.

Start by cutting out a square from the stock. It does not need to be precise.

Put the laser support on your stock material that will later be the backbone. Place the laser on the supports. Roughly 3’ in front of the laser, place the alignment square down on a flat edge. Turn the laser on and mark the height of the laser dot. This will help you center the mirror at the same height.

Remove the items from the stock material. You are now cutting the mirror support from it.

Mark your axis so the existing flat edge of the stock material is the bottom of the support.

Draw the 3 2/8” bounding line that marks off your square support. Draw a parallel line that is 1 5/8” from the cut edge of the stock. Now, use the height from the alignment square to mark a perpendicular line across the line at 1 5/8”. This should mark where the laser will hit. Draw and arch shape from the bottom to roughly 1/2” above the laser point.

Cut out the arch, then cut off the support from the stock.

Test the alignment by setting up the laser on the stock material and check to see if the laser passes through the arch, roughly 1/2” below the peak of the arch. If not, you may need to redo this piece.

This next step requires the most precision. I used a clamp, but you may find another way to secure the support while you cut.

You are going to cut an angled slot for the mirror to rest in. If cutting the support piece is 90 degrees, then this slot should be cut between 90 to 45 degrees. If you cut exactly 45 degrees, the laser will hit the mirror then travel straight down. Instead, you want it to still travel behind the support, but hit the backbone about 3” behind the mirror support. When you cut the slot, only cut through half of the thickness of the support. The angle should be towards the bottom of the support piece. Now cut the slot.

Place the mirror in the slot and test that the laser hits the mirror and hits the backbone roughly 3” behind the mirror support. You may have to repeat this step many times. I know I did!

It is time to test alignment.

Setup the laser, gearbox, and mirror support as shown in the photos. The laser should bounce off the support mirror and hit the 4-piece axle mirror.

If you want this design to be 3’ like I designed it, then the axle will need to be supported.

Cut about 4 additional gearbox supports. They should be identicle to the gearbox support with the axle output.

For each support, attach a 1x4 technic brick using two friction pins. Pass the axle through the center hole.

This is an extra step if you want to take your device off the bench top. You are going to sandwich the laser on the front and back ends and strap it down.

Mark two squares on the stock material.

Measure the distance from the backbone to the center of the laser. This may be equivalent to the height of the laser beam measured on the alignment block used on the mirror support. You want a 1/2” hole for the push button. This can be difficult to drill from the start, so you can take your time and work up from smaller drill bits. Once the hole is drilled, cut the piece from the stock.

Make a similar piece for the front of the laser. The hole will be for the laser beam to pass through. It does not need to be as large. 1/4” drill bit might be large enough, but it may depend on the precision of your measurements. Drill and cut this piece out.

You are ready to finalize the positions by screwing the supports in place.

In this step, you should also determine the final positions of your components. This is also a customizing step that takes your comfort into account. You need to place the stock material in your lap and determine where a comfortable crank position is. For me, it is 15” from the bottom, but I am tall.

Once you have the supports positioned on the stock material, draw lines on either side of each support. Now remove the supports. Draw dots where the screws will attach to the supports. Drill these holes with a drill bit that is the size of the core of the screw. This prevents the supports the from cracking. This is important since you will be drilling into the end-grain of the wood, which is sensitive to screws and cracks easily. Once the holes are drilled, hold the support over the holes in the correct position, and drill holes into the support from the other side of the backbone. When drilling into the supports, the bit only needs to go through 1” of the support, not all the way through.

Now screw the supports in place.

Functionally speaking, you are done!

This may be a bit late, but there are some finishing steps you can do. You may want to do these before screwing the supports to the backbone.

sanding: This can prevent splinters.

staining: This will make it look more of a final product.

cutting corners: If you want to fit your device into a 3” PVC pipe for durability, you will need to cut down some of the edges.

Laser: Purchased mine on eBay for $10 from a company named gaia_unicorn in California

Mirrors: It may be difficult to find the right size. I found the perfect mirrors on Amazon, but now they are out of stock. 3/8" x 2" are not optimal, but they may work. They are currently available on Amazon. You will just have to offset them like a pinwheel on the rotating 4 mirror piece.

Legos: I recommend buying Legos from a community site like Bricklink.com . I find it easiest to search for a part by sorting by quantity and country. This will return a seller that likely has more of the parts you need and can ship to you quickly. You may have to order from multiple sellers, which adds an extra $4 for shipping for every seller. I also recommend buying more parts than you need. Buy at least 1 extra of each part. Buy many more of the axles. You may find that you want to make alterations to the design.

KIT: If you send me a private message, I can send you a kit with the Legos, mirrors, and screws. It will likely cost $20 or less, which will be cheaper than getting the parts yourself since you will not have to purchase excess for items like the mirrors or Lego.