Homebrew Laser Cutter Made by Zach Radding

Zach Radding and his daughter Taylor with some robots he built using his own CNC laser cutting machines.
Check out http://www.buildcoolstuff.com/ to see more of his projects and info on the classes he teaches.

He's built two laser cutters so far.
Click on the little numbered pictures above to learn more about them.

Note: These are not fully detailed plans.
Included are part numbers of all the major components. If you have already built a CNC machine of some sort,
this information would help you adapt it for doing laser cutting. You should build a CNC router table before attempting a laser cutter. The book "CNC Robotics" from Tab books has good plans.
www.nutsvolts.com used to send you plans for two cnc machines with a subscription.
Zach recommends http://cnczone.com/ for homebrew cnc info. He likes Dancam cnc software.

Step 1: SAFETY

First some warnings.

The laser beam is invisible. It can blind you and your loved ones in an instant.

Here are the safety glasses Synrad supplies to work with this laser tube.

Read all the manuals that come with your laser tube and do exactly as they say.

The laser can start fires and generate poisonous gases if it shines on the wrong materials.

Step 2: Zach's First Lasercutter

This first version uses a Roland digital pen plotter to move the cutting lens, and incorporates a number of lasercut mechanical parts.

Zach used the following components. Prices have changed (fallen) since '94 when he bought his, and some
of these things are no longer manufactured. Similar components are available, or you can look for
these on the used market.

Here are the components he used:
CO2 laser tube: Synrad G48-2-285 25 watt laser cost approx $2000
Power supply: Power One Model SPM3E2K 28 volt 27 amp switching power supply. cost approx $300
Mirrors: Four high quality front surface mirrors ~$20 each.
Focusing lens: must be made specifically for the laser wavelength. It must be optically clear to this
color light or it will etch and melt. Zach's lens came as a unit with a 45 degree frontsurface mirror
from Synrad for ~$600

Step 3: The Second Lasercutter

Zach and Taylor show us the second version of the lasercutter.
Version one worked fine, but some movers used it as a box to ship a rabid coyote they thought was a pet of his.
The poor animal totally trashed the machine before it got out and bit Dick Cheney in the woods near D.C.
By then Zach had acquired a heavy x-y stage and thought he'd try a different design.
This version moves the workpiece rather than the laser beam. The major advantage of this scheme
are very simple optics. The optics consist of a single mirror that points the laser beam down through the focusing lens.

If Zach builds another machine he says he'll make it more like the first one. Let's look into the guts of this one first.

Step 4: Power Supply

Power One Model SPM3E2K 28 volt 27 amp switching power supply. cost approx $300

This is a regular switching power supply, nothing special except for capacity and good regulation. The laser tube calls for 30 volts plus or minus 2 volts and thirty amps worth of it. Any supply that will do that is fine.

Step 5: The Laser Tube

CO2 laser tube seen from above.
It's a Synrad G48-2-285 25 watt laser cost approx $2000
Fans in the blue enclosure (absent in this photo) blow air into the holes in this lucite enclosure around the laser. This cools the laser and keeps smoke and other dirt from getting on the front of the laser. This is a good way to keep the laser from burning a hole in itself.
This unit has a number of nice features. It takes a relatively low thirty volt supply. It steps it up to a bazillion volts internally. That's how many volts it takes to make the laser un-lazy. The unit also has a convenient DB9 connector
with a TTL level (five volt) input signal line to turn the laser beam on and off. You can connect a PWM (pulse width modulated) signal in here to turn the laser power down to any level you want. Zach's PWM is at a frequency of 20khz.

Step 6: Motion Controller

Zach says: "The newer laser uses an old Galil-600 motion control card. It came with the XY table. I found
a utility (from Galil) that converts HPGL files to a format that its motor controller can
recognize. I wrote a VB app that allows me to preview the cut and send the motion control file
to the Galil card. I'd be happy to share that, but I don't really think it would help anyone."

Step 7: PWM Generator

This tiny PIC16f675 microprocessor board runs the the control panel as well as pulse width modulating the beam (PWM varies the apparent laser power thus changing the depth of cut).
This processor looks at the step and direction signals going to the stepper motor controllers.
From this it deduces how fast the workpiece is moving and adjusts the laser power to match. Faster motion,
more power. Circles and other curves cause the machine to move slowly as it approximates the circle from a series of tiny line segments. Then the laser power needs to be turned down to match the slow speed. This is more important when etching images onto something than when cutting things out.

Step 8: Mirror and Lens

That's it, the whole optical system.

In this photo Zach's fingers are twisting a lead screw that raises and lowers the focusing lens. This is necessary to deal with materials of different thickness. This brings the hottest part of the beam to bear on the surface of the workpiece. Commercial machines typically raise and lower the platform supporting the workpiece instead.

The black triangular dingus contains a front-surface mirror angled at 45 degrees. The thumbscrews push the mirror around to aim the laser beam in the right direction, which is straight down through the focusing lens.

The focusing lens is a single piece of glass housed in the aluminum block attached to the leadscrew mechanism by two 4-40 capscrews. The lens housing came as a unit with a 45degree mirror attached for ~$600. For this machine the mirror was in the wrong place so Zach cut it off.

Below that are some nylon wireties. They ordinarily hold a hose that sucks smoky air away from the lens.
This is important. Without air flow smoke prevents good cutting. Also it gets on the optics and they burn up which is a tragedy except to those people who sell expensive lenses.

Step 9: Airflow and Smoke Eater

The hose that sucked smoke away from the lens used to go to a blower that blew it out of the building through a vent. The fumes from cutting plexiglass were so malodorous that the stink drifting back in from outside was unpleasant. So Zach bought this unit. It blows the rank fumes through a charcoal filter which soaks up all the nastiness. It's a RSU12-CCHR "Space Saver" model made by Electrocorp. He says it gives him better air quality than an exhaust fan.

I asked Zach about the possibility of a laser cutter that held the workpiece vertically to save floorspace, whether he thought convection would cause fires. He said no, every laser cutter has to have lots of airflow past the cut, so that problem wouldn't be any different.
In his opinion, the big problem with a vertical workpiece is that cut parts would fall out, shift around, slump, and possibly fall into the cut and glue themselves back together.

Step 10: Pen Plotter Based Laser Cutter

Back to Version One. Zach ordered a new digital penplotter from Roland for about $800. It understood HPGL and its own plotter driver protocol. To cut a part, Zach drew the lines and hit the "plot" button in his cad program.
The plotter went to work, not knowing that Zach had attached his laser and mirrors as shown in this diagram. This is the most common arrangement in commercial laser cutters. Zach didn't have any problem with the mirrors and would
use this arrangement again if he makes another laser cutter.
The plotter had a pen change function for different line styles. Zach added buttons at the pen change stations to tell his laser controller what sort of cut was expected. The controller then sent a PWM signal to the laser to control the brightness of the laser. The pen-up and pen-down signal from the plotter was used to turn the laser on and off.

This diagram depicts the machine as seen from above. Mirror 4 points the beam straight down through the focusing lens onto the workpiece. Mirrors 1 and 2 are fixed. Mirror 3 is attached to the (blue) x-axis gantry and moves side-to-side with it. Mirror 4 and the focusing lens slide to-and-fro on the gantry.

Step 11: Roland Plotter X-y Mechanism Top View

This is the mechanical portion of Zach's first lasercutter. The x-axis stepper motor turns a long shaft with two pulleys. Two timing belts move the gantry back and forth.

Step 12: Roland Plotter X-y Mechanism Bottom View

A smaller steper motor on the gantry moves the pen carriage to-and-fro on the gantry. Zach replaced the pen holder with a bracket for mirror# 4 and the focusing lens. Over time Zach replaced frame elements with aluminum extrusions and various brackets with lasercut lucite parts.

Step 13: X Axis Driveshaft Detail

The stepper motor is attached to a driveshaft with a flex coupling. There is a timing pulley at each end of the driveshaft. The two belts are attached to the two ends of the gantry. Pulling on both ends of the gantry prevents it from racking and means it doesn't have to be nearly as stiff or well-supported.

Step 14: Gantry Underside

The gantry seen from below. The carriage has three wheels that ride on the gantry rail. The carriage is attached to a timing belt driven by the stepper motor seen to the left.