Introduction

A Laser is a worthwhile addition to your CNC Machine. It allows you to engrave text, images, and enhance CNC carvings by adding borders, hatching, etc. Lasers can also even be used to cut thin materials (limited), engrave on cloth, do photo engraving, and many other applications. However, Lasers are inherently dangerous to use, and the possibility of eye and skin damage is very real. Let’s take a moment to look at some safety considerations for using a laser.

Laser Safety Warnings

This is a Class 4 Laser Product – 2.8W-7W, 445 nM Blue laser

LASER RADIATION – AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION

Class 4 is the highest and most dangerous class of laser. By definition, a class 4 laser can burn the skin, or cause devastating and permanent eye damage as a result of direct, diffuse or reflected/indirect beam viewing. These lasers may ignite combustible materials, and thus may represent a fire risk. These hazards may also apply to indirect or non-specular reflections of the beam, even from apparently matte surfaces – meaning that great care must be taken to control the beam path. Lasers may create chemical, mechanical, and other hazards specific to particular installations. They may also include materials released during laser processing, such as fumes from cutting or surface treatments of metals or the complex mix of decomposition products produced in the high energy plasma of a laser cutting plastics. Class 4 lasers must be equipped with a key switch and a safety interlock.

Everyone who uses a laser should be aware of the risks. This awareness is not just a matter of time spent with lasers; to the contrary, long-term dealing with invisible risks (such as from infrared laser beams) tends to reduce risk awareness primarily due to complacency, rather than to sharpen it.
Eye protection suitable for the wavelength of Laser in use must be worn at all times when the laser is operating. Laser glasses or goggles should be used when working with Class 4 lasers, especially at close range (within a few yards or meters). They should be selected to protect against the laser’s power and wavelength.
DO NOT USE SUNGLASSES FOR LASER PROTECTION – Sunglasses are NOT laser protective eyewear. They are not rated (e.g., with Optical Density) to ensure light-attenuating protection. Most will not block enough laser light to significantly reduce hazardous exposures.
Additional laser blocking substances such as laser blocking acrylic sheets or curtains should be placed between the laser and any area where persons walking by may be exposed to the beam, including windows, open doors, or other areas where access cannot be controlled. These areas should also be posted with signs.
Access to the area where a laser is in use must be controlled to prevent accidental ingress without proper protective equipment. Doors to the area must be kept locked while the laser is in operation.
Controller Keys must be secured so untrained personnel cannot operate the laser without supervision.
Extreme caution must be used to prevent fires due to the laser stopping in an on condition. Lasers must never be operated unattended.
Caution must be used to make sure materials being lased are not subject to off gassing of poisonous gasses or vapors when exposed to the laser beam. No matter what material is being exposed to the laser, a suitable ventilation system must be used to vent toxic byproducts and smoke to the outside of the occupied area.
The user is responsible for posting signs at the entry points to the area where the equipment is installed to warn anyone entering of the possibility of Laser Radiation. No one shall be permitted to enter the area where a laser is in use without proper PPE and training. User is also responsible for supplying suitable Emergency Stop controls and interlocks if required for safe use.
Never put metal under the laser beam. The beam can reflect off the metal into your eyes and damage your vision. These lasers are not capable of marking on metal.
This is not a toy. Children should never be permitted to use Class 4 lasers. Any teenager using a Class 4 laser should be continuously supervised by a responsible adult.
A Class 4 laser beam can burn skin and some materials. The more powerful the laser, the faster the burn will occur. In some cases, the burn may be almost instantaneous. Avoid skin exposure to a Class 4 laser beam, especially at close range. A skin burn can be very painful, can take long to heal, and can leave a permanent scar.

Installing a Laser onto your CNC Machine

Installing a Laser attachment is a great way to increase the usefulness of your CNC Machine. 3D Tech sells lasers from JTech, they are high quality, have numerous safety features, and are reliable and their output power is tested before delivery.

Prepping the machine

You will need to add power and control leads to your machine. The laser kit usually has at least one power extension cord and a control lead. These must be threaded through your X/Z axis cable chain. Make sure the plug ends of both the leads are on the Z axis side of the cable chain. The control lead will connect to the Arduino GRBL motion controller.

The power lead will continue through the side panel of the Y axis and down the side cable chain if equipped. It may require more than one power extension cable to do this, make sure you inform 3D Tech what type of machine you are installing the laser on so they can provide the correct wiring. If you need to use more than 1 power extension lead, it is important to put heat shrink or tape over the connection between the two leads so they don’t accidentally come unplugged. Thread the power lead out through the side cable chain and out the back, leaving the plug free to connect to the laser power supply later.

Installing the Laser and Control Module

The laser is usually mounted on the front of the existing router mount. It attaches to the same 2 screws that clamp the router into the mount. You will probably need shorter screws; these should be supplied with your kit from 3D Tech.

Note that the laser module comes with fairly long leads. Normally you won’t need these, but do not attempt to cut the leads. The plugs require special tools to crimp on the connectors, and the pins cannot be re-used. Simply wind up the wires and use a tie wrap to secure them.

Install the laser on the front of the router mount with the supplied screws. Mount the laser with the diode module on the inside of the mount, to give it some protection, with the fan at the top. As mentioned above, tie the excess wiring back with a couple of tie wraps to keep it away from moving parts.

The Control Module is mounted next. Generally, there is plenty of room to mount the control module at the top of the Z axis c-beam, using the supplied brackets with 2 screws and 2 post installation tee nuts. Mount the unit by putting a screw through both mounting brackets and a PI tee nut on the back. Make sure the main power switch and key switch are on the right side facing the machine. Secure the module in place by putting the tee nuts in the outside slots of the C-beam and tightening the screws.

Note that the PI tee nuts need to rotate 90 degrees as you tighten the screws in order to lock in place. If they don’t rotate, you may have to loosen the screw more until the tee nut can rotate freely as you tighten the screw. Mount the module on the C-Beam as high up as it will go.

Now you can plug in the laser and the fan to the control module. There are 2 large white connectors on the top left side of the module, and 2 small connectors near the bottom left side. The Laser plugs into the top 2 pin large white connector on the left of the module. It will only plug in one way. The Fan plug goes into the top small connector on the bottom left.

Note: There are 2 identical plugs at the top left of the module that the laser can connect to. Putting the plug in the wrong place can damage the laser or the control module. The top plug goes to the laser, second plug goes to the Arduino. It’s a good idea to mark the plug and the socket of one of these connectors with a colored sharpie so it is less likely to get them mixed up. See diagram above.

Same goes for the Fan connector. The fan connects to the upper small plug on the bottom left of the control module. Again, the plug is polarized so it only goes in one way. While mixing up these two plugs is less likely to damage anything, it may prevent the fan from working and cause the laser to overheat if it is plugged into the wrong connector.

This is what it should look like after the laser and control module are mounted.

Connecting the Control lead to the Arduino

The control lead ran through the Z axis cable chain in an earlier step can now be connected to the Arduino. Strip back the outer cable jacket a couple of inches, then strip about ¼” of each wire. The wires are usually red and black. It is a good idea to either tin the ends of the leads with solder, or put wire ferrules on them to protect the wires and make it easier to insert them into the terminal blocks on the Arduino.

Now, connect the wires to the Arduino. Make sure you verify the pin # designation on the terminal block board itself. The red wire goes to pin D11, second from the end near the USB connector end of the board. Loosen the terminal block screw, insert the wire, and tighten the screw. Tug on the wire to make sure it has a firm connection. Now connect the black wire to a GND terminal. There is one near the other end of the top terminal block, fourth terminal from the end. Use the same method to connect the wire. Use a couple of tie wraps to hold the wire in place.

Note: If your machine has an Arduino Uno instead of the Nano shown, the wiring will be the same but the board looks a bit different. The pinout of both boards is identical, just follow the legend on the board for D11 and GND.

Connect the power supply

Now you can plug in the power supply to the power extension cable ran earlier. Do not plug in the AC plug yet.

Laser Operation

The laser operates similarly to a router, but with some important differences:

The Z axis is generally not used with the Laser. It can be manually controlled with the jog controls to set the laser focus, but it usually remains fixed during operation. The Z axis can be lowered during cutting operations to maintain the laser focus at the bottom of the kerf as it is cut.
The laser on/off/power setting is controlled by the software during use. There are a couple of extra G-code commands used to control the laser. M3/4/5 commands are used to turn the laser on and off, and the Sxxx spindle speed setting is used to control laser power.
GRBL does a few things differently between the laser and router. GRBL has a small time delay in Router mode when turning on, off, and changing speeds that is not necessary for a laser.
GRBL Version 1.0 and up have a special Laser Mode setting in the Settings window that must be changed when switching between router and laser.

Explanation of some of these points is shown below. The following section was lifted from the GRBL Wiki for version 1.0 and above. See https://github.com/gnea/grbl/wiki/Grbl-v1.1-Laser-Mode.

Laser Mode Overview

The main difference between default Grbl operation and the laser mode is how the spindle/laser output is controlled with motions involved. Every time a spindle state M3 M4 M5 or spindle speed Sxxx is altered, Grbl would come to a stop, allow the spindle to change, and then continue. This is the normal operating procedure for a milling machine spindle. It needs time to change speeds.

However, if a laser starts and stops like this for every spindle change, this leads to scorching and uneven cutting/engraving. Grbl’s new laser mode prevents unnecessary stops whenever possible and adds a new dynamic laser power mode that automagically scales power based on current speed related to programmed rate. So, you can get super clean and crisp results, even on a low-acceleration machine!

Enabling or disabling Grbl’s laser mode is easy. Just alter the $32 Grbl setting.

To Enable: Send Grbl a $32=1 command.
To Disable: Send Grbl a $32=0 command.

WARNING: If you switch back from laser mode to a spindle for milling, you MUST disable laser mode by sending Grbl a $32=0 command, or using the Settings tab to set $32=0. Milling operations require the spindle to get up to the right rpm to cut correctly and to be safe, helping to prevent a tool from breaking and flinging metal shards everywhere. With laser mode disabled, Grbl will briefly pause upon any spindle speed or state change to give the spindle a chance to get up to speed before continuing.

Laser Power Setting

Another feature that is used for both Laser Mode and Router Mode in GRBL involves the RPM Max ($30) and RPM Min ($31) Settings. For Router operation, these are used to set the min and max RPM of the router when an external Router Speed Control is used. In Laser Mode, however, these set the output power of the laser. The RPM Min setting limits the lowest power setting, and the RPM Max sets the upper limit of power to the laser. The Laser power is usually set in Percent, 0% being off, and 100% being full power. The base value of the range of RPM in GRBL is 0-255, an 8 bit binary number. Since this is somewhat difficult to easily convert to %, I usually set RPM (power) Min to 0, and RPM (power) Max to 1000. This means that an S000 g-code command will set the laser power to 0.00%, and an S1000 command will set the laser to 100.0% power output. Incrementing the laser power setting by 1 would increase the power output by 0.1%. The Sxxx g-code command is used in the user program to set the router RPM in Router mode, and laser power in Laser mode.

It should be noted that below a certain minimum setting, the laser will cease to operate. This is usually somewhere around 3-5% of full power. Below this setting, the Laser will not light off. You should experimentally determine what this value is for your particular laser and remember it. You could set the RPM Min value to this setting to get a bit more resolution in your power settings. The lowest power setting is usually used when focusing and positioning the laser before a run so the laser does not mark the work or start a fire if left enabled.

Laser Mode Operation

When laser mode is enabled, Grbl controls laser power by varying the 0-5V voltage from the spindle PWM D11 pin. 0V should be treated as disabled, while 5V is full power. Intermediate output voltages are also assumed to be linear with laser power, such that 2.5V is approximate 50% laser power. (A compile time option exists to shift this linear model to start at a non-zero voltage.)

By default, the spindle PWM frequency is 1kHz, which is the recommended PWM frequency for most current Grbl-compatible lasers system. If a different frequency is required, this may be altered by editing the cpu_map.h file.

The laser is enabled with the M3 spindle CW and M4 spindle CCW commands. These enable two different laser modes that are advantageous for different reasons each.

M3 Constant Laser Power Mode:

- Constant laser power mode simply keeps the laser power as programmed, regardless if the machine is moving, accelerating, or stopped. This provides better control of the laser state. With a good G-code program, this can lead to more consistent cuts in more difficult materials.
- For a clean cut and prevent scorching with M3 constant power mode, it’s a good idea to add lead-in and lead-out motions around the line you want to cut to give some space for the machine to accelerate and decelerate.
- NOTE: M3 can be used to keep the laser on for focusing.

M4 Dynamic Laser Power Mode:

- Dynamic laser power mode will automatically adjust laser power based on the current speed relative to the programmed rate. It essentially ensures the amount of laser energy along a cut is consistent even though the machine may be stopped or actively accelerating. This is very useful for clean, precise engraving and cutting on simple materials across a large range of G-code generation methods by CAM programs. It will generally run faster and may be all you need to use.
- Grbl calculates laser power based on the assumption that laser power is linear with speed and the material. Often, this is not the case. Lasers can cut differently at varying power levels and some materials may not cut well at a particular speed and/power. In short, this means that dynamic power mode may not work for all situations. Always do a test piece prior to using this with a new material or machine.
- When not in motion, M4 dynamic mode turns off the laser. It only turns on when the machine moves. This generally makes the laser safer to operate, because, unlike M3, it will never burn a hole through your table, if you stop and forget to turn M3 off in time.

Describe below are the operational changes to Grbl when laser mode is enabled. Please read these carefully and understand them fully, because nothing is worse than a garage fire.

Grbl will move continuously through consecutive motion commands when programmed with a new S spindle speed (laser power). The spindle PWM pin will be updated instantaneously through each motion without stopping.
- Example: The following set of g-code commands will not pause between each of them when laser mode is enabled, but will pause when disabled.

G1 X10 S100 F50
G1 X0 S90
G2 X0 I5 S80

- Grbl will enforce a laser mode motion stop in a few circumstances. Primarily to ensure alterations stay in sync with the G-code program.
  - Any M3, M4, M5 spindle state change.
  - M3 only and no motion programmed: A spindle speed change.
  - M3 only and no motion programmed: A G1 G2 G3 laser powered state change to G0 G80 laser disabled state.
  - NOTE: M4 does not stop for anything but a spindle state change.
The laser will only turn on when Grbl is in a G1, G2, or G3 motion mode.
- In other words, a G0 rapid motion mode or G38.x probe cycle will never turn on and always disable the laser, but will still update the running modal state. When changed to a G1 G2 G3 modal state, Grbl will immediately enable the laser based on the current running state.
- Please remember that G0 is the default motion mode upon power up and reset. You will need to alter it to G1, G2, or G3 if you want to manually turn on your laser. This is strictly a safety measure.
- Example: G0 M3 S1000 will not turn on the laser, but will set the laser modal state to M3 enabled and power of S1000. A following G1 command will then immediately be set to M3 and S1000.
- To have the laser powered during a jog motion, first enable a valid motion mode and spindle state. The following jog motions will inherit and maintain the previous laser state. Please use with caution though. This ability is primarily to allow turning on the laser on a very low power to use the laser dot to jog and visibly locate the start position of a job.

Generally, use a power setting or 5% or less for positioning applications. Always turn the laser off when adjusting the focus ring. Adjust in small increments (1/2 T) and recheck focus. Having the laser on while focusing can result in burned fingers!

An S0 spindle speed of zero will turn off the laser. When programmed with a valid laser motion, Grbl will disable the laser instantaneously without stopping for the duration of that motion and future motions until set greater than zero.
- M3 constant laser mode, this is a great way to turn off the laser power while continuously moving between a G1 laser motion and a G0 rapid motion without having to stop. Program a short G1 S0 motion right before the G0 motion and a G1 Sxxx motion is commanded right after to go back to cutting.

Focusing your Laser 101

This section is lifted from JTech Photonics Website.

So you just bought a fancy new laser and now you are wondering how do I get the results that J Tech is getting when I know nothing about lasers? The answer is that you need to always have the laser be at minimum focus to be able to perform cuts and engravings at their optimal performance. Once you master the art of focusing, then you are on your path to becoming a super laser user!

First off, let me say that this is the point where you will need to ALWAYS make sure to have ALL people wear appropriate safety goggles at ALL times and use proper laser safety for your class 4 laser including laser shielding and interlocks. If you ever have any questions about safety, then do not operate your laser.

Ok, now that we are past that part, let’s review the basics of what your laser is so we can better understand how to get it to focus.

What is a diode laser?

A semiconductor diode laser is a device made out of semiconductor (computer chip) material that takes electricity and converts it into light (photons). This device is very small and contains all the needed laser stuff, like an optical cavity and mirrors on each end. Basically, when current is applied to the laser diode, electrons will be excited and will release photons. These photons will travel down the semiconductor cavity and bounce back and forth off the “facets” or sides of the device until there is enough energy to output the light out of the emitter. This process continues as long as the electrical current is applied.

Why is the beam a rectangle and not a spot and what is all the extra light?

Each diode will have an “emitter” in it that is where the laser light comes from. This is seen in the above picture with the rectangle portion labeled “LASER”. There is also some other light that is emitted from the other portions of the diode that are not included in the optical cavity of the laser. This light is probably what you are seeing. It also can be from various reflections from the very large angle light coming out of the diode. The lens has been designed to reduce these reflections but they can still be present. All of the “extra” light has nothing to do with the actual laser and its ability to cut and engrave.

How does the front lens work?

The lens used is a positive or converging lens in air will focus a collimated beam travelling along the lens axis to a spot (known as the focal point) at a distance f from the lens. Conversely, a point source of light placed at the focal point will be converted into a collimated beam by the lens. These two cases are examples of image formation in lenses. In the former case, an object at an infinite distance (as represented by a collimated beam of waves) is focused to an image at the focal point of the lens. In the latter, an object at the focal length distance from the lens is imaged at infinity. The plane perpendicular to the lens axis situated at a distance f from the lens is called the focal plane.

If the distances from the object to the lens and from the lens to the image are S₁ and S₂ respectively, for a lens of negligible thickness, in air, the distances are related by the thin lens formula:

Basically, you are imaging the output of the laser emitter onto the surface of your material. You want to find the SMALLEST point at which that image exists.

What is the focal length?

The focal length in this case is adjustable. The closer the lens gets to the laser diode the longer the distance from the lens to the minimal focus is. With our lasers we recommend about 1 to 3 inches away from the work surface. We normally have ours between 2.5″ and 3″ to help keep debris off the lens. Being closer makes the “depth of focus” (the amount in the z axis that it stays small) larger. The farther away you get the harder it will be to get the smallest focus. Above three inches, you will be able to visibly see the rectangular shape of the laser diode. It will still burn and cut, but it will not be as efficient and the size of the line will be larger. We recommend setting up your machine so the focus can be under 3″. If your Z axis has to be taller (i.e. because your gantry is tall) then consider making a new mounting plate that is lower or if possible add some material under your work to put it closer to the laser. Especially for fine picture engraving it will need to be 3″ or under.

*Note* The focal point is not really a point, but rather a position in Z where the beam is at a minimum. This area will be the smallest the beam waist can be. The distance of this point from the lens is called the “depth of focus”. On each size in Z, the focus will start to get bigger. It will look like this:

It will look very much like an hourglass

When you are adjusting your front silver lens screw, you are going to be turning it to look for this small part where the sand can barely get through. If you turn the lens and it is getting bigger, then go the other way. You will notice is gets smaller and smaller, until it then starts to get bigger. You just went past the small part of the hourglass. Then, turn it the other way. You notice is gets smaller now until it just starts to get bigger again. Do this a few times. You will then get a feeling where the smallest part is of the beam. This is the best focus you can get. We will now go into detail on how to do this, but remember the hourglass example while you are doing these instructions.

Ok, so how do I get the smallest focus?

If your laser is a 2.8W, 2W, or 1w your laser shipped with the focus set to 3″ if you bought it from us. You can put it on your machine and set it to 3″ from the front of the lens and you will have a pretty good focus. You can adjust it slightly by moving up or down to get it perfect, but it should work pretty good out of the box.

If your laser is a 3.8W your laser shipped with focus set to 1.5″ if you bought it from us.

The HF lens included in the kit has the smallest focus to closer to the work surface you get. On all of the lasers, the closer to 1″ you get the smaller your spot will be.

Great! The focus looks good out of the box, but I want to adjust it myself. How do I do this?

There are a few ways to do this. You are first going to have to turn your laser power down so you can look at the beam without burning a hole in your material. You can do this two ways:

Using PWM control – This way is easiest if you have it. Just simply send a command to turn the laser down from your controller. This works for X carve, Shapeoko (1,2,3), and most 3D printers.
Using the Potentiometer – This way involves turning the laser driver down in current using the jumpers and potentiometer. This is for most Mach3 machines, old CNC machines, and 3D printers running Sailfish firmware (Makerbot).

Here is the detail for a couple of quick methods for finding the minimum spot size focal length. Remember to use laser shielding if possible and your safety goggles when performing this exercise.

Method 1: Using PWM from your controller to turn down the laser and focus. (X Carve, Shapeoko (1,2,3), GRBL, Most 3D Printers)

In this case you don’t need to adjust the potentiometer. It is really easy to set the power down to the minimal level. It basically involves turning the laser power down and putting a white piece of paper on the work surface to see the laser spot clearly. We are going to use the computer controller to set the power level using software to get the laser to turn down power so we cannot burn the paper. For most firmware it will be a low number. Somewhere around 2% to 5% of maximum value should do the trick of not burning the paper and being able to see the laser spot on the white paper better.

Adjust the Z height of the machine so the laser is between 1″ and 3″ (25mm and 75mm). It can be somewhere in this range, but not over 3″. We normally start close to 1.5″.
Set a piece of white paper on the work surface, or ON TOP of whatever material you are going to process (or where you would like to set the focus at).
Turn the driver board on.
Make sure the front Switch is set to TTL (input control mode) and is pushed to the farthest right looking at the front.
Using a sender program or 3D controller software, send a command to the machine/printer to set the power level low. For X Carve or Shapeoko machines we recommend using either UGS or PicSender. UGS tutorial is here. 3D printers we recommend using Repetier Host.

Setting power low (about 2%) for GRBL machines (X Carve, Shapeoko 1-2-3, other GRBL):
For the J Tech GRBL or version 1.1 firmware you will send: M03 S20
For Inventables firmware or standard 0.9 GRBL send: M03 S1400

Setting power low (about 2%) for 3D Printers using Fan PWM control:
For Marlin firmware on a 3D printer with fan control send: M106 S5
For 3D Printers using Repetier Host and fan control use the Manual tab and the FAN slider to turn it down.

If it is too powerful or not enough light then try different levels until you just have the laser turned on.
Now you can adjust the lens to get the smallest spot at the surface. Adjust the lens one direction and if it gets bigger, then adjust it the other direction until the spot is small. It is fine to pass it a couple of times in each direction until you get a feel for where the minimum will be. Remember the hourglass example from above. Once you have finished this, you can probably be done as it will be a pretty good focus.
If you want it perfect, you can repeat the same process, but now using your machines Z axis. Adjust the Z axis to get the best possible smallest spot that you can tell by looking at it.
Now move the Z axis away from your smallest spot in a known increment until you can see the spot get bigger.
Move the other direction in the known increment until you pass the smallest spot and get to the same size big spot in the other direction. Count how many increments this was.
The smallest spot is now exactly between these “easier to see” larger spot sizes. Take the count of increments and divide by two and move the Z axis by this amount.
When you are done, set this new Z location as your “home” location.

You are now ready to process with the laser at its smallest spot size!

Note: If you don’t want to do this procedure every time you try a new material, then focus the spot at the work surface. Then, measure the thickness of the material you are processing and move the Z axis UP this thickness. I.e., if you are cutting 1/16″ Balsa wood, move the Z Axis up 1/16″ so it is focused on the top of the material.

Using a white piece of paper to find the smallest focus.

Method 2: Using the potentiometer to turn the laser down and focus.

Adjust the Z height of the machine so the laser is between 1″ and 3″ (25mm and 75mm). It can be somewhere in this range, but not over 3″. We normally start close to 1.5″.
Set a piece of white paper on the work surface, or ON TOP of whatever material you are going to process (or where you would like to set the focus at).
Then WITH THE POWER OFF, turn the potcounter clockwise ALL THE WAY (approx 21 turns). You might hear a slight clicking sound when it has reached the maximum off distance or feel a clicking.
Then turn the driver board on.
Switch the front switch (mode selector) to CW (towards the power switch). The laser is now on, but will not be lasing because there is no current.
Turn the pot slowly clockwiseuntil you just see the laser starting to shine light. Stop when you can see a bright spot in the center. Should be about 1-3 turns.
Now you can adjust the lens to get the smallest spot at the surface. Adjust the lens one direction and if it gets bigger, then adjust it the other direction until the spot is small. It is fine to pass it a couple of times in each direction until you get a feel for where the minimum will be. Remember the hourglass example from above. Once you have finished this, you can probably be done as it will be a pretty good focus.
If you want it perfect, you can repeat the same process, but now using your machines Z axis. Adjust the Z axis to get the best possible smallest spot that you can tell by looking at it.
Now move the Z axis away from your smallest spot in a known increment until you can see the beam get bigger.
Move the other direction in the known increment until you pass the smallest spot and get to the same size big beam in the other direction. Count how many increments this was.
The smallest spot is now exactly between these “easier to see” larger spot sizes. Take the count of increments and divide by two and move the Z axis by this amount.
When you are done, set this new Z location as your “home” location.
Then switch the mode selector back to “TTL” (right).
Turn off the driver board.
Now follow the instructions in the manual (HERE)on adjusting the current. You will be using your meter and adjusting the potentiometer to the desired current output. (see section “adjusting current” in the instructions).

What is another way to find focus? I am having trouble with using my eyes?

Sure, there is another probably easier way to find the smallest focus that does not use your eyes to figure it out. Basically, you are going to use your laser to engrave at various z heights. Start at a lower height and then increment Z up by 1mm or so. Do this several times and then see which the smallest line is. Here are the details:

Take a scrap piece of wood or other waste material that has some room for lines.
Set the laser power so it doesn’t cut, but instead gives a nice dark engraving without burning too much.
Make a program in Inkscape with a set of lines next to each other will a little spacing between the lines(see below for our file). Open the file in notepad and adjust the Z axis up by 1mm every line.
Set your Z to where you think your focus is somewhere than as good as you can get.
Run the program. It will engrave the first line and increment the Z axis up on each line by 1 mm. If you use our file It will start on the top line in the Inkscape drawing.
Inspect the lines and see if it they get larger or smaller in size. Best case scenario is one line looks thinner than the others. The thinnest one is your best focus. You can then increment the Z axis back to this position (i.e., if it is on the 4th line from the top, then you need to increment the Z axis back up by 4mm in the manual control. )
If the lines just get bigger, then you started too high. Set the Z axis down and then re-run the program again and see if there is a thin line in the group. Set the Z then to this line.
If 1mm is too big an increment, then re-run the program with smaller increments to “hone in” on where the thinnest line is. If 1mm is too small of increments to tell, then make them bigger and then find the thinnest line and repeat with smaller increments when you get closer.

Inkscape File with example lines

G Code File with 8 lines, Z moving up 1mm each

Note: This will set the focus to the top of the material you are using to check focus. If you want to make the focus be at the work piece then just adjust the Z axis down by the thickness of the material you were using. Then, just measure whatever you want to engrave and adjust back up by this thickness to be sure you are at the top of the material before processing.

Example of engraving lines while moving the Z axis to find the smallest focus. This case it is 26 mm up.

Conclusions

Focusing the lens to the smallest focus is a very hard thing to get correct without a lot of practice. It is however one of the most important parts needed to get the results shown in the applications pages on this site. If your laser is out of focus just by a little bit, then the power density of the spot goes way down. Think about getting your laser in focus to back when you were a kid and you had a magnifying glass and you used it to try and catch something on fire by focusing the sun (if you never did this then just imagine it). It is hard to get that little image of the sun to stay in one spot in order to get something to burn! This is the same with your laser, but once you get it right you can dial it in every time as long as nothing changes on your machine! Remember, practice makes perfect and good luck!