Lasers Explained

Explanation of Lasers

by Louie Alvarez

Listen to the 4 part Podcast accompanying this article:
Season 1, Episode 2-5: Explanation of Lasers

Tube types
The most popular type of tube within the Awards & Engraving industry is by far the CO2 laser tube with the YAG laser tube type following a distant second. Each operates at a different frequency range allowing the ability of each to affect different types of materials, but essentially not the same materials, i.e.,

  • CO2 … Wood, Acrylic, Anodized Aluminum, Coated Metals, Leather, Plastics, Glass, etc.
  • YAG … Specifically for marking raw metals, even focus to center of glass for 3D engraving within the glass

CO2 is the least expensive, hence the industry standard allowing for lasering of the most popular and profitable materials and now even raw metal is laser capable with third party solutions from Thermark or Cerdec and now both available from the intellectual property owner Ferro.

Power availability
CO2 lasers come in various power choices. The leading manufacturers (CheckMate Lasers, Epilog, Universal, GCC) range is 12 to 130 watts of power, with the 100, 60, 50 & 30 watt tubes being the most popular purchased wattage on the market (in that order). Price being an obvious difference what else does the additional/higher power wattage gain you?
1) Depth of engraving. The harder the wood (the most popular engraved material) the more power required to mark the surface with a deep enough and dark enough burn to give the best contrasting results.
2) Thickness of cutting. Thicker acrylics (the most popular cut material) require more power. A properly configured and well-built laser engraver should be able to perform the following cuts with the noted power:

40 watts … 3/8” cast acrylic single pass cut
50/60 watts … 1/2” cast acrylic single pass cut
80 watts … 3/4” cast acrylic single pass cut
100 watts … 7/8″ cast acrylic single pass cut
120/130 watts … 1″ cast acrylic single pass cut

Granted this is the thickest cut possible for the wattage noted so you’re system will be cutting at the highest power setting with the slowest speed, but this also translates into thinner pieces cutting easier and faster. NOTE: You should never cut materials with more than a single pass. If you must cut with multiple passes obtain a higher wattage. The subsequent cuts simply make the edge quality unacceptable and multiplies the time to complete the job extends the throughout by a factor of x passes.
3) Speed at which to raster engrave certain materials. Marble, hard woods, glass, metal marking & 3D engraving all require a tremendous amount of power to obtain acceptable results. A 40 watt laser engraver requires the machine speed to be dramatically reduced so the laser beam has time to dwell long enough to do its job. With more power you can begin to increase the engraving speed of the laser machine to achieve the same results.
4) Finally cost. The lower the wattage, the less expensive the machine will be, while the higher wattage units can and will cost significantly more. I would be remiss not to add that the initial savings of purchasing a lower wattage will cost significantly more in the long term by time lost (having to run your laser slower) and by not having adequate power (to work on thicker acrylics or harder materials). Don’t skimp on power, ensure you get a power wattage that can grow with your business.

As a recommendation 40 watts is the minimum recommended power you should consider with 50/60 being optimal. To put this into perspective keep in mind that “Time is Money” so although the 12 watt can do what the 40 watt tube can and at a great cost savings initially, the 1/3rd speed reduction in speed to duplicate what the 40 watt produces will cost the average shop over the long term in terms of time vs money. So for all intents and purposes the 40 watt tube is the minimum you should ever consider for standard awards & engraving projects.

Power Upgradeability
If your not making money then you obviously will not be interested in upgrading your laser tube. If you are profitable and require more power you will most likely purchase a second more powerful machine to increase (double) production. Tube upgrades are no more than a marketing ploy. Get the power that your budget will allow today and when your ready for more power tomorrow consider a second unit with the latest and greatest technology at the power wattage you require and double your production significantly.

Dots Per Inch (DPI) ranges from the major manufactures is 125 at the lowest (draft mode) to as high as 1200 (fine mode). Unlike traditional printers that are adding ink of various dot sizes of various colors to achieve an image the laser engraver is removing material as the laser beam vaporizes the surface. With regular printers changing the DPI is noticeable to the naked human eye due to the fact that these printers can adjust the size of a dot and changing copy paper to photograph paper will provide for incredible prints. Not so with laser engravers, the beam size NEVER changes and you must remember that you are removing material. 600, 750, 1000 or 1200 DPI only forces your laser job to take that much longer and the naked human eye simply cannot distinguish the difference in the laserable materials to justify the additional time required to laser at these high resolutions. Market competition is what forces laser manufacturers to provide these high resolutions but in everyday laser projects you will rarely if ever will exceed 500 DPI.

Pulses Per Inch (PPI) represents how many times the lase tube must fire in a given inch distance. This setting usually can be increased or decreased to fine tune how well the final cut of your material will be. A guide to begin your testing would be: a high PPI setting for acrylic, mid-range setting for wood, low setting for plastics.

Rule of thumb: DPI is applicable to raster engraving, whereas PPI is applicable to vector cutting. When “raster engraving” your image will determine how many times the laser tube must fire to produce the image you desire so PPI will be ignored. On the other hand when vector cutting your PPI settings is determined by you while DPI will be relatively ignored.

Lens Availability
All major manufactures provide a 2” focal distance lens as a standard with their machines. But they also offer 3 or more additional lens for various purposes. For all intents and purposes the 2” lens will suffice for 99% of all traditional laser engraving projects. Following is a list of the most common size lens, beam size and possible usage.

Lens | Approx. Beam Diameter | Useage
1.5″ | .003″ | Fine detailed lasering, i.e., Italian charms
2.0″ | .005″ | The happy medium for engraving and cutting with emphasis on engraving better than cutting
2.5″ | .007″ | The happy medium for engraving and cutting with emphasis on cutting better than engraving
4.0″ | .012″ | Deep material distance engraving, I.e., bowls, rotary engraving, etc. and thick material cutting

The focal distance essentially means the hottest point at the smallest point size the beam can provide based on the specific lens used. Compare this to using a magnifying glass to focus the sun’s heat on a tree leaf to heat it up enough to cause it to catch on fire. As long as the magnifying lens is out of focus from the sun to the leaf the width of the beam is to wide with not quite enough concentrated power to cause a fire. Bring it into focus and bottabing you have fire. The laser tube is essentially the same, the beam out of the laser requires focusing to provide the hottest point for utmost quality results.

Ventilation and Air Assist
Ventilation is a necessity not an accessory, the more “Cubic Feet per Minute” (CFM) of air moved the better. Your manufacturer will recommend a minimum CFM that your particular machine will require, typically based on the cabinet size. Never operate your laser without a properly operating exhaust ventilating outdoors at the minimum CFM recommended. This not only removes smoke and dust from the cabinet of your laser engraver but exhausts any dangerous fumes.

Finally NEVER vector cut ANY material without an air assist connected to an adequate compressor. The air assist is essentially a hose plumbed from outside (inlet) of the laser engraver fed throughout the machine to point at the area (outlet) in which the laser beam is located when engraving/cutting. When connected properly to a compressor and turned on a steady stream of air is blown at the surface of the material that your laser is working on. This provides three essential services.

  1. Cleanliness: Keeps the lasered area clear of debris
  2. Airborne: Gets the vaporized material airborne allowing for better exhaust
  3. Flamage: Finally most important; eliminate flamage. The very nature of combining heat with certain materials (wood, plastic, acrylic, etc.) will cause flamage which not only will ruin your material but could also damage the lens assembly, plus an unattended machine could be disastrous. Cutting without air assist is foolish and should never be done. Air assist equals safety.

Speed vs Power
The material and the wattage of your laser system will determine the best Speed|Power settings for the desired effect. The best method of testing a material to determine the optimal settings is to use scrap material and laser a one inch square at 100% speed/100% power (base guideline), next to this square laser another at 50% speed/100% power (simulates twice the guideline depth at twice the time to complete), then another square at 100% speed/50% power (simulated same speed but at half the guideline depth). Finally laser at 250dpi and 500dpi setting to determine which dpi will achieve the best results in the most acceptable time frame (keeping in mind that 250 will complete twice as fast as 500 dpi). Add these settings should be lasered as well underneath the squares for future reference.

New vs. Used
Buyer beware! You get what you pay for including issues the previous owner had to contend with. Without the support and knowledge of the equipment, maintaining it adequately to perform well may be out of reach for the uneducated, untrained, uninformed buyer. Do your diligent research and seriously consider only new lasers.

What will a new laser get you that a used one won’t? Warranty, training, support, installation, configuration, driver updates, access to tutorials, videos, similar laser owner peers, less expensive parts and accessories, etc. Each manufacturer and dealer/distributor provides various levels of each of the items listed whereas a used laser will leave you with nothing but your own skills and ability to self-teach ones self.

Laser engraving technology has surpassed those initial growing pains and the technology has greatly matured. Today’s laser engravers have eliminated the issues that haunted the early days of the industry. Motion systems, bearings, belts, laser tube, optics, software driver, quality of raster engraving and vector cutting, general maintenance and overall knowledge of the laser engraver capabilities has vastly improved with this maturity.

With that said if your budget will only allow for a used unit, test it extensively prior to purchase. Vector cut circles (are the circles round or oval in shape and did the beginning and end meet properly?), vector cut squares (are the corners meeting correctly?), then cut again with round corners on the square (did the beam get through the curves as well as the straight lines?). Raster engrave logos, photographs and text (is the lasered surface flat and consistent?) Compare a file with various settings (determine quality and consistency). Finally do you know the age of the unit (might no longer be supported)? Does the manufacturer still provide spare parts (could be very expensive if hard to locate)? Is the tube nearing recharge time (this can cost thousands of dollars in recharging fees and weeks of down time)? No manufacturer has a timer on their laser tube so it is impossible to know definitively the time usage of the laser tube or at what average power was used on the laser tube, nor is there a way to know how many hours of life is left on the tube. Finally, where will you obtain support (you may have saved $ initially but when you call on an expert for assistance, don’t be surprised by the $3000+ maintenance/contract/support fee)? All these things are important issues to consider and determine prior to the purchase of a used unit.

Consider yourself forewarned!

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