Tarkin

Tarkin is the new large-format laser cutter in the space. It's a custom-built laser cutter based on an RF CO2 10.6um laser and CCM linear rail motion system with a Ruida RDC6445G controller running Lightburn software. It features 225W of power on a 1.6M x 1.0 M (63"x39") cutting bed, powered Z, 8MB alignment camera, and air assist.

It's quite large and capable -- we don't think there's anything like it in central Texas.

A new class will be required for users. The Ruida controller utilizes a workflow that will be common among Asmbly lasers.

Important Terms

(just proposed for now, following documentation needs editing to use these consistently)

Machine bed

the physical machine's actual work area.

Control Panel

the Ruida hardware panel on the physical machine. Small color LCD and membrane keys. Not to be confused with the Lightburn software.

Material

your physical stock- a piece of plywood, acrylic sheet, etc. You'll be placing it on the machine bed and cutting your job on it.

Lightburn

the software on the PC for CAD, specifying what to cut and how, and has control for some live interaction with the machine. Your job is created within a workspace inside Lightburn.

Workspace

Lightburn's work area on the PC. This is the same as the machine bed only if you make the workspace size the same as machine bed size and operate in absolute coordinates. Otherwise, where your job is placed on the workspace is not necessarily where the job will be when you go to the machine bed, and your workspace can be declared in a different size than the machine bed. Note that in either case, your job (the actual content) will probably be smaller than the whole declared workspace, and cannot be located outside the workspace when you actually want to send it to the laser.

Job

your content- vector/raster operations you want the laser to do. The location of the job on the machine bed is flexible and can be moved from the control panel, or it can be fixed. Your job exists in two forms- on the workspace (Lightburn software), and on the machine bed (physical machine). In the case of user origin, they may not be in the same place.

User origin

your job's origin. It is not used in absolute coordinate operation. The user origin also has two forms- it is represented on the workspace with a green square, and can move in relation to your job. At the control panel, you will set the user origin to the current head position with the ORIGIN button, which moves your job so that the green square will be at that point.

Origins

Tarkin's origin is commonly set in one of three ways:

Absolute coords

using a workspace the size of the machine bed. The location of your job is fixed and the user does not operate the ORIGIN button on the panel, as there is no user origin. The camera may or may not be activated

User origin

Your material is placed anywhere on the bed that is convenient, and the user moves the head to the desired origin point and presses "ORIGIN" to work around that spot. In this case, it is not important where the user places their job on the PC's workspace, or that the workspace be of the size of the laser's bed at all. Lightburn will automatically create a bounding box around all the user's job within the workspace, whether or not it is designated to be sent at that time. The user can specify the work origin to be in the center, any of the 4 corners (top left most common), or 4 sides (uncommon). It is possible to place the origin in a way that the job will eventually run off the machine bed, this will result in "FRAME SLOP ERROR" and will not run. Correct the origin position and use the FRAME button to verify its bounding box. Note that moving your job around the machine bed via the user ORIGIN button does not move your job on the workspace.

Camera-placed absolute coords

Your material can be placed anywhere visible to the alignment camera, the Lightburn workspace is set to the full machine bed size, the user jogs the gantry out of the line of sight (not obscuring your material), and then Lightburn takes a camera snapshot of the machine bed that shows up as a graphical background with your material on the workspace. The very rear of the machine bed is not visible to the camera for alignment purposes, as the lid is hinged closer than that. The user moves and aligns the vectors/raster job across the workspace so it is over the actual material by moving the job in XY and, if necessary, rotation and resizing may also be done. Lightburn will automatically change to absolute coordinates in camera mode, and the user does not operate the ORIGIN button. This method can also be used for hybrid work- for example, color printing paper graphics that were glued to plywood earlier, this material is then placed and aligned via camera and cut out into desired shapes with the laser, or an existing manufactured object is placed on the bed and the job aligned over it. There is no auto-recognition of printed registration marks, but printed registration marks do make alignment easier and more accurate. Another example might be a unique horizontal slice of a tree can be traced and artwork can flow with that arbitrary shape in size and alignment. So far, the accuracy has been better than 2mm, and may be improved with further calibration.

User Origin, CENTER, is the safest option if you are using clamps. The head will return to that origin at the end. So, that origin point being in the center of your job, no clamps should be in the way. However, the head will of course have to travel in a line from wherever it is to the start point, so if the user origin was not set correctly or the head is for some reason located outside the job before starting, it might still be possible to strike a clamp. Currently we do not think head strikes will be a big problem for the machine, mostly it would mean your material gets knocked around and your job could be spoiled.

Lightburn has a database of known-good values for cutting and rastering on Tarkin, listed by material. Feel free to use them, but these can only be created or modified by admin. If you want a new entry, please submit the parameters and if possible a piece of that material and we can include it. Pearl will also have a Lightburn material database after it is converted to that controller, but it will have different values as the beam's power is different.

The machine's top axis speed is set well over 1000 mm/sec, but this is not likely to be important for rastering as this sort of speed is not commonly used. If the user's job asks for a speed higher than the machine can travel, the machine will limit its speed and proportionately scale back the % power to deliver the specified energy per mm of length.

Rastering

Types of Rastering:

FILL

just marking/carving out even blocks. Line intervals <0.15mm cut deeper (typically not of value, just slows down job)

GRAYSCALE 2D

laser power is modulated by grayscale shade. Goal is not depth, but shading. Line intervals <0.15mm cut deeper (typically not of value, just slows down job). Grayscale works if your material can show good dynamic range (shade darkens proportionally with beam). Dynamic range of material must be investigated carefully- for example, plywood veneer may start light, burn darker with more beam, but past a certain point we cut through the veneer and briefly get a red shade from the glue and then a totally different shade from an inner ply. This would be a very poor dynamic range.

Some materials such as black marble would have an inverted dynamic range- unburned is black, but it becomes white when burned. In this case, Invert Image button may be desired.

GRAYSCALE 3D

Same mode, but different goal. Laser power is high enough to carve into the material, depth is proportional to shade. Works with wood and acrylic. If you want to avoid creating obvious unburned areas where the shading is very light, set MIN POWER parameter >0%

DITHER/HALFTONING

Works well with material with a poor dynamic range. Image is made of burned and unburned spots. The size of the burned spots increases with darker shade, but darker does NOT make the beam stronger. A wide range of methods are available that arrange burned vs unburned regions.

Dithering/halftoning MUST use correct Line Interval that matches the beam width. The width of the beam at good focus is approximately 0.15mm. Line intervals >0.2mm will create parallel lines rather than a solid fill.

If you are doing photographic raster work such as dithering/halftoning, line intervals <0.125mm will distort the image shading. The scheme of dithering is we have the original unburned surface and burned "brown" areas and nothing in between. The appearance of "shading" is created by a ratio of these, not by turning the laser intensity up and down. When raster lines overlap, the area that was intended to be bright and unburned on one line may actually be made brown by the line(s) above and below it, and the image will have distorted shading or even lost entirely in a mass of brown.

RASTER EXTEND SPACE: what's that?

All rastering is done when the laser head is at the specified constant velocity, for image consistency. This requires "extend space" on the margins of the raster for the head to brake to a stop and accelerate back, and the amount of extend space required scales up with raster speed. For this reason, rastering cannot be done at the far left/right margins of the machine bed. If your job requires extend space that exceeds the machine bed, it will abort with a "NOT ENOUGH EXTEND SPACE" error when you press Play. Move the raster work from the edge or reduce raster speed to shrink the extend space needed.

Extend space creates a slightly complicated relationship with raster speed and ultimate job time. 500mm/sec is very little extend space, >1000mm/sec requires quite a lot. For example, with a raster image only 10mm wide, running 1000mm/sec will actually take longer than 500mm/sec as it must use a wide margin of extend space to brake and reverse up to that high speed that is only used for 10mm. However, for a 1m wide raster, 1000mm would be substantially faster. The time wasted braking and reversing through the extend space on each pass is fixed, but the bulk of the time is spent on the 1m raster job which goes twice as fast.

The FRAME button does NOT show the bounds of Extend Space. Take care when placing clamps to the left or right of a raster. There is no easy way to see how much Extend Space will be used. The amount of Extend Space also depends on the machine parameters, which may be tweaked from time to time.

Materials

Usable

Same as CO2 lasers- acrylic, plywood, wood, cardboard, some plastics.

Glass and stone can be etched, but they cannot be cut

Paper and other light materials may be susceptible to being blown around by the air assist. This may result in a piece flying out and laying across the material, taking an extra hit and shielding that material from the beam on a later cut.

Prohibited

NO PVC

NO PVC or ANY FORM OF "VINYL". This is 60% chlorine atoms by weight, and the fumes are corrosive to the equipment. Do not attempt!

NO Polycarbonate

NO POLYCARBONATE ("LEXAN"). Although it looks very much like acrylic, polycarbonate does not cut. It turns brown and cracks and produces a ton of soot chains that dirty the optics.

NO METAL

Currently, NO METAL. This included removing paint, aluminum anodization, or fusing Cermark/moly dry lube to steel, aluminum, brass, and copper. While we can normally mark (not cut) metal with a a beam of this power, the reflections may be capable of damaging the laser. If you have such a project, please contact workshop and we can supervise and see how this works.

Copper Wire Flame Test

When in doubt, there is a copper wire "flame test":

https://www.youtube.com/results?search_query=laser+cutter+flame+test

Machine Errors

WATER PROT

coolant flow not detected. Most likely, the chiller is not turned on.

SYS ALARM, MACHINE PROTECTED

Most likely, door is open. Also, in rare cases, the motor drive has faulted due to collision or excess raster speed

FRAME SLOP

The job sent, with the current user origin, would go outside the bounds of the machine bed

NOT ENOUGH EXTEND SPACE

The raster's extend space will go outside the bounds of the machine bed, even if the raster art does not.

Current Quirks

Table shifting when moving Z

X and Y can shift slightly when Z is moved. Be sure to move the Z before placing the origin. This will be corrected soon.

Excess power in vector start/stop/cornering

By design, the motion controller always scales back the beam power when it is not able to achieve the specified velocity, due to acceleration limitations. However, the Ruida is not scaling back enough and can deliver excess power where vectors start, stop, or sharply corner or perform very tight curves. This appears to be a limitation of the Ruida controller and has no immediate way to correct.

This may affect vector engraving, producing excess depth. This depth inconsistency is more noticeable on clear acrylic, but it requires close inspection.

Currently this occurs roughly 6mm before and after any full stop.

This is a nonissue for normal cut-throughs, the extra power will not affect the cut. It will mean that vector start/stop points may achieve a full cut-through near the start/stop points even though the speed is set too high to produce a full cut. To ensure a test line accurately represents the cut, perform test cuts at least 20mm long.

This issue does not exist when rastering

Possible Resolution

Tweaking of cut parameters, more technical solution may be called for.

Fixed air assist

Air assist is a strong flow and has no adjustment yet, and cannot be turned off as that would quickly overheat the lens. This may present a problem for cutting light things like paper, especially thin pieces. Small pieces of thin. light material (including plywood) can also be moved. Inside Lightburn, be sure to select "Cut Inner Shapes First", and manage the cut order in Layers so a piece is not cut free and then something else lasered inside it after it might have shifted in the air flow.

Limit on Y size

The far side of the Y is not accessible due to a limitation of where the homing sensor could be easily placed. The current available work area is 1600mm x 866 mm. This will be corrected soon.

Drive Faulting

If the motor drive capabilities are exceeded and a drive fault occurs. the machine will stop immediately, and throw a generic "System Protected" error, the same as if the lid is open. This error might occur if excess rastering speed is demanded (>1000mm/sec?) or crashing the head into the material, clamp, or jig. Of note, the problem axis cannot be jogged with the control panel, even though the panel coordinates increment. The other axis moves normally. This fault is resolved by cycling Main Power on Tarkin and letting it rehome. If this fault occurs due to rastering or any case other than crashing the head, please contact workshop with details about settings and, if possible, a copy of the Lightburn project with the settings that led to the fault.

Cone clipping

If the machine is not cutting as fast as usual, please check the temperature of the air assist cone immediately after cutting. Be careful, it can be hot. It is normal to be warm, however, if uncomfortably hot to the touch, the final mirror may need realignment. Please contact workshop immediately, as operation while badly misaligned may damage the lens. This has not been a problem yet.

Maintenance

This tool is owned by Danny Miller and hosted at Asmbly for members to use. Please contact the workshop committee if maintenance is required.