Ruida Controller Home/Limit Switch Configuration

A discussion on the LightBurn forum prompted an investigation of how Ruida laser cutter controllers handle their homing operation. This is a lightly edited version of (some of) my comments with added pix.

There being nothing quite like a good new problem to take one’s mind off all one’s older problems, I just did some tinkering with the X axis settings…

This is on a Ruida-ish KT332N, but the manual’s verbiage is pretty much the same as the 6445G.

Changing the settings requires a controller reset, which will trigger a homing operation if it’s enabled.

Limiter Polarity inverts the sense of the limit switch input signal. My OMTech has Normally Open proximity sensor switches:

OMTech Fotek PL-05N proximity limit switch
OMTech Fotek PL-05N proximity limit switch

So the default setting of False makes it inactive in the middle of the platform.

I set it to True, which made it active in the middle of the platform:

Ruida KT332N Controller - inverted X limit switch
Ruida KT332N Controller – inverted X limit switch

So True would be the correct setting for a Normally Closed switch.

Direction polarity sets the direction the axis moves during reset, which must be toward the home switch. Mine was set to False and it homes toward the right side where the limit switch sits.

I set it to True and it started homing toward the left, where the limit switch isn’t. Hitting Esc on the control panel stopped the homing process and left the head in the middle of its travel, unhomed.

Apparently Direction Polarity directly controls the DIR signal to the stepper motors, because both the control panel keys and LightBurn’s motion buttons then moved “the wrong way”.

That does not affect LB’s machine coordinate origin, which remains at the top right of the layout, or the orientation of the X axis, with values increasing toward the left as usual.

Invert keypad direction inverts the motion direction with respect to the homing motion. Mine was False, but flipping it to True reverses both the keypad and LB directions.

I think Limit Trigger refers to “hard limits”, which requires a limit switch at each end of the axis, but my controller does not have the + inputs that would allow me to test that. The controller doc says it uses “soft limits” to prevent out-of-bounds motion by using the home position and maximum axis travel value.

So the available options allow all possible combinations of:

  • NC or NO limit / home switches
  • Homing direction
  • Keypad / LB motion commands

A reasonable sequence seems to be:

  • Set the switch polarity to match the hardware
  • Set the homing direction toward the switch
  • Set the “keypad” direction to match your expectations

With that in mind, careful experimentation on the actual controller in hand seems prudent …

Laser Engraving vs. Acrylic Mirror: Scattershot

The improved Holly Mirror Coaster looks pretty good:

Holly Coaster - overview
Holly Coaster – overview

Until you realize some of those specks aren’t surface dust and take a closer look:

Holly Coaster - mirror speckles 1
Holly Coaster – mirror speckles 1

The surface scratches are doubled by their reflection in the bottom mirror. The little dots that aren’t doubled reveal marks in the mirror surface itself.

An even closer look:

Holly Coaster - mirror speckles detail
Holly Coaster – mirror speckles detail

As nearly as I can tell, those are random speckles caused by the laser tube firing when it shouldn’t, due to the chaotic nature of the gas discharge going on inside.

In this case, they cause defects in the mirror coating allowing alcohol from the fat-tip permanent markers coloring the engraved areas to hit the acrylic. The starbursts come from stress cracks around the punctures.

Peering even closer shows similar cracks along the edges of the colored areas:

Holly Coaster - mirror speckles tight detail
Holly Coaster – mirror speckles tight detail

Not much to do about the random speckles, but it’s obvious I must up my coloring game.

Which would be significantly easier if rattlecan spray paint sprayed at winter temperatures …

Holly Coaster: Improved Mirror Setup

Other than demonstrating that it’s possible to laser-engrave a 3 mm deep pocket in a ¼ inch thick piece of scrap paneling, the process didn’t have much to recommend it:

Holly Coaster - mirror flaws
Holly Coaster – mirror flaws

So I re-did the layout to put the 3 mm mirror in 3 mm thick plywood:

Holly Coaster - overview
Holly Coaster – overview

The coaster has a self-adhesive cork pad on the bottom, which required an intermediate adhesive layer holding the aluminized Mylar reflector on the bottom of the mirror to brighten the colored areas.

The LightBurn layout shows all the pieces:

Holly Mirror Coaster - LB layout
Holly Mirror Coaster – LB layout

The plywood cuts with the good side down, although “good” is certainly a judgement call with B/BB grade plywood. I cover the good side with blue painter’s tape to reduce scorch marks. In a real application, you’d do some sanding and finishing, probably before cutting; in this case, I want to see what happens to bare wood in coaster duty.

Engrave and cut the mirror with the backing upward:

Holly Coaster - removing mirror layer
Holly Coaster – removing mirror layer

The tracer rounds may be burning aluminum.

I colored the engraved areas with fat-tip permanent markers, despite knowing the alcohol will crack the acrylic. In real life, you’d use spray paint, probably with laser-cut tape masks.

The adhesive layer extends 2 mm beyond the mirror perimeter to stick onto the bottom face of the plywood:

Holly Coaster - adhesive placement
Holly Coaster – adhesive placement

Peeling off the paper reveals the adhesive tape stuck to the back side of the mirror:

Holly Coaster - adhesive exposed
Holly Coaster – adhesive exposed

Apply the similarly embiggened aluminized Mylar to the adhesive:

Holly Coaster - mylar placed
Holly Coaster – mylar placed

Cutting the holly shape directly from the original foot-square adhesive sheet lets me tuck smaller shapes into the remaining uncut areas. In a production environment, however, joining the Mylar and adhesive (perhaps using pre-cut squares), then cutting them as one sheet would definitely simplify the process.

Then peel-n-stick a cork disk (thus explaining why the plywood is exactly 4 inch OD) on the bottom:

Holly Coaster - edge view
Holly Coaster – edge view

I’ve been aligning the cork by feel, which explains the half-millimeter overhang along the right side. Inexplicably, I have yet to justify an alignment fixture.

The LightBurn SVG layout as a GitHub Gist:

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Frosted Snowflakes

After the first two snowflake coasters, it finally penetrated my thick skill that putting a 1 mm hole in the flake cut from the center of the plywood would convert it into a decorative window hanging:

Snowflake Hanger - plywood
Snowflake Hanger – plywood

Admittedly, I may be using the word “decorative” in a manner you had not previously encountered, but work with me on this.

Cutting a similar flake from transparent acrylic looks better:

Snowflake Hanger - blue acrylic
Snowflake Hanger – blue acrylic

Transparent acrylic turned out to be, well, too transparent, so I set up a LightBurn layout to “engrave” a light frosting on the flake before cutting it out:

Snowflake Hangers - engraving in situ
Snowflake Hangers – engraving in situ

That worked for all subsequent flakes, but I had to do something about the first few flakes. After realizing that the time to engrave an object depends only on its width, I set up a rectangle with the proper parameters, snugged two forlorn flakes next to each other, and fired the laser:

Snowflake Hangers - retroactive engraving
Snowflake Hangers – retroactive engraving

I thought using cardboard was a Good Idea™ for a stable backing, but lightly vaporizing the top layer produced an unbelievable amount of filth:

Snowflake Hangers - frosted
Snowflake Hangers – frosted

I had to scrub those poor flakes with dish detergent and a toothbrush to get them even close to their former pristine state; the blue one may never recover.

Anyhow, frosted flakes look good if you don’t look closely:

Snowflake Hangers - frosted
Snowflake Hangers – frosted

The grid pattern comes from the window screen in direct sunlight; the vertical bars are DIY BirdSavers.

The LightBurn layout produces 120 mm coasters to fit my 20 ounce mugs:

Snowflake Coaster 120 mm - LB Layout
Snowflake Coaster 120 mm – LB Layout

You get two hanging flakes: one plain plywood and one frosted acrylic!

The LightBurn SVG layout as a GitHub Gist:

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Snowflake Coasters: Kerf Compensation

A flurry of snowflake coasters:

Snowflake Coaster - assortment
Snowflake Coaster – assortment

The two on the left are the original snowflakes with interchanged innards and, perforce, no kerf compensation.

The upper-left coaster has a wood flake surrounded by acrylic, which makes a sharp clack when you set a glass down on it. The wood surrounds emit a much more pleasing clunk.

The next two have 0.1 mm compensation applied to their acrylic snowflakes, which produces snug fit (original on the left, compensated on the right):

Snowflake Coasters - kerf corr 0.0 vs 0.1 mm
Snowflake Coasters – kerf corr 0.0 vs 0.1 mm

Applying 0.2 mm compensation makes the flakes impossible to push in, so the true compensation is somewhere just over 0.1 mm. I think you could optimize for a specific wood and acrylic combination, but, as with 3D printing, any change requires something different.

The little arrowhead shapes tend to get lost, so collecting them on a strip of tape while you’re hunting in the chip tray helps:

Snowflake Coasters - plywood cutouts
Snowflake Coasters – plywood cutouts

The dark flake on the right got a coat of walnut stain, as did the two darker coasters in the first picture. It looks better in person than in the photo, although Mary still thinks the lighter wood sets off the white acrylic just fine.

The two large (120 mm OD) coasters fit my 20 ounce mugs, with the Nanook Memorial Coaster in the lower right.

Ersatz Library Card

The rather battered library card on the bottom has been rattling around on Mary’s keyring since late in the last millennium:

Library card tags - front
Library card tags – front

I made the one on the top as a replacement, because Mary wanted one, but the library no longer issues keyring cards these days.

The front surface was laid out in The GIMP, inkjet-printed on good paper, cold laminated, laser-cut with LightBurn’s Print-and-Cut process, then affixed to the acrylic tag with really good double-sided tape:

Adriance Card - LightBurn PnC layout
Adriance Card – LightBurn PnC layout

I cut and applied the tape after cutting the tag, but the next time around I’ll apply the tape to the stock and cut both together to improve the edge alignment.

The rear surface data is engraved directly into the same Trolase laminated acrylic I used for the plant tags:

Library card tags - rear
Library card tags – rear

The smaller text uses dot mode and the bars & number are engraved:

Library card tag - detail
Library card tag – detail

In retrospect, it’s painfully obvious the engraving passes should run parallel to the bars, rather than perpendicular to them.

The barcode uses Codabar encoding generated with a Codabar font. I scaled the graphic block slightly larger than the original in the hope of making it more readable.

I determined the start and stop characters by trial and error; for this card, they’re A and B. Which could, perhaps, stand for Arlington Branch, but might equally well be coincidence.

It worked perfectly on the first scan at the library counter and apparently went entirely unnoticed. I trust duplicating a library card does not constitute a federal offense.

For what should be obvious reasons, however, I’m not posting the LightBurn layout.

Sears / Kenmore Vacuum: Design Tweakage

Despite cogent reasons for not buying another Sears vacuum cleaner, the brand currently represents a local maximum of the desirability curve: cheap, readily available, works well enough, and, surprisingly, bags for the defunct Progressive (whatever that meant) vacuum seem to fit just fine.

But the new one does come with some annoyances, starting with trendy dark gray engraved / molded control markings:

Sears Vacuum - power and cord controls
Sears Vacuum – power and cord controls

Quick: from the other end of the vacuum hose, which one must you stomp to turn it off?

Well, I can fix that:

Sears Vacuum - marked power switch
Sears Vacuum – marked power switch

After the Progressive’s bizarre and overly complex tool fittings, the new unit has tools that slip-fit onto a classic steel tube, which means I can throw all those adapters into a box of 3D printing examples for use in the unlikely event I ever do another show-n-tell presentation.

It also has a simple rotating suction control ring at the handle:

Sears Vacuum - marked suction vent control
Sears Vacuum – marked suction vent control

Which, as you can tell from the fluorescent tape, featured the same embossed and unreadably small dark gray markings.

Because that ring and its glaring tape is invisible from the user’s end of the handle, I eventually duct-taped the ring in position to prevent another inadvertent loss-of-suction accident.

If we ever need reduced suction on a regular basis, I’ll conjure a better ring from the vasty digital deep:

Sears Vacuum - suction vent doodle
Sears Vacuum – suction vent doodle

I obviously no longer form deep emotional attachments to these things …