Diamond-Drag Styrene Engraving: Line Width

Engraving all the Tek Circuit Computer scales on a single sheet of styrene plastic with a diamond drag tool produced a test piece with plenty of lines and characters:

Diamond on styrene - engraving test - in action
Diamond on styrene – engraving test – in action

I covered one quarter with good old black Sharpie, a lacquer crayon, and well-aged black acrylic wall paint:

Diamond on styrene - engraving test - raw color fill
Diamond on styrene – engraving test – raw color fill

Applying a sanding block removed the rubble + scribbles and brought the surface down to the engraved patterns:

Diamond on styrene - engraving test - 225 250 300g 2400mm-min
Diamond on styrene – engraving test – 225 250 300g 2400mm-min

The lacquer crayon doesn’t seem to adhere well to styrene:

Diamond on styrene - 225 250 g 2400mm-min - lacquer crayon
Diamond on styrene – 225 250 g 2400mm-min – lacquer crayon

A closer look shows I probably sanded off too much of the surface, perhaps above some grit below the sheet, because those lines almost vanish:

Diamond on styrene - 225 250 g 2400mm-min - lacquer crayon
Diamond on styrene – 225 250 g 2400mm-min – lacquer crayon

The crayon may adhere better to deeper lines. These are obviously too shallow and the pigment seems to come off in chunks:

Diamond on styrene - 300g 2400mm-min - lacquer crayon
Diamond on styrene – 300g 2400mm-min – lacquer crayon

The acrylic trim paint filled its patterns, despite having turned into a gummy mass during decades on the shelf:

Diamond on styrene - 225g 2400mm-min - acrylic paint
Diamond on styrene – 225g 2400mm-min – acrylic paint

The Sharpie ink, being basically a thin liquid, completely filled its patterns and (apparently) soaked into the rough side walls. The lines seem to be 0.1 mm wide at 225 g downforce:

Diamond on styrene - 225g 2400mm-min - Sharpie
Diamond on styrene – 225g 2400mm-min – Sharpie

They’re less uniform at 250 g:

Diamond on styrene - 250g 2400mm-min - Sharpie
Diamond on styrene – 250g 2400mm-min – Sharpie

A 300 g downforce produces (somewhat) more uniform 0.15 mm wide lines and slightly distorted characters:

Diamond on styrene - 300g 2400mm-min - Sharpie
Diamond on styrene – 300g 2400mm-min – Sharpie

I have no way to measure the actual engraving depth. If the 60° diamond tool had a perfect point, which it definitely doesn’t, then a 0.15 mm wide trench would be 0.13 mm deep. I’ve obviously sanded off some of the surface, so those lines could be, at most, 0.1 mm deep.

All in all, the engraving came out better than I expected!

Tek Circuit Computer: Styrene Engraving Test

Engraving all three Tek Circuit Computer decks on a single sheet of styrene plastic with the diamond drag tool:

Diamond on styrene - engraving test - overview
Diamond on styrene – engraving test – overview

The three patterns overlap here & there, but the intent was to have plenty of engraved lines for further study:

Diamond on styrene - engraving test - in action
Diamond on styrene – engraving test – in action

The vivid blue glare comes from a flashlight at grazing incidence off to the left, with brutal color correction back to something sensible.

Engraving each deck at a different depth gave a range of downforce:

EZ='EngraveZ=-0.5mm'
Runit Bottom Engrave

EZ='EngraveZ=-1.0mm'
Runit Middle Engrave

EZ='EngraveZ=-2.0mm'
Runit Top Engrave

I fed all three of those G-Code files into bCNC, applied them to the same sheet with the same origin touchoff, and it worked fine.

The tool holder rate of 200 g + 50 g/mm produced downforces of 225, 250, and 300 g. In retrospect, the range wasn’t really broad enough, so Moah Force may be in order.

The diamond produced plenty of swarf:

Diamond on styrene - engraving test - swarf
Diamond on styrene – engraving test – swarf

Wiping the surface with a strip of masking tape clears away the loose rubble:

Diamond on styrene - engraving test - cleaned
Diamond on styrene – engraving test – cleaned

The innermost scale comes from the top deck, engraved at 300 g. The long shadows from the plastic pushed up along the tick marks seem to indicate the deepest trenches, although I don’t have any way to measure their depth.

I scribed and snapped the sheet into quarters so I can (mis)treat the engraved patterns in various ways:

Diamond on styrene - engraving test - raw color fill
Diamond on styrene – engraving test – raw color fill

What a mess!

Diamond Drag Tool Wear

The diamond drag tool now in the MPCNC LM3UU holder has appeared in several holders and suffered considerable misuse along the way:

Diamond Drag Tool tip - MPCNC
Diamond Drag Tool tip – MPCNC

A closer look at the spalled section on the flank:

Diamond Drag Tool tip - MPCNC - detail
Diamond Drag Tool tip – MPCNC – detail

The tool in the (much better) CNC 3018XL LM6UU holder has engraved mostly plastic, plus a few hard drive platters, and seems only slightly rounded:

Diamond Drag Tool tip - CNC 3018
Diamond Drag Tool tip – CNC 3018

An unused tip comes to a neat point:

Diamond Drag Tool tip - unused A
Diamond Drag Tool tip – unused A

As does its companion, arriving in a twofer deal from halfway around the planet:

Diamond Drag Tool tip - unused B
Diamond Drag Tool tip – unused B

They’re brazed on 3 mm OD shanks and ground to a 60° included angle.

Slide Rules: Real Engraving vs. Pilot V5RT Pens

A 0.5 mm Pilot V5RT pen produces good-looking results on presentation-grade paper:

Tek CC - V5RT black - glossy presentation paper
Tek CC – V5RT black – glossy presentation paper

Peering through a measuring magnifier shows a bit more tremble in the traces, but they’re still OK:

Tek CC - V5RT pen width
Tek CC – V5RT pen width

The desk light off to the upper left casts shadows from the reticle on the three different sheets.

A closer view of the linear scales:

Tek CC - V5RT pen width - detail
Tek CC – V5RT pen width – detail

The pen lines seem to be 0.25 to 0.3 mm wide, with 0.4 mm dots at the end of each stroke.

For comparison, the engraved lines on my trusty K&E Deci-Lon slide rule are under 0.1 mm:

KE Deci-Lon Slide Rule - scale detail
KE Deci-Lon Slide Rule – scale detail

The digits look like they’re embossed into the surface with shaped punches, rather than engraved like the lines. Of course, I don’t know how K&E’s production machinery worked.

A closer view:

KE Deci-Lon Slide Rule - scale detail - digits
KE Deci-Lon Slide Rule – scale detail – digits

I think 0.1 mm is an aggressively narrow trace width, even for a laser engraver.

CNC 3018XL: Arduino + Protoneer CNC

If the truth be known, I wanted to do this as soon as I discovered the CAMtool V3.3 board hardwired the DRV8825 PCBs in 1:32 microstep mode:

CNC 3018XL - Protoneer atop Arduino - installed
CNC 3018XL – Protoneer atop Arduino – installed

The Protoneer CNC board has jumpers, so selecting 1:8 microstep mode is no big deal.

As before, I epoxied another row of pins along the I/O header for Makerbot-style endstops:

Protoneer endstop power mod
Protoneer endstop power mod

I’ll probably regret not adding pins along the entire row, but, unlike the MPCNC, the CNC 3018XL won’t ever have hard limit switches. I plugged the Run-Hold switch LEDs into an unused +5 V pin and moved on.

I modified the DRV8825 driver PCBs for fast decay mode:

DRV8825 PCB - Fast Decay Mode wire
DRV8825 PCB – Fast Decay Mode wire

Then set the current to a bit over 1 A:

3018XL - Protoneer setup - Z 1 mm
3018XL – Protoneer setup – Z 1 mm

Six hours later I hauled the once-again-functional CNC 3018XL to my presentation for the ACM:

Spirograph - intricate sample plot - detail
Spirograph – intricate sample plot – detail

Memo to Self: Time to get another Prontoneer board …

CAMtool V3.3 vs. The Fat Fingers of Death

As is my custom, the day before showtime I talked my way through a final full-up dress rehearsal, with the HP 7475A plotter and the CNC 3018XL running their demo plots. As if to justify my attention to detail, the 3018 refused to home, with its X axis motor grinding in a manner suggesting something had gone terribly wrong with its driver.

OK, I can fix that™.

Turn off the power, verify the leadscrew turns smoothly by hand, check all the connections & connectors, then pull the DRV8825 PCB to see if anything looks obviously wrong. It didn’t, so I carefully re-plugged the driver and moved the whole affair to the Electronics Workbench for further study.

I turned on the scope and Tek current probes, then turned on the 3018 power supplies, whereupon a great cloud of Magic Smoke emerged from the CAMtool board and filled the Basement Laboratory with the acrid smell of Electrical Death.

It seems I carefully and meticulously re-plugged the DRV8825 PCB into its socket exactly one pin too high, which, among other Bad Things, connects the +24 V motor power supply to the driver GND pin.

Obviously, this did not end well:

CAMtool V3.3 - blown stepper fuse
CAMtool V3.3 – blown stepper fuse

The fuse, put under considerable stress, vented smoke & debris in all directions across the board; note the jets above the white motor connector. Surprisingly, the 1 kΩ resistor just below it is in fine shape, as is the rather blackened electrolytic cap.

The fuse measures the same 150-ish mΩ as the fuses in the other two axes, but I doubt it’s actually a fuse any more.

Astonishingly, the Arduino clone on the board worked fine, so I could extract the GRBL configuration.

Memo to Self: Never plug things in with your head upside down!

ACM Poughkeepsie Presentation: Algorithmic Art

In the unlikely event you’re in Poughkeepsie this evening, I’ll be doing a talk on my Algorithmic Art for the Poughkeepsie ACM chapter, with a look at the HPGL and G-Code transforming math into motion:

Superformula - triangle burst - detail
Superformula – triangle burst – detail

The PDF of the “slides” lacks my patter, but the embedded linkies will carry you to the blog posts & background information:

See you there! [grin]