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]

CNC 3018XL: Pilot V5RT Pen Holder Lock Screw

Flushed with success about the MPCNC drag knife locking screw, I installed a similar screw on the V5RT pen holder for the CNC 3018:

Pilot V5RT holder - lock screw insert - assembled
Pilot V5RT holder – lock screw insert – assembled

A dark ring of epoxy around the screw holds a shortened M3 brass insert in place:

Pilot V5RT holder - lock screw insert
Pilot V5RT holder – lock screw insert

As it turned out, the original recess left only a few threads for the M3 SHCS, so the much longer screw wobbulated alarmingly. I drilled out the threads, turned the knurls off the insert, shortened it a bit, masked the pretty knurls on the aluminum ring, then glopped the insert in place while the Sherline held the screw vertical:

Pilot V5RT holder - insert epoxy
Pilot V5RT holder – insert epoxy

While I was at it, I added a thin ring of foam rubber under the knurled ring to keep it from clacking against the upper bushing.

Now I can’t lose the hex wrench when I take the thing out for Show-n-Tell sessions …