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Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Slipstick

Diamond-Drag Styrene Engraving: Scraped Enamel

For the first time in a loooong time, I applied Testors Gloss Enamel paint to styrene plastic:

Engraving Testpiece D – Testors Enamel – red

Two coats of black paint produced the larger areas along the inner scales and completely filled those engraved lines:

Engraving Testpiece D – Testors Enamel – red black applied

With exactly the correct paint on exactly the correct material, it cured into a non-removable layer. Being enamel, however, the last coat requires two or three days for a full cure, so this isn’t a short-attention-span project.

It’s “non-removable” unless you’re willing to abrade the surface:

Engraving Testpiece D – Testors Enamel – scrape sand – overview

Sanding tends to remove too much plastic, particularly when confronted with raised walls & suchlike along the grooves. The darkest scale down the middle was engraved with 300 g downforce and is deep enough to retain all its paint:

Engraving Testpiece D – Testors Enamel – sanded – 250 300 g – detail

As expected, paint scrapers produce better results:

Engraving Testpiece D – Testors Enamel – scrape – 250 300 g – detail

There’s not much visible difference between the 250 g and 300 g scales.

All the scraped lines are over 0.1 mm wide, with the heavier downforce producing maybe 0.12 mm.

The double-coated lines are flush with the (scraped) surface and visibly matte. The single-coated regions have the usual glossy enamel finish remaining deep in the lines & numbers, with a thin matte outline flush with the surrounding surface. It’s basically impossible to photograph those features, at least for me.

The colors are crisp & vivid: enamel paint is the way to go!

The next testpiece should run downforce variations from 300 through 500 g and speeds from 1000 to 2400 mm/min. Scraping off the raised plastic before painting should deliver a better ahem painting experience without much surface damage; the trick will be clearing all the debris from the engraved lines.

2020-03-10
Diamond-Drag Styrene Engraving: Scraped Sharpie
Applying only two Sharpie colors to the third quadrant of the engraving testpiece produces a more restrained result:

Diamond on styrene C – scraped red-black Sharpie – start

Instead of sanding the surface, I used a paint scraper to remove everything down to the engraved grooves. The scraper in the upper right is a Rubbermaid 54807, which is apparently no longer available. If I ever buy a new scraper, I’ll spring for a carbide blade.

A dirt speck under the plastic sheet can still obliterate the markings, though:

Diamond on styrene C – scraped red-black Sharpie – first clearing

Overall, the results look just like a real slipstick:

Diamond on styrene C – scraped red-black Sharpie – 225 300 g scale detail

The upper scale was engraved at 225 g downforce, the lower at 300 g, with corresponding differences in width & depth.

Seen at higher magnification with omnidirectional light through the microscope, the tick marks have more detail:

Diamond on styrene C – scraped red-black Sharpie – 225 300 g line detail

The upper ticks are 0.1 mm wide and the lower ticks a scant 0.2 mm wide. Both ticks on the sanded Sharpie sample were close to 0.1 mm, which suggests:
- Scraping removes less plastic
- The grooves have a flat-ish bottom and side walls roughly matching the slightly worn 60° diamond tool
Sharpie ink is, of course, soluble in alcohol:

Diamond on styrene C – scraped red-black Sharpie – alcohol wipe

That’s not unexpected, as I’ve been removing Sharpie with alcohol forever, but it’s worth keeping in mind. I don’t know if spraying a clear topcoat (Krylon FTW!) would provide good sealing with enough wear resistance.
2020-03-09
Natural Enemies

I couldn’t resist setting this up for my next Digital Machinist column on logarithmic scales:

Homage Tektronix Circuit Computer with HP 50g calculator

The caption will read “Photo 1: A replica Tektronix Circuit Computer shown with its natural enemy, an HP 50g Graphing Calculator.”

It’s my desk calculator. In the Basement Laboratory, I use the HP 48 calculator app, with a couple of $10 Sharp calculators in harm’s way.

2020-03-08
Diamond-Drag Styrene Engraving: Sanded Sharpie Colors

Attacking another quadrant of the engraving testpiece with All The Sharpies produced a cheerful mess:

Diamond on styrene B – Sharpie colors

The “300 g” notation is wrong: the innermost scale is on the middle deck, which I engraved with 250 g of downforce, and reads through a window on the top deck. The next scale outward, the inner half of the green block on the left, would be on the upper deck at 300 g, just beyond the innermost scale.

I removed the excess marker with a 320 (-ish) grit abrasive sanding block, producing a remarkable amount of gray dust in the process:

Diamond on styrene B – sanded

The general idea was to find out what the colors looked like when confined to narrow engraved slots:

Engraving Testpiece B – Sharpie colors – 2×600 dpi

It’s enlarged a factor of two from the 600 dpi scanned image by the simple expedient of changing it to 300 dpi, then assuming all the downstream image handling will Do The Right Thing, which could happen.

I sanded it before fully appreciating how even the smallest particle of crud under the styrene sheet ruins the result:

Engraving Testpiece B – debris oversanding

In this section, the scale with green numbers and black ticks was engraved at 300 g and is slightly less abraded than the adjacent scale at 225 g. Guesstimating the depth at 0.13 mm, 0.15 mm at most, the sanding block doesn’t remove much plastic at all … just enough to remove the scales.

The lines are all about 0.1 mm wide and, to the naked eyeball, look about the same as the lines on my K&E Deci-Lon slipstick:, done on a real production line with an actual engraving tool and somebody who knew what he (I’m sure) was doing:

KE Deci-Lon Slide Rule – scale detail

The red CI scale reads right-to-left and, under magnification, you can see where the red ink made its way into the adjacent tick marks. I doubt they were using a pen, but it might be a mechanized roller or dauber.

All in all, sanding works, but it’s messy and poorly controlled.

2020-03-06
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

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

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

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

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

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

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

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

They’re less uniform at 250 g:

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

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!

2020-03-05
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

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

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

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

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

What a mess!
2020-02-28
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

A closer look at the spalled section on the flank:

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

An unused tip comes to a neat point:

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

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

2020-02-27