Mind the Swarf and Deburr the World

Nearly all of my fasteners (nuts, bolts, washers, et al.) come direct from the ol’ Big Rock Candy Mountain [#], usually in heat-sealed clear plastic bags bearing adhesive-backed labels that have been run through thermal printers and have the same hand feel as thermal-printed receipts. The crisp black text on some, though not all, of those labels is doomed to fade until it eventually becomes completely invisible. This happens in the span of a few months to a year or two. The text on others will remain jet-black indefinitely. AFAICT, there’s no way to examine a newly-received baggie of fasteners, look at one of these labels and discern whether it will turn out to be a fader or a stalwart.

As the image below demonstrates, however, even the relatively stable-inked labels are not necessarily chemically inert. At least some of them are doing something. Suffice it to say that one probably shouldn’t sleep on a mattress stuffed with thermal-printer paper receipts or next to a mound of individually labelled bags of fasteners from Taobao.

To an empty region of the seller’s label on a newly-received baggie of hardware, I add a small blank sticker of my own on which I’ve written the purchase date in fade-proof ink, to make looking up the order details on the Taobao site later on (in the event that I need to re-order the same thing or something similar) as fast and easy as possible. Next, I dump the bag’s contents into a clear, rigid plastic container. It’s usually a screw-cap bottle but extra-long bolts or coupling nuts or something else that’s an odd shape or size might go into a telescoping CNC tool packing box. The seller’s label, scissor-snipped out of the plastic bag, gets slipped into the same container, facing out so that it’s visible through the side of the bottle/box. The cut-up remains of the bag goes into the trash.

On more than a few occasions, these bags (in addition to the actual washers, bolts, or nuts) have contained loose, razor-sharp pieces of metal swarf left over from the thread-tapping step. More often, some of the fasteners themselves retained protruding needle-like burrs. I’ve watched some videos documenting fastener manufacturing processes and they always show one or a couple of operations designed to eliminate burrs and loose swarf but it seems that some factories, in some places, and at some times may treat these steps as optional.

Recently, I acquired some lengths of 4-point (4分) aka DN15 (aka half-inch) 304 stainless steel pipe with threaded ends. Some are male-female, others are female-female, and others or male-male (male here meaning external threads and female denoting internal threads). According to the DN15 specs I see online, it seems that they regular DN15 pipe has an outer diameter of 21.3mm, but I opted for a seller’s explicitly-listed-as-thickened version and the un-threaded exteriors of mine are all a smidge under 25mm in O.D., 20.5mm O.D. over the threads on male ends (before any cleaning that could conceivably have removed material), and have an I.D. a hair over 15mm. I’m using the pipe to assemble a small frame for other gear that happens to require 2.5cm-diameter mounting posts, so their O.D. suits my purposes just fine.

The pipes and fittings arrived acceptably clean and shiny on the outside and dusty, gritty, and (in a few cases) a bit rusty on the inside. The rust, where I spotted it, seems to be very superficial surface rust. 304 Stainless steel is less susceptible, but not impervious to rust. After picking the pieces I needed, I cleaned them up: brass-bristle brushes for the insides, light-abrasive hand pads over the threads, and a rinse with WD-40. The fittings (some elbows and tees) and really small bits of pipe, for which full immersion was feasible, got dunked in WD-40.

The bit of metal nastiness shown in the photo of an internal-threaded (female) pipe end above was the only cartoonishly large piece of clinging swarf I saw in the threads on these pipes and fittings. I yanked it off with a pair of needle-nose pliers and tossed it into the trash. Threads in and on some other pieces were slightly janky, rough enough to the touch that they caught slightly at the skin when I gingerly ran a fingertip over them.

Happily for me, judging by the results of a second round of fingertip testing, the hand pad treatment seems to have been enough and there doesn’t appear to be a need to go at the threads with an abrasive flap wheel or something similar this time around.