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Kenneth Finnegan

19 Nov, 9 tweets, 3 min read

Engineering: "Make sure to not put solder mask on top of the high speed 56Gbps differential traces to reduce dielectric losses"

Manufacturing: "lol, sticker"

My favorite manufacturing problem I was personally involved with is still the time I was working on an RF assembly about the size of a small suitcase, and as soon as we transferred the design to volume manufacturing, the screws suddenly started seizing.

It was a welded aluminum box about 18" on the long end, with a removable lid held down by 43 stainless steel #6-32 screws threaded into helicoil inserts in the main enclosure body.

We built maybe two dozen of these assemblies between our engineering lab and pilot manufacturing, and they all worked great.

As soon as we moved them to the full scale volume facility, the screws started to seize in the helicoils.

We had torque specs for these screws, that were being followed.

We checked calibration on the torque handles, and they were find. We took some of the screws off the volume line, and they worked fine in our lab.

What the heck.

It was the gloves.

We didn't wear gloves in the engineering lab, and the pilot line was supposed to, but they didn't bother either.

They wore gloves in the volume manufacturing facility like they were supposed to.

Here's the thing about stainless steel: it galls. If you screw a dry SS screw into a dry SS thread, there's the possibility for the two parts to cold weld together.

So why did this suddenly start happening once they were wearing gloves?

Because when we handled the stainless steel screws with our bare hands, oils from our skin would get on the threads and lubricate the screw just enough to prevent galling.

When we transferred it to a shop that actually kept the screws clean, galling started being a problem!

So we had two choices for how to fix this problem.

Either we ask the manufacturing techs to lick the screws before they install them, or spec out a thread locker to lube the threads to keep them from seizing during installation.

Manufacturing is hard.

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More from @KWF

Kenneth Finnegan

@KWF

27 Nov

Me: "Huh... I wonder why this Ubuntu 20.04 image is still using the SysV networking service..."

Me, two hours later: *The internal screaming intensifies*

In case you can't figure it out, this is a really stupid trick I've seen on IPv4 to save address space where you assign a /32 to the public interface, then point default via a static on-link route to the router on any other address you want.

I have never seen this trick on v6.

"If it's stupid and it works..." does NOT fucking apply here.

It's stupid, and it working doesn't excuse that.

Read 4 tweets

Kenneth Finnegan

@KWF

27 Nov

I can't remember the last time I played a video game, but I bought shapez io for this weekend.

It's definitely enjoyable. All the puzzle solving of Factorio without the combat or resource management

Who doesn't love shapes?

And colors!

Read 4 tweets

Kenneth Finnegan

@KWF

27 Nov

Through a long series of unfortunate events, for our smallest Thanksgiving ever, my dad has ended up cooking a 19lb turkey.

Granted, we also usually do two turkeys and a ham, so I guess just a single turkey of any size is more reasonable.

It's important to remember that a mind boggling number of people are food insecure today, and that's a truly terrifying sensation that's hard to imagine.

Read 5 tweets

Kenneth Finnegan

@KWF

5 Nov

Active Optics Cables, or AOCs, are essentially patch cables desired to plug directly into *SFP cages.

They're just like DACs, or Direct Attach Cables, but with more length options and the cable routing advantages of fiber.

The nice thing about AOCs over using SR4 optics is that it isn't connectorized, so you don't need to assemble three parts to make a link, and "cleaning fiber ferrules" is a ball game you don't need to get into.

This is a 400G OSFP AOC.

400Gbps
Octal Small Form factor Pluggable
Active Optical Cable

And let us all pause for a moment to admire how awesome OSFPs are and how they look space age af.

Read 15 tweets

Kenneth Finnegan

@KWF

5 Nov

Let's talk about Cisco 6500 line cards.

Because I'm currently sitting on a concrete floor dicking around with 6500 line cards.

The 6700 series line cards were actually modular, in that the forwarding engine on each line card was a daughter card that you could replace!

The CFC module is the chump change "punt everything to the supervisor" card that limits the whole box to the capabilities of the supervisor.

So like... 20 million packets per second?

Only.

Read 11 tweets

Kenneth Finnegan

@KWF

4 Nov

So let's say you have a nice server with a set of 8x3.5" disk bays in the front of it that you want to use for storage.

What you typically don't want to do is also install your OS on the same disk array.

You could burn one or two of the disk bays for the OS, but that sucks, and if you're doing something like ESXi or Green as, you don't need that much space.

But servers will have USB ports inside the case to boot off a flash drive! Literally just boot off USB forever!

But USB really sucks if your OS isn't mostly read-only, so your next option is to use one of the SATA ports inside the case.

Some server cases will sneak a 2.5" bay in the back by the IO panel.

Read 8 tweets

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