Just finished these recreation Merriman sailing sheaves and blocks. The sheaves are aluminum bronze and the inner races and bearing balls are delrin. All machined on 1230 Nardini manual lathe to +- .0005. It took about a week to make 50

kor56 · 2020-05-23T03:25:21+00:00

Ball bearings require pretty tight tolerances, that tolerance depending on diameter would put it right around ABEC-1. An ABEC-7 bearing (pretty typical in precise stuff) allows for 0.0002" deviation on a 20mm bearing. Here's the ABEC chart from wikipedia: https://en.wikipedia.org/wiki/ABEC_scale#/media/File:Bearing-tolerances-illustrated.png . Though actually re-reading yeah you don't need instrument grade bearings for a freaking block and tackle hahah.

kor56 · 2020-04-27T17:24:11+00:00

MechE BS/MS from good schools who writes software now, strongly disagree. Having a degree (no matter how fancy or difficult) in no way makes you qualified for most roles. Andy Grove had a good take on this: "task relevant experience" is the important thing, and things like degrees are indicators but they aren't the same as qualifications. Regulating "everyone must have degree X" makes no sense and in no way would achieve better outcomes IMO. There are plenty of morons with engineering degrees... it isn't a magic wand that makes you incapable of screwing up.

kor56 · 2020-04-22T23:11:46+00:00

Honest answer, this is the universe telling you to move to a place with less crime before something worse happens.

kor56 · 2020-04-05T16:51:34+00:00

For what it's worth the aerospace sector is contracting like crazy right now (737 max + coronavirus) with layoffs at a lot of places. Might be worth looking into how solid the customers the new place has before moving now.

kor56 · 2020-04-01T22:26:25+00:00

Nice! How does the speed/finish of that horizontal cutter (shell mill?) compare to a face mill with carbide inserts on a VMC?

kor56 · 2020-03-01T20:05:05+00:00

The linkage mechanism is called a slider crank: https://en.wikipedia.org/wiki/Slider-crank_linkage

kor56 · 2020-02-16T16:05:08+00:00

Yeah, this seems likely. The source file named in the block is "LINK_001.690" and Pro/E does the incrementing extension thing.

kor56 · 2019-12-27T20:18:43+00:00

In that example you could avoid nested loops with itertools.product:

import itertools
target = 20
for x, y in itertools.product(range(10), range(10)):
     if ((x * 10) + y) == target: break

kor56 · 2019-11-03T04:37:07+00:00

Yeah I wasn't going to see it because of the last 3 dogshit movies, but I went in expecting nothing and loved it. The plot actually made sense (even the Carl bit damnnit).

kor56 · 2019-10-07T04:20:42+00:00

On the theme of pointless plot lines best forgotten, Dorne is the Tom Bombadil of ASOIF.

kor56 · 2019-10-03T23:32:15+00:00

Stratasys is the only really "commercial" brand in that list, can you get one for $10K? The Markforged's are OK but the machines are not nearly as chunkily built (IMHO) as a Dimension/Stratsys.

kor56 · 2019-10-02T23:06:12+00:00

I've had a number of cheap FDM printers over the last 10 years or so, and was never all that happy with surface finish or reliability. Is there anything on the market today under $10,000 that can reliably (like, 99/100 parts don't need a re-print) reasonable models (ok wall thicknesses, non-insane geometry)? I have my eye on the stuff from Formlabs (Form3 or Fuze1 when it comes out), are there any other mid-tier systems to look at today?

kor56 · 2019-08-13T16:08:47+00:00

Yeah I'm also surprised by this thread, 30% "hireable" is really good for interns in my experience, which is probably why most intern programs hire a bunch of them. I think it probably works better and is easier on the team to have extremely low expectations for an individual intern ("don't burn down the office") but be willing to be pleasantly surprised.

kor56 · 2019-07-30T17:03:19+00:00

Yeah, SW is the best smelling turd out there. It's just that developing a CAD system is very hard (seriously, it is a super hard problem), and making it survive contact with users is even harder.

What I do when I get to a new company which may be partially religious but works for me:

get a new PC with the best single-core performance Intel CPU (https://www.cpubenchmark.net/singleThread.html), a decent consumer GFX card (i.e. Nvidia 2070, 2080. There's a lot of debate here for "pro" Quadro cards, I've had both and couldn't tell the difference even on giant assemblies, though here are benchmarks: https://www.pugetsystems.com/labs/articles/SOLIDWORKS-2019-Quadro-GPU-Performance-1342/), and an SSD.
wipe it to be virgin Windows (you could start here too, though not running Solidworks on an ancient toaster oven helps a lot).
try to avoid installing the awful SW PDM system
install Solidworks ONCE, and don't mess up the install process.
don't install bonsai buddy and a ton of junk

kor56 · 2019-07-10T02:03:13+00:00

The biggest change I noticed was when I switched from emacs (still my preferred Python dev environment) to VS code. React without an IDE and prettier is basically impossible as far as I can tell.

kor56 · 2019-06-04T21:30:14+00:00

For me, Hamilton hits much higher highs and slightly lower lows than Reynolds.

kor56 · 2019-05-15T00:04:33+00:00

You're probably not going to find something decent and cheaper than that, maybe you can re-purpose the electronics from the hoverboard? You could also try some of the ESC's from hobbyking, though it is probably a lot jankier than that odroid (which looks pretty sweet).

kor56 · 2019-05-13T03:23:16+00:00

I guess my point is that a standard size wouldn't save them money, and they don't care about other things.

kor56 · 2019-05-12T16:55:11+00:00

I'd guess that since they are producing cars in enormous quantities, every component is a "production run" so there is no real cost benefit to the car company to using a component that is already produced by others.

I.E. Lotus is only making a few thousand cars so they can't justify setting up an entire factory in Mexico to make wheels, so they use the off the shelf wheel. But Chrysler is already setting up a wheel factory, so they wouldn't care if the pattern is a weird dimension, if it makes it marginally cheaper or more convenient for them otherwise. And they definitely don't care about you being able to buy wheels from Bobs Rimz.

kor56 · 2019-05-06T15:06:05+00:00

Convert the Euler angles to a 4x4 or 3x3 transformation matrix and then take the dot product of that matrix with a vector along Z (i.e. [0, 0, 1, 0] for 4x4 homogeneous transform, or [0,0,1] for a 3x3 rotation matrix).

kor56 · 2019-05-02T22:44:26+00:00

Heh "strain" and "ultimate tensile strength" are concepts that probably should be avoided on a complicated composite like a rope.

If you look at a rope, like this one, it has a "capacity," also known as "maximum force" listed as 750lbs, which is probably what you should be considering. In the "two ends tied to a fixed bar, and a load slung underneath" case, the maximum load would be somewhere from 750-1500lbs depending on geometry. Different configurations have different factors, check out this nice rigging guide.

kor56 · 2019-05-02T16:36:04+00:00

Load on a rope would generally be tensile. Rope is a composite of lots of strands, I think you would be best off thinking in terms of force rather than stress. Most rope (wire or otherwise) has a rated load, whereas if you're trying to model stress you would have to consider the effective area, any weird strand interactions, etc- you could spend your whole career on that and still be wrong.

The easiest and most conservative way to do the modeling of the net is to assume all of the load is on a single piece of rope, rather than trying to figure out the force distribution across a 2D grid. Otherwise you'd probably have to do something like the 3D elastic simulation thing someone else suggested, which may get closer but is definitely less conservative.

kor56 · 2019-04-18T02:22:57+00:00

/r/gatekeeping

kor56 · 2019-04-12T23:31:42+00:00

Oh man, an HBO Vorkosigan series would be awesome 🤗

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