mechanical engineering

FEA: Saint-Venant’s principle

If you’ve done FEA, you know that you can get some funky results near boundary conditions. Fixing a face such that absolutely zero motion is allowed, for example, can create high stress concentrations that may not be real. However, thanks to Saint-Venant, we don’t usually have to care. Because… “… the difference between the effects [...]

Tagged as: Finite Element Analysis (FEA)

frequently held false beliefs in product design

I recently posed the following question on Quora What are the most frequent false beliefs in mechanical engineering and product design? I find the answers compelling and hope you do as well. Design doesn’t depend on context The designer knows more about the user than the user does The idea is the hard part The [...]

Tagged as: prototyping

video: quantum levitation

Came across this today. They even tease you with just enough of a physics explanation to get you curious. How it works According to the website, the ceramic, once brought down to a low enough temperature, becomes a superconductor (more like a super-duper conductor as they claim zero energy loss). Now that it is a superconductor, [...]

Tagged as: magnets, materials, physics

badass trajpar equations

if you never use pro|e, stop reading lest you get a serious case of CAD envy. If you do use pro|e, yet of never heard of trajpar (short for “trajectory parameter”), it is a parameter that varies from 0 to 1 along the path of a sweep (0 at the start, 1 at the end). [...]

Tagged as: CAD, surfacing, trajpar

this has always bugged me.

In fact, 1 fl oz of water weighs 1.04 oz. (Full math at bowl of plenty)

Tagged as: conversion, units, water

some notes on nonlinear fea with contact

So I haven’t had an opportunity to be much cool FEA lately. Still, I’m pretty regularly in reviews where we are reviewing setup, discussing solving approaches, analyzing results etc. It seems lately that most of these analysis involve a fair amount of contact (the presence of which, I have mentioned before, is an indicator that [...]

Tagged as: analysis, Finite Element Analysis (FEA), nonlinear

how to design a product

I’m running out the door but I wanted to toss this up to the readership, as I feel you are uniquely qualified to add to it. Someone posted the following question on Quora: What is the process for developing and readying a product for manufacturing? I jumped on it, and answered. I’ve copied my answer below; [...]

Tagged as: process, product design, quora

why rectangles?

I suspect this post will be a touch more abstract than most. A few weeks ago I was at Trident Booksellers (wonderful place) and snatched Minimalism from the clearance rack. It’s a collection of images depicting minimalist attire, products, architecture etc. I was flipping through it for the first time and I found myself getting [...]

Tagged as: minimalism, Minimalism (book), rectangles, Universal Principles of Design

crayon physics

Quite possibly the best thing ever. I saw this technology a few years ago (I think it was MIT… can’t find the link). It appears it’s been commercialized, and commercialized well.

Tagged as: physics

when in doubt…

A colleague of mine recently quoted a professor he had in school: When in doubt, make it stout, out of materials you know about. Great advice for mechanical engineers. Of course, the ideal is to not be in doubt (nonlinear fea can help with that), and know about a lot of materials(check out these materials [...]

how engineers + designers should use Evernote

They should use it like I do. Or, if you prefer more delicate wording: I am an engineer, I use Evernote and I like to think I use it well. For those who may not be familiar, Evernote (whose motto is ‘Remember Everything) is a freemium multi-platform note taking service that has been around for [...]

Tagged as: getting things done, productivity

notes on micromolding

A while back we had a visit from a top-flight micromolder. Below are my notes I probably should have put this up a while back, but it slipped. Truth be told, the only reason I’m putting it up now is as an example for how I use Evernote. Still, the information is wortwhile… MTD (Micro [...]

Tagged as: Injection Molding, manufacturing

flow in product design (with music to get you there)

Flow: a state of concentration or complete absorption with the activity at hand and the situation. It is a state in which people are so involved in an activity that nothing else seems to matter -Mihaly Csikszentmihalyi, Flow: The Psychology of Optimal Experience As designers and engineers, we are at our best in flow. Once we have fully [...]

Tagged as: product design, productivity

rubber material tradeoffs

Going through a rubber design guide I snagged from MN Rubber a while back, I saw this nifty chart. A great way of communicating information. Manufacturers looking to create a design guide (in addition to engineers for more obvious reasons) should definitely check out this. The GE injection molding design guide doesn’t suck either.

Tagged as: product design, rubber

engineering sets the pace

This is in regards to continuous deployment of software projects, but it’s enough to make you drool if you imagine being able to do this with physical products… engineering sets the pace. We get shit done, we get it done fast, it goes into production within 15 minutes of pushing it to master (feels like [...]

Tagged as: agile, product design

Reaction Injection Molding (RIM) design guide

I’ve written before about reaction injection molding as it pertains to memory foam. Recently I’ve had occasion to dive back into it, and have found the following design guide to be pretty helpful. (notify me if the link ever breaks, I’ve got the PDF locally). Much of it is really basic (i.e. outside corner of the [...]

Tagged as: foam, Injection Molding, RIM

when to use nonlinear finite element analysis

Dig even a little bit into the different fea packages out there and you will notice a distinction between linear and nonlinear analysis. You might then wonder under what circumstances to use linear analysis and what circumstances to use nonlinear analysis? First off, let me say that mechanically speaking, there is no such thing as [...]

Tagged as: CAD, Finite Element Analysis (FEA)

FEA insights

Bob Ketelhohn (a colleague of mine) put together a pretty swell writeup over at Farm on FEA. Some of my favorite nuggets: FEA is a prototype reducing tool. It does not eliminate the need for real prototypes. Trust your gut. If it looks wrong, it probably is. Comparative analysis is your best friend. Mesh density [...]

Tagged as: Finite Element Analysis (FEA), product design

gaussian and mean curvature

So I’ve been doing some fancy surfacing lately and spent a few minutes digging into the math behind the surface tools. The math itself is a little esoteric, but I also came across a really nice, digestible description of gaussian and mean curvature. These are the types of curvature (along with maximum curvature) that CAD packages like [...]

Tagged as: CAD, curvature, Pro Engineer, product design, SolidWorks

pro|engineer (or creo, or whatever): a few more things

A bit over a year ago I wrote about problems I was having with pro|engineer (now creo) and SolidWorks. It was one of my more popular posts and inspired some passionate responses. (I also copied the image from that post even though I’m primarily going to talk about pro|engineer…lazy) Well I’ve been doing some heavy [...]

Tagged as: CAD, Pro Engineer, SolidWorks

robust CAD models

I’ve been thinking lately about what makes a robust CAD database. I considered writing down a checklist, but as projects differ I find the checklist to be overkill or incomplete, both of which render it useless. Instead I asked myself: What principles are always true when building a CAD model? Take note of my use [...]

Tagged as: CAD, Pro Engineer, product design, SolidWorks, Unigraphics

video:curvature continuity between splines in sketcher

This was birthed out of a conversation that started over at mcadcentral. The inital problem was trying to make two splines curvature continuous to each other (which this video shows how to do in a particular context), but I also end up showing the differences in C0, C1, and C2 continuity. note: it occurs to [...]

Tagged as: CAD, curavture continuity, Pro Engineer

black chromium: black hard anodizing for stainless steel

You can’t hard anodize stainless steel, I know this. But today I wished I could. I was looking for a black, low friction, wear resistant, corrosion resistant coating to put on a stainless steel part. So I looked around for a while, and came up with something similar (as far as I can tell): Black Chromium. [...]

Tagged as: black chrome, finishing, guns, plating

metal injection molding (MIM) notes

There was a forum question over at Core77 about metal injection molding, and it just so happened I had an exhaustive set of notes on the process. I’ve since gotten enough follow up questions that I thought it would be worth re-posting here. We had a guy from Precision Made Products present to us [...]

Tagged as: Injection Molding, manufacturing, metal injection molding, product design

video: do lock washers actually do anything?

I regularly cruise around eng-tips to see if anything piques my interest. Today I came across this thread from ’08 regarding the efficacy of lock washers. The thread is worth reading in it’s entirety, but there here are a few highlights: From NASA fastener design manual, page 9 (bold mine): The [helical] lock washer (like the one [...]

Tagged as: fasteners

video: inverted peaucellier mechanism

I was recently screwing around with mechanisms for straight-line motion and came across the Peaucellier mechanism. I modeled it up and inverted it to see if I could get the straight line in a smaller footprint. There are a lot of pseudo straight-line mechanisms out there, but this one is pure.

Tagged as: linkgage, mechanism design, straight line motion

video: flexible shaft couplings

Some components (like machined flexible shaft couplings) just don’t look too awesome in photos. They need videos. Check out the video below featuring Heli-Cal.

Tagged as: couplings, mechanism design

injection molding side actions: in depth

If you don’t know what a side action is, that cool. Check out these two brief videos on how side actions work. You also would do well to check out what Protomold (parent company of First Cut) has to say about side actions here and here. Recently I had occasion to dive into mold-making techniques [...]

Tagged as: cam, Injection Molding, plastics, product design, side action

video: makerbot print quality keeps getting better

Now thanks to a stepper motor upgrade to the extruder. From Makerbot Using a stepper motor to drive your extruder brings a host of advantages. Fussy DC gear motors are history: stepper motors live substantially longer as they do not have internal brushes to wear out. Stepper motors are also much more precise as the [...]

Tagged as: makerbot

apple dual anodization

ismashphone reports the apple is filing a patent on dual anodization (links mine): A metal surface treated to have two anodized layers or regions may be used in electronic devices. The surface treatment may include performing a first anodization process to create a first anodized layer, removing the first anodized layer at select locations, and [...]

Tagged as: anodizing, apple, hard anodizing, product design

best mechanism design library

I’ve been sitting on this one for a while, but the Kinematic MOdels for Design Digital Library (KMODDL) is probably the best collection of mechanisms and mechanism-related materials I’ve found. The site (which is shamefully difficult to come across via google, and not much easier to navigate internally) is full of images, videos, CAD, tutorials, [...]

Tagged as: mechanism design

injection molding plastic part design guide (GE)

I’ve got a treasure trove of design guides. Even when you are super comfortable with a process (like injection molding) I find it good practice to use them as a low-cost checker. So i figured I would share one of my favorite design guides, the GE Engineering Thermoplastic Design Guide. It’s a concise, 15-page guideline [...]

Tagged as: CAD, Injection Molding, plastics

MEMS: a brief introduction (MIT OCW)

This post contains my personal notes from MIT 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, available to me through MIT OCW. what is MEMS? It stands for Micro-Electro Mechanical Systems, and it’s a manufacturing technology for tiny (think 1mm max for a whole device) things. At it’s core, it is adopted from the [...]

Tagged as: MEMS, MIT OCW

Berkeley Bionics: elegs

Some REALLY cool work coming out of Bay Area startup Berkeley Bionics. They’re mission is near and dear to my heart (my capstone project in engineering school was a bionic ankle). Just check out the video…talk about being technically awesome (in the true sense of the word) while doing real good.

Tagged as: doing good, human factors, robotics

connecting devices to the internet using mbed

About 6 months back I had an idea to connect a home appliance to the internet. I knew there had to be something out there that would enable someone without a CS degree (me) to do something like this. Sadly, I found nothing. Then today (via Joshua Newth @ Mindtribe) I come across mbed: mbed is a [...]

Tagged as: embedded systems, internet, Make: Electronics, rapid prototyping, software

four bar linkage 3 position synthesis (4min video)

I’ve had occasion to do some four bar linkages lately, and it got me thinking that it might be worthwhile to do some short screencasts on some mechanisms synthesis techniques. This video shows how to define a four bar linkage based using 3 different positions of the coupler bar (the middle bar in a four-bar [...]

Tagged as: four bar linkage, mechanism design, mechanism synthesis

statistical tolerance analysis basics: Monte Carlo Simulation

image courtesy epcp First thing first, a Monte Carlo stack up typically uses a normal distribution as a guide for it’s simulation, so I highly recommend that you read my post on RSS Tolerance Analysis so that you understand how to derive that normal distribution in the first place. monte carlo simulation theory The theory [...]

Tagged as: monte carlo analysis, monte carlo simulation, monte carlo stack up, simulation monte carlo, tolerance analysis

designing for impact on off-road vehicles

What kind of impact can a device expect to see in an off-road vehicle? That’s the question I asked myself a while back, and after alot of research, I had nothing. It just isn’t the kind of information that you can readily google (or “wolfram” for that matter) In any case, I eventually found the [...]

Tagged as: automotive, impact, vibration

video: mechanisms, courtesy of Ralph Steiner

I’ve mentioned some great mechanism resources before, as well as supplying the 507 mechanical movements pdf. But while they really are great resources (and they are… I use them all the time!), there is something to be said for video. I submit for your consideration, the work of Ralph Steiner

Tagged as: 507 mechanisms, mechanism design, mechanisms and devices, product design

thread-forming vs thread-cutting screws

When forced to users fasteners in plastic I generally try to incorporate thread inserts into the design, but if that’s not feasible you have two choices: thread-forming screws (left) or thread-cutting screws (right). (Be-careful, people mix up the two all the time) thread-forming screws When screwed into a pre-drilled hole (spec sheets will tell you [...]

Tagged as: fasteners, thread-cutting, thread-forming

touch screens: capacitative or resistive?

A few years ago I did some design work on a piece of lab equipment that required a touch screen. Early on we had a vendor come in to help us spec the appropriate screen for the application. He touched on a lot of stuff, but one of the main ones was the difference between [...]

Tagged as: product design, touch screen, usability

designing with nylon

I recently had occasion to dive pretty deep into Nylon(polyamide). For some applications it’s perfect, but you will consider the following before you start lock it into your design. nylon absorbs alot of water To give you a from of reference, typical engineering polymers like ABS & PC absorb ~0.3% – 0.5% water (by weight). [...]

Tagged as: nylon, plastics, tolerances

chinese-made cheap 3d printer

I’ve been on a cheap 3D-printer kick lately, and it continues. From BoingBoing The UP! personal 3D printer from China retails for $1500, with goop running at $50/kg. Fromthis early adopter’s review: It runs at 0.3mm resolution, and the finished models show striations from successive layers of goop, but light sanding produces a smooth finish. [...]

Tagged as: 3d printing, rapid prototyping

3d printing hack

It’s not going to replace Makerbot or your local rapid prototyping house anytime soon, but still a pretty impressive hack.

Tagged as: 3d printing, hacks, makerbot, rapid prototyping

makerbot build video

For those of you who aren’t familiar with the industry, Makerbot is the (in my opinion) at the leading edge of the RepRap movement. Or, with less jargon: Makerbot is a build-it-yourself robot. It makes things out of plastic. It’s worth checking out their website for the details, in the meantime check out my buddy Nick’s [...]

Tagged as: 3d printing, makerbot, rapid prototyping

liquid metal (as awesome as it sounds)

Just came across LiquidMetal today. Wow. At first I thought it was just a twist on Metal Injection Molding (MIM). Digging in a little further I realized that the really cool part isn’t the process, it’s the material. Liquid Metal isn’t actually a material, but a class of alloys, check out their website for more [...]

Tagged as: alloys, apple, liquid metal, metal injection molding, springs

something you didn’t know about #6 screws

Came across this fun fact today… 6-32 screws have the worst ratio of torque that can be applied to torque necessary to shear the screw. In other words, they are the screws most likely to shear off. Good to know.

Tagged as: fasteners, screws

hard anodizing

A while back I had the need to get some sheetmetal (every spell check in the world keeps telling me it’s “sheet metal” and not “sheetmetal”, but I digress) and machined parts hard anodized. I’ve been meaning to post my notes on the process for some time… and now I am. what is hard anodizing? A [...]

Tagged as: aluminum, anodizing, hard anodizing, hard coat, plating

using diamond pins for locating

When two parts need to be precisely aligned. It’s tough to beat a two pins. One goes into a hole (that fixes X + Y translation), and the other goes into a slot (that fixes rotation). It works great, but it’s always seemed a little sloppy to me. Then I was turned on to diamond [...]

Tagged as: diamond pins, locating, pins

recycled resins: sometimes they’re just better

The biggest hurdle to overcome with regards to using resin containing recycled content is something I like to call the performance bias. Our performance bias tells us that in most cases, second hand materials aren’t going to perform as well as their brand new counterparts. It’s a bias that generally serves us well, but during [...]

Tagged as: Injection Molding, recycle, resin, Valox iQ

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