mechanical engineering

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

Thumbnail image for how side actions work: two brief videos

how side actions work: two brief videos

When I first heard the term “side action”, I got what it was… but couldn’t quite envision how the tool worked. I was told that: A side action is something that allows you to create a feature with a pull direction that is at an angle to the primary pull direction. In hindsight that seems [...]

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

Thumbnail image for statistical tolerance analysis basics: Root Sum Square (RSS)

statistical tolerance analysis basics: Root Sum Square (RSS)

In my last post on worst-case tolerance analysis I concluded with the fact that the worst-case method, although extremely safe, is also extremely expensive. Allow me to elaborate, then offer a resolution in the form of statistical tolerance analysis. cost A worst-case tolerance analysis is great to make sure that your parts will always fit, but [...]

Tagged as: example, manufacturing, root sum square, RSS, rss tolerance stackup, rss tolerancing, spc, stack up tolerance analysis, statistical tolerance analysis, tolerance analysis, tolerance analysis fundamentals

Thumbnail image for First Cut prototype

First Cut prototype

I’ve heard some bad things about First Cut. Some complained about the poor tolerances, others that First Cut won’t tap holes (UPDATE: they tap holes for $2 a pop!), still others complaining about maximum part size. They’re right, each one of them. But if you’re willing to accept tolerances of ±0.005 (give or take) and tap [...]

Tagged as: CNC, machining, prototyping

Thumbnail image for statistical tolerance analysis basics: worst-case tolerance analysis

statistical tolerance analysis basics: worst-case tolerance analysis

fair warning: if you’ve never heard the phrase “tolerance analysis”, you’ll likely never have to perform it and should just spend the next 5 minutes elsewhere. Otherwise… A well-performed tolerance analysis will add years to your life. No worrying about parts fitting together, no worries about sloppy fits. A well-done tolerance analysis both proves the [...]

Tagged as: example, root sum square, stack up tolerance analysis, tolerance analysis, tolerance analysis fundamentals, worst-case tolerance analysis

Thumbnail image for urethane castings: 3 things to ask before you hit ‘send’

urethane castings: 3 things to ask before you hit ‘send’

A while back I shared some things you should know about urethane castings. I focused mainly on when you should use them, and not so much on some of the actual design considerations. So here you go… design considerations. The overarching theme is that rapid prototyping houses like to do things a certain way. Sometimes though, [...]

Tagged as: example, product design, prototyping, urethane casting guide

CNC Motorcycle Helmet

This ridiculous video made the rounds on some forums a while back, I was just reminded of it today. It’s a motorcycle helmet CNC ripped out of an aluminum billet.

Tagged as: CNC, machining

Thumbnail image for sealing medical cushions: <br/> RF vs ultrasonic welding

sealing medical cushions:
RF vs ultrasonic welding

Once your kickass memory foam design has been molded or fabricated, it’s probably going to need to be covered. That means upholstery. When you think of upholstery, you probably think of stitching and sewing. If you’ve got some practical experience, stapling might even come to mind. But when you start talking about designing medical cushions, [...]

Tagged as: fabrics, medical, RF welding, ultrasonic welding

Thumbnail image for 507 Mechanical Movements PDF: another great mechanism resource

507 Mechanical Movements PDF: another great mechanism resource

Not too long ago I told you about three great mechanism references, one of which was the not-so-cheap Mechanical Devices Sourcebook. Well times are tough, and I’ve been reminded of the Sourcebook’s Grand-daddy: 507 Mechanical Movements. The link is a free PDF (507 has long since crawled out from under copyright protection) and there is no [...]

Tagged as: 507 mechanisms, mechanism design, mechanisms and devices, mechanisms and mechanical devices sourcebook, references

Thumbnail image for Dear SolidWorks and Pro|Engineer:fix these problems

Dear SolidWorks and Pro|Engineer:fix these problems

Everyone has their preferred CAD package, and most look down their nose at all the others. The Solidworks guys rag on the Pro|Engineer guys, a few yucks are had, and you go back to work. But isn’t what we really want for one of these CAD programs to really get their act together? To decimate [...]

Tagged as: CAD, Pro Engineer, SolidWorks

Thumbnail image for CAD job trends: or why I pity students that learn Unigraphics

CAD job trends: or why I pity students that learn Unigraphics

There is an interesting thread over at eng-tips regarding current CAD job trends. The content itself isn’t so groundbreaking, but the recommendation of Indeed.com’s Job Trends tool made it worth the read. “Finally!” I thought. “Some objective data to prove that Unigraphics is dying!” I wasn’t disappointed: (note: I think the “inventor” is inflated, as job [...]

Tagged as: CAD, Pro Engineer, SolidWorks, Unigraphics

Thumbnail image for a quick tip for preventing PCB-induced stress

a quick tip for preventing PCB-induced stress

Most of the products we design have at least one Printed Circuit Board. The design process usually goes something like this: Specifiy the components (sensors, batteries, switches, etc.) required for the device to perform it’s desired function. CAD-up the components per their respective spec sheets. Drop them into the CAD assembly to see how much [...]

Thumbnail image for three great mechanism references

three great mechanism references

Mechanisms are awesome, but they don’t seem to get much love in the search engine world. All told, these are the three best references I’ve seen that actually help in mechanism design. Flying Pigs Paper Animation has some nice flash of your standard mechanisms. Boston’s Museum of Science has a wall of mechanisms, so be [...]

Tagged as: mechanism design, mechanisms and mechanical devices sourcebook, references

Thumbnail image for brainstorming in 109 words

brainstorming in 109 words

Brainstorming can be seen as fluffy, even superfluous. Seeing engineers and designers make recommendations like “fill it up with helium to make it lighter” or “what about aerogel” can be a little frustrating (especially if you don’t believe in brainstorming AND are the one paying these engineers). But what’s happens after a (good) brainstorm is [...]

Tagged as: brainstorming

free body diagrams in product design

Free body diagrams are old-school, and when I was in school I didn’t think I’d use them much. Truth is, I actually use them alot. When I’m doing a feasibility study for a mechanism concept or calculating rough safety factors and don’t have time for an FEA simulation, free body diagrams are the best tool [...]

Tagged as: Finite Element Analysis (FEA), free body diagrams, statics

Thumbnail image for design with invisible hinges

design with invisible hinges

A colleague of mine used these recessed hinges on a design a few years back and got some real good results. It’s the best solution I’ve seen to the problem achieving clean rotation without big gaudy hinges mucking up the aesthetic. Check out more from Bartels.

Tagged as: hinges, hinges design

Thumbnail image for help make your stainless steel…stainless? what?

help make your stainless steel…stainless? what?

If you’re thinking, “Wait. Isn’t stainless steel already stainless?”, you’re aren’t the first. Everyone thinks the very same thing the first time they hear “stainless”. I for one was under the same impression until I asked some embarrassing questions at my first co-op… an aerospace manufacturer that makes a living on stainless steel. But can we really [...]

Tagged as: stainless steel

Thumbnail image for 6 non-sucky materials sites

6 non-sucky materials sites

As product designers we deal with materials every day, but it’s a messy world out there and a surprising (or maybe not so surprising) number of materials websites suck. These ones don’t. I promise. MatWeb MatWeb is the big daddy when it comes to engineering materials. Their enormous selection of generic (i.e. polycarbonate) and proprietary [...]

Tagged as: materials, references

Thumbnail image for urethane casting guide: 5 things you need to know

urethane casting guide: 5 things you need to know

I like urethane castings. They always look so clean and pretty. Use them for the wrong project however, and you’ll be stuck explaining to your client why you dropped a few grand on prototypes and have nothing to show for it but a receipt. When I evaluate castings for a project I’m working on, I [...]

Tagged as: prototyping, urethane casting, urethane casting guide

durometer table graphic

80 Shore A? 30 Shore D? It seems every time a question of durometer pops up, I’m digging through the library looking for samples or googling “durometer table” to find the info I need. This graphic from Mcmaster-Carr suits most of my needs. Do yourself a favor and tack it up at your desk.

Tagged as: durometer table, elastomers

design guide: memory foam manufacturing

Designing with polyurethane memory foam (a.k.a viscoelastic foam, a.k.a tempurpedic foam) is different. It’s not as conventional or dimensionally stable as plastics or metals, but when it comes to comfort, it can’t be beat. So how do you do it? How much does it cost?

Tagged as: CNC, Injection Molding, RIM

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