Cardboard Mockup: The Original Rapid Prototyping

I often find it hard to get a sense of scale when designing things using CAD software. Staring at a model on a 24″ screen can sometimes make small objects look massive, and large objects tiny. Placing  references (such as a person) next to your model helps some, and there are many free human models for pretty much all CAD platforms. However nothing beats a physical prototype. If your part is small enough 3D printers are perfect. For larger parts you have to get creative. The final frame will be made of 80/20 aluminum framing, but I did not want to commit to cutting it up just yet, as I was still playing with the frame dimensions. I needed a cheap material that was easily formable, yet sturdy enough to hold its own weight, next to my door was the answer: double wall cardboard.

Just as architects use cardboard to construct scaled down buildings, I built a 1:1 model of my mold-a-rama replica. Using only packing tape and cardboard, I was able to quickly (and cheaply) build a model that’s accurate to about 0.25″.

I started by measuring the outside dimensions of my model in solidworks, and transferring those to cardboard. Here’s some tips I learned from doing it:

  • The boxes I had on hand were medium to small-sized, with fold lines all over. If you can’t cut around the lines, take another piece of cardboard and tape it over the fold line to reinforce it.
  • Reinforce the corners by making a long  L-bracket and tape it to the inside.
  • Cardboard tabs can be used to prop up unsupported spans of cardboard.
  • Get some good blades for your utility knife, I like Irwin bimetal blades. They make cutting through thick double wall cardboard a breeze.

And here’s the end result:

Cardboard mockup

Those 3rd grade arts and craft skills are finally paying off.

As I suspected it was bigger in full-scale than what I thought it would have been.

Another benefit is that the interior volume is very close to the usable space inside the actual machine. I was able to place most of the bulkier components inside, allowing me to play with layout:

Interior layout

From left to right: air compressor, injection cylinder, plastic melt tank, water pump (blue thing peeking out), water chiller.

Moving components around inside the cardboard model was so much faster than doing it in CAD. It also gave me a better idea of how much space I need between components.

The layout above is mostly complete. I have since gotten an air tank that sits in the back left corner. The stainless box you see is the starting point for the plastic melt tank (I’ll go into more detail in the next post where I’ll show off some of the components  that have already been bought)

This method really only works if what you are building is mostly flat panels that meet at right angles. If you’ve got a contoured model and you are set on using cardboard, make an STL file of your part with layers that match your cardboard thickness and print out patterns. This can be done using the free software AutoCad 123D (http://www.123dapp.com/make)

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Modern Dining Table: Part 1

I’ve started designing a dining table for our new apartment. I really like the aesthetic of reclaimed wood and steel tables, unfortunately a pre-made table like this costs in the $1500 to $3000 range. Way more than I can spend on a table. The designs are very simple and I figured I could make one myself. After some digging I found a local shop that will build the table top out of reclaimed douglas fir. The legs are designed by me and will be either made by myself (pending purchase of a TIG welder) or will be sub-contracted to a fabrication shop.

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Automated Piston Cycler Device with Arduino

I built this control box to cycle a piston in some of our assemblies at work. We had problems with rebuilt assemblies sticking after a few hours of cycling. The rebuilders couldn’t test this because they would have to manually cycled the piston back and forth many times to verify the functionality (time-consuming). This piston cycler is capable of automatically cycling a dual action cylinder at an adjustable rate, and enable the operator to pause the motion to make adjustments, and continue testing. The counter keeps track of the number of cycles for record keeping purposes. Here’s how I made it.

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Process Control Using Arduino

This project involved designing a device to regulate the flow of chilled water through a heat exchanger based on the coolant temperature of an internal combustion engine. It’s made up of three parts: A controller, a motorized valve, and a temperature sensor.

The controller consists of an arduino, a LM298 based motor driver, resettable fuse, LCD and misc. buttons/connectors.

The motorized valve is a standard ball valve with a bracket to support a gear motor and a encoder for position feedback.

The operator inputs a desired coolant temperature which is maintained by adjusting the flow through the heat exchanger. During this project I learned about driving inductive loads with a micro controller, PID tuning, and closed loop feedback control.

Machine Shop Madness

Being able to operate basic machining equipment should be an essential skill for every mechanical engineer. It’s really sad how often I hear 3rd and 4th year ME students say they have virtually no practical engineering skills. Granted most ME’s will never be required to operate a lathe or mill as part of their job, knowing the capabilities of the tools that will be producing your products helps you when designing those very same products. College teaches you a lot of equations and methodology, but you don’t really learn anything useful until you start designing and building stuff with your hands. So when I had the chance to take the machine shop course offered by my school I jumped at the opportunity.

Fortunately for me I have access to equipment most home machinists can only dream about. This is a Bridgeport vertical mill with a DRO on the x and y-axis. The device hanging off the right end of the table is a power feed, which comes in handy when making long slow passes in the x direction.

IMG_0170

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