Week 5: Computer-Controlled Milling
making it big with small cuts

The Assignment

make something big

  • The Problem: How to make this jig easier, adjustable, and cheaper so we can bring it anywhere for pop-up workshops!
  • The Solution: A cut out jig using OSB and a milling machine
  • Time Investment: 20 hours (8 hours designing 3D pieces for precise bike fitting, 10 hours prepping Mastercam, 1 hour cutting and putting together)

Quick Concepting

but slow realization

Having designed out original bike jig, I had a good idea of what needed to happen: tolerances, measurements, and angles.

A great introduction to SolidWorks helped me put things into perspective and quickly made me doubt the viability of the approach I was using. The material itself is not stiff enough. Nevertheless I decided to try out the fabrication technique to put this jig together.

I decided to try out a new CAD software, Rhino. It took me much long than it should've, but I spent the day translating my very precise hand sketches into the software. Stupidly, I tried make it all 3D even though all I really needed was 2D curves. A lot of time spent learning the software and I didn't even really need to make it 3D!

The Material

OSB... splinters galore!

Knowing that this would be a prototype I decided to go with the lowest quality, cheap OSB. It's pretty nasty stuff... probably only a few pegs above cardboard.

I also originally was planning on using the super cool, tool-changing machine in N52, but pretty much our whole section had the same idea. So I decided to cut my board in fourths and lug it over to archtecture shop's less fancy Shopbot which wasn't getting any love.


machine speak

With my 3D Rhino in hand, I thought it'd be a pretty quick deal: load the file, choose an end mill, and go!

Unfortunately, there's still a quite a bit to do. I needed to take the Rhino file, load it into Mastercam, and go through a million different options before generating a g-code. To be honest, I think this process could be MUCH MUCH faster but because we aren't allowed to use the machine on our own we spent a lot of time waiting for and working with the authorized people. (Much thanks to those teaching assistants and workshop managers btw!)

As mentioned before turned out I didn't need to make my design 3D and that through a bit of a wrench in things. Also, the bed of the Shopbot was significantly smaller than the machine in N52 so I spent a little time rearranging the parts into four sheets and then identifying places to screw down the material.

The Cuts

Drill and Cut

We first put the OSB on the bed and had the Shopbot drill in some precisely placed holes. We then bolted the board down to the bed.

Tool selection actually takes a lot of thought: upcuts, downcuts, compressions, feedrates, spindle speeds, etc. But, in the end we couldn't find the compression mill we were looking for so we just went with an upcut 1/4 inch endmill since I wasn't too worried about the finish. As you can see, the upcut really tears it up on top.

All in all, the cutting is very quick.

Some Mistakes

doublecheck what you checked

Despite checking for this problem, somehow some of the pieces missed me and the TA's review. Mastercam cut along the inside of the line on some pieces rendering them ineffective to be pressfit. The photo to the left shows to pieces that should have been identical but cut along different lines.


piecing it together

The pieces actually fit pretty snuggly together to my surprise. The 1cm chamfer helped quite a bit I think.

The Results

might work... but not well

Even despite the miscuts, the pop-up jig actually came together pretty accurately. Unfortunately, I haven't had time to try out the bracket, dropouts, and headtube to see how well they're aligned, but with care, I believe someone would be able to make a 54cm bamboo bike on this.

With that said, it's still not nearly stiff enough. The goal of a jig is to be assured that everything is aligned and not moved, and for frame design it's best to be within millimeters. With this jig, just one tap causes the whole thing to flex too much.

Some of our current jigs in Guangzhou


building better jigs... and more of them

As I described in my original final project, I want to make a better jig. One that is adjustable, light, cheap, and easy to design a bike with (as opposed to designing a bike first before moving your hands). So far, aluminum extrusion has proved the best material, and definitely superior to OSB.

How To Make (almost) Anything
MIT Media Lab MAS863.15