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The Rise of the TowerBot Part 2

Scaling my design up to my desired size, next I had to design a printer to print that big. Already, I was keen on using 3/4” EMT conduit from building a MPCNC the previous year. EMT is relatively cheap galvanized steel tubing for routing wires for building. Sold in 10 ft. sections for about $6-7 each. If it was too wobbly, I figured I could added cable cross-bracing with turnbuckles.

The more popular 3d printers used moving build platform, but knew on a print that size could cause shifting as it grew taller, and would have to account for the weight of the print. With stationary platform, my logical choice for moving the print head (hot end) that oozes the molten plastic was CoreXY. This system uses two motors and belts (usually) that move the hot end vaguely like an Etch-A-Sketch.

Now to determine should the build plate or bed move down or the CoreXY mechanism move up. If the bed moves down, it might be a bit wobbly up so high, and more of a challenge to service hot end. I settled with the bed at the base and then have the CoreXY frame move up.

Last year before Midwest RapRap Festival (MRRF) 2018, I had an idea for a PRUSA i3 style 3d printer with an EMT frame. For the lifting the printhead, I thought of a cable drive. The advantage would be you could more easily and cheaply change the height. Lead screws mechanics can get a bit pricy and more work and parts to change.

One the great things about MRRF is most folks are approachable. I ran into Sanjay after his grew talk on their tool changer. I asked him what he knew about cable drive systems and asked for my email address. Ask he searched on his phone, he sent me a link to a Standford professor’s lecture on cable drive systems. Explained he didn’t study them much but said I should watch this.

I did the next day and learned a lot. I googled a bit more and ran across another 3d printer cable drive idea. It inspired my design ideas and incorporated it in to this:

But sat on the idea for a while and figured a horizontal moving bed would limit taller, and heavier prints. What I really wanted to explore was CoreXY. So I studied it a bit and made some 3d models.

I often deep dive rabbit holes for information. An infojunkie needs his fix. Wanton to learn and drawn to understand. So I accumulate odd bits and bobs of information that often bubbles up when needed, or trigger other rabbit hole dives for accompanying information. From my two tower lift, could I figure out a way to lift all four corners?

So I started sketching on my iPad. Building on the frame idea for my three-headed printer, had to figure out the best better way to route the cables and get it to work.

Many sketch ideas began to appear. I need to visually work things out.

Should the cables cross on the bottom? Try routing through inside the EMT, but harder for testing a prototyping.

Evolving directions. As one side of the cable moved up,mute other side moves down.

Started color coding directions.

Then the more fun stuff figuring out pulley angles and placement. And repeatability. Nice to have reusable parts from one design.

Attachment points.

How the tubing is joined.

Ways to grip the cable/line.

CoreXY cabling.

Pulley placements.

Cables high and low and potentials for conflict.

It’s one thing to read about something, but for me, I need to sketch it out or model it to begin to really understand the concepts.

(check back soon for part three.)