void charles_builds_stuff( ) {

melon-scooter {

razer-revolution {

make-a-bot {

2.009 {

//todo: make a page for this

segfault {

//wtf slashdot?

}

}

…?!

This semester, I seem to have fallen into a habit of neglecting projects for long periods of time in order to work on other ones, and subsequent others still. It’s like opening multiple brackets when you’re programming in Arduino. Well, hopefully now it’s time to start closing some of the brackets. For starters,  Segfault now gets to join the rank of “random cool interactive things MITERS can put on display to recruit froshlings”. With it operational, but a little short on battery life- something that I will just randomly fix one day without thinking, it’s time to take a step back and see what I’ve left behind.

…

Hey, what’s this aluminum sculpture sitting in the corner here?

It’s still smiling after all these months.

Oh, that’s right… I was working on a 3d printer, wasn’t I?

I’ve been working on Make-A-Bot in the background a little, including ordering some of the final parts needed to complete it. I purchased the ABS extruder head from the Makerbot Industries, along with all the control electronics and the cute little automated build platform. Stock equipment, but it’s equipment which they’ve figured out and which would take me longer and cause me more pain to re-engineer again. Past that, though, the last month and a half has seen little physical progress because of my other obligations – mind you, both my 2.009 work (to be detailed) and Segfault were actually for class for once. Imagine that.

Make-A-Bot was left at a stage typical of my projects where I have built everything I designed already. That means without further design, I just have a Fancy Aluminum Sculpture. As lovely as sculpturework is at times, I’d rather have a 3d printer.

First, I put together the Plastruder 5 head for kicks. I must say, this thing is adorable and pretty intuitive to build. It is a bit bulky, though, on the motor end of things (Dear god, why such a GIGANTIC motor?). Maybe a possible direction to explore in the future. I was also a bit dissatisfied with the mounting surface, which doesn’t seem to actually have a solid mechanical connection to the rest of the head, but it could just be a consequence of me trying to adapt it to my own custom mounting configuration. A quick nylon through-bolting solved the issue anyway.

I have yet to try actually heating it to full temperature and shoving some of the ABS filament through.

Anyways, onto the designs:

How can you tell that I got a new widescreen monitor?

I jumped back into Inventor and started designing the support equipment cabinet that will house the feedstock filament, the power supply, and properly mount all the electronics. Without something to organize those components, MaB is just a rickety imitation of a small manual milling machine. The cabinet I designed (essentially all on-the-fly with little forethought) is actually more of a pedestal for the machine proper. Designwise, it looks like the rest of the bot with all of its edge-stitching and interspersed T-nuts. I discovered that designing panel footprints in increments of 1/2 inch made the t-nutting and edge-stitching process very fast, since the layout is always symmetric about a center line. This beats my previous tactic of calculating precise widths for the slots and tabs such that they end up symmetric. Forget that – just beasting it solves the issue, as usual. I’m fine with that.

All the important electronics – three axis controllers, the motherboard, the extruder controller, and the auxilary relay board, get a home on the “backrest”. I even OCD’d enough to model (blockily, anyway) the protruding components on the boards. I lined up the important connections to face each other or be close to each other, so the wiring should end up clean.  The electronics backpack also has slots and holes to pass wire through cleanly.

Make-A-Bot looks cute sitting on its couch-like pedestal until you realize how huge the whole thing is. That base is a full 22 by 12 inches and the top of the wooden backrest thing is 14 inches tall. Add MaB’s own height to it and this whole thing is already over 2 feet tall.

Man, this whole widescreen thing really makes my CAD screenshot proportions weird. Anyway, having purchased like 10 miles of ABS filament (which came in a massive donut-shaped coil), I decided I needed a method of keeping it all in line so I don’t have to constantly feed the filament. Makerbot does sell a spindle kit for such an occasion, but this was one part I decided to just tackle myself.

Above is the filament spindle design. There’s a truss piece under the top triangle shaped plate which holds the vertical spars together. The top plate can come completely off for filament changing, but otherwise has provisions for a detent-lock effect supplied by the vertical spars and a few degrees of rotation. It will all become clear after the fabricated pieces are assembled.

People prone to vertigo should avert their eyes:

Come on into THE VOID.

What’s THAT?

Over the course of a few days of on and off thought, I decided that I’m not going to run the automatic build surface. I’ve come to dislike the bed-type design I settled on for MaB 1.0 (Yeah – I’m already thinking about what 2.0 will be like!). Such a design is great for applications where the machine is many orders of magnitude heavier than the workpiece usually is – like most milling machines. When this is not the case, a changing workpiece weight can affect the dynamics of the machine greatly. A moving work surface also puts force on the workpiece when it accelerates. The axis inertia is much greater and also mismatched because one axis must be installed on the other (i.e. in my case, the X platform is mounted on the Y carriage). Therefore, MaB 2.0 will be an overhead gantry type machine with an fixed work surface that only changes in Z height to print layers.

What on earth does that have to do with the trippy-ass PCB up there? Well, that PCB is just my take on the Makerbot Heated Build Platform. For now, I’ll just keep the surroundings of the workpiece nice and warm. I really don’t mind limiting myself to one thing at a time. It’s just a little bigger than the stock part. And by a little I mean it’s 7 inches square and designed for 50 watts of heating power. It took a while and even more OCD to get those trace lengths correct. There will be a thin aluminum plate thermal-transfer-epoxy mounted to the center heating coil section (not bolted down, but legitimately adhered with silver-bearing epoxy).

This piece is reusable in any future MaB versions since it’s already pretty substantial in terms of square inchage.

making the makings of the make-a-bot

After designing, the next step is of course for me to build have expensive computer controlled machinery build it all. Spoiled so much I am…

Here’s the spindle laser-cut from 6mm white acrylic that I had on standby, holding the Giant ABS Donut. You can see the click-lock fingers easier in this picture. To unlock, rotate a few degrees counter-clockwise and then lift up. To lock again, drop the top plate over the 3 prongs and twist clockwise. This system turned out great. I can actually add a few thousandths more “click” to the prongs, since the laser cutter kerf removed most of my designed interference.

And now, for something completely different:

Hey, what kind of wood is that?

Long story short, I thought there were large stocks of 1/4″ hardwood ply hanging out around the Media Lab – our group usually has a pile for making quick prototypes and displays – but alas, it had been run out and not yet replenished. Not knowing where we got the wood from, I just went ahead and plucked some acrylic panels from McMaster. Acrylic, wood, same thing, right?

I elected to get tinted panels this time to try out the looks, along with plain clear panels.

The next step was to pitch it all on the laser cutter wake up in time to run to the shop before it closes and laser-cut everything. This actually took a long time, as in several days of preparation and missed (and actively suppressed) alarms; as soon as term ended, I immediately restabilized to my 9-to-5 sleep schedule. Yes, my day job is sleeping. Take that, industry. It does make interacting with a shop that is open from roughly 9 to 5 difficult.

I am, however, very glad I went with acrylic:

Let the case mod begin. My favorite part of building things is always the case mod – what can I make unnecessarily shiny, backlit, glowy, and translucent?

I made the base out of clear acrylic and the sides (and everything else) from the tinted stock. It created some unexpected contrast that I enjoy alot.

The L-shaped side plates were split in two for more convenient cutting. Since the “electronics backpack” is not supposed to bear structural loads, I just joined the two legs of the L with a ninja-tail (not quite a dovetail). The “backpack” portion drops down from above after being pre-assembled and is secured by requisite t-nuts.

The completed pedestal. Hey, if nothing else, MaB can be turned into a absolutely beastly PC. There’s even a cutout for an ATX power supply already.

Oh, so that’s what the A in Course II-A stands for.

And the moment of truth – does it actually support the machine weight?! Curse me for building a contactless tool out of heavy \m/etal.

Make-a-Bot itself sits on four little rubber shock mounts. They weren’t necessary, but I figured they were worth including anyway.

I think the design looks gorgeous. The glossy tinted sides complement the raw metal components well, and should look even better once I have some internal mood lighting.

Previously unknown fact: The spindle sits on a large 9″ diameter turntable bearing. This allows the extruder head to tug on the filament at its leisure. The bottom of the turntable bearing is not fixed to the machine. It just kind of sits there – this is not exactly a heavily loaded or high speed application here.

Oh, another detail: Check out the spring-loaded front lid that drops down for easy filament removal. When the lid is opened, its own weight keeps the hinges down, but when it’s vertical, there’s enough force to keep the whole thing closed.

As many random features as I’m putting on this thing you’d think I’m intending on making a production version or something. Not really, but I hope designers of commercial kit machines find some of these aspects helpful.

srs metal

With the pedestal completed, I turned my attention to back to the machine itself. It still didn’t have the steppers installed or the axis belts mounted yet. I decided to tackle that problem first.

The pulleys came with a 5/16″ machined brass bore that by itself is an okay bearing surface for low speeds. I would have just put it on a 5/16″ smooth precision shoulder screw, but could not find one around that was long enough.

Solution? Mock one up from a 1/4″ bore, 5/16″ OD bronze oil bushing and a 1/4″-20 cap screw. The cap screw uses the bushing as a standoff of sorts and a nut keeps the whole thing rigid.

With a few drops of teflon-infused oil at the interface, the glide is almost as smooth as greased ball bearings. Being a millimeter or two longer than the pulley bore, the bronze bushing allows for smooth pulley rotation without much regard to how hard the screw is tightened.

The steppers I ordered came with 15 tooth 2mm GT pulleys already installed on their shafts. So why bother changing them out to the stock 17 tooth ones? The smaller pulley gets me more force anyway.

I should be able to adjust the machine travel-per-step in software.

Every elegant engineering solution has a complementary ugly hack. Remember my Awesome Adjustable X-Axis Endstops?

When I become ambivalent and lazy, they become Dude, You Just Bent The Existing Contact Arm On The Switch A Little X-Axis Endstops.

Hey, it works.

The ATX power supply has its own cubby at the back of the pedestal. The bright polished brass between the dark acrylic makes the whole thing look classy.

And everything as of now. I’ve attached the axes to their respective belts, and they feel alright. No obvious jamming or tight spots, though I still don’t like the X-axis ceramic-coated rods. Important mechanics left include the attachment of the other limit switches and attaching the Z-axis leadscrew to the stepper motor. After that, I should be able to run an all-axes motion test!

The Man has been holding me down.

And by The Man, I mean MIT, which is well known for holding you down. There’s this little quirk about senior year called “graduating” that comes at the end if I behave. I think I should at least make some effort towards it, which is why I’ve been missing for a week. Most of that time has been absorbed by the Mechanical Engineering senior design course, 2.009, an exercise in realizing the futility of large team dynamics, the sanctification of rigidly defined process structures, vapid goals, forced decision-making, and irrelevant gimmicks An Exciting and Wonderful Adventure into the World of Product Design and Engineering Processes.

Right.

That.

So, when I last saw MaB almost two weeks ago, it was still a bundle of rendered lines and pixels on a screen. I decided to take my own advice for once and not look at the design for several days, letting the little intricate details settle and sort themselves, rather than staring at the design over and over. I’ve been well known historically for convincing myself that some incredibly numbskulled design choice was a good one… like the entirety of Segfault… simply because I got tired of inspecting the design. MaB was going to consume all the aluminum plates I had on standby, so I wanted to not make it completely fail.

Mix in a few classes and you have me forgetting the thing existed until a few days ago. But let’s get started:

ffffssssssssh.

I carefully tiled all the parts onto my four spare 1/4″ thick, 12″ x 24″ 6061 plates. These were all leftovers from the robot builds, collected over the past several build seasons. As it turns out, 4 plates was just enough to fit all the structural components on and still allow for fixturing area and dead space.

Next, it was to pop the entire frame out on the Machine Without Which I Am Nothing.  I pretty much devoted an afternoon to a marathon waterjetting session in which all the parts were cut without incident. Now, I’m pretty traumatized by the complete loss of heavily tiled parts in the past, but this time, the worries turned out to be unfounded.

Well, mostly. It helps that I was careful and kept a close eye on everything. This could easily have turned into a nasty situation – the closely tiled parts on the inside of the perimeter caused the nozzle lead-in to separate the scrap into two pieces… one of which proceeded to jut upwards.

I caught this moments before the machine was to make a pass to the left again. After every part outline finished cutting, I’d retrieve it out of the plate for peace of mind. That usually unnecessary action probably saved this whole plate.

Something I decided to play with on this build was the nozzle offset setting on the machine. Normally, the machine tries to stay one nozzle radius to the right or left of the cut line to finish exactly on dimension. In the past, I’ve accepted that the draft angle that results from such an action causes my tabs to not fit into their matching slots – while the nozzle side face is on target, the bottom could be as much as 4 or 5 thousandths larger on a 1/4″ thick part.

I’ve just dealt with the sanding and occasional light machining that is a consequence of this. But after observing how well the Cupcake parts fit together, I realized that I might as well try to see if I can get even more lazy by not even having to sand the parts afterwards.

Because Makerbot Industries cuts the vast majority of their parts with a laser cutter – which cuts on the line, ignoring the kerf offset, holes and slots are always slightly bigger, and tabs always a little smaller than nominal dimension.

I changed the offset a thousandth of an inch at a time – normally it’s set to 0.014″ for a .028″ diameter orifice. I started turning this down to 0.013, then to 0.012. At that point, I could just push the two parts together for a perfect fit. If you’re keeping track, that means my ODs are 0.004″ in total length (two offset…offsets) smaller on average and IDs are .004″ larger on average..

So this is what a pile of MaB looks like. That’s all the parts I have designed so far…

Oh, so I never let a post involving waterjet cutting go without mentioning Big Blue Saw at least once. You, too, can have your own pile of MaB (or pile of anything you feel like designing). I’ve been so utterly spoiled by MIT’s multiple machines that some times I forget about the fact that not everyone has access to one…. and some times, the next best thing is to just hire it out. Surprisingly enough, it doesn’t cost 9 billion dollars per part, and for larger quantities you practically break even on the foregone material cost.

Now merge into this pile a second one of McMaster, SDP, and Ebay orders that had accumulated over the past week or so, and dump it all on a table at MITERS. This is (about 50% of) Make-A-Bot, the other half being the electronics and the software that actually makes it move. You know, The Course VI Part Of Things that I have to deal with every time I build something, since as a Mechanical Engineer I absolutely must build complicated cross-discipline coupled systems projects with electronics in them somewhere.

The McMaster orders contained the majority of hardware, including fasteners, the axis guide rods, bushings, bearings, etc. I nabbed 4 NEMA 17 long-case stepper motors from eBay, which should have about twice the torque of the stock Cupcake CNC motor – hopefully more than enough to muscle the heavier aluminum frame around. Next, from Stock Drive Products, were the two X and Y axis belts and several 44 tooth and 17 tooth timing pulleys.

Alright, so I’ve cut myself a puzzle. Now let’s start putting it together.

The time: 7PM

Because of my “compensated kerf compensation”, everything sort of fell together. For the sake of convenience, I dashed some of the parts over a belt sander anyway for a free-slip fit rather than a push fit. I figured all of this has to come apart again eventually because I installed something backwards.

(I did.)

Above is the base and some of the Z-axis tower assembled, but relatively unfastened.

The X-axis stage holder is probably the best finished, most well-kerfed assembly I’ve made yet.

As usual, blitzCADing means I left a few details out. For example, while I made these cute frog-eyed axis rod stops, I neglected to transfer their hole pattern to the actual front and back baseplate walls.

Oops. I guess that’s what a clamp and cordless drill are for. The rod stops were clamped onto their anticipated final location and then #4-40 tap drilled.

The action’s picking up a little now. This is the whole Z axis attachment point, with an almost terrifying amount of interleaved T-nuts. Some of these things MUST be redundant.

I didn’t care. Square nuts are easily slipped in from the side, and I’m going to wager that Z-axis fine alignment can be changed by selecting which nuts I tighten.

After I fully assembled the Z axis tower, it was time for the Pass-or-Fail-at-Being-a-Mechanical-Engineer test. By that, I mean dropping the Z linear guide rod down the holes which are supposed to support it, and see if it falls all the way through by itself.

Okay, so I cheated: All nominally 0.500 holes in aluminum were given a run-through with a 0.505″ reamer. I was after the slip-fit, not a press fit or shove-fit, again for convenience of assembly. All the bronze guide bushings were also given the same treatment. After pressing them into their carrier holes, their IDs deformed enough such that they no longer  mated with the guide rods. A pass with the reamer in a cordless drill cleaned up the bores again to something freely sliding.

After that, both Z axis guide rods made it all the way to the bottom without incident. The compression rod is also shown (That’s not the Z axis leadscrew – it’s just a threaded rod that will be used to load the Z-axis tower in compression)

After the Z rods went in, I pitched together the Z stage. The bushings had already been given the once-over by this time, and the assembly… compiled, I suppose, with the help of a rubber mallet.

And it was beautiful indeed. No stick-slip, no jamming, no tight spots throughout the travel. I was very surprised it turned out this way, and I’m willing to bet the flexure bearings are accommodating at least some movement that would otherwise have caused total disaster. But with the Z axis rods as well-aligned as they are, maybe not?

After securing the base and the Z tower, I moved on to hammering the Y axis carriage together.

Here’s a quick assembled view of both axes. The Y axis motion is also extremely smooth. Due to its lack of gravitational preload in a convenient direction, there’s some stick-slip between the bronze and the polished steel, but it’s nothing a dose of Teflon-bearing oil didn’t fix. That, or just some exercising and running to fit the two cylindrical surfaces to each other.

After slipping the carriage onto the Y-axis rods, I installed the X axis guide rods. Note that they’re a different color and texture than the smooth steel Z and Y ones.

Out of the interest of reducing axis inertia, I elected to try some ceramic-coated aluminum guide rods. McMaster priced them out at just a dollar less expensive than a case-hardened steel rod of the same length and diameter, but the primary motive was to try and save the pound and a half that was the difference between the aluminum and steel. The coating on the aluminum is supposedly harder than the equivalent case treatment on a steel rod.

But after trying them out on the X-axis stage, I’m not sure if I like this setup. The bronze bushings exhibit strong stick-slip with the coating, even with a healthy dose of oil… and it even seems to be scraping off bronze onto the rod surfaces. My guess is that while the ceramic coating is harder than the steel, it’s not smoother. The case hardened steel rods have been subject to some pretty intense polishing.

I wasn’t nearly as satisfied with the X axis feel as much as the Y and Z. As a result, if axis inertia proves to be a false demon, I’ll just switch back to steel. Sadly enough, they don’t make hollow steel shafting in this size.

Otherwise, there’s always ninja linear bearings.

The coated aluminum rods only came in 13″ and 15″ sizes for whatever reason, and I needed 14. So enjoy this cute robot face that is the result of trimming the rods to length.

Enough silliness. This is where the hardware stood at 2 AM, after 5 net hours of assembly time (because there’s always things to distract yourself with at MITERS). There is currently no…

• Head
• Motors
• Belts
• Pulleys
• Leadscrews
• Motherboard, driver boards, extruder controllers
• … or anything else, really.

Oh, speaking of the leadscrew, I’m 99% certain that the new Thing-O-Matic uses a 3-start “rounded” ACME threaded rod and matching flanged nut, 3/8″-12 diameter, for 1/4″ of vertical travel per turn. Makerbot Industries hasn’t released details yet, but I extracted what I could from all the up close, almost pornographic images I took of the 3d printing exhibits at Maker Faire.

Example: McMaster 6350K151 and its matching screw, 6350K113. Problem? The screw only comes in stainless steel, in 6-foot sections, at a shiny $133 each.

…

No, not happening. So what else goes 1/4″ per rotation and is 3/8″ in diameter? A two-start 3/8″-8 ACME leadscrew, of course. I’ve spec’d out McM 99030A315 for the leadscrew and 95072A126 for the nut.

I piled everything onto the base and slipped it in an empty corner for now.  Until another day, Make-A-Bot!