@madpilot rants

Converting a Makibox – Aluminium frame is done

I’m pretty happy with how the aluminium frame has come together. I’ve kept the X-axis pretty simple, though I tried a few iterations before coming to this shape.

Originally I had the vertical X-axis supports butted on the top of the horizontal Y axis base, but I was concerned with keeping the vertical… vertical. I could have used right angle brackets, but decided that by putting them in the inside of the base, I can add additional points of contact that would better support them. This configuration also gives a slightly larger base, so should make it slightly more stable. They are now attached in two dimensions which effectively works like a right-angle bracket.

The motor mount and bearing mounts are pretty simple, bridging the two verticals on each side. I toyed with running the bolts in a horizontal extrusion that would stop them from slipping down, but that would stop me from adjusting the heights when tramming.

On the topic of adjustments, I’m starting to regret the dual-carriage design, as there is an extra dimension that needs to be aligned – not only do I need to align the X, Y and Z axes, I need to make sure both slides are exactly parallel. I’ve bought a digital dial indicator which should help in squaring everything up – we’ll see how that goes.

I now have a complete bill of materials for the frame:

Qty Description Length
3 40×40 Aluminium Extrusion 285mm
4 40×40 Aluminium Extrusion 260mm
2 40×40 Aluminium Extrusion 401mm
1 40×40 Aluminium Extrusion 205mm
16 8mm Square Washer
32 16x16x6/M8 Square nut
32 M8x16 Button Head Socket Screw
8 End cap 40×40 Black

The order cost me just shy of $200, which already takes me over my $250 budget, but I’ve been reconsidering how much I’m spending, as I assumed I could use my Dremel 4300. After a bunch of reading, I think I’ll need to by a different spindle that has less runout.

Converting a Makibox – Designing the Y-Axis

I’ve been iterating the Y-axis in Fusion 360. A common design I have seen on other moving-bed designs is four linear bearings – one bearing at each corner of the bed. The problem with this design is you lose the distance between the bearings in travel. Since I have only have a maximum of 165mm on this axis, I didn’t want to lose too much to dead play.

Example of a moving bed with 4 bearings

Round 1 – Two Bearings

My first thought was use a single bearing on each side, introducing a minimum lost travel of 12mm (the width of the bearing). This looked like it would cause rotation problems, though – especially when dive cutting in the outer edges of the build area.​​​

Drilling on one side of the axis, causes excessive rotational forces at the bearing

Round 2 – Four Bearings

I went back and looked the parts I could salvage from the Makibox, and it turns out I have four 170mm linear rods at my disposal. This means I can create a passenger carriage – one that isn’t driven by the lead screw, but instead is pushed along it’s rails by the bed itself. This design gives four points of contact, eliminating the radial moment of the two bearing design (Note: this doesn’t deal with linear rod or bed flex, just the rotation issue). The disadvantage is the base is now double the size, but as the bed would have moved outside of the frame envelope during operations, it’s not that big of a deal.

Here is a render of the Y-axis. If you imagine a bed on top of it, attached to the two carriages – the left (driver) carriage is driven by the lead screw, while the right (passenger carriage is pushed by the bed. (I tried making a video, but the Fusion 360 animation workspace doesn’t support animating joints!)

Dual Y Axis Render

The Y-axis will have a 131mm travel – the loss is 7mm from the ball bearing, 7mm from the coupler and 20mm from the anti-backlash nut.

Issues

There are still a couple of side issues I still need to work out:

  1. ​The mount holes for the anti backlash nut are too close to the shaft, so I can’t heat fit brass inserts to screw in to – I may have to thread the plastic. I may be able to find some small nuts to secure it. Ideally once the mill is working I’ll be able to machine a bracket from a small plate of aluminium
  2. I have brass inserts in the carriages because I initially thought I would screw the bed down from the top – making replacement of the spoil board easier. This may not be an actual problem though – I’m not sure how often the spoil board needs changing. I may just make them screw holes, and be done with it. I have to think about it a bit more.

Next up: the X-axis

Turning a Makibox into a PCB Mill

You might remember the Makibox A6 – it was a sub-$400 3D printer that, like a lot of cheap printers at the time, was crowd-funded. It took forever to deliver, and there were a lot of problems with it.

The MakiBox A6LT

Personally, I managed to print a single cube on my first print. On my second print something went wrong and I blew up the control board. I suspect because of the stalled extruder motor. The extruder needed replacing, as did one of the plastic lead screws (that was my fault – I over tightened it).

In the process of trying to get the parts replaced, the delivery got lost – they claimed it had been delivered, but I hadn’t received yet. While trying to work this out, I had to quickly move interstate for work. To make matters worse, the company that made the Makibox disappeared around the same time, so I resolved myself to writing off the printer.

I decided to move to Melbourne permanently, so I flew back to Perth to collect my belongings – included what was left of the Makibox – and jammed it into my car for long drive over the Nullarbor.

And there is sat almost four years – dejected, in a cardboard box in my workshop.

On a recent trip back to Perth, my mother handed me a package which a person I worked with have given her. Apparently. it was delivered to the office years ago – so I had no idea what it was.

Low and behold, It was the replacement parts from my Makibox! Well, this was a sign. I put the parts next to the printer, as I wasn’t sure what I was going to do with it. I had an M3D printer which was pretty terrible – maybe I could frankenstein the two designs and get one printer out of them?

Fast forward a couple of months – I come in to a bit of spare cash after selling off my time tracking application, and I decide to bite the bullet and buy a real 3D printer – a Lulzbot Mini. After setting it up and kicking out a number of awesome prints, I placed the M3D next to the Makibox. I now had a collection of old, cheap and not very good printers. I had to do something about that.

Upcycling a Makibox

The Makibox has some decent steppers and screws in it (the M3D really doesn’t – half the problem really) so I started looking at the parts and wondering if I could convert it to a PCB mill. Ideally I’ll eventually want a proper mill that can do aluminium and stuff, but I reckon I can cobbled together something good enough to grind a few hundred micros of copper off some fibre glass. Bonus points if it’ll drill through holes.

What’s the worst that can happen? I have a broken Makibox?

Research

I’ve been doing some research into PCB mill designs over the past couple of weeks, and I’ve decided to go with a fixed gantry design (based heavily off the cheap Chinese machines). This means I only need three motors, and three lead screws.

I’m giving myself a $250 budget for the conversion.

Due to the existing hardware that I want to reuse, the actual build area for this machine will be relatively small, so I’m hoping that will help with the rigidity of the system (smaller builds should be stronger than larger ones). Given that this PCB mill gets decent results with a wood base, I’m feeling pretty confident we can get some good results with this.

Stocktake

  • 4 x NEMA 17 sized motors (Longs: 17HS 42BYGH 1.8°)
  • 1 x 218mm T8.8 (8mm diameter, 8mm travel per revolution) trapezoidal lead-screw
  • 1 x 165mm T8.8 trapezoidal lead-screw
  • 1 x 147mm T8.8 trapezoidal lead-screw
  • 2 x 226mm x 4mm steel rod
  • 1 x 170mm x 4mm steel rod
  • 1 x 164mm x 4mm steel rod
  • A bunch of cap hex screws
  • Plastic couplers
  • Plastic anti-backlash nuts

The plastic anti-backlash nuts are surprisingly good – I can’t detect any backlash (with the naked eye). The injected plastic piece has some thread that acts as a preloader – quite clever really. Regardless, I decided to order some metal anti-backlash nuts – I’m not sure how the plastic will hold up to the additional force of milling.

I also ordered some aluminium couplers (to replace the plastic ones), LM4UU linear bearings (to slide on the steel rods), and round bearings to hold the lead screws. Total cost so far: $79.68.

Everything else looks useable (at this stage) – I’m a bit concerned that the steel rods aren’t straight enough, but I’ll run with them for the moment.

I’m going with 4040 aluminium t-slot for the frame. I’ve found a Melbourne based supplier so I should be able to get high-quality stock quickly (and cut to size!). But before I order them, I’m going to design the mill in Fusion 360 so I can test for fit and size.

You can see the render of the Y-axis here:

Render of the Y-Axis

The X-axis will be a (wider) copy, rotated 90 degrees. The Z-axis will still need some thinking.

I will print the motor bracket, bed and bearing holder on my Lulzbot Mini. This is is the cause of the weird design – it needs to fit in the 150mm x 150mm build envelope of the 3D printer.

Based on the dimensions from Fusion 360 the design should allow a Y-axis travel of around 168mm 156mm (Update: I didn’t take in to account the linear bearing width). I still have to work out the X-axis travel.