Around a year ago, when the ShapeOko 3 was first being announced I started getting the idea that it would be really awesome to just buy the rails and build my own machine. It just sounded like the kind of challenge that I was looking for. Unfortunately, it quickly became apparent that the ShapeOko 3's rails weren't going to be available by themselves. This realization of course didn't deter me too much, I simply started looking at ways that I could mimic the performance of the ShapeOko 3's non-general-purpose linear motion rail.
Of course, as I'm writing this there are two very simple paths to get rails for the build I was initially envisioning. The first is by getting a Shapeoko 3 xxl expansion pack. Although, at $700, it's a bit on the pricey side. The second option is to get some MegaRail 80 shipped over from the UK. Unfortunately, neither of these options were available when I started procuring materials for this build.
Around September 2015 I decided that I'd thought about the build long enough, and if I was going to build something I should probably start doing it. With that decision made, I went about procuring all of the raw materials needed for the build. For the rails I settled on using some 1/4" thick extruded aluminum rectangle that measured 4" x 2" x 36". I really felt like I was gambling with this choice, but I got lucky and the extrusions ended up usable for the project. Now, there are several options for rail that I could've used.
One of course, was Open Build’s OpenRail. The second option would be to use hardened steel rail which is available from numerous vendors. Finally, the third option that I considered was hard coat anodized aluminum rail.
I sort of ruled out OpenRail because I felt that Delrin V-wheels might not be able to support the weight of this machine, and even if they could they'd end up being the weak link for this build. I had almost come to grips with the fact that I was going to have to spend a ton of money for steel rail. Then kind of out of the blue I discovered a guy on eBay selling hard coat aluminum V-rail. It was so much cheaper that I had to take a look and figure out if I could run steel V-wheels on it. It was kind of hard to find any solid proof that the rail would even work.
Ultimately, three things swayed me to try the hard coat rail. First, was obviously the price compared to harden steel rail. The second was that I had found some hardened steel rail that matched the hard coat aluminum rail's dimensions. This means that if the hard coat rail doesn't hold up but the machine ends up working great I at least have a relatively simple option available to fix a bad decision. The third thing that persuaded me to go with hard coat rail was a post by Bart Dring in which he answered a question about hard coat maker slide:
From reading this, I'm reasonably confident that the rail will last long enough to prove the machine a success or failure and save a bit of money right now anyways. However, I do believe there is a strong likelihood that the hard coat rail will eventually wear out. Although, it sounds like keeping the rail clear of debris will potentially aid in maintaining the rail for a longer period.Bart Dring on buildlog.net wrote:I have run experiments with various combinations. With a high duty cycle and a dirty environment, steel wheels on bare aluminum start to wear the aluminum over time. The wear looks like a general rougher surface, that looked like streaks, to the aluminum with the occasional pitting.
I set up a test fixture to test steel wheels on hardcoat and it ran non stop for 2 days. It was a clean environment, but I saw no notable wear. The carriage was loaded to about 20 lbs with 4 wheels, with the load sideways, like the camera slider. My plasma cutter is intended to use hardcoat. The current version is just a half scale version and I expect a few other changes, so I decided to prototype it without the hardcoat. I don't have a lot of hours on it yet, but there is really no wear to speak of yet. Once the design is stable, I do plan to get the rails hardcoat. It think the hardcoat might be more robust to the plasma effects. I know a lot of people who have made DIY CNC routers with steel wheels on aluminum angles and they held up pretty well. I saw one that was over a year old. It had quite a bit of scratching and pitting, but owner said he could not really notice the effects in the work it was doing and did not plan to rebuild it at the time.
After spending most of a month sourcing and purchasing components for the build, I figured that I would be able to get the whole thing built by the end of November 2015. Boy was I wrong! Turns out that when you don't have the experience or the equipment for such a project, things take a lot longer than you think they might. Then add in the uncontrollable factors of life and work, and I find myself nearing the middle of April with less done than I thought I'd have at the end of October last year.
So... What do I have done? Well, all three of the rails are finished. I'll go into a separate post detailing their build process later, but for the sake of brevity (ha TL;DR am I right?) I'll finish this initial post up with just a to do list, and a bill of materials for the project.
To do list:
- Make a to do list (Nailed it!)
- Make a BOM (WIP)
- Build three linear motion rails similar to the SO3 specs. (Done)
- Design and mill motor mount and end plates. (Done)
- Design and build a z-axis. (Done)
- Build a flat and level table for the machine to mount to. (Done)
- Wiring (what a nebulous term)
- Add to the to do list.
- ???
- Profit (TBA)
Bill of materials:
The Rails
- 3X 1/4" thick 6063 extruded aluminum rectangle 4" x 2" x 36"
6X 36" hardcoat anodized aluminum V Groove rail.
1X 1/4" thick 6061 aluminum angle 1" x 1" x 24"
22x M5 8mm Low Profile Screws Per assembled rail.
8X 1/4"-20 Screws Per assembled rail.
- 2X 3" x 8" 1/4" thick 6061 aluminum plate
2X 5" x 8" 1/4" thick 6061 aluminum plate
- 1X 7" x 9.5" 1/4" thick 6061 aluminum plate
- 2X 7" x 9.5" 1/4" thick 6061 aluminum plate
- 2X 1" x 3" x 1/8" x 4' aluminum rectangle tube
5X 1" x 3" x 1/8" x 3' aluminum rectangle tube
1X 4' x 4' x 3/4" MDF
