Large Table Assembly for X2 Mini Mill

Tuesday, January 31, 2012
Mini Mill Large Working Table Next to The Stock Model

I've had my Harbor Freight mini mill for over a year. Overall I like the mill, and can't imagine living without it, but after I started making some larger parts for my CNC router, I keep bumping into the limited Y and Z travel. I was almost set on getting an X3 mill, but one evening, while browsing LittleMachineShop's catalog I noticed that they had a "Mini Mill Large Table Assembly" for $299.95 (roughly $340 shipped). According to the description, the table provides 30% of extra movement on both axes. Long story short, I placed my order last Thursday and today UPS dropped (literally) the package at my garage door. The table came preassembled in a standard wooden shipping box, bolted down to the bottom board with two bots. UPS managed to seriously bust the box, but luckily the contents were undamaged. I haven't had a chance to install it yet, since I'm doing some other upgrades at the same time.

LED Display for DIY DRO - Introduction to MAX7219/7221

Friday, January 27, 2012

This is the first part of a tutorial on driving MAX7221/7219 display drivers with STM32VLDiscovery board. In this part we will cover the basics, i.e. how 7-segment display work, how the shift registers work and how to talk to MAX7221/7219 chip. In the next section I will post the source code for STM32 Value Line Discover board and explain the kay points. 

As I mention in the post on DRO Design Considerations, I decided to use standard 7-segment LED display for the position readout. Since the DRO is targeted at a small milling machines, 6 digits per axis is more than enough *. This means that we need to drive 18 dits total, and by far the most convenient way is provided by Maxim 7221/7219 shift registers. Many hobbyist are intimidated by these ICs, but under the hood they are very simple. Both chips use SPI protocol to receive data and can drive up to 64 LEDs, or 8 7-segment displays. MAX7219 and MAX7221 are almost identical, with one minute difference: MAX7219 is not SPI-compliant. I will elaborate on this a bit later, but for this project they are interchangeable.

Reading Grizzly iGaging DRO Scales with Arduino

Thursday, January 19, 2012

As I'm waiting for the parts for my do-it-yourself Android DRO, I'll start doing some proof-of-concept prototypes with the parts I already have. So, first things first - we need to figure out how to read the Grizzly/iGaging scales. The easiet way to reverse engineer the protocol is to connect a logic analyzer (Open Lgic Sniffer in my case) and see what's happening in the wires. The screenshot below gives a good idea how those things tick (no pun intended).

iGaging 21 Bit protocol captured by Open Logic Sniffer
21 Bit Protocol Capture

A Better DIY Power Feed for X2 Mini Mill

Wednesday, January 18, 2012
Power Feed Prototype on a Bread Board

Power feed is generally pretty useful, and a Mini Mill model can be had for about $150 from, but as usual, I want more than an off-the-shelf model could provide. I'm making some part for my CNC router and will have to do repeated passes to a specific position. Initially I was going to rig-up some sort of adjustable limit switch, but after some experiments discovered that they are not very repeatable (at the leas the ones I had). A stepper motor, on the other hand, could be programmed to stop after a predefined number of steps. I didn't want to do a full CNC conversion, so I decided to go with a simple microcontroller-driven driver that would let me set 0-position and then jog the table to that position multiple times.

Let’s Get Stated with the DRO Project

Sunday, January 15, 2012
First of all, after sleeping on the design for a few nights I decided to break the project into two stages. The first stage will be to make a functional DRO with basic DRO functionality. The second stage will be the stepper control and CNC functionality. The main reason is that the DRO will be useful by itself, and I think doing a proper G-code interpreter and stepper controller will take some time. As an added benefit, this makes for a smaller initial money outlay.

More Microcontroller Options for DIY DRO

STM32VL and STM32F4 Discover Boards
In yesterday's post I compared Arduino, LPCXpresso and few other microcontroller options for my digital readout project, but I completely forgot about my two newest toys: STM32VLDiscovery and STM32F4Discovery. I got them just a few weeks ago and haven't even had a chance to play with either, but they show a lot of promise.
These are ST Micro's evaluation boards for ARM Cortex-M3 and ARM Cortex-M4F microcontrollers. Mouser sells them for $9.88 and $16.25 respectively, placing them well within the reach of most hobbyists. Both boards come with built-in ST-Link/V2 programmer/debugger, and Unlike LCPXpresso's LPCLink, ST-Link is not locked into any particular IDE. There are even some reports of people using it with GNU C compiler and debugger. Better yet, the ST-LINK/V2 can be used to program any STM32 chip by manipulating a couple of jumpers.

Microcontroller Choice for the DIY DRO

Saturday, January 14, 2012

Arduino UNO, TI MSP430 Launchpad, FEZ Domino, LPCXpresso and MSP430F2132

The core of the DRO is the microcontroller, so that's where I will start. After some "back of the envelope" calculations, here are the basic requirements:

DIY Digital Readout Design Considerations

Friday, January 13, 2012

In my last post I mentions that I'm starting to work on a new DIY project - a “Digital Readout on steroids” for my Harbor Freight (Sieg X2) mini mill. I imagine it will be one of my “constantly evolving” projects, i.e. there likely won't be a “done” state, and new features will be added as I think them up. For now I pretty much made up my mind on what will be included in the initial version, but I will try to leave some space for future improvements. The first step will be to prototype the hardware and get the basic low-level functionality working, i.e. reading the scales, writing the position etc. I will make the design as modular as possible, so the parts can be reused or easily replaced if the magic smoke runs out. The unit will consist roughly of the following building blocks (I will go into more details in future posts...)

Some Ideas for the DIY DRO Project

Thursday, January 12, 2012
I bought my mini mill in January of the last year, and it didn't take long to realize that 16TPI lead screws with their silly 0.0625” per revolution were, to say the least, suboptimal. In other words dialing anything that involved more than one revolutions sucked really bad.
After some spelunking on the forums I was set on getting a DRO, but my puny toy budged wouldn't bear anything more than a Shumatech DIY DRO kit with a set chinese calipers. These kits are great value for the money, and with their new DRO-550 design running OpenDRO software they are simply a "cant's meow", but at that time Shumatech didn't have any in stock. Luckily one of the GrizHFmill goup members pointed me to Grizzly T23012 12" Digital Scale with Remote Readout scales. These work the same way as digital calipers, but have a remote display with a magnetic base (and are much easier to mount).