I'm converting a mini-mill to CNC, and I wanted to create a build log. I thought about putting it on CNCZONE as yet another X2 conversion, but since it is intended to make ebike parts anyhow, I decided to put it here on the sphere instead - in the spirit of nechaus' "makerbot" thread. There are a lot of folks here with skills and tooling that far exceed mine and will regard this project as laughably naive, but hopefully there are others who are interested in seeing what is involved. Usually I post here ONLY based on my direct experience, and that will be the case for the rest of the thread as the build progresses, but this is new ground for me so the first posts are OPINION based on the reading and research I used to design the project. I am sure I misunderstood some things along the way, so take it as the ravings of a CNC noob trying to learn.
Since I took a Machine Tools class a few years ago (my sole experience to date), I have wanted a vertical mill at home, so I could make my mistakes in private, and the tools I break are my own instead of depriving students trying to learn a trade. I also wanted CNC control, if possible.
During the class I almost bought one of the cheap chinese router/engraver tables that had just hit the market at the time, which today are available on eBay from dozens of vendors. I'd start out with one of those $800 engravers in my cart, upgrade to the VFD spindle, throw in the bonus 4th axis table, add kings ransom in shipping, and suddenly, you are way past $2k... I held off long enough to read feedback from others, finally concluding that the mills are better suited for engraving, and were not powerful, rigid, repeatable, or capable enough for the type of milling operations I had in mind.
I realized for the same $2k+ the Chinese engraver cost, I could get a decent large vertical mill - so what if it didn't have CNC. I started looking at the Sieg X3 clones, then I rationalized in upgrade after upgrade - consider getting 220v service installed at the house, to handle the larger Sieg X4 clones, then the RF-45 clones... Then I rationalized down in size a few models as a trade off for adding in CNC. Then I'd work my way back up the size range again until I was at the RF-45 with a CNC kit. Then I'd figure well since I was spending all this money, I should get a professionally converted mill...
About this tiime, I realized I was planning on spending 10k on a mill, as well as getting 220v service installed and giving up my spot in the garage permanantly, to install a mill to build the occasional ebike part. I'd get frustrated with the futility of implementing the ultimate mill, and all the time I'd wasted thinking about and researching it, so I'd forget all about it for a few months. Then some project I'd read about, some part I'd need, would trigger the craving for a mill again, and I'd go through the whole cycle again, from Chinese engraver to 10k CNC. This repeated for a few years.
Recently, I came across an ad for the Harbor Freight varient of the Sieg X2 mill for $450. I liked that the owner had done the nasty job of cleaning off the shipping grease, had lapped in the ways already, and was only 10 minutes away. Still, I dithered about it for a few days, starting the usual cycle of rationalizing bigger and better mills, until I had a moment of clarity. This HF X2 mill was more than up to the most immediate job on my project work list - milling a brake adaptor to mount a 9" disk brake on a Boxxer fork. Sure, I might get lost in the acres of backlash, and have to go find the edge a few times, but eventually I can locate a spot with precision. Yes my operations will not be precise to .0005 - but I don't need that level of precision - so I bought it.
I figured I'd see how it fared in my workshop, whether it was a tool I only wanted to have, or a tool I actually wanted to use and grow proficient on. If I used it enough, I thought I'd do the CNC conversion, which is a strong driving reason for me getting a mill. I had a taste of G-code in class, I wanted more but I realized because of my learning style it is something I could only pick up on my own, figuring out what I needed for each project until I built up a good body of working knowledge.
As it turns out, while the HF Sieg X2 mill is a good fit for the home mill I needed, the tilting column makes it a challenge for CNC, as the torque of a cut can move it out of adjustment. For light-duty manual milling it is not a big deal to tram the head, even between each cut if needed, adjusting with a rubber mallet - but CNC needs to do cut after cut without interaction, and if it gets a little out of whack each time, eventually you get way out of whack and crash the head. Some people build supports that brace the column to prevent is, and I'd consider that if I had to.
However, there is a single X2 variant, one of the "SX2L" models sold by littlemachineshop.com (LMS), which has a solid column that eliminates the whole movement problem, and therefore is more capable of CNC duty. It is harder to tram in the head because you have to shim the solid column to the base instead of rotating the adjustable column, but without the ability to rotate it will stay square much longer. The LMS X2 also has a bigger table, with so much longer travel in all 3 axis that the total work envelope is DOUBLE the size
of other X2 mills. It also comes with belt drive instead of the noisy/weak plastic gears on other X2 clones, and a 500w BLDC spindle motor with a tachometer output, instead of a 350w brushed motor.
As you can see from this borrowed pic, the walls of the solid column are thicker than the ones on the tilting column, and not hollow inside the dovetail section, adding rigidity. LMS sells the column separately for $175, and it can be used to upgrade other X2 mills because their smaller tables' saddles will fit on it. The Solid column does not lose space to the tilting mechanism, allowing for a little extra Y axis travel. The base of the solid column juts out further, so it's dovetails are lengthened further along the Y axis, also adding travel.
I could overcome the two biggest weaknesses of the HF mill with the solid column upgrade, and replacing the plastic gears with LMS's $145 belt drive upgrade kit. However, the total cost of parts/cost/shipping/HF mill approaches that of the LMS mill, and I still wouldn't have the bigger work envelope or BLDC spindle. I decided I would be better off selling the HF mill to someone who needs just a mill, and buy the LMS mill for a CNC conversion.
Once again I started thinking about the 389lb x3, or the 879lb RF-45, and roughly priced doing conversions on them too. The X3 only cost 40% more after conversion, and had a much bigger work envelope, and is way more rigid and has a knee and can be ordered with a rotating head... Then I looked at the HF mill I have, the space its flooded enclosure will need, and realized that was already more space than I wanted to give up. I also realized that I'm getting older and the 139lb mill was just on the edge of what I feel comfortable moving around. I don't want to have to go through a major 400lb rigging ordeal every time I want to do something to the mill. Skilled people are tuning X2 mills to get .001 cuts out of them, and I could invest time someday to approach that, but very little of what I expect to make will need more than .010 accuracy. It can't handle the occasional large piece, but 99% of what I've thought about making will fit into that work envelope.
That perspective convinced me that a solid-column LMS conversion was the right solution, and despite my earlier plans to wait, I ordered the mill, the conversion kit, and the electronics/software. I read a lot of posts complaining about how high the liftgate shipping was, but because LMS is pretty close to me, Residential Liftgate Delivery was cheaper than picking it up at a freight company. After shipping and tax, the LMS 3960 solid column mill was $972.75.
http://littlemachineshop.com/products/p ... 1387807683
My research found many X2 CNC conversions that used the CNCFUSION.com kit, who also offers a special version for the larger table on my LMS mill, so I went with their kit. The Z axis mount will require me to drill/tap two holes in the column - maybe I can use my HF mill to do that work. Their design's Z axis has some issues - such as blocking the gib screws, and having the screw mounted to the side causes an alignment issue. However, it will suffice to get me started, and I can always upgrade it later. Each axis requires a $24 precision coupling - par for the part - and I'll take them up on $33 to have each ballnut pre-loaded and matched to its screw. That adds $47 to each of the 3 axis, $141 overall. Shipped, the precision hardware was $821.00 .
For the electronics, I settled on the 50v Gecko G540 driver, after reading a lot of documented experiences, it is the sweet spot of price/features/reliability. I researched and considered Geckos 80v drivers and a BOB (break out board), but the power of the g540 is really sized correctly to the X2's rigidity and the simplified installation a better fit to my skill level.
http://www.automationtechnologiesinc.co ... xis-driver
I had trouble settling on stepper motors, until I recognized that the 381oz/in Kelig stepper motors many people were praising because their volt/amp requirements neatly fit the G540's ratings, also had super-low inductance and resistance so they run cooler. Then it clicked - the motor scaled to the gecko driver and both scaled to the mill, and I can use one of my Vicor PSU's to power everything.
http://www.automationtechnologiesinc.co ... -381-oz-in
Software is another issue. CAD lets you design the part. CAM converts it to G-Gode. CNC software drives the mill, and executes G-code. I haven't figured out what I want for cad/cam, but for now I'll just be happy to have the mill under digitial control with CNC software. I found the $175 Mach3 CNC software at automationtechnologies for $149, and since they had the steppers at the same $49 price as Kelig, and the G540 driver at an typical $279. They were the cheapest place to single-source all the electronics/software on my list, and while I was at it I bought a $10 emergency-stop switch for the controller, and a $16 single motor cable as a model for my own cables. $640.50 delivered for all the electronics and software.
http://www.automationtechnologiesinc.co ... cense-file
So, $2,285.25 to buy the LMS solid-column mill and CNC conversion parts, about the same price as a Makerbot 2 but with the ability to work in a wide range of materials in addition to plastic, at 10x the resolution. Another $50 for the PC/keyboard/mouse and $149 for Mach 3 CNC software, so you can build a complete, functional, basic CNC mill 2,484.25 total. Whups, I had a spare monitor and parallel cable, so those costs are not included.
Upgrade costs will include an enclosure with drains, coolant nozzles and pump, home switches. Then there is the cost of a stand, tooling, CAD/CAM software, more tooling, a 4th axis, more tooling...
I got the crate with the mill on Tuesday, my wife received it for me because Hollywood freight missed their delivery window, and there was a dent in the box. I mailed pictures of the dent to LMS, who was very supportive, and said if anything was damaged they would replace the part (they stock all the parts). I freed up time to open the crate last night, and the dent appears to stop short of the table, and I have not detected any problems with the mill yet - yay! I put it up onto the workbench and took comparison pictures, so people could see the difference between the HF X2 and the LMS SX2. On top of all the benefits I mentioned earlier! in person the LMS SX2 presents better quality. The column looks bigger and better, and the edges of the dovetails are sharper and consistent, like they were cut better. The connectors for the wiring are better. It's all the same parts, just better made in many instances. I noticed the SX2 table also has a t-slot.cut into the front.
Anyhow, here are pics: