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Mini-Mill – Part 0

After years and years of avoiding this purchase, I finally broke down and bought a mini-mill. While I’d been envious of other model railroaders who had and used such a mill, I really couldn’t justify the expense for what I needed to do, versus what I wanted to do.

Technically, what I needed was a highly accurate drill press. That is, one that I could use to accurately locate holes, and then drill them perpendicular. I found a good drill press, but I had a lot of problem accurately positioning my models to drill holes that were needed. Two popular solutions to this dilemna are a cross slide vise (often called a X-Y vise) and a cross slide drill press  table with machinist vise. It seemed to me that having it all in one piece would eliminate alignment issues, so I purchased a cross slide vise.

My first project was relatively simple. I was converting an Athearn MP15AC from the included McHenry couplers to scale couplers from Sergent Engineering. One of the reasons I wanted to do this was to use the prototypically narrower draft gear box of the Sergent Engineering narrow shank coupler (the model is about 1/3 oversize here). This involved abandoning the mounting screw for the Kadee coupler (actually, since the screw also serves to secure the shell  to the frame, the coupler mounting pad will be countersunk to accept a flat head screw to mount the shell), and drilling two new holes to mount the Sergent Engineering (Accurail Accumate) draft gear box.

So I clamped the frame in my cross slide vise, and proceeded to align the vise so the frame’s center line was directly under the center of the drill press. Although there are better tools, I simply used a countersink bit, and watching closely how the bit mated with the existing screw hole in the frame. I also measured the distance between the bit and the edge of the coupler mounting surface with my calipers. Once I was satisfied I’d found the center, I moved the model using the longitudinal transverse on the vise the required distance for the first hole. I replaced the countersink with my tap drill, and proceeded to bore the hole.

Disaster. The hole was significantly off center. I removed the frame and filled the hole with an epoxy that contained a metal filler. Days later, I repeated my effort, and repeated having an offset hole. I tried the other end of the frame – the coupler pad that had not been drilled. Same thing.

The only explanation I had was that the cross slide transverses were not perpendicular. As I moved the frame in the X-axis, it also moved in the Y-axis. The model didn’t stay on center line.

Trying to find answers to my problems, I was told by many to forget using a drill press for accurate drilling, and to invest in a vertical mill. Most suggestions centered on various versions of the Sieg X2 mini-mill, as distributed by Grizzley (G8686), Harbor Freight (44991), Little Machine Shop (HiTorque Mini Mill), and Micro Mark (84630). Each has slightly different features, with list prices ranging from about $500 to $675 as I type this. If you want to jump in, Harbor Freight will have a 25% off sale on 1/1/11, bringing their mill down from $600 to $450.

I opted for what turns out to be the most expensive of this lot: the Micro Mark Microlux High Precision Heavy Duty R8 Miniature Milling Machine. There are a number of upgrades on this machine that made it worth my while. For instance, the other mills have leadscrews with 16 threads per inch, resulting in an awkward 0.0625 inch of worktable movement per revolution of the handwheel. The Micro Mark mill has 20 thread per inch leadscrews, giving a much more convenient 0.050 inch of worktable movement in the handwheel. Micro Mark sells a kit to convert the other mills, but it’s nearly $60 (plus shipping, and sweat equity for installation). One of the weak points in most of these mills is a plastic gear in the transmission. A popular fix is to convert to belt drive. The Micro Mark mill has  this included. Little Machine Shop sells a conversion kit for about $145 (plus shipping, and sweat equity for installation). So, getting the Micro Mark isn’t that bad of an option, despite its price.

These mini mills are like the Honda Civic of the hot rod world. Small and underpowered compared to true “big iron” (does that make a Bridgeport knee mill the “Mopar Hemi” of the machine shop?), but with plenty of modifications around to upgrade and refine the capabilities.

Some of the other things I look forward to doing with the mill are more in depth frame modifications, such as those that Brian BannaJoe Bence, Dave Hussey, Elizabeth Allen, and others that have encourage and inspired me to get into milling.

This is titled part 0 because this precedes delivery of the mill. I’ll detail some of the setup and use of the mill once it’s been delivered (tentatively scheduled for December 23rd – just in time for the Christmas/New Years shut down at work).

I especially want to thank Brian Banna and the late, great Larry Jackman (of Smokey Valley Railroad Products) for all  the information they’ve provided. Larry was an accomplished machinist, and if you ever could get past his gruff on-line persona, was a fount of knowledge on practical machine shop practices. I also want to thank Dave Hussey, now heading Cannon and Company, for inspiring me to think of my model railroad projects as an extension of my engineering discipline, and to get me off my duff and start using a mill as a high accuracy drill press.

Thanks for stopping by!