Buying a Mini Mill

Way back in my early teens, my interest in model railroading progressed from a casual pastime to a much more serious sort of pursuit. As I read about railroads and their equipment I swiftly came to realize that my models, even the reasonably accurate (for the 90’s) Athearn Blue Box GP50 in BN’s Tiger Stripe scheme (my pride and joy), were not actually that accurate. I noticed all the usual things: the flat metal handrails, the thick inset window glazing, the horrible (or complete lack of) draft gear. However my main hang up was always the frame. It seemed like every model I could afford (brass being so expensive it might as well have existed solely on the moon) had a frame that made absolutely no attempt to simulate what was actually there on a real locomotive.

Though cutting plastic wasn’t exactly easy, it didn’t take long for me to figure out how to modify a locomotive shell. Cutting a pot-metal frame was a different story though. I eventually figured out how to use a rotary tool and file but I was never satisfied with the results or the amount of time and energy it took to achieve them. Having no experience with metal work and not being the sort of kid that took shop class in school (much to my current self’s disappointment) the path forward remained murky for years. At some point though I became aware of a machine called a “Mill” that could quickly and accurately cut metal. After that I learned that a mill could cut more than just metal and that there were much smaller versions of the giant Bridgeport machines I’d seen pictures of. Finally, the clouds parted and I discovered that other model railroaders had these little machines and were doing exactly what I wanted to do with them. That’s when I decided that someday, as soon as I had both money and a place to put one, I would buy a mill, I would learn how to use it and my models would finally live up to my expectations.

In the 15 or so years that passed before I was financially stable and not living in a tiny apartment most manufacturers started offering HO scale models that included things like a simulated I-beam frame. However, they still screw up the occasional molded on detail and there’s always a bit of unnecessary weight that ought to be hogged out to make room for a better speaker enclosure or motor. So just as I was finishing the renovations on my basement and knew I would soon have a free corner of my planned workshop I took the plunge and ordered a Microlux Heavy Duty 84630 Mini Mill from Micro-Mark.

The Micro-Mark offering is a clone of the Chinese made Sieg SX2 Mini Mill Drill. Harbor Freight, Grizzly, Little Machine Shop and probably others all sell slightly different variations of the SX2 line. I went with the Microlux for a few reasons: First, in 2019 when I bought it none of the others came with a brushless motor (LMS has since added that option to their lineup). Second, unlike the LMS mill, it uses a torsion spring as opposed to a gas cylinder to assist with moving the head up and down. There’s actually nothing wrong with the gas cylinder option (in many ways it’s an improvement since it allows the head to move higher) but it adds quite a bit of height to the mill and with the ceiling being so low in my basement I didn’t think it would clear the joists on a workbench high enough to stand at. Additionally, should I ever have the space and inclination to do so, I can buy an upgrade kit to replace the torsion spring with a gas cylinder. The final reason I went with the Microlux is that it comes standard with “True Inch” .050 inch-per-turn table feed screws and dials on the X and Y axis. The other mills come with .0625 inch-per-turn dials and feed screws. I’ve confirmed through research and conversations with other modelers that .0625″ per turn is as difficult a measurement to keep track of as it seems.

Unfortunately, there are some downsides to the Microlux mill that I’ll get into a bit later. Since I bought mine I’ve come to realize that the LMS HiTorque 3990 is by far the superior version and were it available at the time I probably would have gone with it and just figured out a way around the height issue.

Accessories

The first think you learn about machine tools is that the cost of the machine itself is a drop in the bucket compared to the cost of all the accessories that are required. Before I did anything with the mill I bought what I figured would be the bare minimum to do the sort of work I’m interested in:

All these mills come with an R8 Taper and chuck. These are great for drilling but won’t hold an end mill well enough for horizontal cutting…
So, I bought a set of ER-25 Collets from Micro-Mark. They’re good, lots more sizes than I’ll need, however I suspect that the included R8 shank is tapped with imperial as opposed to metric threads. Either that or the thread pitch is wrong. I was able to thread the metric drawbar that came with the mill on to the shank but it didn’t feel right (no I was not cross threading it). LMS offers a replacement drawbar that has imperial threads, which I may pick up when I place my next order with them. Hopefully I won’t need to re-tap or completely replace the shank. My confusion stems from the fact that Micro-Mark makes no mention of this issue anywhere on their website.
After the drawbar issue I decided I’d learned my lesson and started buying all my stuff from LMS. Brian Banna told me that he has this vise and does most of his work on it. So I bought one too. It wasn’t cheap but it’s well built and very accurate.
To go with the vise I bought this set of 3″ parallels. These are useful for blocking under a work piece when it’s in the vise. They probably have a lot of other uses as well and it seemed worthwhile to have a few sizes.
This 7/16″ T-Slot Clamping Kit may or may not have been a waste of money. I mostly bought it because I wanted the 6 tee nuts. I’m sure I’ll find a use for the rest of the components at some point.
This is a dial test indicator on a spindle mounted test holder. The holder is not very good as it’s difficult to tighten and position but it worked in the end. It’s main purpose is to hold the dial test indicator while the mill is trammed. More on that later.
Finally, we get to the items that you would think would be most important. End Mills. Here we have a set of 1/8″ – 1/2″ HSS single end, 2 flute bits and a couple of individual 1/16″ and 1/8″ carbide, single end, 2-flute bits. Carbide isn’t really necessary for the sort of work I’m doing but it was hard to find HSS cutters in the smaller sized I plan to use most of the time. I’m only using 2 flute bits for now as I don’t plan to cut any of the harder alloys.
The last of the immediate necessities was some oil for the slides and ways and some grease for the feed screws. This set of lubricants is actually for a Bridgeport and I only need the Vactra Oil No. 2 for the slides and ways and the Lubriplate White Grease for the screws but I bought the set because it came in the smallest containers I could find and was reasonably priced on eBay. I’ll find someone to take the other bottles off my hands.

Not photographed was a chip tray that I got from LMS and the set of 1-2-3 blocks I’ve had for years. The chip tray does a pretty good job of containing the mess while cutting but I still find bits of swarf all over the place. There are still a number of things I ought to get but this lot was adequate to get started. Someday I’d like to add a DRO for all 3 axis and a tachometer to measure the actual spindle speed. Those aren’t cheap though so it may be awhile.

Setting up the mill.

The mill arrived un-assembled in two or three boxes (it’s been awhile and I forgot to take photos). It came with excellent instructions and was very easy to put together. The most annoying part of the whole endeavor was cleaning the preserving oil off of it. I’m not really sure what it was as it wasn’t gunky enough to be cosmoline and seemed like it was too thick to be Vactra Oil No. 2… Whatever it was came off easily enough with WD-40 but there were so many parts it took quite awhile.

Once the mill was assembled it sat for a long time while I finished the workshop. I probably should have oiled the slides and ways before storing it but I didn’t know I needed to do that at the time. Ultimately it wasn’t a problem and no rust formed, presumably because it was in a climate controlled room. After I finished the workshop I brought it downstairs and mounted it to the chip tray and a couple of pieces of plywood using lag screws. Now that it was in it’s final position I lubed the feed screws, oiled the ways and slides and got to work on some fine tuning.

Adjusting the gibs.

Tramming the mill.

Squaring the vise.

With the mill itself adjusted I attached the vise using the clamps that come with it. They bolt into T-nuts in the table. Then I put the dial test indicator in the appropriate sized collet, locked the spindle and moved the table so the indicators probe was just touching one corner on the vertical face of the vise’s fixed jaw. Then I moved the X axis so the indicator probe swept across the vise and adjusted the clamps until the indicator stayed at zero all the way across.

Making the first cuts

Now, at long last, I was ready to make some cuts. I pulled an old Athearn SD70M shell, walkway and frame out of my parts box for practice. I clamped the frame into the vise and mounted the walkway and shell to it. Unfortunately I didn’t have the coupler boxes so it wasn’t secured particularly well but it worked fine to get a feel for using the mill and I was actually able to make a few cuts that weren’t too terrible. The most difficult part of the operation and something that I’m still figuring out was getting the Z axis set properly so that the endmill wouldn’t cut into the shell more than necessary when making a final cleanup pass. This is a task where having a DRO would really help as it would make it easier to compensate for the backlash in the column rack.

Nevertheless this exercise made me more comfortable with the mill and helped me come up with some ideas for better securement on future work.

After awhile I got tired of beating up the shell and I made a few passes across the frame itself. These went quite well and the quality of the finished cut was far superior to what I had achieved on the shell because the frame was so much more securely held down.

Hard to see but I made a long pass right along the front edge of the frame weight.

With that practice under my belt I decided it was time to do some work that actually counted. I recently got a set of feed/anti-kickback rollers for my table saw and one of the rollers was binding against the clip that holds it in place. To fix this I popped the roller off, mounted it in the vise on top of a set of parallels and shimmed about .010″ off the central bushing. This cut came out quite good and would not have been possible without the mill. Now the wheel rotates freely without too much slop.

Those stickers were to help me keep track of whether or not I was climb or conventional milling. They ended up just making things more confusing though.

Final thoughts.

All in all I’m glad to finally have a mill. As i mentioned previously, if I were buying a mill today instead of back in 2019, I would definitely choose the LMS HiTorque machine. The fixed column and ease of adding a DRO would be worth the extra cost and I could always switch out the feedscrews and dials for the True-Inch equivalents (which LMS sells separately). Nevertheless I think I’ll be able to do everything I need to with the Microlux and I’m really excited to move forward with some projects that have been on hold for want of a good way to hog out material. Someday too I’d like to get some aluminum or steel bar and make my own frames and other components.

I doubt this post was of much interest to anyone with even a small amount of machine shop experience (except perhaps for a laugh or two) but hopefully it will be useful to someone else just starting out. Most of the books and online resources I found were not terribly helpful as they tended to descend into the weeds about details and techniques that aren’t really necessary for the sort of work required to modify a plastic model. Some of the best help I got came from fellow modelers who kindly suggested what accessories were necessary and what weren’t as well as things to watch out for as I made my first cuts. If you’re also thinking about getting a mill I highly recommend reaching out to your fellow hobbyists with whatever questions you might have.

To close this post out I’ll share a few links to retailers and other resources I found useful. If you have any sources of material or information to add (or suggestions for me as I move forward) please leave them in the comments.

Chris

Useful links.

  • Little Machine Shop – Not only do they sell pretty much anything you might need they also have a considerable amount of documentation that’s applicable no matter which mini mill you buy.
  • Micro-Mark – Somewhat hit or miss when buying stuff here but if you watch for sales and know what you’re buying they can be a good source. I was told to stay away from their end-mills though.
  • Frank Hoose – Frank’s YouTube page has some excellent videos on techniques and equipment all geared towards hobbyist use and new video’s are added every now and then. His Mini-Lathe.com and Mini-Mill.com sites are no longer being updated but also have a wealth of information.
  • Brian Banna – Brian was a huge help when I was figuring out what to buy. He’s an excellent modeler and many of the projects he features on his YouTube page involve the use of a mini mill.
  • All Industrial Tool Supply – This is an eBay seller that Brian recommended as a good source for larger bits.
  • Kodiak Cutting Tools – Another of Brian’s recommendations. Kodiak is a good source for high quality bits smaller than 1/8″

6 thoughts on “Buying a Mini Mill

  1. I would love to own a mill and keep thinking about what size I would need as I model in 1/29. These table top machines would be nice but I’m worried that they would be too small to really do the things I need. The problem is, I’m not sure if anyone makes anything between the table top size and a 3/4 sized full mill. I just haven’t researched it enough yet to find out.

    • Grizzly might be worth checking out if you haven’t already. They make a number of larger mills that might still be small enough to find room for and move around. A bit more expensive though…

      It’s been fun watching your layout progress over on the Northwest Model Railroaders Facebook group. I especially like those feed trucks you’re building.

      – Chris

      • Thanks Chris for the information. I will have to do some soul searching before I start researching the mills. As with everything space is at the premium so it might be more practical not to look at mills.

        The feed trucks have been a fun distraction from layout building, but I’m getting burned out now on them and need to just finish.

    • Thanks for the link to that tach… seems like it should work with my mill as well.

      – Chris

      • The gentleman offering them was extremely helpful. LMS had changed a minor bit and he helped diagnose the issue and re-flashed the tach.

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