I Want a Vertical Milling Machine

I had such a good time working on my first build that I want to go even deeper for my next build and start with an 80% frame.

And I have some ideas about what features I’d like in a slide. Finishing an 80% frame and customizing a slide are best done with a vertical mill; so I set out to learn more.

As I began watching YouTube videos, reading forum posts, and talking with a semi-pro machinist friend of mine, it seemed as if I needed to be able to answer at least these questions to choose a mill:

  • How much are you willing to spend? Keep in mind that there will be significant cost for accessories, measurement devices, and tooling.
  • How much space do you have for the mill? The bigger mills can weight over 2,000# and take up the floor space of a horizontal freezer. Think about the height of your shop ceiling, too.
  • How much milling do you expect to do? Is this going to be a couple of guns a year or will you be making parts and milling components for friends and family?
  • What electrical power is available in your shop? 110V AC is common (the normal wall outlet), 220V AC single-phase is also common (a dryer outlet), but 220V AC two-phase is not typical for a household. That would likely need an electrician and special wiring.
PM-835S w/DRO
PM-835S w/DRO
The broader context for all these questions is that I’m planning on nothing more than some DIY 1911 gunsmithing and lots of learning. I have found that milling can go from model making in plastics and similar composites all the way up to milling parts for ocean going freighters or running high-speed high-production CNC machining centers.

A common key to all these applications is the stiffness of the milling machine. Too little stiffness compared to the application means tool chatter and potential breakage. Not to mention ruined parts and poor surface finish. Cutting 4140 hardened steel slides is not trivial. But the good news for gunsmiths is that the parts, and the length of cuts, is small – certainly less than 6".

A few of the gunsmiths participating on the forums started off with the Grizzly G0704. But they moved up to larger machines, often Bridgeports or clones, as soon as they could. The G0704 is a bench top mill; smaller mills are often called mini-mills, and the larger ones are knee mills. It seems to me that the mini-mills are just too lightly built to be stiff enough for cutting dovetails in slides.

The knee mills, such as the Bridgeport, are too big (2,000#+) and expensive ($5,000+) for my situation. I don’t have the space and I don’t choose to spend the money to get into one. But if I did, the Precision Matthews PM-835S w/DRO looks good to me.

PM-727M w/DRO
PM-727M w/DRO

So I picked the Precision Matthews PM-727M w/DRO. At 475#, it weighs more than the mini-mills and has enough vertical travel to allow a variety of jigs and gadgets to fit between the table and the quill.

Precision Matthews comes highly recommended for its customer service and the somewhat higher quality from their supplier in Taiwan. Another feature of theirs that makes sense to me is their hand wheels are calibrated at .1" per revolution and their indexing wheels are graduated in .001". Many of the other mills have hand wheels and indexes graduated and marked in metric dimensions converted to inches (.065" per revolution, for example).

A Digital Readout (DRO) seems like a must-have feature for novice machinists, to me. Having a display that shows exactly where the spindle is on X, Y, and Z axes and not having to account for backlash in the adjustment gears and screws greatly simplifies milling operations.

My mill should be delivered in the next day or two, so posts about getting it set up and trammed will be coming.

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