Hello, friends. I joined a while back with an interest in getting into the CNC game. But, life got in the way and that interest was pushed off to the side, then others jumped in when things smoothed out. As it turns out, cars were more space-consuming and expensive than I'd like for a hobby, I realized I liked speed to much to keep a motorcycle, and moving an hour away from my nice shooting range kept me from playing with guns as often as I would have liked. So, I bought myself a mini mill to diddle with making gun parts, figuring it could also keep me busy as a second hobby.

Well, turns out this stuff is mindbogglingly addicting. I started with a few basic importetool sets, about 50lbs of scrap aluminum and steel from a local fab shop, and started cutting. One of my intended projects was the standard column support brace folks like to do with these mills. Somehow, that turned into a whole mill design. Two months and $2500 later in parts, tooling, and accessories for my $600 "side hobby," and I am building a >550lb mill in my garage. I had managed to carve out a massive 5x7 corner of the garage, and here I am building a machine that will take up 3x5 of it :P.

It is made up of 2x2x.25" square tubing, and .75x3 A36 flat bar. This was a balance of cost and because 3" is the largest I can hold in the little 3" LMS vise I got for my mini mill. When I first started considering completely custom parts and ways, I was originally looking at using large, heavy plates for the base, saddle, and table, which would have been ideal. But, between the cost of having those machined, and the missed satisfaction of making something myself with the tools I have available, I decided to go this route.

Years ago I started using Excel to skeptch out models of various things I wanted to build (car parts, gun parts, etc), and it has become my ghetto "2D CAD" program. Attached is my top-down look. Each shape is proportionally-sized (you can set a shape's dimensions in excel). Yes, I promise I will find a real CAD program...



The Specs:
-Overall it has 24"x11"x15" XYZ travels with a 32x12" table. I'll be using basic chinese 16mm ball screws with 5mm lead.

-Y-Axis uses 22" 15mm rails spaced about 17" apart center-to-center, with the trucks spaced 11" apart on the rails. Even being 15mm, they should be able to take any load I put on it just fine. Still, I might grab some 20mm rails for perhaps better longevity and, if nothing else, so I don't have to endure tapping a bunch of 6-32 holes in the steel base :P . The rails are far enough apart that the trucks should experience very little upward loading with the table at extreme travels with heavy work or tooling on the far end of the table. If I get worried about it, I might double up on the saddle tubes to help with both rigidity / vibrations, and with keeping the center of mass between the rails.

-The X-axis uses 40.5" 20mm rails spaced about 10" apart center-to-center. Even under heavy drilling at the limit of y-axis travel, being .5" outside the rail centerline will not cause the opposite trucks to experience any upward force. With vise and top surface, the table will weigh about 200lbs. I'd have to drill on the very edge of the table with 2000lbs of force to cause a moment opposite that that generated the table's center of mass. However, the trucks are only spaced 16" apart on the rails. This allows for a 4" increase in travel (from 20" to 24"), with the caveat that the last 4" of travel on each end will be over the unsupported table area. Granted, similarly I would have to drill with hundreds of pounds of force to actually apply an upward moment at the opposite end of the table. But, I recognize that if I wanted to do real heavy drilling on the ends of a large part, I should probably move it closer to the center of the table. Still, I was happy to trade more milling area for less "drilling" area.

-The Z-axis is just a factory mini mill column I bought and milled for mounting. I drilled 5 holes spaced 3" apart for 1/2" bolts, and used the mill to slot them horizontally for x-axis tramming (it has about 2 degrees of total movement in each direction). The large holes in front are for a socket. At the time, I already had some 1/2" bolts lying around and did not feel the need to invest in an extended hex driver and $2-each allen bolts to mount it. Looking back, I'd have probably just gone that route to not have to remove so much material. The actual column is a 2' section of 5x5x.375" steel tubing I bought from that fab shop. I am going to make new mounts out of 1/2" thick 3x3 angle iron that will bolt to the column and base. The mounting holes on the side will be slotted to also allow about 2 degrees of tramming in the Y-direction. Right now a 1/2" piece of steel is bolted to the main column's face, to which the Z-axis attaches. It is just to add a little mass to the column, but I will eventually upgrade the whole column.

-I will be using the head from my mini mill. A steel extension will go between the carriage and spindle housing to give probably a 12" throat, while also allowing much easier alignment of the spindle to the column. For now, I will be using the stock motor with an in-progress timing pulley system that will have a single speed from 0-900rpm. Eventually, I'll just make a whole new column from 4x4x0.5 or 5x5x0.5 tubing, about 48" tall. Using linear rails, I'd make a new carriage to which the spindle housing would attach. Ultimately I'd like something like 30" of Z travel, but that might take some doing to keep the whole thing under 7' tall!

-The plan is to machine all the mating faces flat (just bought a 3" Glacern face mill) and bolt them together. I going to use a large screwless vise in the middle of the table (because I want the larger capacity without the huge mass of a normal large milling vise). I will drill and countersink holes through the top of the vise so I can bolt it directly to the table, both for stability and to act somewhat as part of the structure of the temporary table. Once everything is aligned and bolted down, I will cast the base in an epoxy composite for stability and rigidity, using plywood and boards for the sides and bottom. I'll cast a pair of long pieces of round tubing all the way through the sides to act as handles.


Driving factors for the design:
-Admittedly, the limitations I faced building the mill itself drove some of the ever-creeping increases in mass and table travels, heh. Overall, though, I decided I wanted a "combination" machine that could do a myriad of operations on larger hunks of steel with reasonable efficacy. I'll be moving every few years for a good while, so it is not likely I'll be able to build a large shop any time soon. Thus, counting on having relatively minimal space (i.e. a normal garage at each house), I realized I could basically build a much larger machine and actually have it perform better than the smaller individual machines I'd have likely purchased (say, a 7x14 lathe and and a 12" benchtop drill press), while still requiring a smaller overall footprint. So, the tall Z-axis is for drilling, and the large table gives space to mount a lathe head on for CNC turning and threading operations. And I will be able to basically fit three pretty good benchtop machines into a 3x5 space. The only downside to using this setup as a drill press will be the lack of a standard quill handle for easy drilling (I'll have to crank the screw instead).

-Moving often drove the importance of it being somewhat easy for me to move. The column will be easy to remove from the base with just four 1/2" bolts, and I'm going to make some simple ball bearing keepers so I can pull the whole saddle and table (separately) off the base without removing any screws. The heaviest individual piece will be the base at around 200lb. Aligning the spindle and tramming the axes will be relatively easy with all external mounting bolts, using the "loosen and tap" method.

-As to overall accuracy, I would be quite happy with .005" of flatness across the table's travel. Eventually I'll have a plate flat ground and use that for the top surface, which should help. My limit will be in how parallel I can get the surfaces using my mill. I just ordered a Glacern 3" face mill to surface all the parts. Using cheap ballscrews, I suppose I could realistically see positional errors of several thousands, plus perhaps few thousandths of backlash under load. If I ever feel the need down the road, though, upgrading those shouldn't require much work at all.


I'll post more as I make progress. Hopefully I'll be able to drill all the mounting holes today. Then, once my face mill comes in, I can start facing all the parts. I'd be thrilled if I can be cutting by Christmas!

*edit*

Oh, and I cut everything with a 4.5" angle grinder, so that was certainly a joy...