First off I would like to say hello to the forum, this is my first post.
As the title says, I am looking for some advice from those who are much more experienced than I am. I'm currently a sophomore engineering student and I enjoy challenging myself with personal machining projects. I am very familiar with manual machining, I do a lot of vacuum fixturing design and prototyping for the physics department at my university. A couple months ago I replicated Steffan Gotteswinter's exchangeable anvil micrometer, after surface and tool post grinding, the mic is accurate to about 2-3 tenths over the 1 inch length, which is more then good enough for me. I'm currently in the middle of machining a aluminum rifle stock, and a fully operational scale 4 stroke engine. Although the 20-50 hour projects I have worked on are quite rewarding, I have decided to take on a more difficult challenge, something that would be useful. I'm sure anyone who has actually read this far knows where this is going.
I want to design and build a "bench-top" sized CNC milling machine. Something relatively small but robust enough to machine aluminum without any issues. It wouldn't be a machine to do production job shop work, just something I could use to do small one offs or parts that would be tedious to machine manually. I am not concerned with efficiency, I would be okay running at the largest a .250 end mill or a max DOC of .050". Before my rambling continues any longer, I want to layout the main points I'm looking to have answered with this post.
Overall Design:
- I am in between a conventional style vertical milling machine and at some point adding a small 4th axis, or a PocketNC style machine minus the fifth axis. The PocketNC has a horizontal spindle, with a body made from a giant chunk of 6061.
-I was planning on throwing an initial design together in Inventor, but figured I would try to get some feedback for this forum first.
Size:
-To put in perspective the overall size I am looking for, if I were to model a vertical mill, the machine table would be about 8" x 12" with 6-8" of z travel.
Construction:
-I have a high level of confidence in my ability to manually machine any non-lego part on the machine and I have access to several fully equipped machine shops on campus.
-All of the "machine ways" will be made using linear rails controlled by rolled acme threads supported by radial bearings at each end and anti-backlash nuts.
-For a spindle, I plan on purchasing a straight shank ER-20 or ER-25 collet chuck and pressing the shaft into two opposing tapered roller bearings
-Would it be adequate to construct the table and saddle out of aluminum?
COLUMN: I was more curious about this then anything else. With such a small machine, how picky should I be with the column constriction, I was originally thinking a 3" x 3" x 16" piece of cast iron bar stock. After doing some reading and recognizing how important it is to have a column that wont resonate the vibrations from the tool, I was looking into thick wall hot rolled tubing filled with granite epoxy resin.
Cost: I am lucky enough to be working at a 6 month internship that pays pretty well, so I will have a steady flow of income to fund this, that being said I would still prefer to spend around 1000 dollars.
Conclusion: I am looking for whatever help anyone is willing to give. Whether it be answers to questions asked here or general ideas and suggestions on the machine. Anyway, its 2:30 in the morning and I have to be up for work at 5:30 so I'll cut it there.
Thank you in advance for any help anyone is willing to give.