Hello! A few thoughts on starting out cheaply. This is oriented towards a small machine maybe 12x12 inches to 24x24 inchess x-y and maybe 6-8 inches z coordinate with the ability to mill Aluminum .
First you need a CAD program..I highly reccomend TurboCad Deluxe. Turbocad has been around since 1985 and has had tons of development time put into it. TurboCad 12,14,15, and 16 all run on Vista and Windows 7 in both 32 and 64 bit OS version. Turbocad uses the same ASCIS engine that autocad does, and accepts every cad format. Does 95-97% of what Autocad does..actually it just does not have command line entry ..which you really dont need anyways.. Cost is $25 or less on amazon.com for deluxe14 with a tutorial (and it does 3d!)..Pro TurboCad is better but costs money..TurboCad is very similar to autocad...CAD has an immense learning curve..Cadcourse.com has a free 2d drawing tutorial and a really great training bundle for $65..you need the tutorials. No I dont work for turbocad...its just a great program for the money..Google had turbocad write sketchup for them buy the way..(dont use sketchup..get turbocad instead)
As far a linear motion..stay away from ballscrews..they are great but simply cost way way too much..Go with 1/2 inch 10 thread per inch right hand turn ,single start ACME threaded rod. Mcmaster.com sells it for $7 for a 3 foot long piece and $12 for a six foot long piece..shipping is about 5-6 bucks..cant go wong..I would not use regular threaded rod from a hardware store or better grad ACME right now as you just want to get going and its going to be accurate to .0010 to .001 inch . Two start ACME and precision ACME cost a lot more..General acme will get the job done.
As far a stepper motors go..you dont want to go too big or too small..the smallest I would go is 166 oz/in...127 oz/in wold be sort of ok..the largest..260 oz in..If you get too big of a stepper (..500 oz ect..) then you have a 15 amp fusebreaker in your shop then you will have wiring hazards and possible fuse tripping You can ge 166 oz/in 24 volt 3 amp bipolar Minebea/Astrosyn Hybrid bipolar motor for $12 ea at mpja.com..these are really great motors..remember..the ACME screw holds the gantry in position..the motor just moves it there..(there is also what is called detent torque from the motor..but you dont need a whole lot.)Go bipolar..they are stronger..the old motors are round..new motors are square....you also should have a dedicated computer there to run the CAM software that takes the CAD model and converts it to machine code or "G Code". Any old garage sale computer would work..Load Ubuntu on it .(free Linux) So you also need a second pice of software CAM.CAM takes the CAD model and translates it into "G code " for the cnc machine to read....LinuxCNC.org has ECM for free..its pretty good..in fact Shaerline uses it on their small mills. And its fully documented..Again there is better suff out there but this program would work just fine! As far as controllers for the steppers go..look around..you absolutly must have documentation and operating software for the controller..dont buy a controller without directions! Stay away from expensive controllers for now..ie.. Lizard brand..they are truly great but simply cost too much ! Buy them later when you have more money.
You will need a general electronics book..the best on the market is wirttern by Floyd..Electronics-Electron Flow..$3 for a used copy from amazon..any edition from 1997 onward is just fine..Well illustrated expensive book new though..You also will need a book on Stepper motors and one on Industrial Electonics..again ..used..amazon.com..1997 or later..new costs too much.
Power supply..24 volt 12 amp from Marlin Jones $25..mpja.com..they also sell the Minebea 166 oz/in 3 amp 24 volt motors for $12 ea...not the biggest..but they will get the job done..especially for you since you dont have a giant x-y table to worry about and by the way..the reason people here talk about rapid movement is that moving too slow burns wood and many people here are in a production enviroment..the 166 and single start acme will work just fine in your situation...also some people here are using $250,000 machines! or more$ ! .... Or are on a fast production line..so what applies to them does not apply to you!
As far as a spindle goes either use a porter-cable router or much much better get a real spingle intended for aluminum/ and or precison work..about $95 if you look..read the tolerances..
The ACME general from Mcmaster is Keystone brand and its very high quality for general acme threaded rod...Yes two start might be better..but it costs a lot more..plus its only available in precision grade..ie.. .00001 tolerance..if you can afford the precison two start ACME go for....but get 1/2 inch!.. (smaller diameter flexes or "whips" at high rpm..)
You can build a machine cheaply that will get you .0010 to .001 ....any more precison costs a lot more.. As does the size of the machine..bigger machines cost more..just build it yourself..have a local machine shop cut and drill for you then assembl;e it yourself..Slotslva has a $25 set of plans or design it yourself..Browse the web for cnc builds.I would reccomend a combination of Aluminum and Steel..probably steel for the spindle mount as it absorbs vibration better than Aluminum..Moving parts..Aluminum..Use rubber vibration dampers here and there..As for Linear slides..certain drawer slides have good tolerances..about .001 with a 200 lb weight limit..24 inch travel..cost $25 at home depot.read the specs atthe mfg site first or look at them....PMinMO.com is a great great resource!!..To get .001 you would need the real for cnc router $95 spindle..and have it mounted correctly..Porter cable is good..but your have to buy the entire roiuter to get the spindle..Avoid general hardware stuff in critical places..use it elesewhere for bolting things together..Make sure you get the wiring right ..otherwise it creates a fire hazard!! Also I would enclose it .(use plexiglas on one side so you can see whats going on.three or more different materials snadwiched toigether yeild the best sound insulation.(good safety too..from flying broken bits..shards ect..).put a usb webcam camera with a range extender in with the machine so you can watch it and listen remotely in your living room! Put a fire alarm in with the machine..again you might not be with the machine when its running!..Put the electronics in an old computer case with a fan..Make sure the stepper controllers have the amp capacity for your steppers and the voltage you want..buy a stepper motor with a higher voltage to start with same with amps..they dont really cost much more anyways and its safer to run a 24 voilt motor with a 24 volt power supply anyways..in other words dont put 52 volts on a 3 volt motor for an extended period of time unattended..24 volts is plenty for a small system..and rig up a spray cooling set up for coolant/lubricant..along with a fan to help cool...Most of the items you need will have to come from the internet..You can use drawer slides as linear slides.. from Homedepot or Lowes ect..go look..or read the specs..some have tolerances to .001 in..24 inch long slides with 200 lb capacity cost about $20..I can not remeber which ones had the .001 spec but its on the drawer mfg website..
If you are going to build a machine with x-y coordinates longer than 36 inches go with 5/8 inch ACME..over 4 foot x-y ..go with one inch ACME..bigger tables require a little bit bigger motors..any thing over 4 foot go with 300 oz/inch to 500 oz/in motors..On the longer length tables you would want two pillow block bearing supports on each end about 1 1/2 to 2 inches apart to help prevent whipping..also you can counterbalace the machine from above with a "slinky" type spring mounter above the moving gantry..Some types of wood dust are toxic..if you work with wood you need to know which woods!! And also could explode under certain circumstances..use a brass rod to drive a sparkless fan (mount the fan motor outside of the cnc enclosure.keep the dust out..You can make a vacuum pump out of an old refrigerator compressor if you read about it online! ..And again..soundproof it with walls made of 3 different materials..plywood..rubber..drywall..with a plexiglass window..use a cheap $75 air conditioner for the enclosure if heat becomes a problem..but again think about your fusebox in your house..dont overload the fusebox.if the steppers become hot..attach computer cpu heat sinks to them.or finned copper....again..you should watch overvoltaging the motors in an unmonitored situation due to hazards...but make sure its got heat sinks on all 4 sides so you dont get a cool spot. Buy 24 -48volt motors to begin with (if you can get a good price)..dont put 48 volts on a one volt motor..yes you can get away with it..but..?(thats just my opinion) ! Read the specs before you buy anything to make sure it is compatible with what you have..
Thats my take on building a cheap cnc
Good luck and stay in budget! andy