Newbie- So, I'm thinking of learning how to mill things.

[spasticteapot]

I'm a college student with some fabrication-intensive hobbies (notably speaker building.) I also have no job, largely because of an unpleasant immune problem which for one week every month or two leaves me in massive amounts of pain whenever I try to move. I hope to rectify both with a CNC router.

I'm aware that making money with any CNC router I could buy is not the best possible idea, especially considering that beyond some experience making jewelry, I don't know jack about machining. However, the amount I hope to earn is only a paltry $100/week, and I do have some experience with robotics. The finished product is also to be similarly simple - likely just custom wooden cups for headphones and milled control panels. I'd like to build a mill with a 16" x 30" x 2.5" travel capable of milling aluminum, wood, and a little brass. Precision of 1/4mm is acceptable - nothing I make needs to be super high precision.

The first major question is one of construction. I'm hoping to buy a set of XYZ ballscrews and end mounts from "linearmotionbearings2008" on e-Bay, and pick up some used THK rail and bearing carts from eBay for the X and Y axis and a linear slide block for the Z axis. My travel in the Z axis need not be bigger than 3" anyway, and those linear blocks look like a good way to simplify construction.

I am, however, a bit stumped on what to use for a spindle. Plan A is to use a standard variable-speed wood router, which is unable to trade RPMs for torque like a variable-ratio system. Plan B is to use or modify the top of a drill press, which gives me a handy premade Z axis with variable drive but likely isn't rated for the lateral loads. Any thoughts?

The second question is one of stepper motors. If I read the specs on the ballscrews correctly (http://cgi.ebay.com/3-Anti-bachlash-...QQcmdZViewItem), one rotation equals five millimeters. I'm not quite sure how much torque would be required for this type of machine, but I'm not likely to be using a servo system so it's probably best to get big ones in order to prevent missed steps. How much do you think I need?

Finally, is there a tooling kit out there somewhere that will give me an easy start on this project? And can anyone recommend some good-but-cheap tools to go with it?

[Hirudin]

Regarding the spindle: have you considered a "Chinese spindle"? linearmotionbearings2008 sells them as well. They're somewhere in the neighborhood of $500 including the VFD (speed controller).
If you haven't already, check out this very long thread about these spindles: Cheap 1500W Chinese spindle, experiences?

I'm no machinist, yet, but I don't think a drill press head is a good idea for a multitude of reasons. I may certainly be wrong though.
Here's what pops to mind...
* Too heavy
* RPMs too low, also cumbersome to change speeds
* Likely to have a lot of runout. The bearings probably aren't very precise and I know 3-jaw chucks are not precise.
* Z is likely to have a lot of backlash - not good.
* The bearings are made for axial force not lateral (as you speculated). I've heard that a drill press spindle can come apart suddenly if used to make lateral cuts, which is dangerous.
* Lastly, it would probably be hard to mount / tram (make square)

[ger21]

Originally Posted by spasticteapot I am, however, a bit stumped on what to use for a spindle. Plan A is to use a standard variable-speed wood router, which is unable to trade RPMs for torque like a variable-ratio system. Plan B is to use or modify the top of a drill press, which gives me a handy premade Z axis with variable drive but likely isn't rated for the lateral loads. Any thoughts?

Variable speed routers work fine at all their speeds. I use my PC 892 at the lowest setting (10K rpm) all the time and it has plenty of power. What you don't want to use is a fixed speed router with an external variable speed control. Those will lose power as rpm's decrease.

Many, many people here use variable speed problems with no problems at all. If you want something better, spend the $500 and buy the chinese spindle the previous poster mentioned. They are more powerful, and much quieter, and can handle many more collet sizes.

If you try to use a drill press, the chuck will fall off very quickly from the lateral force.

[analogman]

Well it sounds like you are after a CNC router versus a CNC mill. A CNC mill is a metal mill used for precision machining of metals.

In your sizing make sure you add extra room for the size of the gantry (x axis), the Spindle holder (Y axis) and any spoilboard, vacuum clamps (Z axis). 3" in the Z axis will become 2.5" as soon as you put down a spoilboard, or 2" with some vacuum hold down devices.

I think you will be fine with a router. If you want to go deluxe, get the chinese spindle.

Tooling completely depends upon what you are cutting, what type of cut you are making and the kind of finish you want. As with routers you can get away with simple router bits from the local woodwork shop, or order full spiral carbide bits for a perfect finish on aluminum. I specially have 7 types of parts I make, and 10 different bits for the tool operations.

[Crevice Reamer]

Hi Teapot. Welcome to the Zone!

It sounds to me like you are trying to make one machine do the work of three.

Any Mill with 16 x 30 travels would be WAY too expensive for you.

A CNC router can easily have that travel. Estimate how much it will cost you to build it, Estimate how long it will take you--Then multiply the estimates by at least 4.

Perhaps a small wood lathe would be better for the headphone cups.

Here's some basic CNC info:

http://www.cnczone.com/forums/showthread.php?t=78713.#3

CR.