I've been kicking around the idea of building a miniature CNC mill for a while and decided to finally get started on it. Most of my ideas came from the Tom McWire article on instructables.com, and I'm mostly building this as practice so I don't make any mistakes if I decide to do a big budget mill.

I intend to do mostly circuit board milling and drilling, maybe some plastic too. The "router" is a cheap 12v harbor freight cut off tool. The 12v part of it interested me, since I can very easily add on/off controls with the same power supply. The steppers are 3 NEMA 17's and I plan on using 1/4" 20 for the lead screws. I priced out linear bearings and decided for this project I'll just use roller blade bearings and channel and hope for the best.

The design is still in its infancy, and I'll clean it up and modify it as I'm waiting for the steppers to get here in the mail. The table in the model is 12"x 12", but I will probably reduce it to 8" x 8".

Except for a few missing braces and actual mounts for the steppers, here is what I'm planning on doing.

Any obvious problems in the design?

Your choice of spindle worries me. Even using a Dremel tool would be an improvement in quality. If cost is an issue search Craigslist.

Not sure I follow your design but it looks like your table will be moving in the x and y direction. Not sure how you would support it with bearings in both directions in the U channel. Also the U channel will catch a lot of "dust".

I didn't think I'd be real happy with that design, so I scrapped it. I really just wanted something to experiment with, but i think this will be more fun and changing to the moving gantry makes the work area bigger.

I offset the X axis linear slides, and the Z axis linear slides thinking that it will counter any play in the bearings. I will probably be using brass bushings for now and upgrade to thomson stuff in the future if this design works. I was going to use TGP shafting, but hardened shaft isn't that much more expensive from the local bearing place. I'm thinking .500" shaft, 4 linear slides on the Y axis (the one under the table), 2 on the X and Z.

The cheapo cutoff tool spindle is only shown because I already drew it, I'll get something bigger and more dependable once its built and working.

The rails will be adjustable for alignment, its just not shown in the drawings. I'm not counting on MDF to locate the rails.

Any suggestions or things I need to change?

I’m going to build Tom McWire board too. It’s cheap and easy.
http://www.instructables.com/id/Easy-to-Build-Desk-Top-3-Axis-CNC-Milling-Machine/
http://www.instructables.com/id/Easy-to-build-CNC-Mill-Stepper-Motor-and-Driver-ci/
did you build it already does it work good?
Does it work with Mach3 ?

http://img90.imageshack.us/img90/8248/f5loyu4f5r8qrl0tp3.jpg

I did not build the first design, but I do plan on using his circuit design. I'm not sure if it works with mach 3. I'm pretty new to the CNC thing and the only thing I can tell you about software is that my local fab shop rejects dxf files with splines.

My first table was 12"x12" with 1/4x20 screws and top speed is way too slow. It has other faults, but replacing the screws now will be a real pain.

John

You are probably right about the all thread. I was trying to do this on a budget, but now I'm starting to lean more towards building this to keep for a long time.

I forgot that I owned a rotozip, so I'll be using that instead of the cut off tool. In another post someone linked an ENCO acme thread sale. The motors are on the small side, and I'm not in a hurry so 3/8-12 is looking like the stuff I want.

I got the base built, and the steppers are tested. I need to pick up some parts to finish the controller and get the lead screws on order.

I have read that the plastic housing on the RotoZip can allow flexing. With that in mind, make the mount replaceable. Some of the name brand trim routers seem to make good spindles. I built mine with a Dremal tool, and replaced it before I even got the limit switched hooked up.

John

I plan on making the spindle mount easily interchangable.

What are you currently using as a spindle? And what did you use for your limit switches? I was thinking about some microswitches that kill power to the steppers.

I currently use a harbor Freight trim router. The limit switches are micro switches wired thru my Stepperworld driver to the software. If the limit switches kill the steppers directly, you won't be able to back away from a tripped limit switch with the motor.

Kcam keeps track of the direction when a switch is tripped, and will allow a reverse direction. Mach3 also has a "soft limit" that can be set ahead of the "hard limit".

My second machine is in the planning stage now. It will have a 36"x48" table with a 7" Z.


John

What is the runout like on that spindle? Have you tried aluminum and if so, how did it work?

If it hits the limiter wouldn't that mean the nc code or zeros were off, or the machine has jogged and the part is already trashed? Like I said earlier I have almost no experience with the software yet. My previous place of employment had a dedicated CNC shop using Mazaak stuff, but I was just a simple manual lathe and mill operator and didn't get to mess with the automated stuff.

I have not tried aluminum. as far as the Harbor Freight router, well, let's say you get what you pay for. I got it on sale for $19.95. But it sure beats most anything with a 1/8" collet. Having a 1/4" collet gives a much larger selection of bits. And it has lots more power than a Dremal. Since I have a bigger machine in the works, I don't want to spend much money fixing design flaws on the small one.

I use Kcam. It was simpler for me to figure out. But it is far more limited in what it can do. I would recommend Mach 2 or 3. Otherwise you get to spend money on software twice. Mach has much more help support.

With kcam, if an axis hits a limit it will tell Kcam to stop travel. You can jog away from the limit switch. With Mach, I think you can choose whether to stop travel, or slow down motion. (don't remember for sure.)

If I knew then how much I didn't know about this, I probably wouldn't have built my first one!

John

I downloaded mach3, but there wasn't much it did without having a machine hooked up. Kcam looks pretty sweet and it was able to take nc code generated in meshcam using .stl files without errors, but meshcam has that 30 day limit.

If I knew how much inventor sucked when it comes to actual production type stuff I think I would have switched to something else. I'm taking a class in the fall that uses mastercam, hopefully I'll be able to use that for personal stuff until I can pay the big bucks for something of my own.

I think I'm going to try a maual control first

This should provide an adjustable square wave pulse to change the stepper frequency, and all of the buttons to move it along the 3 axis.

http://people.tamu.edu/~robertf2003/pics/alpine/myschematic.JPG

If I knew how much inventor sucked when it comes to actual production type stuff I think I would have switched to something else.


Do you mean drawing files or outputting files, cause inventor does output dxf files.

With kcam, you can import DXF files and produce G-code. Then run it in a simulation mode while it plots back on the screen. Mach 3 uses Lazycam to do the same thing. It will let you practice making CAD drawings that will produce good G-code. With Mach, you can continue to use the trial version with no time limit but are limited to 500 lines of code. Kcam gives you 30 days.

John

will it do 3d dxf files? My version of inventor will only export sheetmetal parts as dxf, I'm stuck with .stl or .dwf (why does dwf even exist?)

Maybe I'll have to upgrade from the student version in the future, didn't know that was an option.

Both Mach and Kcam do 2-1/2D. The depth of the Z is entered in the setup. You can also tell how many passes to get to that depth. To get 3D G-code, you will need CAM software (don't worry, it's only money!) that supports 3D.

John

cool, thanks for the explantion. I'm afraid to ask what meshcam costs, it looks expensive.


Got the controls about halfway done. The local electronics shop didn't have everything in stock so I'm waiting on mosfets and a few IC's.

Although some people hate it, I shopped ebay and found a copy of BobCAD/CAM with the BobART v20. It is new enough to do everything I can figure out how to do, yet old enough to be affordable. Be aware, the BobCAD sales staff can be quite pushy. I guess it works different from other programs and a lot of people don't like that. I'm starting from zero, so it doesn't really matter to me.

If your wanting to do a lot of carving, Vcarve seems to be a good choice. If I were going to pay full price, I would give it a good look.

John

had this on the backburner for a little bit.

Just got in some thompson 1/2" pillow blocks and 1/2"-10 acme thread. For now I'm going to use regular nuts welded to a plate in the same flange pattern that dumpster cnc sells. The backlash is definately there, so once I get it running I'll swap over. I haven't cut the boards for the gantry yet. I raked it back to get the center of gravity closer to the middle of the bearing. Its kind of a guess since I'm not totally sure what I'm going to use as the spindle.

I'm anxious to see if the nema-17 motors will be enough for this. I tried to design it as modular as possible incase I have to swap to bigger units.

the acme lead screws will be supported with some fr8zz bearings and clamps on the outside. The only thing I'm worried about is my Z axis. I'm still planning on using brass bushings with the blocks I've already cut.

I may add some webbing to the spacers on the Y and Z axis motor mounts, but other than that I plan on building it exactly as shown. Any obvious problems other than stepper motor size or the mockup spindle I have show?