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AVRnj
13-04-2013, 02:25 AM
Hey everyone,

I posted a few weeks back on the New member intros about wanting to build a CNC mill, I got a lot of great suggestions.

I originally was going to do something smaller, but now I figure if I am going to build this thing, I might as well get some extra space, even if I never really use it.

I am now ready to get started.

I am in the US.

I have read some other build logs, and formulated some ideas and questions.

I have some ideas, but I will need some help along the way, hopefully all the great resources on this board can chime in.

I have built a 3D printer, so much of my experience comes from that. Never used a CNC mill before, so this is a whole new world to me.

I don't really have a budget. I would like to do it as economical as possible, but I want to do it right. I would rather not skimp on important parts to save a little bit of money and do it better down the road, but also don't want to waste unnecessary money.

Here is what I THINK I want to build:

CNC Mill
3 Axis, X, Y, Z
Mill materials: Definitely Aluminum, possibly wood, possibly plastic
Millable area: ~700mm x ~700mm up to 150mm height

Things I want to be able to mill:
Robot parts, braces, supports, handles, connectors, etc.
Gears (small and very detailed)
Aluminum frames (support frames, this is where the size comes in, thinking up to 700 x 700 here, screw holes, window openings, etc.
Milled Printed Circuit Boards (PCB's)
Other things as discovered

Here is what I am thinking so far:

Frame: 20mm x 20mm aluminum extrusion (if needed 40x20)
I am thinking big cube, big enough for dimensions required

X,Y,Z axis:
Ball screws for the movement
Nema 23 stepper motors
Linear profile rails or supported linear rail 2 x per axis for balance


My original thought is that my mill plate will move up and down as my z axis.

OR

Have my mill plate be fixed, and have my mill/router on the z axis on my x carriage


My X, Y will be a Y carriage at the top of the cube, and the X carriage will be inside the Y carriage.

Control board:
I am a bit unsure here.
I have read a lot of negatives on the tb6560.

I am leaning towards the g540, but it is a LOT more expensive. If worth it, I will put up the $ for it, but want to make sure it is.

I would be open to other suggestions if anyone has any.

I currently have extra RAMPS from my 3d printer build. For those not familiar, for 3d printers, most people use something called RAMPS. RAMPS is an arduino and an arduino shield, with pololu stepper drivers on the shield. It has a 4 pin connector for each X,Y,Z and an extruder, with a driver for each. RAMPS is controlled via firmware called Marlin, which interprets G code sent via serial connection and executes it on the steppers. I would love to use my extra RAMPS board for this, however, I don't know if its compatible with Mach3 or other CNC G-code generators. Any suggestions/input woudl be appreciated here.




For the ball screws and Linear rails, ebay via China, This is what I did for my 3D printer.

Something like this:

3 SBR16 Sets 3 ballscrews RM1605 3BK BF12 3 Couplers | eBay (http://www.ebay.com/itm/3-SBR16-sets-3-ballscrews-RM1605-3BK-BF12-3-couplers-/250459126798?pt=LH_DefaultDomain_0&hash=item3a5086fc0e)

My plan is to use Mach3 as my software solution for the g-code, but again I am confused if this will work with my RAMPS if I go that route.




So here some questions:

1) Mill plate clamp? I have never milled, manually or CNC before. Do you have to clamp down the piece, I assume you have to do something to prevent it from moving, how is this generally done, what do I need to make this happen?

2) Mill/motor? Do I use a regular router, maybe a variable speed router that I can mount on my X axis? Do I just get a regular DC motor that can be controlled via my control board? What is the best method for this?

3) End stops? In 3D printing, we use end stops to Home our axis' so we know exactly where our position is. Do I need something like this for a CNC mill?

4) Do I need anything else other than Mach3 and the Driver controller board? With a 3D printer we use an Arduino/Ramps with Marlin firmware setup which processes the GCode, and controls the steppers from an interface on the PC. It seems to me that the Mach3 works directly with the control board, but I want to make sure I am not missing something here.

5) water/coolant system? Is this needed for aluminum? If so, how do I go about this? I have no idea on this at all.


So if some could comment on my plans, and help me out in any way with my unknowns, I would be greatly appreciative! I am really looking forward to building this thing!

Also, if I am missing anything, feel free to let me know!

Ross77
13-04-2013, 03:06 AM
Hello, that's an impressive an informative first post,You are on right track as you have realised that it is best to get the correct parts to begin with, I cant answer all your questions but I'l have a stab a few.

I think you will struggle to make a single machine that can mill Ali, cut wood and do PCB work. I think you will need to consider a changeable spindle drive /motor. Ali requires low to medium speed with high rigidity. Wood needs high speed and good to high rigidity and pcbs need very high speed and super low runout. A spindle to meet all of these requirements is going to be very expensive if it existed



1) Mill plate clamp? I have never milled, manually or CNC before. Do you have to clamp down the piece, I assume you have to do something to prevent it from moving, how is this generally done, what do I need to make this happen?

Depends on your bed, T slots are best as they have a good selection of clamping jigs and tools. sacrificial mdf bed means you can just screw the material to where ever needed but not to good for Ali. Pcb work is usually held by vacuum or double sided tape. Again a range of possibilities for one machine.


2) Mill/motor? Do I use a regular router, maybe a variable speed router that I can mount on my X axis? Do I just get a regular DC motor that can be controlled via my control board? What is the best method for this?

A router cant be controlled to easily by mach and wouldn't be any good for Ali or pcb. see above for spindle problems.



3) End stops? In 3D printing, we use end stops to Home our axis' so we know exactly where our position is. Do I need something like this for a CNC mill?

cnc uses limits switches as end stops to prevent over travel and movable home switches to set the start points.


5) water/coolant system? Is this needed for aluminum? If so, how do I go about this? I have no idea on this at all.

Ali needs coolant to prevent build up on the tool and wood will need extraction or jetting to remove chips to prevent re cutting of chips and tool wear.

Good luck

AVRnj
13-04-2013, 01:19 PM
Ross,

Thanks for your comments and feedback!

OK, let me say that my clear priority would be to mill aluminum of different sized thickness, from say 1.5mm thick to 150mm thick.

I like the idea of T-slots, I suspect a bed can be made out of aluminum extrusion, and you can make your own clamping devices using some simple t-nuts?

OK, so I think I need to figure out the following to get moving forward:

control board: Gecko vs other?

motor/spindle

design

limit switches, mechanical contact switches, other?

coolant system

If anyone has any other comments or can help me figure out what needs to be figured out, I would greatly appreciate it.

Thanks!