Hi Everybody, I've been on this thread a few times, this might actually be my first post, I can't really remember. Anyway, I've been working on a CNC mill/router design over the last year or so, and I've really pulled the design up over the last few months. This is my first build, so be kind.

The design started off as an aluminium T-Slot build, but I was convinced to build it from steel, which in the end looks like it will save me about $400, and still have the same cut space.

Basically I want to build a machine that is capable of cutting aluminium, but will mainly be used to cut through woods/plastics/fibers etc. I need to be able to build this machine with the tools i already have (welder, grinder, drill press tap/die screw drivers etc), so a very efficient design is required. I have found a guy that can help with plasma cutting the plates and some small milling of the parts that need to be straight, at a cost of course.

My cutting space is X: 720mm, Y: 950mm, Z: 200mm
The main drive and guides im using are:
Y Rails: Hiwin HGR20, with HGW20 carriages
Y Drive: 1610 leadscrew, with SFU1610 ballscrew
X Rails: Hiwin HGR15, with HGH15 carriages
X Drive: 1610 leadscrew, with SFU1610 ballscrew
Z Axis: THK33, what ever I can find on EBay really.
1.5kW water cooled spindle with VFD
All steppers (4 off) are 387oz-in, driven by a gecko G540.
PSU 48V 10A
A full list of materials can be found here.
You can see on this list which parts I've already purchased, like the motors, G540 etc..
My aim is to keep my entire build under 3K. I've already spent about $600, and I've got about $2100 remaining, so the budget looks good so far.

My design is a cartesian style mill with 2 drives on the Y and a single drive on the X.
here is a snap shot of the CAD model.
Attachment 239570

You can also download a 3D PDF of the model at the bottom of this post.

OK, so I believe I have done all my calcs right, and my running gear should be strong enough to cut aluminium.

The full weight of the gantry is 55kg, but I have rounded it to 60kg is my calcs, the following are the results of my calcs for a 1605 screw, 1610 screw, 1620 screw and 2020 screw.
My power supply is 48V 10A. Im not really sure how I should distribute this on my machine.
The following calcs are based on 3A each for Y, 3A for X, and 1A for Z.
At 48V, 3A, my steppers output about 1.616Nm with a corner speed of 936rpm.
The critical speed for my configuration (1610 screw 1200 long in a fixed/supported configuration) is 1249rpm.
Im basing this on a required cutting force of 10N.

  • With a 1605 screw, to get the the feed rates of 4500mm/min I need 900rpm and 1.692Nm. This is actually above what I have available, so lets try the 2020 screw in my configuration
  • With a 2020 screw, to get the the feed rates of 4500mm/min I need 225rpm and 2.298Nm. This is even further outside my motor limits, so lets try a 1610 screw
  • With a 1610 screw, to get the the feed rates of 4500mm/min I need 450rpm and 1.431Nm. Just inside my limits.
  • With a 1620 screw to get the the feed rates of 4500mm/min I need 225rpm and 1.887Nm. Which is outside the limits.


references:
What size stepper motor do I-need.
http://www.geckodrive.com/step-motor-basics
FSWizard - Free Advanced CNC Speed and Feed Calculator

The 1610 screw is the only screw that suits. It fits my requirements, and I can still lower the 3A down as low as 2.7, allowing more amps to go to other steppers.

I'd like to know if my calcs sound right, and if anybody has had good success with a similar build. Feel free to make comments or suggestions as you wish. This is the 5th iteration of this design, so I really don't want to re-design this that much.

Thanks in advance,
Nick