First Build 5 x 12 Steel Frame CNC router

[Scott Damman]

First I would like to say the information here is amazing and has greatly helped my design and learning for this CNC router build.

Objectives,

5 foot by at least 10 ft of machining area
Z height high enough for paddleboard foam blanks ~ need roughly 12 inches under the tool
ability to machine wood, aluminum, foam
good accuracy/precision (still trying to figure out where I want/need to be)
Vacuum hold down


Parts I already have
Linear rails - INA 25mm 4 row linear rails - I have enough to do all axis's and enough bearings
Y axis ballscrew - 10mm/rev rolled ballscrew
1850 oz/in stepper motors - 2 for X (long axis) and 1 for Y
2 4hp regenerative vacuum blowers
Colombo 10hp spindle with ISO30 ATC

I will start out where I am now and then go into some questions I have.

The gantry legs mock-up 4 x6 x 1/4wall box tubing, 1/2 inch plate for the feet.






Gantry partially welded up, Gantry is built from 4in x 6in x 1/4in wall box tubing and will get blocking in between the 2 tubing with some vertical bracing on the back. I machined the ends of the gantry before welding them up so I can put an e-stop on each end. The ballscrew is laying ontop of the gantry and will live between the 2 box tubing when complete.



Here is the plan for the Z axis, made from 3in x 6in x 1/4wall box as a starting point. I plan to make an A axis and have mounted the motor up and off to the side. Although this could still get in the way. Should I put the motor for the A axis above the spindle motor? This will make the HTD belt 20 inches center to center. If I did that would I be looking for trouble as far as belt stretch is concerned?




Heres what I was thinking for A axis


A few questions,
Gantry and Z axis is going to be ~550lbs (~250kg), am I shooting myself in the foot using steppers for this weight? I would like to get decent speed out of the thing without the risk of missing steps. When I purchased the steppers I was trying to balance cost but now im worried I will have trouble with it when im done.

What pitch should I shoot for on the Z axis screw? I was planning on using the stepper motor with a ~4:1 reduction. Total travel as it stands right now will be 16 inches. Weight of Z with Spindle will be around 100lbs should I add spring assist to this? or air springs etc?

Next steps for me,

I am working on mounting the rails on the Y Axis and getting prepped for pouring epoxy as soon as the temp rises a bit. Here is the plan for the pour and looking for any insight.

Lay gantry on its back
Level with starrett precision level as close as I can in both planes
pour epoxy for Y axis linear slides
at the same time pour the mount pads for the Y Axis ballscrew, in my mind this gets the ballscrew on the same plane (albeit at a different height) as the linear rails
Paint Gantry
Mount the lower linear rail for the Y Axis
Flip gantry upside down
Use precision level on the linear rail and set rail level and also use a precision square and the level to level in the other plane
Pour expoxy on gantry feet (my thinking here is that I can then get the gantry feet 90 deg to the Y axis linear rails and also on the same plane as the linear rails) I would assume there may be some slight shimming still but the epoxy will be close.


Thanks
Scott