[otto29]

Hello,

I am looking to build my own CNC wood router. I currently own a used one that I purchased off someone else who built it. It isn't large enough and I don't particularly want to modify it since it will work for some of my smaller projects.

The current one uses I believe NEMA23 stepper motors for a 5 ft. (X-axis - 1 Stepper) x 6 ft. (Y-axis - 2 Stepper) x 6 in. (Z-axis - 1 Stepper) cut area using a palm router.

I have the mechanical side of the project locked down for the new one, but I need to select the stepper motors and the other electronics that will be compatible.

My General Specs:

Overall dimensions:

X = 6 ft. (overall) (1 stepper motor)
Y = 10 ft. (overall) (2 stepper motor)
Z = about 1 ft. (milling height) (1 stepper motor)

Router weight = 10 lbs. (per online spec)
Gantry = 15 - 20 lbs. prior to stepper motors and router (estimated, it may be less)

max required in / min. = 100 in. / min.
Average milling speed X - Y axis = 40 - 60 in / min.

Rack and gear combo for X and Y axis.
Screw for Z axis.

Any recommendations?

[routalot]

Perhaps you should submit a sketch or screenshot of your intended construction so that experienced eyes can give opinions on the chances of the structure leading to a successful machine.A gantry that spans 6 feet may need to be quite substantial and could weigh a lot more than your estimate.Then there is the matter of the mechanical advantage provided by the leadscrews or rack and pinion combined with the range of torque available in each size of stepper.

[peteeng]

Hello Otto,
X axis 6ft consider using a rack and pinion. This is at the limit of reasonable size ballscrews
Y axis definitely use R&P
Z using 5mm pitch D16 (ie 1605) ballscrew

Speed will be easy to achieve and on a big router like you are describing you will need much faster speeds to get a job done in reasonable time. R&P drives are very fast. Your gantry will be much heavier then 20lbs. I'd use a 5:1 gearbox on the X&Y axis even a 10:1 gearbox... this keeps your torque up and your speed down a bit... What is your construction philosophy? al extrusions, welded steel bits, plywood, aluminium welded?

I would consider servos to get more speed easily vs using gearboxes. Peter

eg using a typical 1.25module 20T pinion at 300rpm its going to be moving at 25m/min 1000in/min so use a 10:1 gearbox to bring it back to 2.5m/min and get 10x the torque... this will also give you over 100kgf at the rack which is adequate for most jobs... use a 400W or 750W servo and you get to run at 3000rpm so at 10:1 gearbox and 300rpm that's 25m/min which is what commercial machines run at... A few things to get into perspective....

looking at the Amana tool info if you have a 1/4" tool they recommend a chipload of 0.06" or 0.15mm. I regularly run at 0.2mm in plywood and timber. CL=feed/rpm/N so Feed = CLxrpmxN so at 18000rpm that's a feed = 0.15x18000x1=2700mm/min for a 1F tool or 5.4m/min for a 2F tool. Very much faster then you are imagining... I assume you want to cut plywood or timber due to the size of the machine...

60in/min is 1500mm/min feed. That's Ok if you run your spindle at half speed. But aim at 3000mm/min is better say 120in/min. CL=3000/24000/2 =0.06mm which is a good fine finishing bite size and chipload.