Router/Plasma CNC Build From Down Under

[Tinkerer]

G'day Everyone!

My name is Richard and I live in Melbourne Australia. I have very much enjoyed reading the various threads on building DIY machines and probably like many on this forum have found and very much enjoyed the learning curve in getting to understand the issues and parameters in building a CNC machine. Unlike many on this site, I have limited experience in building machines, but I am quite a handy person and accustomed to getting my hands dirty on DIY projects. I am waiting for delivery of my TIG / Stick Welder, so my practical learning curve will start with improving my welding skills. Meanwhile I've been on a steep learning curve getting familiar with Rhino as a CAD drawing package (also to be used in designing Kinetic Artwork).

I have created this thread hoping that those more experienced will be able to guide me on my build. So here goes....

1. My Machine Parameters

I plan to build a CNC Router, with the flexibility to use it for Plasma or Laser cutting of steel. It is intended to be a general purpose machine with a high degree of accuracy (if I'm going to the trouble of building something bespoke, then it may as well be accurate).

The main material I will be cutting is timber (plywood up to 25mm thick) and some aluminium (aluminum) to create Kinetic Artwork (wall art etc).

It will initially be a three axis machine, but I intend to build in capability to expand to a 4th axis to turn table legs, carving etc. If I honest with myself, I suggest that the challenge (and resultant satisfaction and no doubt accompanying frustration) of the build outweigh practical applications.

The general parameters of the machine are:

1.1 Working Area

X Axis - 1.5m
Y Axis - 1.25m
Z Axis - capable of 220mm travel, but anticipated generally working to 154mm
4th Axis Capability - Removable working platform to accommodate greater Z depth of 350mm (total) for an additional axis

As the machine will be residing in my garage, I need to make is as compact as possible (car parking will likely be a casualty!).

1.2 Router /Laser/ Plasma Capability

I intend to install a 2.2kW water cooled router as the main cutter.

I have designed a holding water tank and support to be able to cut steel. I understand that compromises are made to do this, however as it is as general purpose machine, speed etc. are very much a secondary consideration. I'm not sure where my Kinetic artwork will take me, so flexibility needs to be built in.

1.3 Frame / materials

I intend to build the majority of the frame from 89 mm SHS, 3.5mm thick.

The Gantry will be manufactured from Steel RHS (150 x 200 mm) reinforced with 10mm Steel plate to sit on the carriages for the X Axis.

I attach a spreadsheet showing the calculated weights expected to be carried by the X, Y & Z axis, which:

X = 112kg
Y = 27kg
Z = 19kg

For obvious reasons I wish to ensure that the removable Steel/MDF platform is robust to ensure accuracy. I have read threads where some members suggest simply building a removable MDF platform to vary the Z depth. Given the depth of the Z axis and flexibility to do some Plasma/ laser cutting, I have swayed away from this, but equally, I am conscious of the additional Steel / weight / work my design requires. Thoughts on alternative variable Z axis designs welcome! My requirement is to ensure accuracy prevails (no movement).

1.4 Motors/Drive

Having read in detail a number of threads relating to similar designs, I have landed on a design which utilises:

Ballscrews - still to calculate / determine whether I need 20mm diameter or can get away with 16mm when considering lengths of:

Y Axis - 1,694mm
Z Axis - 1,762mm

Z Axis Actuator - I will probably look to purchase one for the Z axis, believing that something 2nd hand may be more accurate than anything I will build.

Guides - Looking at LM guides for greater accuracy from the likes of THK or suitable alternatives.

1.5 Drive Mechanism

All Axis (perhaps with exception of Z Axis depending on Actuator used) to be powered by belt drives to reduce vibration and provide flexibility in changing gearing ratios if need be. Initially, I intend gearing to be a 1:1 ratio, but final calculations may dispel this notion.

I intend utilising stepper motors for their greater torque range, and wish to explore the use of an encoder function to provide a closed loop system reducing errors if steps are somehow missed.

Based on earlier research, I expect that I will be utilising something like NEMA 23 motors with outputs around 3 to 4 kN (424 to 566 oz/in) outputs.

I have purposefully held off on this hoping for some feedback on my draft design of the frame (gantry) suggestions on shaft diameters, etc., before calculating final requirements.

I am not sure what cutting speeds I should design to (and hence input for motor requirements). Speed is not essential as I will not be into major production runs, but neither do I wish to watch a job completed at a snails pace. Any input on appropriate / realistic tool speeds for cutting MDF (25mm) or aluminium (aluminum plate say typically 20mm) which I should aim would be much appreciated.

Plasma or laser speeds could presumably be much faster??, but router work should drive the design.


2. Drawings and Spreadsheet

For reference I attach various views and closeups of my draft drawings and spreadsheet showing materials and weights.

I am not totally sure how some components for drives/ LM / ballscrew Nut anchors should be attached, apart from the general understanding that everything needs to be adjustable to tweak tolerances (I/m sure my soon new found welding skills will challenge the need for this!). Thoughts / photos on how items should be bolted together or how I should alter my design to provide for this would greatly assist.

3. Your input

I now lay myself prostrate, seeking input from members who have the skills and experience in building such machines on matters raised or any other items which my design raises.

Please note that I have a thick Aussie hide and welcome your constructive feedback! My first objective is to order steel to build the frame, but also understand that I should have ordered and received guides, shafts etc, before starting cutting to ensure concept and practical application marry up!

Regards



Richard


PS The site wont let me upload images. Will post once sorted.