Desktop CNC With Welded Frame

This CNC router was mostly inspired by Dcorb's tool, what I saw on openbuild.com. Of course, it differs from it on several points, but I definitely thank him.

In this implementation the table is moving and the spindle is stationary. This has advantages and disadvantages. Typically a moving spindle uses less total space for the size of work envelope, and a moving table tends to have a more rigid spindle. A significant part of the cost is the frame. I wanted to minimize this, while at the same time striving for maximum stability. That’s why I opted for the welded steel frame. I made this machine mainly for wood work.

The steel frame is made of 40x40 mm thick walled closed section. When welding, I paid great attention to the exact right angles and keeping the elements in one plane. This is fundamentally important. After all, such a machine is capable of high-precision machining. I made the holes and threads necessary for fixing the linear rails, ballscrews before painting. The linear rails must be perfectly parallel.

The bed or table is made of 26mm thick beech plywood (I actually glued two 13mm boards together). On top of this is the 18mm thick MDF spoil board. Sizes: 520x360 mm. The effective work area is of course smaller than this: 465x300x100 mm.

Initially, I used a factory assembled complete z-axis (the video still shows this). That was a mistake. I was not happy with it because it was not stable enough. So using the most valuable part - 16mm ballscrew - I built a new one from discrete elements. It's perfect, I think :)
The x-axis "table" is a 155x200x10 mm aluminum plate. This will accommodate the 2 pcs. 200mm linear rail and ballscrew of similar size. I attached a vector image of this.

This is an Arduino Uno based CNC router complete with a Isolation CNC Shield panel. The Arduino Uno is cheap and can be used to build a great CNC. However, it is sensitive to electromagnetic interference. Therefore, I was looking for a shield that could reduce these effects. The Arduino CNC isolation shield is like this, the outputs and inputs are isolated with optocouplers and buffers. They come with detailed documentation, making it easy to connect to peripherals. (emergency stop, limit switches, stepper motor drives, probe, spindle, etc.)

The software is free GRBL. This is what needs to be uploaded to the Arduino Uno registers and what “brings the device to life”. This is a good presentation of the process here. The stepper motor driver boards are TB6600 models. Stepper motors: Nema 23 double shaft. The previous ones are powered by a conventional transformer power supply. The spindle is currently a 500 Watt brushless motor that comes with its own adjustable power supply and clamp. The engine speed is 12.000 rpm. I’m happy with it, but I want to replace it with a more powerful one over time. The factory GRBL settings must be tuned to your needs during commissioning. For example, I don't use the "homing" feature, but the hardware limits does. You can find information about this in many places, so I won’t deal with it here right now.

Many CNC builders encounter this problem. Unexpected downtime, program crashes seemingly for no reason. Stepper motors, spindle motor, dust extractor generate a lot of electrical noise. These were a problem for me too and on several occasions my work was wasted. Big trouble when after one or two hours of work the machine stops unexpectedly and you can’t even go on because you lost the zero point. Following the advices of others, I managed to eliminate this problem.

In my case, the speed governor of the spindle motor was the biggest source of noise. So the first step was to move the power supply to the spindle motor to a completely separate housing. Of course in a metal housing with protective grounding. The cable to the spindle motor is shielded. The shielding is at the potential of the housing. This is true for all other cables (stepper motors, limit switches, emergency switch). Grounding and 0V of power supply (GND) are two different things, do not mix the two.

Proper grounding and shielding is paramount. I found the best explanatory figure at www.mycncuk.com, which you can find in the pictures here. It is important that all ground wires start from a single star point. It can also be the metal housing of electronics.

In my case, the problem was that I forgot to ground the cnc metal frame.

Use as short USB cable as possible!

Thank you for reading.

Keep smiling :-)

brillinv

4x SBR12 linear rail length 600 mm with SBR12UU linear blocks

2x SFU1605 Ball Screw set 600 mm

2x SBR12 linear rail length 200 mm with SBR12UU linear blocks for Z axis

1x SFU1605 Ball Screw set 200 mm for Z axis

1x 500W Spindle Motor + Power Supply speed governor

1x Arduino UNO-R3 Board with original ATmega328P micro-controller

3x NEMA 23 Stepper motor double shaft 3A 270 oz

3x TB6600 Stepper Motor Driver Board

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