Spring loaded detail/finger sanders for finishing CNC projects

Sandpaper, as well as sanding blocks and detailing sponges, are essential for all CNC projects. They let us remove flaws, smooth surfaces and prepare materials for finishing with a variety of coatings. For many projects though, especially the small ones, they can be too big and bulky and can indiscriminately remove small, often fragile, details, as well as changing shaped edges away from what we so carefully designed.

So, for newcomers to CNC work, I thought I’d add this short post to quickly mention my experiences with spring-loaded detail/finger sanders. Mine is shown in the photo above and it’s simply a plastic finger with a continuous band of replaceable sandpaper around the outside. They come in many sizes, the one here being 20mm wide, although 10mm and 30mm ones are common. They also cost just a few pounds: try searching for something like ‘finger sander spring loaded’ on eBay or Amazon to see what I mean.

One of the most exciting things about finger sanders is the variety of sanding points. To start with there’s a long flat zone at the bottom, allowing sanding of large areas and straightening of cut edges. There’s also a narrow area at the front which allows for getting the sandpaper into tight places and around curves. Plus the rest of it has compound curves that can be very useful too. And when the paper starts to get worn where you need it, just push the pointy front end inward to slacken the sandpaper so you can rotate it around the edge. Personally I find them very useful as you can see in my photo of a Darth Vader routing project below.

A detail finger sander with a walnut routed Darth Vader

Tagged : / / / / / / / /

Holder for 12mm diameter LASER-diode module

I have a couple of 12mm diameter 1500mW laser modules and heatsinks, plus a cheap Chinese CNC router. However, fitting the lasers is difficult as the heatsinks don’t fit properly into the spindle motor holder. Also, the laser modules are 5V, whereas my CNC only provides a 12V PWM laser output. So, I designed this 3D printing project to hold the laser module and a small power step-down circuit that would fit properly in place of the spindle motor.

You can download the 3D printing files by clicking here, including the OpenSCAD file for customisation as modules, heatsinks and mounting holes may differ for your laser. Also, it can be modified to add a small fan if necessary, to cool the laser when used continuously for a long time. For anyone interested: the step-down circuit is just a 7805 voltage regulator with a 10uF electrolytic capacitor on the 5V side, because the laser module has its own driver circuitry. You can see it in the photo below. Surprisingly for a simple circuit, it seems to work very well so far with GRBL control, but please use that circuit at your own risk.

Inside the LASER holder

Finally, a couple of construction notes in case they help:

  1. I tied a knot in the cable under the lid for strain relief. As the knot is bigger than the hole in the lid, if the cable is accidentally pulled the knot stops it breaking off the circuit board.
  2. The disc part with cutouts is a spacer that sits on the rim above the laser module. It allowed me to keep the circuit, which I glued onto it, away from the module.
Tagged : / / / / / / / /

A simple LASER extractor project

This is a simple 3D printed design I came up with to extract smoke and fumes on my cheap Chinese CNC machine when LASER cutting. Basically it consists of a small collector to fit under the z-carriage (with a holder to glue onto the collector) and a couple of parts to adapt a PC fan to fit standard plastic hoses. The collector, once glued onto the holder, should fit the bottom of the z-carriage as shown in the photo above. It’s designed to be removable for when the CNC is used for routing. The z-carriage on my CNC seems a common design, so hopefully this should work on many CNC machines. The inlet and outlet parts need to be glued onto a 12V PC cooling-fan like in the photo below.

From the outlet I attached a 32mm plastic aquarium hose, the end of which goes out of a nearby window. Between the inlet and the collector I used a bit of 20mm rubbery plastic plumbing hose. Despite the design not being optimised for aerodynamic properties, it does remove most of the smell of smoke away through the window. It’s not perfect though as draughts can result in smoke not getting sucked away. I got around that by making a shield to go around the front and sides of the laser to help make sure smoke and fumes get into the collector. If you want to print your own you can get the 3D printing files by clicking here, including the OpenSCAD file in case you need to make any changes.

The extractor fan pump with 3D printed parts and hoses

Tagged : / / / / / / / /

Adding a shield to a CNC-mounted LASER module

My LASER is an attachment for my cheap Chinese 1610 CNC router so it isn’t tucked away inside a metal case with a tinted window. That means I have to wear LASER-safety glasses whenever it’s running, which can be annoying if I’ve got other things to do. So I designed this simple 3D printed shield with dark red windows (as the LASER is blue). It comprises a small frame that slips onto the LASER module (with a hole for a screw if needed to stop it sliding down) and a three-sided shield that slides onto the edge of the frame, as shown below.

3D view of the laser shield assembly

After 3D printing the front and two sides need to have dark red plastic glued in: I cut mine from a plastic square photography filter I picked up cheap on eBay. Then those three pieces need gluing together at the front corners to make the shield. If you want to add some rigidity then there’s also a bottom component you can stick below the three sides. The shield is then easily removed for when you want to focus the LASER or for removing cut materials. You can download the 3D printing files from Thingiverse by clicking here, and in case you need to make adjustments that includes the OpenSCAD file. The shield also works well with my LASER extractor project, localising the area it extracts air from, which is one reason why the bottom plate is included in the design.

Tagged : / / / / / / / /

Mounting a GoPro camera on a CNC machine

Sometimes it’s nice to make a video, even a timelapse one, of a project coming to fruition on a CNC machine. Maybe just as a keepsake, or to share, or even to make some educational Maker instructions. So being able to add a GoPro camera, or other camera that uses GoPro mounts, is something you may want. I did anyway, so the project shown above is a simple 3D printed mount that clips onto a 20mm-extrusion on the front frame of my CNC, which can be positioned right in-line with the work-bed centre.

It’s a very simple 3D printing project that doesn’t even need any support material, so shouldn’t be a challenge if you have access to a 3D printer. The files you can download from Thingiverse by clicking here, which include the OpenSCAD file in case you need to customise or adjust it. Once made you use it to fix on a sticky mount base like in the photo, for your camera arm to fit onto. And below is a photo of my GoPro session mounted on my CNC so you can get a better idea of how it works.

A GoPro camera mounted to a CNC frame

Tagged : / / / / / / / / / / / / / /

Add Bluetooth to make your CNC wireless

Most cheap CNC machines come with a GRBL controller board that communicates with a computer using a wired USB connection. There’s no problem with that if you want a computer near your CNC, but a much more convenient way to communicate with it is over a wireless connection. That way you can keep your valuable PC well away from potential hazards or even use an Android tablet or smartphone instead. And the easiest way to do that is add a Bluetooth module to the GRBL board if it has serial connections available.

So a bit of manual reading, and looking at the boards’ circuit diagram, are necessary. You’ll be looking for connections for connecting wires to its positive (e.g. 3.3V or 5V) and negative (a.k.a. ground or earth), transmit (Tx) and receive (Rx) headers. Normally they’ll be on pins soldered into the board. Then you need a Bluetooth-serial module which are a few pounds/dollars on eBay or Amazon: I used a HC-05 which is commonly available. The module will need its name and communications speed set up first and I’ve put some tips on that at the bottom of this post.

Then the Bluetooth module needs a connection from positive to Vcc and from ground to GND, to power it. The Tx on the GRBL board goes to Rx on the Bluetooth module and, similarly, Rx goes to Tx. I’ve put a diagram below that shows how I wired my HC-05 to my Woodpecker 3.1 GRBL controller board, which is quite common on cheap Chinese CNC machines. Sometimes Tx and Rx connections are reversed on the Bluetooth modules, so if you have problems you can try swapping them over. And to make it easy to get started consider using female-female jumper wires (i.e. sockets both ends) for the connections, like I used in the photo above, before committing yourself.

Circuit diagram for an example Bluetooth wireless connection
Hopefully now your Bluetooth module will flash an LED when the CNC is powered, to tell you it’s waiting for a connection. If not, check everything carefully, especially your positive and ground wiring. If that’s OK you should be ready to pair with your PC or Android device and have fun doing wireless CNC’ing.

Setting up a HC-05 Bluetooth module with an Arduino

If you know nothing about microcontrollers then now is probably a good time to find a friend who does, or even try to talk an online supplier into doing the setup when you buy. However, it isn’t really very difficult if you have an Arduino as you just need to wire the HC-05 to it as described for the GRBL board above (see www.arduino.cc for help on your particular board). The code below can then be used to set the Bluetooth module to be called ‘CNC’ (which you can change) with a speed of 115200 bits/second. Most modern GRBL boards communicate at that speed but if yours is quite old, and uses 9600 bits/second, you can change ‘BAUD8’ to ‘BAUD4’ or simply remove that line. And then, hopefully, your HC-05 module is good to go.

void setup()
{
  Serial.begin(9600);
  delay(1000);
  Serial.print("AT+NAMECNC");
  delay(1000);
  Serial.print("AT+BAUD8");
}

void loop(){}

Tagged : / / / / /

Measuring water content in wood

The water content of wood we use in CNC work is obviously important for many reasons. One is that the quality of router cuts, and the depth of LASER cuts, will be adversely affected if the wood is wet. Also, and maybe more important, is that wood will change length as the water content changes, and as different woods shrink and expand at different rates that can lead to a nicely finished project coming apart over time (or even a lovely finish cracking). And it can have some bad effects on some finishes causing slow drying or cloudy clear-coats. For those reasons I decided to invest in a moisture-content meter so I can get an idea of how dry my wood is before using it, as well as to let me monitor changes as the wood acclimatises to indoor life before I cut it.

The one I got was only a few pounds on eBay so I’m not expecting really accurate readings, but testing some thin wood sheets at home I’ve been getting sensible readings between around 7% and 12% so hopefully it’ll be useful. Using it is very easy once set to the wood mode: the two metal pins are pushed into a non-vital area (end-grain is a good place too) like in the photo below and, after a moment, the reading appears on the small LCD display. Personally I’m quite happy with it and with a little luck it’ll provide me with a good idea whether my wood is too damp to want to use and let me monitor it to make sure I know when it’s ready for a project.

Measuring water content in wood with a moisture meter

Tagged : / / / / / / /

Improving lead-screw binding with a flexible coupler

CNC machines have plenty of moving parts and if we want our routing and LASER cutting to be as good as possible the movements need to be as smooth and unrestricted as possible. When I built my cheap Chinese CNC it came with rigid shaft couplers for connecting the threaded lead screws to the stepper motors. That meant that the motor spindle and lead screw couldn’t be adjusted to be perfectly in-line, just because of tolerances in parts and mountings. So, for part of a full rotation the lead-screw was binding (i.e. becoming hard to turn) and the rest of the turn was fine.

If you find you get the same problem, you could just do what I did: change the rigid couplers for slightly flexible ones. In the photo below I’ve shown the difference between the two. The bottom one is the original rigid one and changing to the new one involved no more than loosening the grub-screws, moving the lead-screw to the side, then inserting the new coupler, pushing in the end of the lead-screw, and tightening the grub-screws. For just a few minutes work it made X and Y axis motions so much smoother. And, for only a few pounds/dollars per coupler it was a cheap job too.

A flexible and rigid coupler

Tagged : / / / / / / /

Adding a spindle motor switch

I tend to prefer to minimise safety risks when I’m using my CNC, and that includes making sure I don’t injure myself touching fast-rotating cutting bits. Obviously it’s unlikely that the motor will start up when I’m removing or attaching a bit, although it’s a little more possible when the G-Code file includes pauses for tool changing. But, to be completely sure nothing can go wrong, I made the 3D printed switch box below to allow me to isolate the spindle motor from its electrical supply. It prints as two parts which need to be glued together to fit the top of a 20mm extrusion, like in the photo above. The hole in the front is made to house a standard 18x11mm rocker switch. Click here to go to Thingiverse to get the STL files for your 3D printer.

3D model of the spindle switch box

Once the two parts of the box are stuck together, with the switch inserted, the positive wire from the spindle motor controller to the motor itself, which should be red, needs to be cut. The position where you do that needs to be planned so that the wires can be run to the box and the full movement of the motor along the CNC’s x-axis isn’t compromised. Personally I found the best place is near the controller board as on my CNC the red wire ran straight past the box position. You can use standard spade connectors crimped onto the ends of the wire, after stripping some insulation from the end. Below is a photo of the back of my switch box so you can see what I mean.

The back of the switch box showing wiring

Tagged : / / / / / / /