Saturday, 28 February 2015

Project #2: Open Source Laser Cutter, Part 2

Now that I have an easy way to switch controllers into my laser it's time to try out some of the different softwares. I'm quite comfortable with Arduino and I've got a fair few of them kicking round my house so that's a good place to start so GRBL is the first controller that sprang to mind. It's a simple G-Code interpreter and there are a myriad of programs that send G-Code out via a serial port.

The controller:
GRBL is optimised for the AVR328 microcontroller which is typically found in the Arduino Uno so it's very accessible for beginners. The same chip can also be found on the Arduino Nano which can be bought for as little as £2.50 each (which is why I have a box full) so I used one of these instead.
The wiring for the blacknose is very simple, There are only X and Y axis, X and Y limit switches, laser power and laser On/Off. GRBL connections are well documented but it's worth noting that I used the Lasermode variant of GRBL which has the Laser Power on Pin 11 so it can use the hardware PWM.

It took just 3 slow and steady hours making sure the wiring was right and piggy backing the controller onto the break in board. I think I was much more cautious than usual but I was also reconditioning the machine at the same time. The only minor stumble was with the X limit switch, where the switch wires were bundled in with the stepper motor wires there was electrical coupling which prevented the Arduino from accurately detecting the home switch depression. This was solved by separating the two sets of wires along their length (The leetro controllers presumably have some built in filtering to negate the effects).

The firmware:
As already mentioned I used the Lasermode Variant of GRBL, this is freely available and can be easily compiled and flashed to the device using the Arduino IDE. The only minor problem was that I had to use the most recent development branch of the IDE (1.5.8), but that has now gone into stable release (1.6.0).

GRBL is very clever, all of the machine specific settings are stored in EEPROM on the microcontroller. This means if you update the software all the settings remain on the device. All the EEPROM settings are adjustable using text commands over the serial port. Since the software is downloaded using the Arduino IDE it was easy to set up the device using its serial monitor.

The first task is to work out how many steps per mm the laser has. Read the settings to figure out how many steps per mm are currently being used, request the axis to move 10mm and measure how many mm the laser actually moved. When you know how many steps it took and how far it went you can calculate how many steps per mm the machine actually has. The Blacknose has 78 steps/mm on the X axis and 156 steps/mm on the Y axis.

The next task was to set the appropriate direction bits, GRBL has a setting to make sure the direction lines appropriately, the defaults are acceptable. Finally you test the homing cycle to make sure both axis run up to the limit switches and then stop. The image will appear rotated by 180 degrees because GRBL has the origin in the bottom left and the blacknose has it in the top right. It is possible to modify the GRBL settings to correct this but it hardly seemed worthwhile.

The Software:
GRBL accepts G-Code sent to it via the serial port, so you need 2 additional pieces of software, one to create gcode from your drawings and one to send lines of gcode to the machine. There are numerous way to create G-Code but the one that sprung to mind was DXF2GCode. Most vector programs can output dxf so this solution is independent of drawing package.

It's a very simple offering, the file is loaded and displayed in the main window along with the origin point. You are able to turn each of the entities (drawing lines) on and off as required and you can set the feed speed for the drawing. Because it is intended for all CNC machines it includes options for z axis height but we can just set all of those values to zero. The file created contains a series of G-Code instructions that describe the imported image.

To send the G-Code to the arduino I chose to use Grbl Controller, again it's a cross platform solution and it comes with a few useful Jog functions to move the laser head around which makes it good for testing the machine. A handy text box allows you to type commands directly to the controller. You select the required G-Code file and it is sent line for line to the laser cutter. The laser cutter executes each instruction and cuts your required shape.

Results and Conclusions:
GRBL works on the machine, I was able to cut out the test pattern with only minimal editing of the G-Code. I was a bit worried about the response times, There seems to be a noticable delay between turning the laser on and moving the head. With a CNC mill or a low power laser diode this probably isn't noticeable (or may even be necessary to get the mill up to speed), but with a 40W laser this leads to a burn mark on the work piece.

The is no reduction of power as the laser goes round the corner, This is due to the G-Code being fed into the machine but ultimately it means the corners cut better/burn more than the straight lines when the laser head is moving at speed.

It's an extremely functional arrangement that was pretty simple to set up and get running, There was a bit too much manual tweaking to get it running with the big laser so it's probably best suited for small laser diodes. It's all a great learning exercise, next stop is a serious reduction to the amount of metal work on my laser cutter, before moving over to a Laseraur type controller (whatever that entails)

Smoke Rings

I've known about this effect for quite some time but since I had the lid off my laser cutter and I could video easily I thought now was a good time to share. When you're testing the alignment of the laser you cover the mirror with some masking tape and shoot the beam at it. The first shot burns a dot on the tape but subsequent shots increase the dot size, in essence burning a ring around the centre. This ring of burning turns into a ring of smoke which gently rolls upwards from the masking tape. Repeatedly shooting the tape eventually burns through it which may cause damage to your mirror but I did at least manage to capture a few on video.

Friday, 27 February 2015

Project #2: Open Source Laser Cutter, Part 1

I want to get involved with the open source laser cutter movements but there are a few hoops to jump through first. I can't really afford to have my laser cutter out of action for any length of time and with so many offerings I'm not entirely sure which system to use, there are a wide range of options and I'm not sure which one is the best so I'll want to try them all. It all leads to this logical first step.

I needed an easy way to switch controllers in and out of my existing systems so I enlisted some help from James who turn my vision into an appropriate schematic and pcb which we sent off to Elecrow for manufacturing. When the boards came back they look absolutely fantastic, black boards and white silk screen really tie into the colour scheme for Just Add Sharks.

The principle is simple; the board mimics the Leetro controller, all of the connectors sit in the same places and their functions are clearly marked on the silkscreen. Each connector is exposed with 2 plated through holes which makes it easy to patch in any controller you want to. The region marked 'Just Add Board' has no tracks running through it so you can drill holes in it and mount your own controller to our board. Solder a few jump leads to the appropriate laser connectors and you can experiment with a complete brain transplant but also switch back to a working system within minutes.

All of the JAS lasers, most of the HPC lasers and a whole host of other machines use the Leetro controller and our hope is that a board like this will help people launch into the world of Open source laser cutters. 

We're now selling the boards at cost (£20 inc VAT and Shipping) over on the Sharks website.

Say it with wooden flowers

I've been married for 7 years this week and I wanted to make something nice for my very understanding wife. I've had this layered veneer rose planned for some time and I'm pleased with the way it came out. The veneers warped quite badly once glued so you definitely need to have the clamps handy during assembly. If I were making it again I would have bigger overlaps to make it easier (svg here)


Thursday, 26 February 2015

Quality Birch Plywood from Kitronik

I shy away from Birch plywood, it's more dense than the poplar I love so it's useful for more structural things but it cuts slower so I tend to build strength into my designs. Kevin from Kitronik was telling me about their new supplier and how nice the new material was. So I bought some 0.8mm, 1.5mm, 2mm, 3mm and 6mm and I'm extremely impressed with all of it.

The last batch of birch I bought was fairly rough on the surface but it also had a fair number of voids and knots in it. Every time the laser hits one of these it doesn't cut cleanly and you have one of two choices, you can spend just as long freeing the thing up by hand afterwards or you can turn the power up and re cut it. Kitronik has really grasped the idea that quality is essential for laser cutting, I would happily pay a little bit more for quality wood that cuts first time because it's going to cost far more if I have to do it a second time. The best part of it all is that the high quality wood from Kitronik costs the same as the other stuff so there is no contest.

The second thing I've noted is how much nicer the 1.5mm ply is. On previous models I've had a really burnt and black edge and I've had to cut it slower than the 6mm stuff to make sure it cuts cleanly. I'm convinced this is because it was actually non laserable external ply, the Kitronik stuff really is laserable and uses internal glue between the layers so it cuts cleanly.

It's another rave review for Kitronik but with good reason. Get some birch (and Poplar (and Perspex (and Polypropylene))) for yourself, you'll be glad you did.

Wednesday, 25 February 2015

Blacknose Frame

In its basic configuration the Blacknose Laser cutter comes with a water pump and a 35L tub to put water in. I find myself moving my laser around quite a lot (especially while it is in the kitchen/utility room) and it is a pain to move a full tub and the work stand so I laser cut myself a frame to hold the tub onto the work stand. This frame is made from 12mm poplar and requires no glue to keep it together. The two horizontal pieces hook round the vertical legs and stop the frame from sliding off, it also spaces out the vertical slats. The slats have a slight dent in them which stops the tub slipping off the sides of the work stand.

Tuesday, 24 February 2015

Ping Pong Ball Hopper @MFUKLC

An open challenge has been set for the UK Maker Faire this year. Titled the Mega Fun UK Lasercut Challenge (@MFUKLC) the goal is to fire as many ping pong balls as possible at a target in a 30 second time frame.

Well the challenge has been set and busy or not there is no real way we can ignore it so I've had to get my thinking cap on. The competition states that we're only allowed to use an A0 sheet of material which means optimising all the parts to use the smallest amount of material possible. This is a first attempt at a ball hopper, my current launcher design has a lot of capacity but relies on a steady feed of balls so the hopper must hold as many balls as possible and allow them all out in an orderly fashion. This design is easily extendible to include as many rows/columns as required (svg here)