Wednesday, August 27, 2014

Tool to set tungsten length

This tool sets the "stick out" distance between the end of the electrode and the gas cup.
A simple, quick gauge is made from a coupling nut, bolt and regular nut. I sanded the end of the bolt and coupling nut  to make a good flat surface and then cut a slot in the side of the coupling nut for visibility. Dial calipers are used to set the distance of 6mm.
Before starting a build cycle a fresh tungsten electrode is installed. This ensures a stable current flow directly off the tip. The electrode is a consumable and should be inspected and cleaned often.
The wizardry in getting this welding process to function is the metal feed wire needs to hit perfectly in the center of a molten puddle of metal ... for many, many hours !
A pending design improvement is a vernier adjuster for the feed wire angle.

Tuesday, August 26, 2014

It's getting better all the time

Weld sample # 17
Resolution is starting to improve. With better control of the process it's possible to turn the heat and wire speed down which is improving the weld quality and constancy.
This is 5 layers.
Finish height measures 7.4mm ... yet ... should be 6mm.
Some tweaking is needed.

Tuesday, August 19, 2014

Finally ! ! ! Welding again ! ! !

16 May was the last major welding session. Back then I was trying to knock out a decent piece to display at the Makers Faire.
Today is going much better. This is my second attempt after 3 months of mods and updates to the machine.
Definitely in the ballpark now. The stack height measures 20% too high after five layers. The weld is decent and complete.

Wire feeder is working

A few different brands of stepper drivers were purchased for evaluation. All have the same general output ratings. I decided to try the tb6560 first simply because it was the largest physically sized board thus has the appearance of delivering the most power.
It hooks up easy enough.
The first good sign is the board and driver run in the proper temperature range and within a few degrees of each other. Pulling power on the wire is much stronger now. With the original configuration I could squeeze my fingers pinching the wire coming off the spool and stop the motor. Now I can't.
A special THX to John Saunders @ nyccnc for his youtube video ... a big help in figuring out the UNO to tb6500 schematic and code.

Here's the code and driver switch settings for this round of testing.

Code: 10K ohm Potentiometer speed control
arduino UNO to microstep driver tb6560
CLK+ / step / pulse+  wire to arduino pin 9
CLW- / step / pulse-  wire to ground
CW+ / direction+  wire to arduino pin 8
CW- / direction-  wire to ground
potentiometer end wire to arduino +5v
potentiometer end wire to arduino ground
Potentiometer center wire to arduino A0
enable+ to nothing
enable- to ground

int sensorPin = A0;
int sensorValue =0;

void setup() {
  pinMode(8, OUTPUT);  //direction pin
  pinMode(9, OUTPUT);  //step pin
  digitalWrite(8, LOW);
  digitalWrite(9, LOW);

void loop() {
  sensorValue =analogRead(sensorPin);
  sensorValue= map(sensorValue,0,1023,3600,1);

Switch settings for tb6560 stepper driver
SW 1 = ON
SW3 = ON
S1 = OFF
S2 = ON
S3 = ON
S4 = OFF
S5 = ON
S6 = ON

Monday, August 18, 2014

Tidying up a bit

While waiting for the drive board to arrive the build plate was improved by addition of leveling screws and hold down clamps.
Even though this is a welding machine having a wood base has proven to be a good idea.
The wood is a means to easily attach a thin sheet of metal to complete the weld circuit. Long wood screws are used as the temporary hold down.
This metal sheet can be removed from the model after the build is completed.
A section of a recycled oak table top is cut to size and then is covered with an aerogel blanket to prevent fire. Next up is a layer of fire bricks with the metal sheet topping the stack.

Wednesday, August 13, 2014

Testy Testing

Having a speed control for the wire feeder is looking promising.
Although ...
The motor driver is not quite sorted out yet. The chip is overheating while the motor is stalling trying to push the wire and staying at ambient temperature. i.e. the system is not balanced. The same motor had enough power and ran at proper temp when driven by the TinyG board.
A tb6560 chip is the next experiment. It is a common part in many stepper drivers. There is a plethora of pre-made drivers with this chip so there is no reason for me to build a board from scratch.
The biggest cost is the time delay waiting for parts to arrive.

Using CAM software to create an additive tool path is working well for simple objects. The lines of code is about one tenth of a typical model slicer output. This is due to the fact this CAM software can write code for G03 output (circular interpretation). I haven't seen any of the 3D model slicers use this shortcut. A typical slicer cuts the model into a series of lines so something like a small circle can have a big bunch of line segments which can often be seen in how smooth the tool moves.

Thursday, August 7, 2014

"d'oh!" ... A Homer moment

O​h man am I embarrassed.
Before hooking up the wire feeder to the main control board I thought it prudent to check for voltage output at the terminal. I started checking for voltage by probing the top of the terminal screw with no wire attached and found a dead circuit ... or so it seemed. Many hours were were spent looking over the firmware code, investigating the schematics and tracking the circuits on the board to no avail. Everything looked correct but still no voltage to the top of the screw.
While out for a walk it occurred to me to install a short length of wire into the terminal and then clip a volt meter to the wire.
Suddenly there is proper voltage at the coolant pin ???
It turns out that when the screw is backed out and no wire is in place the top of the screw is not conductive. A "gotcha" that wasted at least 10 hours.
 It seems odd that the top of the metal screw has no conductivity without pinching a wire but that was exactly the problem.
The wire feeder is now hooked up and turns on / off as it should.

Now back to trying to weld.