Adding a manual Probe
I like to add a manual probe operation to all my plasma builds. It allows me to check that things are in order before starting any jobs. With the CAP 04 this is even more important, as you have a manual adjustment for torch height.
The CAP 04 has four outputs that are on of off. They are:
- THC UP
- THC Down
Both the Touch an In-Position outputs can be used as a probe in Mach3. I tried to use the Touch output, and while it worked. Getting the sensor ring exactly flush with the torch tip can be problematic. So for this first test I will be using the In-Position output.
Basic Probe Test
Here I set up Mach3 to use the In-Position input as the probe.
When the torch is above the work surface initially just the Down output is active.
As it approaches the preset torch height the In-Position output and the Down output will be active.
Once it the torch reaches its perfect position the the Down output will deactivate leaving just the In-Position output active.
The probe code used.
Keep in mind this code is meant for manual probing so that I can calculate the accuracy of the CAP 04 adjustment setting.
Probe Operation in Progress
Theory Behind this Operation
When using the In-Position output from the CAP04. It will fire even before it is in perfect position. IE the THC Down signal is still active. In order to properly use this signal as a probe input we need to know this offset.
Setting the torch cut height
What I do is move the Z axis down .005" at a time until just the In-Position LED is lit. I then slide a .06 gauge under the nozzle and the surface. I keep adjusting the knob until the In-Position only LED has the nozzle exactly at .06".
On my system this meant that the In-Position first fires with the down LED still active was at .072" and that's what I used in my script.
Due to the nature of the CAP 04, your actual measurements may vary. But are easy to test.
What is an IHS?
IHS stands for initial height sensor. It is used to probe the stock for the correct torch height at the start of each cut. There are a few different ways of implementing an IHS.
- Ohmic Sensor
- Floating Head Sensor
- Capacitive Sensor
In our case its going to be via the CAP 04 using capacitance.
Before doing anything I had to make some SheetCam post processor changes.
I am using the same probe command as I implemented in the above manual probe operation. A few changes were made but it is pretty much the same.
For some reason SheetCam was inserting an extra rapid Z command to the pierce height. If the stock was even a little warped it would cause the torch to make contact with the stock and crash.
To correct this, I modified the OnRapid post processor command, as shown here.
I was advised that you want the THC speed to match the speed of the Z axis. To acomplish this I set the THC speed to 100% and then lowered the Z velocity in motor tuning until the bouncing stops. I also raised the Z axis acceleration.
Until I can get some thrust bearings on my Z axis I changed my Z axis to:
60 Velocity and 90 Acceleration
For this test I will be cutting four 1" squares.
I will be cutting this 30 gauge galvanized sheet. This is the ultra cheap stuff you get from the HVAC section of your home canter.
I have purposely bent this piece. It is about 1/2" high in the middle.
While I should be using very low amperage consumables, the 20 Amp nozzles for the Everlast PT60 torch are hard to find and I am currently waiting for some that are on back order.
I will be using my Harbor Freight 40 Amp consumables. These are fairly old are probably past due for replacement but, for my first test I just want to make sure everything works.
I will be cutting at 25 Amps, 250IPM, 75 PSI, .15 Pierce Height, .06 Cut Height.
Lets Do This
- I start by doing a test run on some flat stock.
- I then move to the warped stock and do a test run.
- Finally I do my first cuts with the CAP 04 as in IHS.
I am very happy with the results of this cut. Here is the uncleaned cuts directly from the machine.
This is actually the back side which is the worst. I did get some little dimples at the entry and exit point that can probably be removed with a little overcut.
This is a cleaned up piece. It measures .995" on both sides so its off by .005" which in my book is very good for plasma cut with old consumables and a torch that has not been dialed in.
Full THC Test
I will be cutting this 4.5" x 1" part. Being cut from 30 Gauge galvanized steel its going to warp.
I'm using the same Mach3 settings shown above, but I did have to make one change.
Mach3 needs an active Torch On (Arc OK, Arc Start) signal for the internal THC system to work. I am not currently using one so I have to assign a pin and set it to Active Low to fool the system into thinking its getting a Torch On signal.
All I have to do is hit the THC button shown here to activate the THC.
In practice, I will use rules setup in SheetCam to turn the THC on and off as needed.
I will be cutting the part out of the same stock I used above. Its nice and warped so it make for a better test.
- I start by doing a dry run on the stock.
- I do it a second time so you can see the Z axis changing during the dry run.
- I then make the actual cut.
Notice how the part warped as it was cut. This 30 gauge stock is so thin, that even the air flow from the torch will distort it.
Other than the nipple at the entry/exit point the cut was very good.
Even the bottom had only a little dross.
After a little sanding.
This part will be used to make a height gauge for checking the THC from time to time.
With my initial tests complete, I came to the following conclusions:
- The CAP 04 does not dive in corners or when cutting small holes.
- The CAP 04 does give consistent results over several sessions.
- When the consumables wear they do not affect the cutting height.
- The CAP 04 does drop when large cut parts drop out. This is kind of moot since they drop mostly when the cut operation is complete.
- The CAP 04 will also drop as it moves towards an edge. At about 1/2" from the edge it will start to drop. This means it can be problem tic if you must cut within 1/2" or closer to and edge. Note that this also includes edges near cutouts.
Some Other Observations
- I don't currently have the Touch signal implemented but when the CAP 04 does touch something it also fires the up signal. This will cause Mach3 to raise the torch.
- Due to the size of the ring you are not going to be able to handle transitions like those found in corrugated steel.
- When using my angle fixture to cut small angle iron parts, I suspect I will need to turn the THC off. This probably wont matter, as with small parts 1/8" or thick you don't get much warping.
- If a cut piece warps and there is a cut within 1/2" or so of that piece it will affect the height of the cut.
It's time to use the CAP 04 on some real projects. This will really put it to the test. Please note this video is version 1 of the build.