Posts tagged #grunblau

Plasma CNC Water Storage System

I finally had time to assemble all of the parts to the water storage system for the water table. I ended up using kegs as water storage containers since they're designed to handle the pressure. The system uses compressed air to force the water up into the table from the kegs.

The good news is that it works well! It fills in a few minutes and drains in about 10 minutes. I'll probably end up welding a bung for the drain to increase the water flow or modify the tap to increase the output diameter. But for now it's functional. And I definitely need to add a baffle on the outputs; the water splashes up when you start & end the filling process.

The bad news is that it only works with the kegs vertical. And unfortunately they are about 1/2" too tall to fit underneath the stand I built. I have two options: 1) cut big holes in the top sheet to fit the tops of the tanks, or 2) raise the whole table about 1". I haven't decided yet which approach to take.

Also, there were a few drops leaking from underneath the 2nd time I filled it. i'll have to check it again to make sure there's no additional pinpoint leaks I missed in my previous tests.

I made a video walking through how it all works:

Posted on April 13, 2014 .

Plasma Water Table

The second step in preparing the Grunblau Platform CNC was designing a water table insert.  I wanted something fairly light that I could take in and out to clean by myself, but sturdy enough to handle a significant chunk of steel sitting on it.  I chose to build a water pan out of 18 gauge steel.  The pan is supported underneath by the cross braces on the Platform table.

I started with a flat sheet.  I cut the corners out with the plasma torch by hand, and then I bent up the sides using a metal brake I built attached to my jig table:

Next I test-fitted the bent-up bed into the Platform CNC to make sure I had it the right size.  I determined that I had to trim a bit off of the top edge of the table, but otherwise it fit well.

I then took the scrap bits I cut off to form corners to weld in.  This is the first time I welded 18 gauge steel, so I chose to double weld both the front & back sides of the seams.  This ended up making the task harder than necessary:

And then I had to test the table for leaks.  I took it outside and filled it up with water.  I found a couple of leaks that were easy to fix with a second pass of the Tig welder:

The next step was fabricating the support braces to fit inside the table.  I chose a simple design based upon material I already had available:  I cut slots in three angle-iron pieces, and trimmed 2" wide slats out of the remaining 18-gauge steel sheet. Then I bent the slats to go between the slots.  This makes it very easy to replace the slats as they get damaged with the plasma cutting:

Finally, on top of the insert I added a sheet of 9-gauge expanded metal.  The theory of this is the expanded sheet has raised points minimizing surface contact area that the plasma can cut, while at the same time providing a great support structure for the material to be cut.  Moreover, this expanded sheet helps protect the underlying slats extending their lifespan.  And when the expanded sheet gets too damaged, it can be very easily removed & replaced:

I am still running tests, but so far this configuration is working very well.  In the next article I will describe the water storage & air pressure forced feed system used to fill/drain the table and show some of the test runs.

Posted on March 29, 2014 .

Plasma CNC Torch Holder

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Last year I purchased a Grunblau CNC table.  I wanted to use it for a number of kinds of fabrication techniques, including milling, plasma 3d printing and laser cutting.  

I decided to start with plasma cutting. To adapt it for that I had to create a mounting mechanism for the plasma torch holder, as well as a water table insert.  

First I created a base to set the CNC table on that I could also use to store the electronics and water storage.  Since I wanted it fireproof, I fabricated the table out of metal tubing and covered it in 12 gauge sheets:

Photo Aug 16, 8 19 36 AM.jpg

For the torch holder, I investigated several design approaches.  The height of the plasma torch above the surface is managed by the Torch Height Control (THC) module based upon the plasma current.  Furthermore,  the Z home position is determined via a touch-off from the metal plate triggered by an ohmic sensor.  Theoretically this means the torch can be mounted statically to the Z axis.  However I decided on a spring-loaded coupling with a small amount of travel attached to a passive rail to maintain alignment.  This provides a margin of error in case the ohmic sensor failed.  And as a secondary backup, magnets mount the torch holder to the backing plate.  If the torch binds on something, the magnets disengage and the torch disconnects from the z axis.  Here is the initial design I came up with:


The Z axis mounting plate has a grid of mounting holes on it.  I first designed a magnetic mounting plate to attach to this with four neodynium magnets.  This way the same plate can also be used for other attachments:

Photo Aug 31, 6 02 18 PM.jpg

Then I added alignment pins to keep the torch holder in place laterally.  To adjust the fit precisely I machined my own adjustment spacer:

Photo Sep 08, 11 45 17 AM.jpg

I simplified the design further by adding a second carriage to the rail and reversing it such that the rail attaches via rings to the torch and the rail itself floats via tension springs:

Photo Aug 31, 6 00 07 PM.jpg

Above the rail I mounted a proximity sensor so that if the torch extends too far into the plate the sensor is triggered, causing a software stop.  

Photo Sep 08, 11 44 49 AM.jpg

The other challenge was to figure out how to mount all of the connecting wires to the torch.  The THC controller includes a small wiring hub that goes near the torch to minimize noise between the sensors and the controller. I decided to mount this on the underside of the bracket behind the Z-axis.  Furthermore, I switched to a larger cable carrier with links that hinge open so that it could accomodate the torch cable, which is very thick.  I had to add a spacer between the cable tray and bracket since the new larger tray has a much larger bend radius than the original one:

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Finally the ohmic sensor wire runs down to the tip of the torch.  I used special wire that is chemically resistant and handles high heat to protect it better from the slag:

Photo Sep 18, 10 57 16 PM.jpg

Initial tests of the carriage under motion showed that the torch holder held firmly and there was no binding of the wires.  Moreover running with the electronics connected showed the sensor were properly functioning.  I tested the ohmic sensor by shorting between the ground of the frame and the torch head with a screw driver.

Part 2 will cover the water table insert and initial test of the full system.





Posted on March 8, 2014 .