Please note that some of the pictures of the CNC Construction Set plasma cutter are from the version 1 machine. But as far as the down draft system goes, nothing has changed from version 1 to version 2 of the build.

Currently, I am using this KRMx02 18" x 14" build converted to a plasma CNC.

The goal here is to reclaim this KRMx02 and replace it with the prototype CNC Construction Set plasma cutter.

 

The KRMx02 made one great plasma cutter. I used to fabricate a lot of small parts.  I need a little larger working area and the ability to experiment with THC systems in the future.

 

Down Draft Cage

Front View

 

Rear View

I created a box or cage that sits under the machines cutting table.

The cage is roughly 28" deep, 16" wide, and 11" deep.

The material is 1/4" cement board.

On the bottom near the front of the machine I bolted an 8" flange 

 

For now the cut parts of the cage are just set in place.  The two side sections actually hold the front and rear panels in-place.

 

Power Source

To pull the draft, I am using a Harbor Freight 8" ventilator. It has two settings of 1590 and 1380 CFM's.

I used the same blower on the KRMx02 plasma and it worked great.

 

Update 3/8/2018

Decommission of the KRMx02 Plasma CNC

Before moving forward, I have to remove the KRMx02 Plasma CNC system.

I decided to dismantle the plasma additions to the KRMx02 as I remove it from its current station.

Cleaning plasma dust is a dirty job, but at least its pretty much contained inside the KRMx02 downdraft table.

With the KRMx02 plasma parts removed and the CNC cleaned up, I can move it elsewhere in the shop.

The Ohmic sensor and floating head will be removed and eventually added to the new plasma machine.

 

The Space

The space is all cleaned up and ready for the new machine placement.

This machine will give me twice the cutting area than the KRmx02 plasma build, yet takes up less space overall.

Note that version 2 of the build gives me a

15" x 25" cutting area.

 

Update 3/21/2018

Before showing the updates, I did have a chance to make some initial cuts using the plasma CNC.

 

Vents

With a T connected to the exhaust side of the blower, I positioned the CNC until the top of the T was aligned with the bottom of my main vent duct.

Since the machine is raised and lowered off the ground to move, I added a simple slip joint that can be lowered onto the T.

While not very attractive, it does work nicely.

I used some Gorilla tape to hold the slip joint in place.

Note

This is not the proper way to vent the downdraft table.  With the blower mounted close to the table, it will blow dust out every single leak in the duct system.

In time you will get plasma dust around all the joints. 

The proper way, is to mount the blower as close to the exhaust duct point where it exits be building.  This means its pulling the dust and any leaks will just add some negliagable reduction in suction.

I have a very large 3HP blower that I will eventually mount near the ceiling where the ducting exits the shop.  This will also allow me to add dampers and the ability to pull from multiple tables.

 

Spark Arrestor

The cement board I used to enclose the downdraft table does not seal very well and I was getting some large burning sparks exiting the machine and making its way into place that made me a little uncomfortable.

I created this metal screen out of parts purchased from my local home center.

The metal screen and sides held up very well but the corner pieces were made from plastic did not.

I added some steel guards with a machine screw that would also act as a handle for easy removal of the screen for cleaning.

The screen sits about two inches from the bottom of the down draft. It rests against the sides and is held tightly in place by some wedges that push the two ends against the screen.

How did it work?

As you can see it catches all the large stuff. This also makes cleanout very easy.  On my final table I will add a small access door on one of the ends to remove the screen and to retrieve any small parts that fall through.

 

The Table

For now I am going to use the decommissioned table from my KRMx02 plasma cutter.

It's smaller but will work just fine in order to perform some more tests.

I added some supports to the inside edge of the extrusions.

Some angle was placed accross these supports.

I also added some thin sheet so that my down draft would be concentrated to the smaller table.

The table sits on the supports, but is clamped to the front extrusion with some drop-in Tnuts.

 

How well did it work?

 

Conclusion

The machine is pretty simple right now. No initial height sensor or THC, but those will come in time.  My next step is to build the perminant table top.