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Testing out the essential Features

A project log for Underwater Plasma Cutter

For cutting metals the silent way

Dominik MeffertDominik Meffert 07/06/2022 at 17:150 Comments

Over the last few days I tested out how to eliminate the main sources of noise in the CNC plasma cutter system which are:

- The air compressor

- The plasma cutter unit case fan

- The plasma arc + airstream

First I tested out how much pressure and airflow is the absolute minimum for cutting 3mm steel which is the material that I later want to cut with the system.

I tested out multiple small air compressors and air pumps and could successfully cut 3mm steel by using a 480W "Silent" air compressor with a 40A pilot/blowback start plasma cutter unit. The air compressor has an output of around 90l/min and is likely the most silent "normal" air compressor that I could find with around 50dB of noise.

But 50dB of noise is still too loud for an apartment at night so I have to find another solution.

So, my current plan is to get multiple fridge compressors and connect them in parallel to reach the same airflow as the 480W air compressor.

Some time ago I converted a fridge compressor to an air compressor so that should not be a problem. I only have to find another sort of oil for it because the current "air compressor oil" that I am using needs to be heated up first before the fridge compressor can start up.

To reduce the noise of the plasma cutter unit I need to replace the case fan with a new fan that has the same airflow but less noise - I guess that should not be a problem.

To reduce the noise of the plasma arc + airstream I did some tests with underwater plasma cutting (with success).

I could also cut the 3mm steel underwater, even though the cutting quality was not as good as cutting in the air. I think 3mm cutting depth is the maximum for this setup, but it is just what I wanted, so it's perfectly fine for me.

I performed the latest test in a 90l concrete bucket with the plasma torch located around 10cm away from the bottom and the water level got raised to around 20cm (50l of water in the bucket).

While cutting I covered the bucket with another bucket. By doing so I could reduce the noise so much that you can barely hear the air bubbles from cutting. A nice side effect of cutting underwater is that the water absorbs the major part of the fumes from cutting so that very little of it gets released into the air. So this part of the project seems to work so far.

On the machine there are a few things left to do: 

- Finding another location for the X axis motor to protect it better from water splashing.

- Include a camera + display to see what's going on inside the bucket.

- Wiring everything up.

All essential features are already working and I think the hardest part will be building the multi fridge compressor unit.

So, I will fix all the smaller problems first and then start working on the fridge compressors.

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