[sru_tx]

I have a Hobart Airforce 400 and I am trying to improve cut quality. I am running it on 220V with air from a 15gal DeWalt compressor rated at 5scfm@90psi with Motorguard M-30 submicron filter to clean/dry the air in addition to the internal filter of the hobart. The 400 specs 4.5SCFM @60psi, no problem. New consumables (tip, electrode, swirl). ICE-27 torch with a homemade guide to provide constant standoff (1/16"-1/8"?) between tip/metal.

I'm not sure my current setting knob is doing much. All the down (CCW) the air solenoid opens to set pressure. Once I turn it up enough to cut the air I'm not certain I'm actually changing the current.

Is there a way to test current?

Why am I asking?

I was messing around the other day and could get reasonable cut quality on 16 gauge when cutting straight lines using a straight edge and maintaining a swift cutting speed (but not too fast). When cutting freehand I had a fair amount of dross on the backside. I'm sure handspeed was one issue. I was experimenting with air pressure (45psi - 60+) and torch current. I just didn't see much difference. I though dropping the current down might help.


Furthermore, I was cutting out 2" stencil-shape letters and can say the look was "rustic". I'm not expecting CNC-quality cuts but I have see other folks freehand plasma work and I'm getting nothing comparable. The dross appears to be globular and on the bottom side which indicates slow torch (I believe). To further complicate issues the plasma arc occasionally drops out and I have to re-initiate the plasma. Restarts everytime. I'm not approaching the machines duty cycle.

The Hobart was a pawnshop find that was very clean inside and out. It cuts but the quality leaves a lot to be desired. I'd like to know if I should cut my losses and look for another. I haven't used it very often but would like to in future projects but don't see myself ever working with anything over 1/4" material. Otherwise my main cutting tools are a Milwaukee portaband/SWAG table stand or a 4" grinder w/ cutoff.

as always, thanks.

steve

Added pics

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image.jpeg (42.06 KiB) Viewed 1947 times

[Poland308]

Looks like maybe a ground issue?

[noddybrian]

Not familiar with that particular unit but looking at your results the obvious things are keep air pressure set as per spec for torch - there is little gain in going up or down on that - by all means try to find the " sweet spot " but do it on clean metal in a straight line test - plasma will cut dirty metal but it does not do it well or cleanly & can cause " flame outs " plus it reduces consumable life so clean the material before cutting - at least on the top side - stencil cutting is always tricky to keep a consistent cut speed around the shapes - looks like you are going way slow trying to keep a steady hand & using way too many amps - I realize this is a very small unit but dial down the amps to minimum - do a test cut in a straight line using a straight edge guide to get a feel for the optimum travel speed on that thickness - only up the amps if you " outrun " the arc strength & don't achieve constant cut - if you can find a " drag " tip for that torch get one - it is way way easier to keep steady & consistent travel - in much the same way as walking the cup with tig VS freehand without any prop - if you can't find a purpose made tip carefully file a shallow cross on the tip then clean the jet with a nozzle cleaner ( oxy / fuel thingy ) - keep this for doing difficult shapes & use a stand off / regular tip for easy cuts.

[sru_tx]

noddybrian, you've made several really good points. The one that I'm really interested in is your suggestion regarding dialing back on the current. I tried varying current and the only effect was the air solenoid kicking on at the low end to allow pressure adjustment. I saw no difference in cut quality. I'm really wondering if the current is changing or if I have a Fisher Price/Playskool potentiometer.

The other suggestions of a cleaner workpiece and solid grounding are both details I need to consider. thanks Poland308.

steve

[Bsmith]

Looks too hot and too slow. Those cicrles are where your stopping. And we never clean when we use the plasma. Speed and not stopping is the key for neat clean lines like your looking for. We dont slow down till we get to sch 160.

[Otto Nobedder]

I feel the first step is to work with clean metal. To get a feel for what your settings do, you need to eliminate variables, and dirty metal is a huge variable. Have you ever tried to TIG rusty metal? The TIG arc is essentially a plasma arc using argon ions, and the least bit of rust will screw you up.

If you can't get it working with fresh metal, then it's time to consider other possible issues.

Steve S

[sru_tx]

thanks for the input y'all!

I will start with clean metal and a solid ground and see how it goes. (sheesh, with my background electronics one would think I would know better).

s

[sru_tx]

I got a chance to do a couple of quick tests and learned quite a bit.

1. Air pressure adjustment. Rookie mistake. I was previously adjust pressure without air flow. Today I dialed the current know to zero so the air solenoid would kick on. The air pressure dropped a ton! I found that i needed to raise the pressure from my compressor and the cutter's internal regulator.

2. Current measurement. For a couple bucks I bought two low resistance high wattage resistors (0.0125 ohms/20W) and put them between the ground clamp and the working piece. I found that the front panel current numbers were dead nuts on. Geeky think to do but I really wanted to rule out Fisher-Price controls.

3. I could not get to any of my grinders but I had a scrap that was a bit cleaner than the piece pictured above.

A couple of test cuts looked much better.

Will all of those questions answered (thanks to all of the suggestions), it's time for me to lay off the caffeine and hope for a steadier hand.

[noddybrian]

Glad you got it figured - sorry we all forgot to mention pressure is set under flow ! hope to see some much improved cuts.

[sru_tx]

No worries. I've used plenty of regulators and am familiar with self-relieving vs. non. The big difference is that those applications were all low flow and the droop is very small. The 4-5scfm flow rate of the cutter was enough to throw the pressure off. I guess it falls under the "now you know" category.

[jimcolt]

To add to the good suggestions so far:

-The torch you have was made by Hypertherm. It is designed for drag cutting.....so run at full amperage and drag the nozzle right on the material for best cut quality. If you are holding a standoff while hand cutting....expect more heat input and more dross.
- If you have rusty material.....leave the rust on it and put the rustiest side on the bottom. Dross will be less as it cannot grip the loose rust as easily as a clean, dry surface. If the material is clean....spray some mig welding anti-spatter spray on the bottom side....similar to rust it makes the dross not stick.
-Cut speed.....easy on a cnc machine. Finding the DFZ (dross free zone) is critical. Keep cutting faster until dross goes away....this takes practice when cutting by hand. Dragging the torch makes this easier though!

Best regards, Jim Colt Hypertherm

[sru_tx]

Thanks Jim. Dragging w/o the standoff will make things a lot easier as there will be a better view of the working area and less stuff to get hung up on. The only reason I made a standoff fitting for the torch was a line in the user's manual stating that a standoff of 1/16-1/8 would improve cutting speed and tip life. I will go back to dragging.