Sorry about being off topic, but this forum is amazing for the knowledge on it so its time to pick your brains. I just picked up a Hobart airforce 250A plasma cutter for a pretty good deal ($625). I changed both the consumables in the tip and was cutting some 1/4 plate, I cut about 6 inches of it and then it wouldnt cut through all the way anymore. Is that as long as the tips last? It was doing a great job until then. I know 1/4 may be a bit thick, but it sure did a nice job to begin with. Thanks for the input.
Well, I'm no expert, but are you holding the tip to the metal? As in making contact while you cut? You are supposed to hold it about 1/8" away from the material youre cutting. Otherwise tip will clog up from heat and metal being cut.
This the machine you have? http://www.hobartwelders.com/products/airforce250a.html First problem I see is you are cutting material thicker than your machines maximum cutting capacity. Your on board compressor cannot deliver enough airflow AND you reach the upper limits of your duty cycle in a very short ammount of time.
I know I'm overworking the machine, but it worked great at first. I don't know anyone who has one local to even get an education on it.
Try cutting some thinner scrap and see if it works. If it doesn't stop until you do, you're just cutting stock that's too thick.
This is exactly what the problem is, That machine has a 35% Duty cycle. That means the internal transformer/inverter will overheat and shut down or the electrical wave pattern and frequency will break down and become erratic. When this condition exists the cut quality will seriously degrade. Also of note, the harder you push this machine the shorter it's lifespan. This machine was primarily designed for mobile installers and home hobbists doing light gauge sheetmetal work and minor structural work. Please read the PDF it explains alot more. http://www.hobartwelders.com/products/pdf/spec_sheets/211798_AirForce250A.pdf
I don't have a Hobart, but have a Blue-point (by Snap-On) smaller unit.... I bought the unit used over a year ago.. the first time I used it cut just fine for about a foot, then stopped cutting all together. It wouldn't make an arc at all... when checking over what I thought could cause this, I found the wire on the safety switch for the air pressure was loose. Tightened this up, and haven't had a problem since. I realize your unit may have an on-board compressor, but it should still have some sort of safety switch that interrupts the elec signal if there is not enough air in use. may not be your problem, but could be something to check.
I didn't hit the duty cycle, it just wouldn't pierce through the steel all the way. It still cycled ok, maybe I was close to it shutting down though. I wasn't planning on using it on heavy stock, but I figured I'd try it.
I'm not sure you understand the term. Yes, there is a thermal switch in some machines that will shut down if it becomes overheated, but that isn't what I am getting at. [FONT=Times, Times New Roman, Bookman, Schoolbook, Century Schoolbook]Duty cycle is a welding equipment specification which defines the number of minutes, within a 10 minute period, during which a given welder can safely produce a particular welding current.[/FONT] [FONT=Times, Times New Roman, Bookman, Schoolbook, Century Schoolbook]For example, a 150 amp. welder with a 30% duty cycle must be "rested" for at least 7 minutes after 3 minutes of continuous welding. [/quote][/FONT] Taken from this website: http://www.zena.net/htdocs/FAQ/dutycycle.shtml [FONT=Times, Times New Roman, Bookman, Schoolbook, Century Schoolbook][/FONT] [FONT=Times, Times New Roman, Bookman, Schoolbook, Century Schoolbook] Plasma is odd. The range in which it is designed to operate can be very limited. The more expensive a machine is the more flexibile it will be at cutting various thicknesses and materials. Your machine is good for what it was designed for, outside of that range you should break out your Victors.
Check that you have a good ground connection too. If you're cutting hot rolled steel plate, it'll have a dull dark grey ugly coating on it. Grind that coating off down to shiny steel where the ground clamp makes contact. Another thing that might help is to make sure you're plugging the unit into a good outlet into a circuit that's not overloaded with other stuff already -- preferably not very far from the circuit breaker panel. But it sounds like you're probably trying to cut something thicker than the machine was meant to cut. When you go beyond what the machine is rated, the "consumables" get eaten up a lot faster. If you can keep a small gap between the tip and the metal plate, that'll make the consumables last longer. My Miller 375 cuts 3/8" plate no problem, and it'll cut 1/2" very slowly, but the tips don't last very long cutting the 1/2" stuff. Once in a while I'll have a lousy ground connection and that seems to ruin the tips pretty quickly too.
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