About to cut 1/2" Plate Steel - Have questions

[engine_boy]

I have been cutting a couple of years now with my Hypertherm Powermax 1000 and am very happy with it. I am about to cut my version of the Miller Arcstation table top. As luck would have it - I have a 30" by 30" piece of 1/2" plate steel that I have been using as a welding table. This is thicker than the Arcstation, but I see this as a benefit.

I have never cut 1/2" plate before. I see in the cut chart the following info:
- 60 amp tip
- 27 IPM
- 141 Volts Torch Height Control
- 1.5 Pierce dwell

Does anyone have experience with a Powermax 1000 cutting 1/2"?
- What is the Kerf width?
- is 1.5 seconds long enough (or too long) to pierce?
- What is the best Lead In?
- Any other hints?

I am asking all these questions because I do not have any material to practice on - and really need to hit it correctly the first time (Inside Clamping slots).

Thanks for you help.

[engine_boy]

Good point - I think I can manage 4 - 1" circles - hopefully that will be enough.
Thanks

[jimcolt]

Engine boy,

I have cut tons of 1/2" plate with my 1000. Best bet....follow the specs in the Powermax1000 operators manual on the mechanized cut chart...just as Hypertherm suggests. Practice should not be needed.

Here are the specs:

Consumables: Shield..120930, Retaining Cap...120928, Nozzle...120931, Electrode...120926, Swirl ring...120925

Amperage: 60

Voltage: 141

Pierce height: .2"

Cut height: .062" (adjust voltage during steady state cut to maintain this height)

Pierce delay time: 1.5 seconds

Optimal cut speed: 27 IPM (slower may square the edge a bit, but will produce more dross. If speeds are slower, then arc voltage will have to be higher in order to maintain the .062" cut height...which is critical)


Of particular importance.....pierce height and pierce delay. If these are accurate and repeatable the nozzle orifice will stay in good sahpa and your cut quality will be constant throughout the cutting job. One bad pierce (too close or too short) and the cut quality will change due to nozzle orifice damage. Cuts should be relatively square (check torch squareness to plate) and have minimal dross.

Jim Colt Hypertherm

[PlasmaCraft]

I would have to agree with Jim on this one. I've also cut tons of 1/2" with the 1000 and as long as you go by the cut charts in the book it should be just fine. Good Luck!

[WSS]

A note on the 1" circle, depending on the system you have it may freeze the THC or slow on small circles giving a different kerf width than the rest of the cut. My table freezes the torch under 3.14' cut length (circle) and slows 60% of feed rate. I set these parameters in my machine settings and they work good for close tolerance small holes on .5' plate. Saturday and Monday I cut 80sq feet of AR500 in .5" plate using only two sets of consumables. I cut at 22.5ipm and 144v I have a good THC that starts, backs off and pierces for 1.5 secs and then goes to .08" for .5 seconds before letting the voltage take over. On small holes, voltage never takes over, just cuts at .08' above the plate. I use anti-spatter spray around the pierces, this helps shed the pierce glob and lets the torch hold true, no vibrating or chattering.

WSS

[jimcolt]

All good advice from WSS. His description of the height control functions is correct.....on a properly running height control system.

Jim Colt

[Joey]

I don't have a 1000 but I have cut hundreds of sheets of 1/2 inch plate with my 1250. My advise on heavier plate is to start with the slowest cut speed listed in the hypertherm manual. Usually the cut will be square and the slow speed dross is easy to remove. I use a small hatchet, works good. Then increase your speed until you find the compromise between cut squareness and dross levels. Just my two cents.

[engine_boy]

Thanks for all the info. I was able to do a straight line test to confirm my Kerf width setting of .080" wide - it was .081" - close enought. I cut 4 squares at 1.75" each - they came out at 1.752" wide. The corners had a little bit of wash out at the very bottom - but very good overall and certainly not enough to worry about. Overall - it worked perfectly and I saved my settings.

BTW - I am using a Torchmate system. The Automatic Torch Height Control works very nice - but the arc voltage that I have to use is always higher than what the book says - it has to be my system. For instance, the Hypertherm book states 141 Volts for 1/2" plate - I started at 175 and moved down to 172 Volts. All of my settings are significantly higher than the reference. Any ideas of why this is this way? Lose connection?

Thanks

[jimcolt]

Arc voltage that is listed in the Hypertherm manual is a reference voltage that is correct....but only if you are:
1. Following all of the book parameters exactly (lower speed will require a higher voltage to maintain the same standoff)
2. Are using new consumables (electrode and nozzle wear will create a higher voltage feedback, which causes the THC to lower the torch to achieve the desired voltage)

In about 98% of installations....there is also a calibration issue with the arc voltage. If you actually put a voltmeter from the plate to the electrode (which is what this voltage represents) you will often find that there is a difference between what your THC says the voltage is, and what the actuall voltage at the plasma arc is. This can be caused by:
1. Installation and voltage drop between the plasma system and the THC system. Most THC systems have a voltage divider that mounts near the plasma that drops the voltage of the plasma arc to a safer level....usually it is a ration of 50:1, or 25:1 of the actual voltage. This low voltage is then connected via a wire into the THC electronics for monitoring voltage and comparing it to the THC set voltage. If there is a voltage drop in this cable...the actual voltage will not be accurate.
2. A loose or poor work connection between the plasma and the plate you are cutting.....dirty table slats, small piece of material, etc, can cause this.
4. Many THC systems require a calibration procedure when they are installed as there are different cable lengths and different machine set ups. Calibration requires doing a plasma cut at a fixed height and monitoring actual arc voltage with a DC voltmeter (raw arc voltas at the plasma power supply), and comparing it to what the THC is recieving at its voltage input. On many systems that use a voltage divider there is a calibration potentiometer at the voltmeter that can make this reading more accurate.

Is it necessary to make the actual arc voltage match the THC setting? No. What is important is that the physical standoff of the torch is correct....when the standoff is correct, the voltage will be what it is!

Jim Colt ypertherm