Standoff Height & Speed

[suryak]

I Have a Cutmaster 81 with home made plasma cutting table. I usually use 60 Amp Tips for cutting 3 mm, 5 mm, 6 mm, 8 mm & 10 mm sheets. The gas pressure maintained is 80 psi. I also have a Automatic Voltage Controller to adjust the standoff height.

Can anybody suggest the cutting speeds & voltage for above?

[peepers]

I use a Hypertherm Powermax 1000 myself so I dont have any real input on the Cutmaster 81 other than a chart in a manual iI have. I had considered buying one before I went with Hypertherm. I would assume it would be a good starting point. I found this in the Cutmaster 81 Manual. Here is a link to the manual I have. http://www.thermadyne.com/IM_Uploads/Li ... 0X4641.pdf
Page 54 and 55 have the cut speed, volts, and height.
I hope that will help out.

[Wine Country]

When I first used my Dynatorch table, I went with the plasma manuals settings for standoff and speed. I had nothing but
torch crashes, and became totally frustrated. I spoke with the lead engineer at Dynatorch and he said I need to slow my speed by 25% to %30 percent,and increase my arc voltage 5 to 10 volts. It has worked fine since then. I do tweak the speed and arc voltage by a small percentage to fine tune things and save them in my cutting library. I am using a Hypertherm Hypermax 1000. I found out there is a learning curve, but it seems to go quickly,especially when parts start turning out nicely
and confidence is built up. Marty

[suryak]

thanks for the help guys. I already have the manual & the speed chart mentioned in it is no good. Get a lot of dross & bevel with those settings. Will try reducing the speed by & increasing the voltage. Will let you know about the results soon.

Thanks for your response.

[Wine Country]

Hypertherms website mentioned that the vertical lines in the cut kerf created by the torch should be about 15 degrees,
with the top leading the bottom by this amount. I find this figure to be pretty accurate at judging proper speeds,as most of my cuts turn out almost dross free. They also mention "slow speed dross" flakes off easily,and "high speed dross"needing to
be ground off. You will find out soon that running your machine will be rewarding instead of frustrating as I did. I am sure all of us on the forum have been in your spot. My day is not complete without checking out the site. Marty

[jimcolt]

Here's the way to adjust speed and arc voltage:

1. Most air plasma systems are designed primarily for hand cutting.....for hand cutting applications, the speeds published in the manual will work.....although often will cut with some bevel. Since the human hand has many axis of manipulation....it is easy to tip you hand a bit and compensate for the bevel. I guarantee the maximum cut speeds listed in all of Hypertherms air plasma system manuals are achievable! Over 95% of air plasma systems are used for hand cutting...so many manufacturers do not pay much attention to the machine cutting applications.

That being said...this thread talks about cnc mechanized cutting. In the Hypertherm manuals there are two speed columns- maximum speed and optimal speed. Optimal is the best starting point for mechanized cutting.....Maximum is the absolute max speed that allows the arc to sever a particular material. If you do not have a Hypertherm system....then reduce the cut speed by about 25 to 30% of the suggested speed for mechanized cutting....this will provide a resonably square cut edge with little or no dross (more about dross later), assuming everything else is correct.

2. Most plasma system manuals also list suggested arc voltage. Arc voltage is proportonal to torch to work distance, or standoff. A higher voltage at a given speed will make the torch run higher off the plate. If the voltage is too low, the torch will drag on the plate. If the torch is too high....expect a positive bevel on the part you are cutting. Getting the arc voltage based height control set correctly....is a balancing act between cutting at the best speed for your plasma or process level.....then adjusting the voltage setting on your height control while cutting at that speed....to achieve the manufacturers suggested standoff height. Generally for cutting thin gauge steel al 40 amps with a Hypertherm plasma...this height will be at about .060" (about 1/16").....

A couple of other comments about the height control: The height control reads the arc voltage between the electrode of the plasma torch and the plate. If the plate warps up closer toward the torch during a cut.....the length of the plasma arc gets shorter....this means the voltage gets lower.....when the height control looks at the voltage reading and sees it is lower than the selected (by the machine operator) voltage....the thc moves the z axis motor up, moving the torch away from the plate until the voltage is correct. This process can be affected in many ways.....if you decide to reduce the cut speed in the middle of a cut...while the height control is active....expect the torch to move closer to...or crash into the plate. This is because the plasma torch is still operating at a fixed power level...you have slowed the travel speed...so the plasma arc is burning a wider kerf and effectively has to reach further (arc gets longer, voltage gets higher) to find a path from the electrode to the plate...the thc reacts by moving the torch closer.

So....if the manufacturers manual says to cut 10 gauge steel with a 40 amp nozzle at at optimal speed of 60 ipm at a vaoltage setting of 115 volts......and you decide to slow down......you must increase the arc voltage in order to maintain the physical standoff between the torch and the plate.

3. Once you have established a speed and voltage that give the best edge angularity and maintain the manufacturers recommended standoff height.....if the cut looks good to you.....write down all of your settings....they will work next time! If the edge looks good....but has too much dross....do the following: a. do a series of test cuts increasing (yes, increasing the speed will eventually reduce or eliminate dross with plasma) the speed 5 or 10 ipm at a time. You likely will have to also reduce the arc voltage with these increases to maintain the correct standoff. Eventually you will reach a dfz (dross free zone) where the dross is mostly eliminated.....you will likely still see dross near corners or fine detail where the material gets hot...but on long straights the dross will go away. This is assuming that you have a system that is capable of cutting dross free (some plasma systems just can't do it!), and that you are using the correct consumables and power level for the material you are cutting.

Happy cutting. Jim Colt Hypertherm

[Wine Country]

Jim, I thought your name sounded familiar, and your post was very professional. I have another question you can
answer. Why is the cutting capacity of a machine torch almost 50% of a hand cutting torch? Even when the same
consumables are being used. Marty

[jimcolt]

Even though the Hypertherm hand and machine torches for the air plasma systems are internally identical....and even use the same consumables....we rate them differently when used by hand or by machine. The thicker ratings are for hand cutting...and lighter ratings for machine...heres why:

Pierce capacity: While both hand and machine torches have the same power.....a torch in your hand can easily be tilted to allow pierce blowback to miss the front end of the torch. If this molten metal sticks to the shield and gets into the shield orifice....it will cause internal arcing that will damage the consumables on the first pierce. In mechanized applications the torch is fixed perpendicular to the plate.....and while better torch height control systems can set a higher pierce height....the blowback tends to hit the front of the torch. The max mechanized rating on Hypertherm torches is what you can safely pierce the plate at with the torch at pierce height...but perpendicular to the plate.

Duty cycle: Air plasma systems...designed primarily for hand cutting are in a competitive market. Cut thickness, cut speed, consumable life, size, weight and ultimately purchase price are the driving factors for our customers. Hypertherm competes in this market with Thermal Dynamics, Miller, Lincoln, Esab.....and a few dozen others. None of these machines are continuous (100%) duty cycle like our line of industrial plasma systems are......because to make the same power with the ability to cut continously would add size, weight and cost. The human hand gets tired.....it is difficult to exceed the duty cycle rating of the major brand systems when cutting by hand. Hypertherm systems have the toughest duty cycle ratings...the Chinese imports are by far the worst! With a machine mounted torch....you could easily exceed duty cycle if you cut thicker material...as the cut speed is slower and the arc voltage is higher.....and arc current is higher. The rating for machine use is adjusted for this reason.

With all that in mind....I have a Powermax45 in my home shop on a PlasmaCam machine. The 45 is machine rated at 3/8".....I often do 1/2" with piercing....have occasonally done 5/8"...and have edge started and cut 1". I don't cut production quantities at these thicknesses...if I did I would exceed the duty cycle....which would cause a thermal switch to shut down the power supply until it cooled adequately.

Hope that answers the question about the different ratings between hand and machine torches!

Jim Colt

[Wine Country]

Thanks Jim , that answers the one mysterious question I have had for quite some time now. I often do art and signs that
take 35 minutes of cut time. My Powermax 1000 performs flawlessly, with only the cooling fan kicking in from time to time.
5X10 Dynatorch table with T60M . Marty

[suryak]

Thanks for all your replies guys.

The speed chart given in the manual is of no use. However, there is point mentioned in the manual that you have to maintain a standoff height if 3-6 mm between the torch & the plate. I asked the machine supplier how to do it. They told me to make a guage of 3 mm, turn off the automatic height control & with the help of the gauge maintain the torch height from the plate at 3 mm. Start cutting & observe the voltage. The voltage observed is the required voltage.

Used this method & found the voltage for all my thicknesses ie. 3mm, 5mm & 8 mm. Turns out my quality has improved a lot using these voltages. I'm attaching the chart below for your reference. Let me know if it works for you too:

Thkness---ARC Voltage---Pierce HT---Pierce Delay---Amp---Comp Air---Cutting Speed
3 mm---88 V---0.15 inch---0.5 Sec---60 A---80 Psi---1300 mm/min
5 mm---97 V---0.15 inch---0.75 Sec---60 A---80 Psi---860 mm/min
8 mm---104 V---0.15 inch---1 Sec---60 A---80 Psi---500 mm/min

[jimcolt]

It is very important to keep records for plasmacutting.....once you find what works on your particular machine....it will likely work the next time you are cutting the same material, provided all parameters are set correctly!

One of the things I really like about my PlasmaCam DHC2 machine....is with the torch height control. Instead of setting an arc voltage....you set a physical standoff height....andwhile it tracks that height using arc voltage feedback there is no "trial and error" experimenting with raising or lowering the voltage to get the torch height exactly right.

You set the pierce height, set the cut height, click the tab for check height before cut.....and the systems finds the surface of the plate, retracts to pierce height, fires the torch, pierces, rapidly moves to the cut height then starts moving....in the first few seconds of the cut the cnc samples the actual arc voltage and locks on to that voltage as the correct height.....it works flawlessly, the torch is always at the right height regardless of the chosen cut speed. I use the height control on 26 gauge up to 1" material without issue. I am using a Hypertherm Powermax45......and yes, I edge start and cut 1" occasionally.....I pierce up to 5/8" with this 45 amp plasma!

Jim Colt

[Loyd]

Cutting 1" with a 45amp machine! Jim, You are the man!!
Loyd

[jimcolt]

I wouldn't recomend cutting 1" on a regular basis with a 45 amp machine....definitely no piercing, speed is about 9 ipm.....lots of dross.....although it chips off easily, and the edge quality is very vice. The last time I did it I was cutting the wedge for a logsplitter......picture attached.

Jim