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CNC Plasma Cutting

Since we will be working primarily with 1/4 inch steel on a 74ft boat, we selected a Hypertherm Powermax1000 with a 50 ft umbilical between the machine and the hand torch; part number 083179.  The price was just over $2,400 with shipping from www.bakersgas.com in early 2008.  We don't need 50 ft of umbilical for the CNC table, but it will come in very handy when working out on the boat.

Plasma torches require lots of dry air, or they will not cut cleanly and they will burn up the expensive consumables faster.  We already had 5 HP compressor capable the required of 6.7 cfm at 90 psi, however we added a low cost "3-in-1 Refrigerated Air Dryer" unit from Harbor Freight for $300. 

Conversion to CNC


(1) Hypertherm plasma hand
torch opened up.
(2) Micro switch for torch trigger
 

(3) Add a wire to each side.
 
(4) Notch the handle and route
the wire out.

(5) We strapped the wires down
along with the cable cover.
(6) Kay made a cover for the
plasma torch too.
(7) The wires are neatly hidden
away under the touch cover until
they are needed.

We purchased a used CNC router table and got it into working condition, and now it's time to convert it to for use with the Hypertherm.  They make "machine torches" specifically for CNC tables but the hand torch is easy to adapt so there not need to buy another torch. The first step is to modify the torch trigger so that it can be trigged by the CNC machine instead of manually.  Because our CNC machine currently dives a router, there is already a 110 volt AC power line coming from a relay in the control box that lets the controller power on and off the router.  We are simply going to unplug the router from the end of that cord and replace it with an AC coil relay switch.  So when the controller powers the line, the relay will close two normally open contacts just like the micro switch inside the Hypertherm's hand torch.  So all we need to do is and two wires to the hand torch on either side of the trigger switch that connect to the AC relay.   It's important to note, that the coil on this relay is AC.  Most relay coils are DC and the switches in the relay can be used for either AC or DC.  So just because you see 120v AC on the relay, does not mean that the coil is 120v AC.

Maintenance and Supplies

The Electrode and Nozzle are the most frequently replaced.  As the nozzle wears the plasma arc will get wider, more dross will be produced, and the cutting kerf will get wider. Check the hole in the nozzle and replace it when the hole is oval or has a notch in it. Even if the hole looks good, you can try a new nozzle to see if the cut quality improves.


Hypertherm, T60 Consumables

The electrode has copper surrounding a hafnium core that is slowly burned away.  Once the hafnium erodes back into the tip the arc will start burning the copper.  The arc will have a greenish color and the plasma stream will be wider, which will quickly eat up the nozzle.  When replacing the electrode is a good bet that the nozzle needs to be replace too.

The Swirl ring only needs to be replace if it has noticeably damaged or if you have replace the nozzle and electrode and the cut quality is still poor.  When you do change the Swirl ring, use silicon grease to lubricate the rubber o-ring.

The Shield gets replace only when the hole is no longer round and the Retaining cap is only replaced when physically damaged.

The T60 torch has a separate set of consumables for gouging which is cutting the surface without cutting all of the way through the metal and fine cut for accurately cutting thin sheet.  For more details go to www.hypertherm.com and fine the Service and Operator manuals under the Library tab.

Consumables Part Number Price from www.harrisweldingsupplies.com 
Electrode 120926 $31 for 5
Nozzle/Tip, 60 amp 120931 $23 for 5
Nozzle/Tip, 40 amp 120932 $21 for 5
Swirl ring 120925 $12
Shield    120929 $10
Retaining cap 120928 $23

 

 

 

 

 

 

Tips for extending consumable life

  • The pierce height of the should be as far above the plate as possible without causing a misfire.  A misfire is when the touch is too far from the plate to start an arc.

  • Always start and stop the cut on the plate.  Do not run the arc off the edge.

  • Make sure the ground is good, especially on thin sheet.

Cut Quality

  • If the cut is not 90 degrees to the surface check the height of the torch.  The shape of the cut will match the shape of the arc.

  • With a normal clockwise Swirl ring the right hand side of the arch as you cut away from you will be more vertical and cut a straighter edge. So Right is Wight.

  • A little dross or slag is normal on the top surface. Dross on the bottom is a sign that the cut rate is too fast or too slow, or the consumables are worn.

  • Arc voltage, feed rate and torch height are all inter related. When cutting faster than what is recommended in the cut charts you need to lower to voltage, and when cutting slower that recommended you need to increase the voltage.

  • It is best to use Nitrogen as a plasma gas when cutting aluminum and it will increase the consumable life however air will work fine if the highest quality cuts are not necessary.

  • Routinely test the pre-flow and cut-flow gas pressures.  Not have the proper flow will quickly destroy the consumables.

Hypertherm Cut Charts