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CUTTING HOLES WITH PLASMA

Q. What is the good rule of thumb when cutting a hole for a bolt to pass through? I have some 1/2" flanges to cut and the holes are supposed to have a diamater near a half inch. I don't want to cut the part only to find out the holes aren't usable. For this job, I was planning to use a Powermax65 with a 65 Amp nozzle at 65 Amps. However, I also have a 45 Amp system and FineCut consumables that I can use as well.

A. I use a one-to-one ratio for good quality hole diameter to plate thickness on steel. The key to good holes is as follows.

1. Use the lowest power consumables that will cut your thickness.


2. Make your lead in start in the center off the hole. This allows time for the torch to index from pierce height to cut height while still on the lead in.


3. Don't use a lead out. Instead, use an overburn (go about .100" past the lead in kerf, staying on the hole radius).


4. Feed rate for holes under 1" should be 60% of the feedrate suggested in the manual for cutting that thickness at the power level.

Height control is critical. You will not get consistently good hole quality without a properly functioning height control. Owner's manuals for Hypertherm's Powermax65 and Powermax85 suggest the use of the 45 amp shielded process up to 1/4"; however I actually use it up to 1/2" if I want the best hole and edge quality (although a little dross will be present). You can use the exact cutting specs from the Powermax45 cut charts on materials between 1/4" and 1/2" with the Powermax65 and Powermax85.

This info will improve hole quality with most plasma systems…..Hypertherm has technology with its HPRXD systems, when used in conjunction with the correct CAM software as well as certain CNC’s and Height controls called “True Hole” that fully automates hole cutting…..eliminating taper and start/stop dings and divots without any operator intervention.

Here are some pictures of holes cut on 1/4", 3/8" and 1/2" material using Hypertherm 45 Amp shielded consumables.

Example of a hole on 1/4" thick material

Example of a hole on 3/8" thick material

Example of a hole on 1/2" thick material

This information will improve hole quality when using most plasma systems. However, for the very best plasma hole quality, you will want to use Hypertherm's True Hole™ technology. To take advantage of this technology, you will need a HyPerformance HPRXD plasma system, Hypertherm ProNest software, and certain CNCs and torch height controls. True Hole technology fully automates hole cutting, eliminating taper and start/stop dings and divots without any operator intervention.

Hypertherm, Inc. Etna Road, P.O. Box 5010 Hanover, NH 03755 USA

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