Piercing holes

[tulsaturbo]

Is it possible to have sheetcam, using the plasma cutting tool, just pierce the center of the circle without cutting out the the circle itself? Or just pierce the center of drill cross marking?

[sadisticiron]

the only problem with that is its a pain to drill because of the molten steel is now harden and you cant drill it

[jimcolt]

You should be able to just program a tiny hole with no lead in or lead out. It is better if you just cut the holes with the plasma. I do holes with mine that generally do not need any rework, unless they are smaller than about 1/4". Here is a picture of a piece of 3/8" steel with 3/8" , 1/2" and 3/4" holes. I programmed each of the holes .010" oversize and bolts fit through nicely. These were done with a Hypertherm Powermax45 on a PlasmaCam machine, no special techniques. If I wanted smaller holes with tighter precision, I would program them about .020" undersized and then either use a drill or reamer to size them more accurately. An air plasma creates a nitride hardening that is about .005" thick....so good quality drills that are made for drilling T1 (or other hard steels) plate is required. You cannot buy these at Harbor Freight or KMart! Good drills are available from Enco and other machine tool suppliers.

Jim Colt

[tulsaturbo]

Jim, the holes I'm having to deal with are 3/16 and under. I did figure out how to just pierce holes on another thread and its been great. I do use a set of drill bits from harbor freight and they have been awesome. I use Titanium Nitride Coated High Speed Steel Step Drills and never had an issue. Its been a few of months of cutting / drilling and I'm still on the same set of drill bits.

Here is the link to the other thread:
Piercing holes

[sadisticiron]

when u pierce for a hole do you ramp down into or do it normal with a lead in and a lead out.

ive tried expensive bits and cheap bits and still have a problem drilling. but i have tried the ti bits though i might have to order some from enco

[jimcolt]

For holes:

-I pierce at about 1.5 to 2 times the recommended cut height.....so if cut height is .062", pierce at .125".

-Use a lead in that gets as close as possible to the center of the hole for 2 reasons: 1. There usually is a slag puddle on the top of the plate..if this puddle stays on the radius (contour) of the hole, it will cause the plasma arc to waver and create a divot or ding in the hole. 2. A longer lead in gives the plasma arc time to stabilize (pressure and energy take a while to ramp up), also allows the height control to index down to cut height before it gets to the contour of the hole.

-With an air plasma, it is best to have no lead out. Let the arc shut off right at the 360 degree position on the hole contour. Some software has provisions to keep the arc on for a time period after the motion stops....on steel under 1/2" this usually is not necessary.

- Cut speed on holes should be right at about 60% of the speed used to cut the outside contour of your parts....this will create some low speed dross on the bottom of the hole, but will minimize taper in the hole. Some machines will do this automatically on all holes under a certain diameter, such as 1", while other software may have to have the G Code manipulated to achieve this.

-Ensure that cut height is correct. Usually on holes under 1" diameter it is best to disable arc voltage control....allow the pierce height, allow indexing to cut height, but don't allow arc voltage height correction...as the slower speed used for cutting holes will cause the arc voltage height control to move the torch too close to the plate.

-Try spraying some mig welding anti-spatter spray on the top of the plate before cutting. You may be surprised at the improvement in hole quality. The spray usually makes the top spatter from piercing non -existent,minimizing arc wobble on holes. While you are at it spray a little on the front of the torch to keep spatter off the shield/nozzle. Do not use the dip type, and I recommend the water based spray vs silicone or oil based.

-last, but not least....use the lowest powered consumable set recomended for your material thickness for best hole quality. This will reduce cut speeds but will give you better results. If it is Hypertherm use FineCut consumables for all holes on material thicknesses under 3/16", 40 Amp shielded consumables for thicknesses above 3/16" to 3/8", 60 Amp consumables for thicknesses above 3/8" to 5/8".

The nozzle and shield orifices must be perfectly round, no nicks, dings or craters. Inspect with a 10x eye loupe....if they are not perfect, use these parts for hand cutting or contour cuts that are not as critical. The orifice shapes the arc, the arc shapes the part you are cutting. Piercing too close or too thick can damage a nozzle orifice in one pierce.

Try these things out...let me know how they work out. Also remember...all plasma torches are not created equal. Do not expect the same quality, performance from every brand and model plasma. Some have better consumable life, better gas flow control, better DC power control, and better consumable life engineered into their designs.

Jim Colt

[bogger44]

I put a point in the middle of the hole then put the point on one layer then put the circle in another layer then I just cut the point not the circle. no lead in or out just the point, the machine goes to the point pierices then goes to the next cut.

I have them labled in sheetcam 1/4" pierice, 3/8" pierice