Questions from a beginner...

[safe60]

Hi all. I have a couple of questions about the correct way to calculate cutting toolpath. I have experience in milling toolpath but not at all in cutting, so excuse me if my questions are of very low level.

My question is related to start/stop of the torch. In milling, the spindle can run even if it's not in contact with the workpiece. This usually happens during rapid motions. In cutting I think this is not absolutely true. The torch must be started at the beginning of the path and stopped at the end. My first questions are :

When is the good time to light the torch ? I mean.. before activating the torch, the exact cut start position must be already reached or there is some delay of some kind so it's better to light the torch in advance ?

Torch deactivating is another issue. When is the correct time to turn off the torch ? I can imagine that the last position must be reached first but I don't know if there is some delay in shutting down the torch that could damage the piece if the torch stay at the same distance while shutting.


Thi info will be very useful for me in order to put cutting support in the program I have already written for milling. Sorry if the questions are so simple for you guys, but I have no experience in cutting technology.

Sandro

[jerrybarrett]

I always set my machine to have a LEAD IN beginning inside or outside depending on part For example if cutting inside circle convert on inside of drawing The thinner the material the shorter the LEAD IN can be . On 3/8 to 1/2 " plate i set at about 3/8" distance. Jerry Barrett

[safe60]

thanks for the suggestion. I had not thought to a lead in feature. I will put it in my code. A lead out is also reccomended ?

Sandro

[AnotherDano]

thanks for the suggestion. I had not thought to a lead in feature. I will put it in my code. A lead out is also reccomended ?

Sandro

I set my cuts to end 1/2 the width of the kerf at the end.
Also, if you can angle the cut-in to flow into the cutline, the less-abrupt direction change will give you a smoother cut.

[safe60]

Many thanks for the suggestions. Is the kerf the witdh of the cut ? I'm not familiar with cutting technical terms. I quickly made a google search and I got some images but I would liket be sure to not misunderstand the term.

How wide is the kerf usually ? Does it depend on air pressure or Amps ? And which is the distance between the torch and the metal to be cut ? It's constant during the cut ? Ok ok.. too many questions.

Sandro

[AnotherDano]

Many thanks for the suggestions. Is the kerf the witdh of the cut ? I'm not familiar with cutting technical terms. I quickly made a google search and I got some images but I would liket be sure to not misunderstand the term.

How wide is the kerf usually ? Does it depend on air pressure or Amps ? And which is the distance between the torch and the metal to be cut ? It's constant during the cut ? Ok ok.. too many questions.

Sandro

Yes, the kerf is the width of the cut. Think of carpentry; the thickness of the sawblade. Woodworkers are taught early to cut along the edge of the line. Remember that mathematically, a 'line' has no width.

My kerf offset is .014 with a Hypertherm Powermax-30. That is half the kerf of .028, placing the edge of the kerf just at the 'line'. Your machine and it's settings will determine the kerf width. Just run a straight-line test cut and measure the width of the cut to see what you have.

Your kerf should be constant, but the pierce will give you a larger 'hole', resulting in a 'buttonhole' cut. This can be reduced by entering the cutpath at an angle, and ending the cut just before the end of the cut (in my case, I use .013)

[safe60]

Thanks for the precious suggestions. I'm putting all this in my code. Some changes are needed but I shouldn'have too many problems. Another thing.. Is there some site where I could download a sample of code of CNC cutting ? I don't know if there are special commands or if the NC code is the same like milling.

Sandro

[AnotherDano]

Thanks for the precious suggestions. I'm putting all this in my code. Some changes are needed but I shouldn'have too many problems. Another thing.. Is there some site where I could download a sample of code of CNC cutting ? I don't know if there are special commands or if the NC code is the same like milling.

Sandro

I understand what you're looking for, Sandro. I'm an old programmer who worked on file protocols for 35 years - even helped develop one. I believe that most are proprietary but there must be some organization like ANSI that has what you need. I use PlasmaCam and it is locked away tightly.

You could always try using a file dump of a DFX file and do things the old-fashioned way; looking for patterns. But that might take a long time.

What language are you using to develop your code? You may be better off using an off-the-shelf version of Corel (for example) and reverse engineering it. Are you any good at hacking?