Offsets and Lead Ins

[Jfile]

Question from a newbie...

Can I improve my cut quality by putting "drop out" pieces in a separate layer from the main piece and setting up two different operations in Sheetcam with the appropriate Inside or Outside offsets? Or... do I still need to build "lead ins" into each pierce point?

I tried just selecting the "lead in" box in Sheetcam but it doesn't know which pieces are waste and which pieces are keepers so that really doesn't help me any. So, if I do need lead in points, do I have to manually build those into the drawing?

Thanks for any feedback!

[tcaudle]

SheetCAM has a rich set of tools that can help you plan and execute your cutting. Use the layer tool in SheetCAm to group cuts of the same type together. Then use a separate operation to cut the layers. You can also use layers to sequence cuts so you group the smaller inside cuts onto a layr and cut them in one operation. Things like holes can be put on a layer and use the Operations to do a speed change and set the minimum cut length for DTHC ON so it does not try to turn on for small holes. I always group the pieces that need to be inside offset and may need lead-ins together and cut the online cuts on another and finally the outside off sets While SheetCAM can usually figure out what needs to be an inside offset its not always right. Just cutting everything in one operation offers you no control over the process. Its up to you to define what you define as "waste" and what is not. If you group things properly and use the correct offsets then you also control the lead-ins and where they start and what kind and how long they are and you can change it in each operation.

[Jfile]

Thanks for the feedback. Allot of great information. Obviously I'm still learning but this helped tremendously. I do have an additional question though. In fairly simple terms, can you explain DTHC and why I would want to set a minimum cut length to keep if from turning on? Just trying to understand the advantage to that.

Thanks again!

[WyoGreen]

Hi Jfile,

Digital Torch Height Control is a system for controlling the height of the torch above the material, generally about .060. It works off measuring the voltage produced while cutting and compares it to a preset value set in your control system. If the cutting voltage goes above the preset value, it will lower the torch, if the cutting voltage goes below the preset value it will raise the torch. This helps compensate for things like warped material or uneven table height.

The reason you want to set a minimum cut length is because when the torch first fires, there is a voltage spike. If the DTHC was on, it would slam the torch into the material in an effort to lower the cut voltage to the preset voltage. The minimum cut length keeps the DTHC off until the cut voltage settles down.

Steve

[djreiswig]

Wouldn't that be the DTHC delay? The minimum cut length keeps the DTHC from turning on for cuts under a certain length. You could use it to keep it from turning on when cutting small shapes. You don't really need it if the cut is a small circle. There isn't much chance of warpage on small cuts since there isn't much heat input. DTHC shines on really long cuts where the gantry is traversing the material and the slats aren't quite even or the metal begins to warp up slightly. It keeps the arc gap consistent and produces a better cut.

[WyoGreen]

Sorry, Djreiswig is right. I misread the question and gave an answer for DTHC delay.

Steve

[djreiswig]

And it was a good explanation, WyoGreen.

[tcaudle]

Actually it has to do with two things: A short cut (of any kind ) does not offer enough time for the voltage to stabilize like Steve says and the motion may not reach full cut speeds so the voltage will be higher than the chart. It's especially true on small detailed cuts like holes . Its primary purpose is to prevent torch diving that would be caused from the motion not being at the full cut speed Its somewhat mitigated by VAD (part of CaommandCNC) that does not allow the DTHC to be active if the actually feed-rate is lower than the commanded feed rate . Several things affect voltage besides just the arc gap (height. One is the cut speed (feedrate). The slower you cut the more air you are cutting (arc is starved for material ) and the voltage