Need sharp inside corners

[tnbndr]

Ok, I know corners in plasma are slightly rounded and I can loop outide corners to achieve square corners if needed. But what about inside corners?
I have searched and found no info.
The rounding is too magnified on small pieces and doesn't look right, see pic of small star.
Any tips welcome.

[acourtjester]

one thing that might help is using inside offsets to get rid of the pierce dots on the point shown in you image.
but that will not get you sharp points on stars

[tnbndr]

I am using the dropout, so that is an outside lead in as intended.
Thanks for the reply.

[Thor]

The plasma stream is round, no way to get a sharp square inside corner. Same as milling, corner radius is determined by the size endmill you use, can make it smaller but only to a limit.

[tcaudle]

Small detail on thin material will not follow the toolpath. You are going to have to cheat.
1. First SheetCAM won't let you shove a tool of a given kerf width into a tight corner. If you cut it ONLINE that rule will not apply OR make the kerf width smaller for that tool but the size will change
2. The CV in MACH is keeping the toolpath from being dead on. It cannot perform the moves you want it too at the speeds you have selected Sooo... turn off the DTHC and slow down the feedrate. Try increasing your acceleration on XYA but not so high you start losing steps. As you slow down try using the smallest nozzle you can and lower the cut current. Radius of the flame goes down with smaller nozzle size.
3, There is a way to force MACH into Exact Stop Mode (G code command) that will turn off CV and run to each corner and stop then accelerate the next segment. It can work on objects that are just lines (like the star) but not on arcs/curves. Be sure to use the G code to turn CV back on at the end
You can edit the code and drop in the proper G code at the start of the operation for the stars

[Capstone]

It almost looks like the entire star is drawn as a single node or the node types on the star within the drawing aren't registering as actual corners, but rather narrow arc from each point. I know within some drawing programs you can create stars automatically, but like this example below, the star on the left was converted to a vector object, but the one on the right was left as is; notice there's only two nodes shown when it's selected. maybe this is causing the weird cuts? I don't know, for sure, but maybe look again at the drawing to see? what do the drops actually look like? are the corners sharp?

stars.JPG (19.99 KiB) Viewed 2211 times

stars.JPG (19.99 KiB) Viewed 2211 times

[tnbndr]

I did draw the star as lines but then converted to one polyline as this typically lowers drawing size and cuts better. After the bad cut I exploded the star into individual lines hoping that would help but it cut the same way.
The star is only 2" across but it looks like it is chamfering the inside corner a whole lot more than necessary.
I am going to play later with slower speeds and maybe no offset to see what happens. And I may try individual lines with a slight gap so it cuts each side, but that would require 8 pierces per star which I really don't want.

[vmax549]

Your axis accelleration values are too SLOW for the speed you are cutting. THAT is why it is rounding so much. You can try running it in G61 mode ( exact stop) to see IF that helps but it may just shake the table a lot more. I would experiment with the motor settings (Acceleration) to see if I could squeak out some more accelleration from the system before it starts loosing steps. What are your numbers for Vel and Accelleration on XY ?

What guage metal and Feedrate and amps are you cutting with.

(;-) TP

[Nacs Fab]

I will check tonight what my Acceleration values are. Here is some parts that have sharp edges in them. Each one of these badges were only 2.75" wide by 1.75" tall cut from 14 gauge. Letters are only 0.06" wide!!! I thought they turned out fairly well.

[tnbndr]

What are your numbers for Vel and Accelleration on XY ?
What guage metal and Feedrate and amps are you cutting with

Not sure where to find the Vel and Acceleration numbers?
I am cutting these out of 16 gauge with a PM45 at book specs for 45 amps(350ipm & 112volts). I tried cutting at the 30 amp specs and turning down the plasma machine, no difference. Cut the speed in half, no difference, except in the cut quality.
Tried applying several cut rules, no difference again.
Not proficient enough at G code to edit or know where to insert the G61.
Fortunately these were being cut for my daughter and not pressing issue for a job but I do want to ge something figured out for future projects.
Thanks for all the replies.

[acourtjester]

To check or change Vel and Acc numbers you find them in Mach 3 under the configure tab and motor tune. Each axis has it's own setting click on the axis you want and then save if changes were made.
I'm not completely sure but under the configure tab is General config and in the middle there is a box with "Motion Mode" and you can select Constant Velocity or Exact Stop someone with more knowledge may have a better answer