Sheetcam and trying to generate spotting gcode.

Its quite possible there is a better way to achieve this.
This feature was used by a couple of us pre plasmac based on a PP used by CommandCNC which used the CENTERPUNCH tool the same way we are doing it here.

But back then we were doing a pierce and turning off the torch when we received an ArcOK. Now Plasmac is a bit smarter and allows a duration to be specified.

I'm not in front of sheetcam now but the best way would be to allow the jet operation settings window to allow the user to set a hole diameter below which spotting the plasmac way was done so no tool change is required.

I haven't tried using a jet operation for spotting yet, I had been using drilling operations.

I was playing with using a jet operation. It seems to me that the proper way to do it this way would be to make sure you have a lead in and set its length to at least half the size as the start from hole center setting. Does that sound correct? Would that interfere with folk's already established lead in settings?

phillc54 wrote:

To me it is unintuitive to expect a drill operation to be a plasma centre spot.

IMHO the drill operation should be removed as a centre spot option and kept for a drill spindle down the track.

The whole intent of using a centre spot is to drill a hole later. If you don't have a drill mounted on your machine, its intuitive to me.
I am at work now and had a play in sheetcam ignoring any tools.

To spot the centre of a hole regardless of the tool used, you need to do two things
1. Move holes to a new layer so they are not cut on a normal jet operation
2. Use a drill operation where the holes to be spotted fall within the minimum and maximum diameters in the drill operation

I tried other methods but could not get sheetcam to move to the centre of the holes.
You have to use a drilling operation to locate the hole centre.

I suspect the intent of the original PP we followed was to allow a drilling operation with the named tool to spot with plasma (eg "Centre Spot') and would also support a drill if say there was another tool that was called "10mm drill" if a drill spindle was used.

Here's my metric test file if you want to play with something. I set the max diameter of the holes in the drilling operation to 20 mm (0.75 inch if you are that way inclined)

Without trying to cut it, see how you can get the holes centre spotted and the inside and outside profiles cut in the Sheetcam simulation.

rodw wrote:

I tried other methods but could not get sheetcam to move to the centre of the holes.
You have to use a drilling operation to locate the hole centre.

To use a jet operation
1. Inside offset
2. Set your size of circle to start from center really big
3. Set your lead in really big, at least half of step 2

I set it to something like 5in (130mm) so it's obvious. This should force sheetcam to locate the center of the hole.

It's easier to just use a drilling operation.

I also agree with you rod, in my mind's eye I'm marking for drilling so using a drilling operation makes sense to me.

phillc54 wrote:

So how would you guys propose allowing for a drilling head?

I would have thought just like the tool offsets used for the engraver and use another spindle. Not as though there is any shortage of them with Linuxcnc.

Actually was talking to a guy today keen to migrate to Linuxcnc that had a router/plasma setup but was thinking about lightening the gantry and removing the router spindle to get better plasma performance. So in practice how many need more than spotting?

The only DIY table with a drill I've seen was one by Grotius in his early days. He was just using an electric hand drill. I know the big manufacturers offer them on high def tables but the one I saw was a $15k upgrade to a $130k table!

Phill, I've proposed an idea on the Sheetcam forum because Les has chimed in there on Beefy's thread and offered to help.
At this stage I don't think you need to do anything except maybe read that post.

I personally don't see why spotting can't stay the same as it is on spindle #2 with the current tool names and spindle #3 is used for a real drill so it could all coexist with a minor change to the post processor.

Unless Les has other ideas, I think spotting has to be used as it is. In fact I used it today because I had to drill and tap some holes.

It would be good for Les to take over the post processor so it becomes part of Sheetcam and is deployed as a standard post. That offer has always been there.