Cutter Compensation

[bsharp]

Profiling Burning table.
I am still having trouble with cutter compensation.
Some times if I stop a program and restart it it will just make a strait line with a little circle at the end and then stop.
It will do this even if I put a G40 in the head of a program? If I run a G40 in MDI and then reload the G code program. It will run fine.
It seems that the cutter comp in Mach is buggy as hell. Is there any light at the end of the tunnel for cutter comp in Mach or is it dead in the water?     

[Vogavt]

I was having similar issues and by happenstance used a G90 code from within the MDI without reloading the code.

Problem went away. Give that a whirl and see if you have the same result.

Must be a bug but not sure. 

[MarkC]

Maybe try putting a G40 in the "all resets" line in general config?

Mark

[jimpinder]

I don't know a great deal about cutter compensation, but, as far as I understand it, when cutter compensation is applied, you must then have a "run in" move for the tool - i.e. when you apply G41 or G42, the tool does not move to the new cutting position, but uses the next move to get into the right position. I assume it might take more than one move if the appropriate axis does not move (although thinking about it, that is doubtful, since, just moving one axis will get you into the right position)

If you are saying that, after you stop the program, for whatever reason, then restart, it says in the tutorials or the manual, that Mach 3 may take two or three moves to regain position.

I have recently been cutting some printed circuit boards, and I was having trouble with the Z axis not lifting properly, which caused the cutter to foul and then snap off (it is only 0.6mm). Stopping the machine had to be quick, but the point is, when restarting I had no idea where the tool was in comparrison to the program, particularly if I had jogged to change the tool.

I examined the GCode, and ran back to the last G0 movement, i.e. a move where the cutter was moving from one place to the other, without cutting. This would mean the cutter was well above the work, and the tool would move to the next cutting position accurately. This applied from whatever position I was at, whatever height the tool was at and whatever compensation I had on.

If you then looked at the code, the next move was "tool down", and the next move was "cut".

So, move back to a G0, click "set next line" and "run from here" and click "cycle start". The initial G0 move allows the cutter to move to the next position, apply the compensation, take a breath, and then get back to work again.

Restarting the program will obviously "start again" and if you look at the top of the 1024 Milling profile, you will see a list of the GCodes that are applied, and see that things are put back to a single profile, so that Mach kmows where to start from. If you look on General Config, left hand column, you will see a similar list of "tasks" when M30 is encountered.

We all have to, from time to time, stop in the middle of a run, but the thing is, after each stop, you must say to yourself "has the machine enough information to carry on from where it left off". This is particularly important if you use sub-routines and offsets, where information might be carried over. If the machine hasn't the right information, then performance is unpredictable.




 

[ger21]

There are some bugs that Brian is going to start working on pretty soon. Probably a good idea to send him examples of any problems your having so he can fix all the problems with comp.

[bsharp]

Maybe try putting a G40 in the "all resets" line in general config?

Mark

Thank You all for your replies
I would like to try putting a G40 in the "all resets" but am not sure what or where "all resets" is?
Do you mean putting a G40 function on the stop and reset button?
Or is there somewhere else that I don't know of?

[bsharp]

Basically I am cutting large circles out of plate with a leadin with two linear moves at 45 degrees tangent. These circles may be oriented at odd angles to provide better utilisation of material. When I stop the program I normally start it back at the beginning of a complete coordinated block of code. I normally don't try and use the "run from here" and edit the code and reload it. Most other controllers that i have used that require a preparation move for the cutter compensation to be initiated need only a move slightly longer than the offset value.

[bsharp]

There are some bugs that Brian is going to start working on pretty soon. Probably a good idea to send him examples of any problems your having so he can fix all the problems with comp.

I will see if I can compile a list of examples and post them.

[bsharp]

Ok after trying just about everything possible. I think it all boils down to two problems.
1:
I think there is a problem with the Stop function if you are using cutter comp.
If you start Mach load a program and hit Cycle Start it will run fine all the way through.
If you press Pause Stop then Rewind and then Cycle Start
Or if you press Pause Stop then edit the code and Cycle Start it will do some very strange things!
But if you type G40 in MDI and run that prior to running the program in any of the above situations it runs fine.

So after contemplating this for a while I figured I would change the rewind button to run a G40 and then an M30.
I also made sure that an M30 and a G40 was in the initialization string and I set to all resets.
So now if I press Pause Reset Rewind and then start it works fine no crazy stuff.

2:
The cutter comp still doesn't work correctly. If I use a linear and an arc lead to cut a circle and also use an arc lead out it will merge the lead in with the lead out and never cut the part  .
I have a bad feeling that this problem is a little bigger than just a little bug. For starters it messes up at strange orientations of the same geometry. This would make me think that the logic for the offset geometric creation is not vectorized.     

[Graham Waterworth]

Hi Bsharp,

It is normal on most systems to have to issue a G40 before re-running a program that uses comp.

That said, hang in there, I was discussing this very issue with Brian while he was over here in the UK, I should not be telling you this but cutter comp is to get a rewrite on his return to the US. 

This was all achieved with the power of good quality hand pulled beer 

Graham