Possible new feature, if/when time allows

[Sentinel]

Today I've been bitten with Constant Velocity/Exact Stop thingie in Mach3. Tried to pocket a small rectangle, ended up with alien looking shape.

I've redid the thing again, and used Exact Stop mode in Mach3 for pocketing shape only. Turned out as expected.

Now, something is bugging me, so I am going to bug you too (again ).

From what I understand (I've read it on Mach3 forum, so I might be completely wrong), CV/ES modes can be controlled using G61 and G64 codes. Seemingly, you can input them into your existing g-code project, if you want to have parts of it cut in CV, and parts in ES. Or so I understood.

When I was pocketing something today, I had a circle and a rectangle. Looks like this:



When it was being pocketed, rectangle was done quickly (because those were only 4 spindle moves, if I read it right). However, circle took ages, because cutting circle involves many many small moves.

Question is - could VCarve possibly have an option to define which toolpaths to cut using CV mode, and which using ES mode? For example, I could create pocketing toolpath for these 2 objects. Then, I'd just select rectangle, right-click on it (or press CTRL+ALT+SHIFT+something_else, or whatever way could be feasible ), then mark it to be cut using ES mode. When G-code is generated it could input G61 (or G61.1 - one seemingly means "Exact Path" mode, and another one "Exact Stop" - I presume someone more knowledgable can correct me) before part of G-code that pockets the rectangle, and then put back G64 when rectangle is done.

It could look something like:



That is, if I understood the whole thing correctly

Now that I think of it, VCarve could maybe just have an option to create pocketing toolpath with ES mode, so no need for anything fancy like popup menu options, etc. I'd just select rectangle, and create new toolpath in ES mode.

This would simplify life for Mach3 users, I guess, so we don't need to bother with config options in Mach3, in order to cut in ES/CV modes.

Thanks.

P.S: And of course, I now realize I've selected the wrong vector on the bottom picture. Rectangle should be selected and have "EXACT STOP mode" checked, not the circle, yay

[CRFultz]

You bring up a interesting point.

But i have to ask, why would are machines be that much different in respect to CV or ES.

I have had CV checked for over 2 years and have never had a problem with any cuts.

The reason i ask is because I'm always looking for ways to tweak my machine to make it run faster and possibly smoother.

When I first started using Mach 2 I was told Constant Velocity would work better when cutting materials that could
possibly burn. That way the bit won't stop and then move on. Moving up to Mach 3 was the same.

Is there a advantage to exact stop.......could it be just the open loop stepper setup that I have works best with CV?

I guess maybe I'll need to get some machine time for testing.
Then again...on a homebuilt machine like mine....once your at a point of it working good you don't really want to mess with it.

Chuck

[Sentinel]

I have to be honest and say that I don't fully understand ES/CV implications, I just know it affects work sometimes.

For example (forgive the crappy photo):



That was a small (27mm wide, forgot the height) rectangle. I was pocketing with 5mm end mill, and I expected round corners.

However, I didn't expect to end up with what is on the picture. The other part I've cut on the same piece has even more distorted rectangle, but I didn't take photo of it.

With exact stop, I got proper result.

Some people have problems, some don't. It seems that playing around with acceleration settings (and some other voodoo magic inside Mach3 configuration options), one can possibly get perfect setup that will always work in CV mode. Assuming you get those settings right, somehow

Trouble is (for us newbies, especially). I'd need to spend X amount of hours, use Y amount of MDF, and dull Z amount of bits in order to potentially get those settings right. Assuming I can ever get them right, and there isn't something else that affects CV vs ES results. So I'd rather use ES from time to time, knowing what result I'd get, than hope that CV will always work right. I've read topics on Mach3 forums, but there isn't an "universal setup" that can solve ES/CV problems. Everyone has different experiences. Like feeds and speeds, hehe

I am also puzzled because I got the problem on this small rectangle, but had no trouble while cutting out bigger objects. I even went so far as to printing an object (small guitar body), and laying the cutted object onto the paper - cut was perfect, doesn't seem like CV mode affected cutout of 28cm x 14cm object at all. Seems that (in my case, at least) it only affected small rectangle, and I never had any trouble getting perfect circles with CV mode. Some others had trouble with circles, so I have no idea what really affects ES/CV modes.

I wonder if anyone else would actually have use for feature I talked about. If I am the only one, then I think it explains where is the problem (me, not the VCarve/Mach3/CNC machine ).

[James E]

Art posted a great explanation of this problem on the Mach 2/3/4 forum, saying imagine a car racing down a street coming to a corner, it has to slow down or cut across the corner or a combination of the two. There are look-ahead factors and all sorts.
When I read it I decided there's no way anyone could work this all out so the machines work, and yet they do.

Jim

[Markm]

Sentinel

You can do something like this by editing your postprocessor. You could make all circles cut in ev mode and all lines in cv mode if you wish. I do not think that you could seperate out the pockets at this time however. If you cwant some help woth the first let me know.

Mark M

[Monte55]

Please read Pocket Radius posted on May 24.........I have a similar problem.........

[TReischl]

You guys are right, there is a lot to this es/cv stuff.

Someone metioned they were told to use the cv mode to avoid burning. Which is correct. You also use it to avoid overcutting into a corner. When the tool stops for that instant, all tool pressure is relieved, then the pressure is back on again. And you wind up with a ding at the corners. Depending on your feedrate, the ding could be very noticeable.

One thing you do not mention, or else I missed it, is your feed rate. You also do not mention your accel/decels in Mach 3.

It is hard for anyone to tell you a magic setting, because we all have different types of machines (with different weight gantries or tables, etc, etc). The settings are there so you can adjust the software to YOUR machine and it's dynamics.

One thing I have stopped doing is trying to make my machine go as fast as it possible can all the time. It finally dawned on me, I am not a high volume production shop to begin with, the machine is NOT running 24/7, not even 8/5. While it is running I am doing other things anyway so who cares if a part takes 5 minutes longer? OK, so it uses up 5 minutes worth of electricity. . . . .

The way I set up my machine was to program a small square, about 3 inches. I put a g92 at the front of the program so I could just jog to a new spot for another test and I started tuning. When the machine accelerated smoothly, made nice square corners, and stopped smoothly at my chosen highest feedrate, I stopped tuning.

You can find your highest feedrate very easily, it is the feedrate at which your machine does not lose steps. By the way, your computer can cause you to lose steps too, it is part of the equation. Once you have that speed, start playing with the squares and the tuning page in Mach 3.

Hope this helped a bit.