LinuxCNC, Plasma, THC questions

Greolt wrote: I really don't wish to sound rude or arrogant. Please forgive me if I do. But that does not answer my question.

If that doesn't answer your question, then I have misunderstood the question.

Can you re-phrase the question in a manner that makes it clear why my answer is not an answer?

(There are many other options, such as limit2 and pid, but for a THC I actually think that setting stepgen accel and velocity limits is sufficient and adequate)

PCW wrote: Sure seems like it answers the question

Thats is if you set the acceleration limits of the stepgen
those limits will be obeyed regardless of where the stepgen
position or velocity command comes from, be it axis position, THC position, THC velocity, phase of the moon, or whatever

"those limits will be obeyed regardless of where the stepgen
position or velocity command comes from"

OK I will take that as a yes.

Thanks very much.

andypugh wrote:
If that doesn't answer your question, then I have misunderstood the question.
Can you re-phrase the question in a manner that makes it clear why my answer is not an answer?

Sorry. If I asked on a Mach3 forum if THC moves included an acceleration ramp, 99% of users would say yes. They would be wrong. Most Mach3 users don't use Plasma. They would just assume that the answer is yes.

So I was just hoping for a definitive YES or NO answer from knowledgeable Plasma LinuxCNC users.

My apologies.

I think there may be confusion because Mach3 handles THC differently than normal Z motion, and does not apply acceleration. There is a setting for THC velocity which is a percentage of the Z's max velocity, and you have to set it low enough that the near-instant acceleration does not stall the motor. So even though Mach3 has acceleration limits for the Z, they are ignored when doing THC.

In Linuxcnc on the other hand, as has been pointed out, acceleration is honored for THC commanded motion just like commands from any other source.

Greolt wrote: Sorry. If I asked on a Mach3 forum if THC moves included an acceleration ramp, 99% of users would say yes. They would be wrong. .

I understand the problem, and even as someone who does not use Mach I have seen this on other forums such as CNCzone.

On this forum most of the moderators are developers of the software or are hardware suppliers. If you see "Moderator" or "Administrator" in the side-bar of the poster then you can be fairly confident in the answer if it is stated as fact. If it is stated as an opinion or a guess, then you certainly need to wait for consensus.

Of course, as this is an open-source project, you have the option of seeing _exactly_ how the code works. This is where the accel limits are applied in the software stepgen:

git.linuxcnc.org/gitweb?p=linuxcnc.git;a...6571954;hb=HEAD#l904

mozmck wrote: In Linuxcnc on the other hand, as has been pointed out, acceleration is honored for THC commanded motion just like commands from any other source.

Thanks for that mozmck. Just the response I hoped for. And the answer I hoped for too. Looks like LinuxCNC is now in my plasma table plans.

andypugh wrote: On this forum most of the moderators are developers of the software or are hardware suppliers. If you see "Moderator" or "Administrator" in the side-bar of the poster then you can be fairly confident in the answer if it is stated as fact.

I take your point.

Thanks all for your patience.

I might ad that after upgrading to 2.7 my plasma table cut much better with the new trajectory planner it maintains requested speed even for files with a bunch of tiny moves. Using true type tracer which outputs nurbs the letters come out perfect.

JT

Nice one PCW,
Here it goes again with some more explanations,
When i built my THC i had to test how fast they would react and to what extent they can be pushed while actually cutting so i made a new Z axis using belts (normally i use screw rod on all Z axis for plasma, very efficient but slow) that would move the torch up/down @3meters per minute and i went on to see how far i can push it, so it can do about 5cm in height for every 5cm of cut (that is a 45 degree slope ) easily, but climbing down it could not do more that 3cm for 5 cm length.
So i had to change the acceleration and speed of the Z axis to make this work ( the axis using a screw can have acceleration set very high without any problems, but the one with belts must have a small ramp so the acceleration had to be set at 500mm/mm otherwise it would just stall, in contrast to 2000 when using the screw).
Al this is to show that i am sure it does obey the acceleration and speed set in the ini file.
Regards,
Tom
P.S.
I agree with John, i did get much faster speeds overall when using 2.7 and much less vibrations on the machine when doing sharp corners. One of them had a wobbly z axis!!!!

Thanks Tom

Looks like I will be going for a Proma or equivalent simple THC. Then I will be looking at your recommended setup.

Have you seen the Mesa THCAD thing? (I am not sure if it is equivalent to the Proma or not)
store.mesanet.com/index.php?route=produc...oduct&product_id=128