Advanced Search

After pulling my hair out trying to figure out why G33.1 wasn't working on my lathe while attempting to test the problem raised in this thread, @cmorely pointed out I'm having the same issue.

forum.linuxcnc.org/38-general-linuxcnc-q...pping-problem#319786

So I can confirm spindle synchronization start points vary with spindle speed in G33.1 as well as G76 - and it's way worse on my lathe than the OP reported on his.

In my case a difference of 140rpm (60 vs 200) resulted in appx 0.750" difference between the Z-start point when synchronization kicked in on a 1/20 pitch (0.050").

According the the formula Andy posted earlier, my Z-axis requires the following distance to get up to speed

 

I don't understand why there is such a significant difference between what I'm seeing and what the OP's lathe is doing.

Unless somone has other thoughts, I think this is a bug.

Joco wrote:

Don’t make that assumption re feedhold. And tapping. The planner is taking things direct from the Hal pin. Not from the lcnc motmod module.

it needs to be explicitly tested. Unless someone has done so already and can confirm what the behaviour is. 
 

I can confirm that LCNC 2.10 disables feed-hold while synchronized motion is in progress.  FH has no effect during a G33 or G33.1 command until after the synch move is complete.

cmorley wrote:

I would expect speed changes to change the sync start point.
There is another post about non syncing threads with speed changes.
In linuxcnc, you can't change the spindle speed and track the same thread, the sync point moves.

Linuxcnc moves the axis as fast as possible till it is moving at the approximate correct 'pitch' speed. It then works to get the exact pitch and maintain it. This distance to get up to speed is kept track of for use of calculating position and position error.

IIRC linuxcnc allows 10 rotations past target before deciding there is an error.
 

Thanks for giving this some thought Chris.

I understand that LCNC needs a short period/distance of max accel to go from zero speed to synch speed - the other thread has a code snippet which explicitly states this in a comment.

What I don't get is why LCNC is moving so far to get up to speed.  My lathe has pretty aggressive acceleration - it can reach max speed in a very short distance.

But it's moving over an inch at rapid speed to get to the synch point at only 200rpm with a 0.05" thread pitch.  Feedrate at that spindle rpm and pitch is really slow - like 4ipm or so.

I guess what I'm seeing is identical behavior from the other thread... but much worse start point variation.

The other thread:
forum.linuxcnc.org/38-general-linuxcnc-q...s-with-speed?start=0

If you can use any Linux x86_64 on it, then download the official ISO and try installing it, but might have issues with RT kernel running in a VM.
You can try Debian 12.x or Linux Mint Debian Edition 6, and if they work just install LinuxCNC with
sudo apt install linuxcnc-uspace
This will also install the RT kernel, but it will not be the default one, so LinuxCNC should work OK in SIM mode.

Position mode = 0
Velocity mode = 1
Step type 0 = step/dir
Step type 1 = up/down
Step type 2 = quadrature
I think, been 15 years since i was deep into it, there are 10 step types, so 3 should be 3 phase at 120 degrees, and some more 4 pin types, and 5 pin/phase types.
Yes, LinuxCNC can do 3 and 5 phase stepper control, i still have some of those in the shop, i was very happy when i saw 5 phase motors move using 5 darlington transistors and 5 resistors from a parallel port.

tommylight wrote:

Did you notice i edited the post?
I saw you clicked on thank you after i posted so probably not.

I see it now, i will try your suggestions. Thanks a lot again

tommylight wrote:

No.
Several things will cause that:
-not enough air pressure
-worn nozzle
-to slow cut speed
-
I would also say to much current, but not exactly the same result, so i will just throw a stab in the dark at very, very low accelerations set in the config.

I thought so
I tried with many different air pressures and not much different, that was with 75psi at nozzle.
Consumables was new and speed getting low because i guess is small part??
I will check to set higher accelerations and see.
Accelerations is best to be the same on X-Y axis or not matter?

Thanks a lot

Did you notice i edited the post?
I saw you clicked on thank you after i posted so probably not.

No.
Several things will cause that:
-not enough air pressure
-worn nozzle
-to slow cut speed
-
I would also say to much current, but not exactly the same result, so i will just throw a stab in the dark at very, very low accelerations set in the config.
Edit:
I did not read the settings when i replied, i just browsed over them, so yes it is low acceleration, but probably there is not much more you can do, that is very small for plasma cutting and would in the end require very small nozzles or "fine cut" as Hypertherm calls them.
Now i would say it might be improved a bit, but not "earth shattering" changes.
Try something thicker, at least 2mm or 3mm then some 5 or 6mm.
There is a procedure i do with my machines to tune the cutting and i can not recall if i posted those here, so here it goes in short:
-tune the cut speed and THC roughly with 3mm material
-tune the air pressure till you get the best cut, does not have to be perfect
-tune the THC by raising or lowering the voltage
-tune the feed rate/cut speed
rinse and repeat for other material thicknesses and nozzles.
This is something you have to do for anything that changes, sometimes even moisture in the air will affect the cut quality, and we do get a lot of moisture despite no sea in site. All mild steels are not the same, etc.
Also, after all that you can test with lower or higher cut current and how it effects the cut speed.

How is the drive connected to LinuxCNC?