Low Speed for 3d Printing application

Hi, i just finished to put together my linuxcnc based 3d printer, i'm still working on a few details, but the first issue that i'm facing is that i seem to be getting very long machining time, more than i expected.

Just to have an idea, my prints usually take more than double the time estimated by the slicer (cura).
I understand that that kind of software is calibrated on very small and light (and not very precise) consumer grade machines, but i'm hoping that i can at least try to get near to those estimations.

In particular my machine takes the "bigges hit" while printing profiles made by a lot of small lines, the speed drops from the usual 3000mm/s to 1/3 or less, and the movement of the machine isn't very smooth at all.
I already tried to fiddle with G64 P.. Q.., but i'm not seeing a huge improvement.
The acceleration limits that you can see in the attached file look way too high to be the cause of the problem, so i really don't know how to improve the situation.
Could the PC be the issue? It's an old workstation (3.6GHz Pentium 4, 1GB RAM, ati firegl ...) with the usual chinese bob.

I'm also thinking about switching to a mesa 7i96, could that change something (of course comparing the 2 at the same programmed speed)?

Considering the time, the effort and the money i put in this machine i really want to have it to have at least comparable printing speeds with what you can find on the market.

Any ideas?

max vel is 50 that seems on the slow side.

With your base thread you should get at least 100 (393mm) inch per min maybe a little more. I was able to get about 120 inch per min on my paraport with a similar base thread

50 mm/sec is very close to 120 IPM

I didn't realize mm was measure in seconds.

My ender 3 is set to 60 i believe and usually prints an hour extra from what cura says on a 6 hour print

AFAIK all ini file machine velocity settings are in machine units (inches or mm)
per second.

Now that I think about it mine is set for about 1.7 per second

Yes, it's 50mm/s, 3000mm/min.
That's the maximum I could get without following errors.

However I reach that speed, but I also can Se the machine going quite slow in some perimeters (in cura I have ALL the Speed settings on 50mm/s) which it looks like are made by many small segments.
I don't know if Marlin or other firmware for 3d printing are better at converting those into curves or splines, but more than double the time for me is quite hard to accept.

Yesterday a 1h32m long print took more or less 4 hours

Could it be a jerk control or Accel /decel setting?

I suspect the issue is using an actual motion axis (U) for the extruder
AFAIK the trajectory planner falls back to simple parabolic motion with
1 segment lookahead when using more than XYZ

PCW wrote:

I suspect the issue is using an actual motion axis (U) for the extruder
AFAIK the trajectory planner falls back to simple parabolic motion with
1 segment lookahead when using more than XYZ

Ouch, any workaround?
The extruder axis should work independently in this case.
Also because decoupling the 3 main axes from the extruder could be useful for another reason: the extruder should be a little ahead to avoid plastic blobs in the corners.