When doing helical ramping to drill smallish holes (1.5D), the spindle stutters,

When doing helical ramping to drill smallish holes (1.5D), the spindle stutters, even when cutting in air. It looks like what I see when the buffer is starving, but the SPJS queue depth indicator says its not.

Any ideas what could be causing the stuttering? I use Fusion 360, Carbide3D Post, and a GRBL CNC.


Can you post a screen shot?

Here is a screen shot of the tool path in F360 and one in CP. The stuttering occurs when helixing down to the next level in the holes. Hope these image links work.



Oh I meant a screen shot during the run when it is stuttering so we could see if your buffers are being starved. In your shot you aren’t showing the spjs widget which is where the buffer counter is. Also with grbl there is no buffer reporting like TinyG has in cp so none if us would know how that planner buffer is doing. My gut says starvation of buffer. Why don’t you pre upload 10k lines in the settings icon in the gcode widget

The spjs buffer was getting low but never hitting zero. I agree that it did feel like planner buffer starvation.

The troublesome section is 30000 lines into the nc file, so not sure if preloading will help but I’ll try it.

What device do you prefer to run spjs on, John?

Raspberry pi 3

Okay, just ordered one. Hopefully it can keep up with the GRBL, even when it occasionally sprints through a bunch of small segments.

Oh, it’ll keep up alright. Did you fix the real problem though which is you were sending Gcode too slowly from the Gcode widget? Did you change your settings in that widget yet?

Yes, I’ve done a lot of testing with pre-uploading (1000), mult-iline (200), and delay (500). The SPJS buffer depth never drops below a few thousand.

But even with CP dialed way back on CPU and SPJS process set to realtime priority, the moves (carving in air) still don’t sound smooth in the parts where the toolpath segments are really small (like the motion planner is starving).

Seems like a 2.8GHz Core Duo laptop should be able to keep the GRBL fed, with CP minimized… It is working a lot better than it did, but still not the smooth stepper motor sounds that I’m looking for.

Okay, got SPJS running on my new RP3.

Do the CP folks generally use wired or wifi for attaching the RP3 to the network ?

Also, are you doing anything special to protect the RP3 against loss of power (which may cause SD card corruption, apparently)?

Many folks use WiFi. ChiliPeppr receipts all sends to SPJS to ensure delivery and packet order, so if your WiFi is a bit slow/packet loss, you are fine.

I’ve never done any loss of power mgmt and have never had a problem.

Probably not the right place to ask but… been spinning for a couple hours and could use a hint.

I can’t get into the RP3 GUI to set up the wifi. Typing startx returns “-bash: start: command not found”. Hint anyone?

The Rpi3 starts automatically into the GUI when you have an HDMI monitor connected to it.

Mine start in terminal mode on the HDMI monitor. I followed these instructions to get SPJS installed.

Otherwise its a fresh Jessie-lite install. Ahhh… maybe Jessie-lite doesn’t have the GUI?

raspi-config lets you reconfigure how the boot works into command line or GUI.

Did try raspi-config without success.

I’m downloading the full version of the Jessie 4.1 now. I’m thinking that working with the lite version was the snag. Thx