Ramping Profiles

Can gSender modify/adjust ramping (down then back up) feed speed/motor profiles when coming into corners, curves, or sharp corners?

Does anyone experience frame flexing/vibrations/violent equipment movement when the above tool path maneuvers happen?

Not sure if I am explaining/asking the question correctly.
In my past cnc router life I had to adjust the motor profiles so any extreme tool path movements were smoothed out, to make a continuous, smooth, cutting tool path.

Thanks to all that reply.

This should be the job of the CAM program.

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@JHahn I remember tuning the stepper motors in Mach3, to control how fast the steppers increased & decreased their rpm, so maybe I asked the question wrong.

I do remember that the tuning changed the sound the steppers produced/made when working.

Is there a way to tune the stepper motors in gSender?

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@RustyR Rusty: In reply to your first question, I have not experienced any flexing issues when the Mill enters into corners. That may well be because I am conservative in my feed rates set in the CAM software. You mention your previous CNC experience. What machine was that experience on? I’m thinking that maybe it’s max speed and the speed that was set in the CAM software was such that slowing down going into corners was necessary. The Mill maxes out in X and Y at 4000 mm/min or about 150 in/min. So, it’s no speed demon. :grinning:

I believe that it’s fair to say that the 1/8" bits that I use more often than not will flex long before anything else on the Mill. It’s easy to address that by setting reasonable feed rates and cutting depths per pass.

I don’t know if the steppers can be tuned to slow down going into corners. I would think that capability may be limited by the limitations of grbl itself, but I expect others here are much more knowledgeable about that than I am. (You mention using Mach 3 on past machines and I don’t believe that is used on grbl-based machines.)

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The GRBL firmware handles most of this for the user on the firmware side. It uses a centripetal acceleration formula to calculate what the exit velocity should be for every movement - which means that exit velocity will be near the current max feedrate if the angles of two movements are similar (like a cut that is a continuation of the current movement) or near 0 if the angle differs greatly (if the next cut is at a sharp angle to the current movement).

What this means in practice for you is that straight-ish cuts stay at relatively consistent speed. If you have sharp corner, the head will decelerate at the end of the movement before beginning the next cut. This will prevent frame flexing/sudden stops on the hardware side.

GRBL handles curves in a similar fashion. Curves aren’t true arc movements, since GRBL converts the arc into a series of very short straight lines approximating the arc. The same principle above applies for acceleration/deceleration though - so again no violent movements.

You can configure/customize what the max acceleration is for each stepper motor in the EEPROM, which is a variable that is used in the above calculations. However, the default settings the machine ships with should be more than fine for 99% of users.

In short: gSender/you don’t need to ramp down feedrates for sharp corners or curves since the firmware already handles it. If you want to change the max acceleration for a specific motor, you can alter that as an EEPROM value, but you probably don’t need to.


Thanks @gwilki for clarifying the max feed rate. I prefer machining on the slower side.

Thanks @KGN for the clarification/explaination of the acceleration/deceleration movement, greatly appreciated.
It is great to know that I will not have to tinker with making any extra settings/changes.

I am very impressed with how much thought has gone into making and setting up the Longmill, great job guys. Makes my purchasing decision much easier, just need to decide on the size format.