inches per minute increase in corners

[MattTheCutter]

You will quickly realize that I am not a professional so most likely I am missing something obvious.

Machine is home built CNC router. Clearpath servos, dedicated computer setup according to the centroid documentation running CNC12.

I design parts and produce the G code using Fusion 360. Homing, auto square, etc works fine.

My problem is the machine is very jerky without smoothing on and it speeds up when it is cutting curves. I thing the jerky motion is from speeding up whenever a change of direction happens. I set all of the smothing setting to their lowest slider position and turned on smoothing and it runs more smoothly. But it still accelerates on curves.

I have tried to search for a solution but havent come up with anything. I dont know if it is the fusion360, clearpath servos, cnc12, or the acorn board. I have put alot of time into fusion trying to see if there is something in there that would cause this but have not found anything. I am only cutting using 2D in wood because the jerking and accelorating changes breaks bits.

The servos are tuned properly and set according to their manual so that has left me looking at cnc12 and the acorn board. I have attached a report and will supply any other information needed.

I still suspect that the problem could be in any of the components but decided to start here.

Thanks in advance, Matt

[cncsnw]

What feedrates are you using in your CNC programs?

When you dry-run the job (e.g. with no tool in place, or with the Z axis part zero set up above the material), with the feedrate override at 100%, what numbers do you see in the feedrate display in the status window at the upper right?

[MattTheCutter]

cncsnw I will go out and look now.

First I was at the machine trying to make a video when I realized that when I rapid the machine using both the x and y axis at the same time the speed is higher than the speed I have set for rapids. My rapid speed is set to 300. When I use the macro I to move the machine x40y40 the speed readout is 424. It is also 424 when I park the machine back to machine x0y0. I dont know if this is normal but I would assume that the software would make the machine move at the set feed taking into account both motors so when moving at an angle across the table it would run at 300ipm along the hypotenuse.

I am going to make a short video of one of my jobs that illustrates the problem

Matt

[cncsnw]

No. Max rate is a per-axis value, and a G0 "Rapid" move means get there as fast as possible.

Therefore, if X can go 300 in/min, and Y can go 300 in/min, and you ask for a rapid move on a 45-degree angle, then X and Y will both go at 300 in/min simultaneously. In that case the combined speed will be higher than 300 in/min. If, on the other hand, you ask for a linear feedrate move (G1) at 300 in/min (or less), then that is the speed the tool will move at, regardless of direction.

If you write a program in which you ask for a feedrate that is higher than the Max Rate for one or more of the axes, then the control will do its best to honor your request, without making any one axis exceed its max rate. Therefore if you can go up to 300 in/min on X and on Y; and you write a program to mill a circle at 400 in/min, it will go faster where both axes are moving at once (making it possible to achieve the requested 400 in/min); and it will go slower where only one axis is doing all or most of the movement (limiting the overall speed to 300 in/min).

[MattTheCutter]

So, it is in the gcode? Or can cnc12 control it? I have a couple of pictures that show the difference between smoothing on and smoothing off. I don't want to have to amend every time I generate gcode!

[MattTheCutter]

With smoothing ON the straighter the line the closer to 100ipm the sharper the curve the faster it moves. With smoothing OFF the straighter the lines the closer to 100ipm the sharper the curve the slower it moves.

[martyscncgarage]

Can you show pictures of your machine?

[cncsnw]

Also, post a copy of the exact CNC program you were running for these tests.

How does it work with smoothing on, if you turn the "Curve feedrate modifier" (Parameter 230) down to 100% or less?

[MattTheCutter]

Here are some pictures of my machine. I included a screenshot of fusion 360 while I was setting up a test to check actual speeds vs call speeds. I made all of the toolpaths 100ipm but in the simulation it says feed: rapid. When I run the simulation it says it's going 100ipm. So I'm guessing there is a disconnect between how the machine determines how fast to run and how fast the machine moves and how my brain thinks all this happens.

One thing I definitely don't understand is why the speed around corners changes so dramatically when I use smoothing. It runs smoothly when smoothing is off and rougher when it's on probably because when smoothing is on it is accelerating in the corners and decelerating when smoothing is off.

I would show you a video but my phone is old and doesn't sent large files anymore. I will breakout my camera when I get a chance

Thanks, Matt

[MattTheCutter]

More pictures