Hey guys,
I have what used to be a CNC Shark Pro Plus (not HD), but I completely rebuilt it with a homemade aluminum gantry and fully supported rails. I'm a bit annoyed at how slowly it moves around curves, even very gradual curves. I understand that with the original machine there were flex issues with higher speeds, but now that I have a much stronger gantry and not more than 1/10 the flex of the original machine, is there some way I can program it to run faster around curves? Essentially I want to do everything I can to shorten total cut times and take advantage of my upgraded machine.
First thing to do is to re-calculate your cutting parameters for RPM, feedrate and plunge rate in your toolpaths. Assuming you're using Vectric VCarve, those can be found in the tool definitions you assign for each toolpath.
Then, if you're actually going over what the control panel software limits are, you **might** be able to adjust those. This only works (to my experience) on the v2.1 of the Shark Control Panel. With that up (and the CNC controller turned on, though I don't think it actually sends anything to the controller during this), type Ctrl-G, and then enter the password 787. Once you get the configuration dialog boxes, you'll want to check the maximum speeds and acceleration for the X, Y and Z. Note that setting them too fast can cause it to "lose steps" when things are moving under load. Save the new values and you should see a speed-up.
But, even with that, you're not going to see 400 IPM type speed! I have mine at 100 IPM horizontal, and 80IPM vertical. Some toolpaths I run at 80+ IPM horizontal, but I've never set a plunge rate above about 20 IPM for a real cut.
Hope that helps, but yes, I realize it only does if you're running that version of the control panel.
Regards,
Thom
===================================================== ThomR.comCreative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)
Firstly, great job on your upgrade. The fully supported bearings, elimination of plastic, the z axis changes, and metal motor mounts will really help your machine.
The "speed change around curves" is a function of the "g-code to stepper motor movement" translation going on in the controller's firmware.
Basically, what is happening is that your controller is designed to slow down for direction changes rather than just drive into them at full feed rate. How the controller calculates that can be quite complex, depending on the sophistication of the controller, how it "looks ahead" at the upcoming G-code, and what maximum values for speed and acceleration limit the movements.
I believe all of the USB versions of the shark are based on the original NCpod controller (which seems to have pretty much disappeared from the open market about the time that NWA started using them.) While you may be able to change the maximum values for some of the parameters, it comes with a trade off of possible missed steps. These parameters can be accessed though different key combinations for different versions of the controller, and were most likely not intended to be field adjusted by owners for unmodified machines. However, your machine is no longer unmodified.
The value you are most concerned with is maximum acceleration limit for the x and y axes. The z is a little different in that it needs to lift the weight of the router on "retract" movements (which can also be at fast feed rates). Missed steps in the z can lead to the downward creep of the z zero position during a run.
At the end of the day, you may get to feeling adventurous and replace the entire shark controller with something like a Mach3 - smoothstepper- gecko G540 system. This would allow you to do much more with larger stepper motors, limit and home switches, pendants , etc. All the parameters governing speeds and accelerations are user adjustable , so you can fine tune it to your particular machine situation. (the mass of the moving parts is important). You would however give up 'virtual zero" if you use that function. At that point you have pretty much built your own entire machine.
Thank you for the help, my curiosity is satisfied. I hadn't thought of it that higher curve speed might cause missed steps; I was thinking only of flex in the machine. That makes sense though, and I can't afford to lose steps! I've had that happen a couple times and it is really aggravating. I'll just use it as is and be happy.
