I have never heard of anyone placing a machine into a "price class" based on the feedrate, rpm, and part sizing. I dunno, I think more in terms of "price ranges" rather than "classes". Sure, I have heard something like " Such and such is a $100K machine" but that is not a class, just a statement of the cost of the machine. Gary, where do these "price classes" exist? I have been around a long time and have never heard the term as you stated it. The ability to hold a given tolerance at a given feedrate in a given material." This is how CNC machines are placed into "price classes". "With all of the above being true, it is the operators job to run at the fastest feedrate and lowest RPM that returns acceptable edge quality and part sizing. And then there is the thing you touched on, the motors may not have the ability to accelerate the gantry without losing steps. Trying to accelerate the mass of the gantry too fast causes a negative reaction in the base of the machine. That whole (for every action there is an equal but opposite reaction) starts to make itself known. At that point the motors are starting to move the machine itself, not just the driven elements. The mass of the gantry causes a problem at that accel/decel. That is why I made the comment about how my machine started to react at 37 in/sec2. Surely a lot depends on the mass of the gantry, spindle assembly though? A lightweight router on an aluminium gantry is going to have a lot less mass than a 6hp spindle on a steel welded one for example.Īll my experience with acceleration, deceleration is with the design of racing cars rather than CNC admittedly but my gut instinct says mass will play a major part and I expect the ability of the steppers/servos to handle that deceleration without skipping as well. Here is what happens when the accel is increased by 20% in the first calc on the left: The machine is not heavy enough to resist the forces those accels/decels create. I have had mine as high as 37 but I was not comfortable with the way the machine was reacting as a whole. But it is running as fast as it can.īTW, 25 in/sec2 is not a really fast acceleration for a machine. The machine slows down and does not reach programmed feed rate. Later in the video when it is finishing shows what happens when the moves are much shorter and involve rapid changes in direction. During that roughing there are long runs where the machine runs at 350 IPM. The second video I posted above is an example of why a person might want to program for the fastest possible feedrate that does the job. I was sort of surprised by what this stuff looks like, I was thinking that it would take much further to reach a speed of 300 IPM. The one on the right shows that it takes 1/4 the distance to reach one half the velocity of the one on the left. Because acceleration is based on time squared these calcs are not linear. The chart on the right shows the same info to reach 300 IPM. This shows that at an accel of 25 inches/sec 2 it takes the machine 2 inches to reach 600 IPM, it will also take 2 inches to slow down if it is making a sharp turn at the end of the move. Machine rapids to wrong spot, ooops, Ted, you forgot to reset your zero for this part! If I am doing multiples I just comment that line out when I know it is in the right place. That way I can make sure that the program is running from where I planned to run it. I also do a couple of other weird things, like move the machine to program zero and then do an optional stop at the beginning of every program.
Since I do it that way my rapids when moving the machine manually are still fast but I can slow them down during a program if I want to observe better. I have my post set up so that it does not output G0 moves, instead it outputs a G1 with a feedrate controlled by a variable defined at the top of the program.
I might be the only person on the planet that does this, but. Heck, I can most likely cut at 800 if I really wanted to.įrom what I have seen of your machine I would certainly think so. I can cut at 500-600 and possibly faster.