Sweet dreams CNC - more than one step beyond...

[sweetdream]

The suicide test;

So the machine is running without smoke pouring forth, all the bells are ringing and the whistles whistling.. (why don't bells belling?) spindle has been powered up and a couple of small tests run. so still air cutting at this point. ...Commissioning continues.

Time to up the ante.

Bearing in mind that body parts may well be found in the same vicinity as gantries and other moving parts, cue the suicide test.

The suicide test
Set gantry at one end of the X axis.
Set speed in excess of 30 metres per minute.
Hold down the button and drive the gantry at the highest speed you can get into the stops at the other end of the X axis!
Wait for the very loud bang!

Repair as required



I hit the switch and there was a whirr and a blur as the gantry shot from one end to the other in what seemed like well under a second. There wasn't time to take my finger off the button before the limit switches did their job. I don't have an exact figure of the speed it reached but I can tell you that the gantry was still accelerating when it crashed into the the Omcron microswitches at the far end of the profiled rail. lol.

The switches have 3mm of movement, .1mm between open and closed. Assuming 4mm of total travel, the speed of the gantry when it hit the switch can be calculated from the time taken between the switch being activated and the distance traveled before stopping. The speed of light and the price of mars bars being unequal, the gantry was travelling in excess of a "greased lightning" when it got to where it was going!

Confidence went much higher after that test. The limit switches worked great, even in the worst case scenario of a runaway gantry, the worst that I'd expect to see was a crushed switch as it didn't get as far as hitting the metal stops.

If you are building a machine, fit the limits and estops before you wire the motors. Watching a gantry move at high speed is really not something you want to see from the wrong place. If your gantry moves as quick as this one did, you'll never make it to the power switch in time.