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

[JAZZCNC]

Haaaaaaaaaaaaaaaaaaaaaaa

[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.

[sweetdream]

The CNC is primarily steel box section,welded AND bolted! There are some new thoughts on the design, assembly and set up. I've not followed the classic route for a gantry CNC, I believe that there are major improvements that can be made to the 'normal' design which improve strength and accuracy both on the Y and Z axis. The X axis is probably the easiest one to strengthen.
On the Y and Z axis, the ball screws sit between the profiled rails, with the trucks outside the rails of the adjacent axis.

The Z axis is 20 mm ECO plate aluminium, built into a small but very strong arrangement. We had a large 4x4 parked on it at one point without any effect.

[sweetdream]

The cooling system is mounted onto the Z axis and all contained on it. Standard arrangement to the spindle but one side fed from the 12v pump which gets the coolant from the clear reservoir. the return side heads to the twin fan cooled radiator and the radiator feeds the coolant back into the reservoir via a bubble trap. a couple of chunks of styrofoam give a visual that the coolant is moving as it should. The radiator and fans are mounted on the back of the Z axis, making it a very compact solution. total length of the pipe work is less than 4 feet.

Other bits about the Z, the trucks are mounted top and bottom, side by side, giving maximum load carrying in each direction that the forces will be applied. Ballnut is through the centre and in-between the line of the trucks.

[IanS1]

This thread definitely needs more pictures.

[sweetdream]

Phew... been a busy couple of months there..

If anyone is around the Lemington Spa area, the beast (must be 400kgs... F.heavy!) is on display and making large bits smaller at the model engineering exhibition from Thursday through Sunday, 16th to 19th October.

If you are going, come and say hello.. Full tours available! :-)

EDIT:
Forgot to mention there is at least one other CNC there, CNC lathe and I understand some 3d printers and laser cutters too... During a brief wander around earlier I also spotted some reasonably priced end mills and nice chunks of alloy I shall be revisiting. :-)

[GEOFFREY]

Hi sweetdream, thanks for mentioning exhibition at LS. I have just booked tickets on line for tomorrow, so will probably see you there. G.