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

[njhussey]

Liking the cut of your jib...looking forward to seeing details of the build and the machine...

[Washout]

I think any man with a beer fridge in his workshop is going to fit in well around here

Although chilling Spitfire is not an approach I would advocate ;)

[sweetdream]

I think any man with a beer fridge in his workshop is going to fit in well around here

Although chilling Spitfire is not an approach I would advocate ;)

I thought the fridge was a requirement for joining this illustrious gathering??

There's got to be a joke about spitfire and cold in the spirit of the other ads.. just can't think of it..

[Jonathan]

I think any man with a beer fridge in his workshop is going to fit in well around here

Does chocolate in the 'fridge' at -70°C count?

[sweetdream]

Does chocolate in the 'fridge' at -70°C count?

..chocolate counts only if you can eat it!

[sweetdream]

As mentioned the frame was initially going to be 80mm box section, measuring the steppers showed that by careful arrangement, the frame could act as the stepper motor mounts, saving the costs of dedicated mounts [pic] this worked rather well on the X and Y axis but as there was no box section on the Z, it couldn't be done there. The Z axis had its own design spec, small, as compact as physically possible and strong, very strong.. The Z stepper mount needed to be adjustable in one axis (same as the X as it happened) but solid in every other. 4 pieces of 10mm alloy sorted that.

Getting the spindle as close to the gantry as possible, mainly to reduce the leverage effect from the spindle under load, was another area I spent some time on. It's ended up 140mm from the centre of the spindle to the centre of the Y axis and the Z axis is 144mm wide! This minimises the amount of table space lost to the spindle. The only parts on the table, profiled rail, and ball screws that have to be there but cannot be used by the Spindle when the Z axis is 1mm off the stop switches is 146mm on the Y Axis, 73mm each side.

It should also be remembered that smaller chunks of 20mm ECO plate are cheaper than Large chunks of 20mm ECO plate! :-)

[pic]

The height [?] is where the space was found to mount the cooling system pump / reservoir and the Z axis stepper pulley arrangements. A couple of junction boxes take care of the wiring and act as an anchor for the twin runs of echain.


Very happy with the result, the Z axis stays within the confines of the 4 Y axis trucks wherever it moves, the Horns do their job and the 5mm thick steel triangulated plates that were shown not to be necessary on the simulation, but for the sake of 30mins welding, "over engineering" was preferred to "always wondering". lol.

[sweetdream]

I mentioned earlier about the 'boring soldering'! One of the things I anticipated happening when I started running a new untested machine, at least for the first few times, was that you needed eyes on a swivel! Even by phasing the testing to only specific circuits, there comes a point where you have more new bits running than you have eyes to watch them! The automation of voltage and temperature checking etc. meant that I could focus on stopping the spindle diving into the sacrificial bed or any other undesired behaviours.

The wiring shown is for 5 LCD screens mounted into a console at the front of the CNC. The screens show various information about the machine without have to go look for it or fret about it. This is in addition to the touch screen mounted onto the frame, but facing away form the swarf! :-)

The Blue LED section in the wiring pic (above) alerts you by turning red if anything goes outside the parameters you set. For the startup tests, this was set somewhat conservatively! :-) During the tuning phase these parameters were relaxed somewhat as the machine was dialled in.

The screens are augmented by override buttons, for instance, capable of turning fans on if they are off, or off if they are on. They are fed from 2 CaT5 cables, one from the Z one from the rear wiring.

[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.