CNC Controller Rebuild / All the things I wish I knew Beforehand

Ok I’m still getting some problems with interference while using the CNC machine. The last thing that happen while making my super chisel was the spindle moving up in the z axis. In fact it moved in that direction, and luckily because I had hard limits in place when that crashed into the top it just stopped automatically. I also had another problem while cutting where the job just stopped mid cut… That could have been from a loose connection somewhere along the wiring.

Something else that happen, and I don’t know if this is related or not but if I stopped a job mid cut the coordinates changed on my software – and in particular the z axis always seemed to change and it’s never consistent. I’ve obviously done something wrong with how I’ve wired this up so I think I need to investigate this and  possibly redesign how this is put together.

The first thing I should mention is that… I don’t want this video to become over-complicated – and I can already admit I hadn’t filmed everything, so what I’m going to do is just talk about where I think I’ve made mistakes, the things I’ve changed and how I think these changes will improve the machines performance.

The first is that I used braided earthing strap to shield cheaper cables to the from the VFD. The problem with this was that the metal braided shield is not insulated from other metal contacts, and it would be with SY cable which is what I used in the end. So I’m going to have to replace all of these.

I think I’ve also created problem areas where I’ve tried to expand the use of the controller – so I could connect it to a laser engraver. And to have the option to switch between  this (the laser) and the VFD. In reality it’s meant I’ve had to run wires a lot further than I would otherwise had done.

I also don’t feel like I did a great job with the aviation panel mounts, which I used between the controller and both the spindle and steppers. Not only was my soldering skills poor, but the panel mounts made the continuity of the cable shield more complicated to maintain.

So this one here, really what I should have done was use a gland and kept the wire intact passing through this point and then to my VFD.

I also think I may not have earthed the shielding correctly – all of which should led back to a single star connection, which I had instead branched. Everything is connected but in reality something may be looping in ways which may not seem apartment.

I’ve also over-used power supply units – and cluttered the enclosure with wires. In retrospect, my hard limits switches, and homing proximity sensor, steppers motors and controller could be run from the 24v PSU – which would have been a lot easier to wire up.

The VFD I used was poorly documented and made wiring more difficult. That said I worked out how to programme it – but basic instructions were not well translated in the English manual. I doubt the VFD had an internal EMC or EMI filter, and I may have wired the external one I bought incorrectly. I also didn’t place ferrite cores on the wire to the spindle and earth terminal on the spindle hadn’t been connected to its housing.

Moving on from the VFD there’s other areas that I need to look at. One thing is the voltage dividers that I’ve used… I use voltage dividers to convert the signal from the homing proximity sensors from 12v down to 5v, however this method doesn’t isolate noise returning to the control board.

Ok so, what I’m going to start doing is slowly dismantling the cables and taking things apart so I can have better access to the core wiring, and then I’m going to look at the power management first, and the go through the various stages of re-fitting the VFD and re-wiring the homing switches and so on – and hopefully by the end of it this will look a little bit neater and also work.

On a manual for a different VFD whic his available in the UK from RS tools there is one section here about wiring up to the motor. EMC guidelines. So this is the bit I don’t get. To prevent radiated noise, motor cables should be put in a metal conduit. Alternatively an armoured or shielded type motor cable should be used. For effective suppression of noise emission the cable armour or shield must be grounded on both ends to the motor and the inverter ground. I was told you should only ground on one end so that’s confusing me. These connectors should be as short as possible. Motor cables and signal lines of other control equipment should be at least 30cm apart. So there’s lots of information in this actual manual, that I can interpret which is illustrating lots of things I should think about.

So this is the enclosure since I’ve done all the re-wiring it looks a lot simpler and there’s a few new things inside. The first is I’ve taken all the power supply units out and replaced them with a single 24v 400w unit. I’ve also added a opto-isolator board which is connected between the controller and the terminal block with runs off to the sensors. I’ve also done a lot of tidying up of the wiring.

I think the first thing I’ll do is talk about the VFD. I’ve taken off any shielding which I additionally added for example onto this ribbon cable because I was worried that would might contact something and create some kind of ground loop. Everything is pretty much the same in here although I ended up changing the wires to thinner gauge ones for some of the signals. The main thing I did was re-wired the power coming in and the ground I took it to the EMI filter terminal and then run it to my terminal block. And the section here is the start connection.

Here you can see the ferrite core which the cable loops though. I also put ferrite cores on the main plug and the USB cable.

 

I’ve removed the aviation panel mount here and replaced it with a gland, so the cable and shielding is not interpreted . This runs all the way to the spindle.

The spindle is a little bit different now. There’s two things that I’ve done. The the armour or shielding – this braided stuff in the cable. I’ve actually let it extend out a little bit and clamped the aviation socket to it. But it actually isn’t connected to the chassis of the spindle. Just compare it to Nathans machine – which is connected.

So clamping the braid onto this isn’t doing what I though it was going to do. That said I have used the machine a couple times since finishing it and it seems to be performing ok but only time will tell. The other thing I did was, most spindles I’ve seen have four pins. One is written down as the earth but there’s never anything connected to it. So what I’ve done in this case is actually wired to a crimp which I’m putting through a mounting machine screw. And this connects the housing to ground. If you do ground the housing of the spindle it will mean that the terminal you use to do your probing have to be placed in a specific way so the ground is then connected to the bit and the signalling is essentially your touch plate. I think it is important to connect the spindle because in my current set-up it’s obviously isolated because of the mounting method and material.

Obviously having a permanent connection makes it a little more hard to move around. At the front of the machine you can see I’ve replaced all the aviation panel mount with glands. So they are all through cables and nothing interrupting that. Soldered at one end and physically connected to the controller or the opto-isolator at the other end. You can see where I got rid of the switches for the laser here. And this is where I’ll plug in an extractor. The only thing I’ve kept the same is the probe wire. The reason I’ve done this is because I’m planning to use a couple different probing methods and tools which I’ll talk about in another video.

I also changed the wire which runs to the hard limit switches around the machine, to a continuous wire and there’s a gland there just to stop it from being pulled out.

I really wanted to keep the display panel at the front of the machine plus this selector switch or toggle switch to go from the PWM signal on the controller to the potentiometer.

I’ve created solder connection for a lot of things instead of screw terminals where I can, to create better connections. I did swap a lot of the cables to thinner stuff. I realised I didn’t need such chunky wiring as I was using before. I just twisted it and made sure it was clear from everything else. And here we got the isolation board. 24v comes in. I think there must be some kind of resistors in there as when I take a reading from this side the voltage drops to 8v. So on it’s un-triggered state it’s 0.45v and when the sensor is triggered is jumps to 5v.  I also 3d printed this bit at the bottom here to hold this in place. It’s not great but at least it won’t flip over or get pulled. And I made a similar thing for the bucks voltage regulator which I’ve connected to the power supply unit, and it’s drops the voltage down to 12v so I can turn the LED’s on – which I put in a while ago.

This is the 24v relay. One side is going to the hard-limit switches while the other goes to the socket for the coolant although it would be a lot better if it could function as a switch for an extractor to be honest – and that could turn on and off, or I could just wire this up instead.

So this is the main terminal block where the power comes in, and then goes to the contractor and fuse and allow the power to go to the rest of the system. While filming I did a bit more reading about this particular cable. I’m not sure if it can be deemed as shielding but I think it will work if I do create a physical connection between the metal and the metal underneath.

The other thing which I should have done was used galvanised steal as the backing plate here and not aluminium. Coz this can oxidase and effects how electricity flows through it.

The is the manual for the VFD I was considering buying but I didn’t particularly want to spend £150 on it just yet but maybe I will still. There’s a lot of really interesting things and worth a read. Here it says if using an external EMC input filter it must be mounted under the drive and connected directly to the line supply via an un-shielded cable. You can see how they’ve shielded the cables – literally screwed directly to the backing plate by the looks of it. The a cable must be connected to earth on both ends, the shielding must be continuous.

So that’s essentially what I’ve learnt, and the changes I’ve made to the electronics of the CNC machine and it’s controller. I’ve been cutting stuff out, on and off now for several weeks, and I’ve not noticed any unusual behaviour. So it seems that the changes I’ve made to the controller have made a difference – but I still need to fine-tune the steps, acceleration and nut-block tensioning for the x, y a z axis, which is what I’ll be looking at in the next video.

Thanks again for watching and you’ll catch me then.

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