Assembling Aluminium CNC Machine (Continued) / Hard Limit Switches / Lowering Wasteboard / Insert Nuts

In this video I’m going to show you the last things I did to get my CNC machine up and running. To start with I cut the top and bottom pieces of the z axis so the spindle wouldn’t hit into these. Later I further cut the bottom one to re-fit the old dust shoe onto the spindle.

I also decided to change the positioning of the aluminium profile under the wasteboard – to make it a little more rigid, and to also lower the wasteboard and increase my cutting capacity.

I’ve just taken everything off. It seems like it’s 63cm.

I got the sub-wasteboard cut externally on a larger CNC, based on a design I drew up in fusion 360. The previous version had gaps around the machine which debris would build up underneath, and it was difficult to clean.

The aluminium extrusion slots into the grooves. I’ve made pretty much most of this up. And I’m just going to now finish the last section which will be the front of the machine. I’ve already got eight t-nuts on this. The protrusion is about 49.5mm.

Because I knew on the far end of the wasteboard the profile was pushed up against the rebate – I used my feeler gauge to work out the offset from the opposite rebate and made sure that was consistent all the way along.

I’m just tightening this side first underneath. Then the middle. And now the far side. I’m just measuring either side and it looks bang on. I’m making sure I’m holding it down flat at the back, and the extrusion is ever so slightly creeping over 67cm. So it’s like 67.2 or .3 or a mm. And it’s the same on this side.

I then careful re-tightening the brackets making sure to secure the face against the profile I had just fixed ensuring the front and the back aluminium profiles were parallel.

So this is going to be the front because the extrusion is poking out ever so slightly beyond the MDF. And it means that providing that it’s square I’ll be able to clamp material onto there to do end-grain milling.

So what I’m going to do is secure all the plates in the four corners, fit the angle brackets underneath, and try and tidy up the wiring. I’m just going to cut the camera here and then come back after I’ve done that.

I’ll recap on what I’ve done in a moment, but I’d like to jump directly to how I’ve wired some hard-limit around the CNC machine. These link directly to the reset or e-stop terminal on the controller.

I’ve set up this relay here – it’s a 12v relay. I’ve got a loop of limit switches to the extremities of the CNC machine. They’re all on normally closed terminals. The 12v signal goes all the way through the wires and when it breaks, the 5v signal from the controller is interrupted by the relay and that triggers the emergency stop. And what this allows me to do is to have a failsafe in place which will prevent me crashing the machine in anyway. I’m not sure if this is the best way to wire it, because the relay is held in suspension. If I turn it on you’ll see how it works. So if I press one of the switches it goes to zero, and if I show you the… so that is 5v going through and when it’s pressed that drops to zero, and it means the signal is interpreted as an emergency stop.

So I’m going to to move the z axis up 100mm. If the switches weren’t in place this would crush the limit switches. There’s about 2mm of room.

So after the plate hit the limit switch, I had about 2mm of distance which I could still move upwards, before I started to actually damage the switch. I’ve adjusted this (screw) about 1mm between that so that this (the screw) physically stops the plate from crushing the parts.

Each time I moved along a different axis towards another limit switch, I had to back off away from the limit switch and unlock the arm-setting on bCNC. If I hadn’t done this before moving to the next limit, the incoming plate wouldn’t stop.

Each time I moved along a different axis towards another limit switch, I had to back off away from previous limit switch and unlock the alarm setting on bCNC, If I had unlocked the alarm status and hadn’t backed off from the limit that I’d just pressed, the controller wouldn’t recognise the already pressed limit as an alarm, and in theory I could move across to another limit, along another axis, and the incoming plate wouldn’t stop if I hit into it.

I’ve got a message on this – alarm 3 , reset while in motion. GRBL cannot guarantee position, lost steps are likely, re-home is highly recommended. So that’s happens I have to re-home the machine and if I press reset I’ve got the alarm, so I have to press unlock.

The other thing I did and didn’t bother filming, was to fit the homing proximity sensors at rights angles to their incoming plates. I used a bit of angle bar to do this and this will prevent them being accidentally crushed.

I’m now going to check whether I can home the machine while the homing proximity sensor is triggered. I was hoping I couldn’t.

Ok you can’t see this but this is already pressed – I’m going to move the z axis a little bit higher so that when the axis moves back it’s still in the sensors range and now I’m going to press home and see what happens. If it kind of misses that. And I get an error here saying hard limit triggered, machine position is likely lost due to sudden and immediate halt, re-home is highly recommended. So once I’ve trammed and levelled my machine I’ve got the failsafes in place with the software and also a physical hard limits wiring into the reset terminal which should prevent me from getting everything to come out of position.

I just glued the acrylic pipe into my original dust shoe. I had to trim this up again, and I did that by jigsawing the majority of the material out and then going over it with a trim bit. While that glues I’ll start levelling the machine. I’ve already used it in a previous video with a different machine but essentially I’ve slackened off the machine screws on either side, you can see I’ve levelled it to the back plate. If I run a light back there and it looks pretty good.

Now I’ll adjust it this way around.

I’m just moving the spindle around the machine just to make sure everything’s ok. Not entirely sure about the ACME thread on the x axis. It just feels like it’s very wobbly even though it’s held in place on either side. It’s just not thick enough.

Ok I think it’s ready to go. I’m just going to bite the bullet and do it. I’ve checked the distance that it can plunge down and I’ve moved the lower limit at the bottom a little further. Once I’ve done this then I’ll re-position it so that if I make a mistake I wont be able to plunge all the way through the actual wasteboard. This is the sub wasteboard which I’ll be screwing he wasteboard onto. I think it’s from the right position – I’m working from the centre of my DXF file – lets see what happens.

While that’s cutting I’ll recap on what I’ve done to the machine – in a mad rush I didn’t film everything but this is the list. The first was to cut top and bottom z axis motor plates – so the spindle movement wasn’t impeded. This was my mistake and I’ve also corrected the 3D model. I also lowered the waste-board height, which involved cutting and re-fitting the aluminium profile. I wired hard-limit switches at the extremities of all the axes, to the reset terminal on controller via an opto-isolated relay to prevent me from crashing the machine. I made new mounts for the homing proximity sensors – which held the limits at 90 degrees to the incoming plates and again prevent the expensive parts from being accidentally crushed. I checked the hard and homing limits. Adapted the old dust shoe to fit the new machine. Levelled and trammed the spindle. Checked the movement. And I also cut the insert nut mounting holes for the wasteboard and fitted the drag chain which included making the aluminium parts.

And this is the finish machine more or less. I think I may have routered these a little too far and there’s some gaps between the rebate and the t track which is annoying. I’ve actually done quite a bit to the controller since the previous shot. Which had dramatically improved the performance of the machine – but I’ll go over those changes in a separate video because they amounted to quite a few. The main thing is the machine itself is complete and ready to use. It’s not the most heavy duty CNC machine out there but for my purposes and budget – it’s evolved into something that both novel with its pivot plates and physical hard stops – which is easy to tram and squaring, and judging by this footage is cutting really well.
Thanks again for watching, commenting and to my supporters on Patreon. And I hope if you’re making a CNC machine as well, that you can learn from my mistakes and work twice the speed.So like I said in the next video I’ll talk about all the changes I made to the controller. Until then.

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