Aluminium Profile Type Router - Initial questions

[CNCRY]

Just a (genuine) question - have you considered belt-drive on the X as well as Y?, for me workshop space is a critical issue and being able to rotate the motors 180 degrees into the frame of the router would be a design goal if only to reduce the depth of the machine as it sits on the bench. If that's not an issue for you then ignore.

Hi Doddy, I considered this earlier but as the gantry is going to extend back on the X axis, beyond the cutting bed size anyway, then the motors don't add to the footprint, and slightly simpler to connect direct. It's on a workbench which is 120cm square, so gives me about 20cm for the motors/wiring etc!

[Neale]

Personal view - there is little point in providing fuses for the drivers. A fuse will never "protect" a driver as the semiconductors in the driver will let out the magic smoke well before the fuse can react in the event of a major fault (and I'm thinking short-circuited motor wires, for example). If the built-in protection doesn't work, then it's already too late for a fuse. Where a fuse might help is in the output of the driver power supply, or maybe in the input to it. In the event of a fault in a driver that causes a high current draw, this will protect the power supply. In fact, the only electrical fault that has happened in my own control box was an internal short in the toroidal transformer which took out the fuse on the input (mains) side - fortunately. Generally speaking, fuses do not "protect" equipment - they help stop wiring, etc, bursting into flames when something has already failed. As I say, this is a personal view and others are paranoid about fuses everywhere. Be interesting to hear if these fuses have ever "saved" anything!

[JAZZCNC]

Personal view - Be interesting to hear if these fuses have ever "saved" anything!

My personal view is that it's stupid not to fit a fuse just to save a few pence. Why risk an £80 drive for the sake of an 80P fuse to protect from the unknown.!.

To answer the question have they ever "saved anything" then it's a BIG FAT YES I've had many cases where things like loose wires have shorted or been rubbed through etc. The point being your not actually always trying to protect the device but the system as a whole from unforeseen circumstances so spending a few quid more for fuses to protect valuable parts of the control box is a No brainer to me.

[AndyUK]

Be interesting to hear if these fuses have ever "saved" anything!

I've already buried the spindle in the work a couple of times, both times have 'gently' blown the VFD fuse before any damage was caused elsewhere. The power loss to the VFD also causes a fault on the controller so stops the motors, which is kinda nice.

I have this for the cabinet layout - does it look OK or any issues?

Three things spring to mind:

• VFD Spacing against internal walls. Read the manual for how far it should be away to allow adequate air flow.
• I'd keep earth near Line and Neutral, thats where it comes in after all, and a lot of the big ticket earthing items will be mains voltage.
• You've made a good start trying to separate voltage levels, but the 5V PSU should be at the low voltage end of the cabinet rather than its current position near 65V DC.
• Think about air flow through the cabinet - At the moment your drivers will get decent flow, but the VFD won't. What direction are those fans? I orientated my drivers to allow maximal air flow through their heatsinks, at the moment your heat sinks are at 90 degrees to the air flow.

Will it work in its current state? Sure. None of these things are big issues, just minor points.

I'm planning to buy these - could someone confirm they are OK choices, especially the contactor! Looks like it is DC

https://www.rapidonline.com/mean-wel...cy-psu-85-5684
https://www.rapidonline.com/schneide...tactor-66-1939

You've gone for the high efficiency and expensive one, is there any reason? This is the alternative to save £10.
https://www.rapidonline.com/mean-wel...il-psu-85-5678

Contactor seems okay.

Couple other questions from the never ending list:)
- Do I need to Fuse the drivers? They have overcurrent/voltage but I notice some people have?
- Are EMI filters needed with decent star grounding? I'm planning to add the EMI filter option on the transformer.

Extra fuses won't hurt.
The advice I found at the time was that some people needed to plug the VFD in at the other end of the workshop to reduce the noise back from it, and I wanted to be able to power everything from the same socket. The EMI filters I used were about £5 each, and although I have no idea if they're needed or not, they do allow me to operate without noise issues with everything running off the same 13A socket.

[Doddy]

Aha, the old benefit-risk balance.

The fuse is cheap, however, the probability of it protecting a driver with a shorted output is uncertain - I can imagine a driver without overcurrent protection popping before the fuse depending on how much you've pissed off your local deity.

The real purpose of the fuse is as a safety device to cover the fault condition and something in the high-hundreds VA rated transformers making something go bang. Or Pfftt! Or Whoosh!. Or whatever sound a decent arc makes... something like Pzzzzat! It could save the transformer as well which could be a good part of a hundred quid worth. And if it avoids a fire, then it might save on the insurance excess.

A fuse on the drivers can't be considered a bad thing but don't rely on it protecting the drivers.

[Doddy]

The power of the internet! One of the key attributes of toroidal transformers is a very low flux "leakage" which will limit any potential induced current. I understand the argument but would challenge the actual risk - if I had a toroidal going spare I'd set up an experiment (it's interesting, and this is the first that I've heard of it, and the evidence from the internet looks to be more anecdotal than academic). Actually, because of this thread I've ordered a toroidal just for this experiment - I'll report back in a few days. My thoughts are any current is likely to be measurable but insignificant. The risk can be mitigated in any event by isolating (air gap) the top of the bolt from the chassis to avoid the short.

Edit: What Clive said. The more I read the more interesting this experiment might be.

[Doddy]

Wow!, just... Wow! I take back everything.

Following the previous post I'd realised I have a bench PSU with a chunky toroidal transformer that I'd previously hacked to pieces. Sounds like a good experimental platform. Ignore all the crap on the bench - I really need to tidy up.

Pic 1: General topology, next-to-nowt resistance (0.1R) from the top of the mounting bolt to the chassis.


Pic 2: Open circuit Vacrms reading from the top-bolt to chassis - about half a volt. A lot more than I'd expected and enough to ignore the fancy stuff with a shunt resistor and 'scope, and go straight for the "blow-the-hell-out-of-the-meter" probe...


Pic 3: Current short, top bolt through meter and 3 metres of meter leads to ground. Some 3.1A.


So, yeah, isolate that top bolt!

[CNCRY]

Thanks for all the replies - I wasn't expecting a full on experiment Doddy :) Good to have some real results though as everything I found was purely theory, no-one tried it until now!
So in summary if the bolt is used along with the chassis to form a "loop/partial loop" around the core then there is some serious potential for amps to flow, but its low risk if the bottom of the bolt only contacts the chassis, as Jazz mentions this is commonly done with no apparent issues.
I happened to have a piece of phenolic offcut so ended up using that on some spacers, plus the bolt itself has a rubber washer between the head and the metal transformer plate. Probably overkill - and I'm sure I'll do something else instead !
PS before I power up.. Red and Yellow (Vsec from each secondary) and Orange/Black (0V) are connected together - is that all correct for parallel?




Ryan

[Doddy]

It was an interesting and eye-opening (for me) quick test - I've learnt from it so all is good for me. Don't blame Jazz re. the mounting method - that's how industry does it - single bolt through the grounded chassis. As Clive says the two rubber sheets are a form of mechanical protection to allow you to positively clamp on the transformer windings without deformation of the windings and compromising the insulation coating on those windings. The sequence is chassis (bottom) -> neoprene washer -> toroidal transformer -> neoprene washer -> steel plate -> nut.

Re. colours - that's a less than useful label on the transformer but I'd interpret it the same as you say - positional reference indicating the phase of the windings. I've had a quick look on Airlink's website and there's no further useful information that I could spot. Your fuse will tell you if it's wrong.

I've missed the earlier conversation on this but guess you're using AC to power the stepper drivers (no sign of provisioning for rectifier and caps) - I'd think carefully at this time of routing the secondaries in a tidy(!) route away from any low-level signalling, to the drivers - I'm sure you're looking to route to the top of the picture of the box.

[JAZZCNC]

Don't blame Jazz re. the mounting method - that's how industry does it - single bolt through the grounded chassis.

Ye go on blame me I've got wide shoulders I can take it..

Re. colours - that's a less than useful label on the transformer but I'd interpret it the same as you say - positional reference indicating the phase of the windings. I've had a quick look on Airlink's website and there's no further useful information that I could spot. Your fuse will tell you if it's wrong.

Here you go you blind bugger.

https://airlinktransformers.com/post...echnical-notes