Earthing?

[Clive S]

Ok A metal enclosure is best by far just make sure it is big enough 600 x 600 x 200 is popular.

The star point is where you connect all the cable screens to including the mains in earth.

Fuses I personally rely on the MCB in the box for the power supply fuse But it does no harm to fuse the smaller PS ie 5V or 24V desperately (good to get din rail type for these)

Regarding the mill the earth to the mains frame is probably for the electronics in the speed controller that might be on a swivel type mounting. You would be powering (mill) this from a separate 13A plug.

[Edward]

Thank you for the helpful answers:)

However, could I ask further about the PSU earthing? This is the PSU which I bought from Zapp ready-made for convenience:

http://www.zappautomation.co.uk/elec...er-supply.html

As you can see, it has no metal case, it all sits on the pcb and I can't see an earth point. Maybe this one has internal earthing, if such a thing exists?

I see you are both using MCB's that's cool, I'll have to investigate this. At the moment, the limit switches (micro type) IO's are fed by the 3.3V supplied by the Kflop board so I don't need additional low DC supply. However, I am going to use proximity sensors instead, and that will require a 24V supply. So as I expand and start to use relays to trigger this and that, I will need an enclosure that allows for this expansion, even though at this stage it may look huge and rather empty.

Another question regarding proximity sensors, I ordered a couple of the cheapo ebay ones for less than 10 quid each to play with, a bit bulky, but are they any good? I notice that some proximity sensors can cost a small fortune. For our type of usage, what does an expensive sensor offer that the cheapo ones lack?

Edward

[JAZZCNC]

Hi Edward.

The PSU will need mounting either directly to the back plate using stand offs or on separate backplate(with standoffs) which then mounts to enclosure backplate or Cabinet side. My prefered way is to mount on separate plate then fasten this to cabinet side as it saves space.
In either case if Metal enclosure you won't need Separate earth as the Whole Box will be Earthed. However if you want to bolt the gate so to speak then run separet wire from Star point to one of the holding boltings. !!!!!! WARNING !!!!! DO NOT put Earth wire to the Bolt which holds transformer.!

If Plastic case and PSU isloated then Good idea to run Wire from Star point to the point plate.

The main thing is you don't have Wires Earthing to different points, if running earthing wire then always to Star point.
Personaly Even with metal back plate and the component does have Earth connection I always take it from the Star point with wire and never rely on the back plate for Earth.
Same with Shield cables, while technicly could connect to back plate I don't. Always back to Star point. This way I never have any issues or chance for ground loops to occur.
Proud to say never have any ground faults or false trips on my machines and these little details are mostly why. These and good components.

In general you want to Fuse all AC devices with MCB ie: Main PSU, 24Vpsu, VFD etc. The DC devices like Drives, fans then I use Glass type fuses.

Regarding the cheap Prox switch then depends on what usage and accuracy/repeatabilty your chasing.?
If just limits then yes they are fine. If Router/Plasma etc then they are also fine for Homing. But if it's Mill and your chasing V-High repeatabilty on Home Sw then may pay to buy better quality.

[Neale]

I am using one of those power supplies myself, and I have just bolted it to the case on stand-offs. Works fine for me. Doesn't need earthing as there is no external metalwork that is likely to come into contact with mains voltages.

I have also just come in from the garage where I have been setting up my new machine. As part of squaring the gantry, I have been checking repeatability of position of the gantry using a dial gauge. I'm using cheap proximity switches (mine cost something like £20 for 10 when I bought them a couple of years back but they are a bit suspect so I've just bought some more at about £10 for 4 although I haven't tested these yet). You can't expect wonders at these sorts of prices, but doing a set of runs where I move the gantry down the X rails a distance, then home it, I'm seeing something like 0.02mm repeatability in the homed position. However, I haven't gone round and checked things like the ballscrew bearing nuts since I first put it together and there might be a bit of play as the bearings settle in after a little bit of use. There's also a bit of uncertainty in the position as my dial gauge isn't ideally positioned and isn't as solidly mounted as it might be. Nevertheless, that's probably acceptable for a machine primarily intended for wood.

[Edward]

Thank you Dean, for the clear advice and for the warning about the transformer! I've learned so much from this forum.

A metal enclosure it will be, more expensive, but worth it.

I think I will try the cheapo prox sensors first, as I am more interested in them acting as limit switches, at least at this stage. I'll keep you posted.

Oh, a last question unrelated to this. What is the average or expected backlash on bog standard ballscrews C7, chinese. My backlash is between 0.045mm and 0.054mm for each axis, i.e. including the bearings, etc. Is that reasonable?

Edward

[JAZZCNC]

I think I will try the cheapo prox sensors first, as I am more interested in them acting as limit switches, at least at this stage. I'll keep you posted.

They will be fine but bit of advise Fit Home switches ASAP. Infact if I could only choose one it would be Home every time. Far more usful than Limits and can use Softlimits to put you one until Limits are fitted.

Oh, a last question unrelated to this. What is the average or expected backlash on bog standard ballscrews C7, chinese. My backlash is between 0.045mm and 0.054mm for each axis, i.e. including the bearings, etc. Is that reasonable?

Edward

About good as it gets for Chinese C7. Acceptabe or not again depends on usage. For Router yes more than enough. For Mill then might want to chase higher but again depends on what your doing and prepared to accept.!

Didn't see you say what type of machine.?

[Edward]

Hi Dean,
Yes, I can designate them as Home or limit switches, or both. I think Mach3 works similarly. With Kflop for instance, you assign a Home button to execute a C file for homing that basically reads the sensors as home switches, homes the machine, then pulls off a little, zeros the coordinates and then turns the sensors into limit switches.

The mill is a Sieg2.7 conversion, which is just a little smaller than an X3, but with better Y range and I think a similar brushless motor, 750W. It's massively better than the SX2 in every sense, for those who want to know. I haven't actually cut anything with it yet, though everything moves as expected. I want to get the electronics in a box to get them away from the muck. In terms of accuracy, well, I am not expecting great miracles, but it's as neat as one can do...for the money spent. We shall see what the pieces look like, the time it takes to produce them and so on, it's my first foray into CNC.

I have been playing with the backlash compensation, and it's pretty unbelievable what software can do! The compensation happens in milliseconds, and using a dial gauge, the backlash "removal" is bang on. I don't know how good it will be in real life, cutting a circle, changing direction, for example.

Edward

[JAZZCNC]

I have been playing with the backlash compensation, and it's pretty unbelievable what software can do! The compensation happens in milliseconds, and using a dial gauge, the backlash "removal" is bang on. I don't know how good it will be in real life, cutting a circle, changing direction, for example.

Backlash Comp is a fudge at best, better if can remove any slop.! . . Not seen one yet that will get of rid the chatter. . .Lol

[Edward]

Hi Neale,

Good to know about the PSU. I will use standoffs too.

The prox sensors I ordered are these:

http://www.ebay.co.uk/itm/1620167184...%3AMEBIDX%3AIT

Maybe yours are something similar. I will play with them when I receive them before I commit. If I get 0.02mm repeatability I will be very happy:)

Edward