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Yes the spindle is only 0.8Kw but most of the cutting I will do is balsa and up to 6mm birch ply. I could have bought a 1.5Kw spindle for less money with a 1 year warranty but the bearings had only 6 months warranty. So I went for a certificated german 4 bearing spindle with a two year warranty including the bearings so no worries for 2 years and the vfd has a 3 year warranty.
One of the worst things with electrical systems is that as long as they are working everyone thinks they must be okay. Also with regard to the VFD and spindle, they would still work with speaker cable. It's only when things go wrong that the difference between a proper installation and something less becomes evident.
Of course as people keep saying it's only DIY so we can just do whatever we want.
Well after fitting up my new spindle and VFD with shielded cable which turned out to be easier than I thought. I have turned a good running machine into one that has lots of Interference with e stops and missed steps. :grey:
Now I know I built the machine with normal wire ( not shielded ) but I was told after it was all wired and ready to plug in that it should have been wired with shielded cable, So now I have to rewire it.
Now just to check 0.75mm/2 4 core cable for the stepper motors and 0.75mm/2 2 core cable for the limit stops. Is the anything else that I need before sending a order off?
Do you have to fit shielded wire from the power supply to the breakout board and to the drivers and the drivers to the breakout board or is it just the limit switches and the stepper motors?
Generally where there is high frequency you need screening, so that means from PC to bob, bob to stepper drivers, stepper drivers to stepper motors, VFD to spindle motor.
I used CAT5 twisted pair for the bob to stepper drivers, CY cable for stepper drivers to stepper motors, CY cable from VFD to spindle motor. Some have said that CAT5 is not flexible enough to run through the energy chain but that depends on the bend radius you have and the type I'm using is stranded not single core.( CAT5 bend radius it's usually considered to be 4x the diameter). Failing that a different twisted pair flexible cable would do. I also used the same twisted cable for the limits as I bought a roll of it, it's the twisting that helps it reject noise.
It's a double edge sword, on one hand you are trying to prevent interference entering the cable and on the other hand you are trying to prevent interference escaping the cable. In general for the first issue screens have been connected at one end only and usually at the same point, hence the term star earthing. For the second issue screens are connected at both ends to meet the EMC regs. So with that in mind are your cables interference generators or receivers, I would say they are all generators except for the limits which are receivers. This implies screens are connected at both ends for everything other than the limit cables. At least then if you do suspect problems you can simply disconnect one end of the screens to see if it helps.
This is worth a read
http://www.nexans.co.uk/eservice/UK-...3_PBE_V2_1.pdf
Though aimed primarily at music applications this is also a wothwhile read.
http://www.phmusic.co.uk/pharri5833/oneend.htm
Thanks Eddycurrent,
I have my spindle screen connected at the VFD end only, should I connect the screening at both ends the VFD and the spindle?
I did twist all wiring when I built the CNC router as I knew this helps with screening but since I am going to totally rewire it I am going to make sure that it is properly done so that there is no chance of interference again.
Another question is, there is eight wires at the stepper motor four pairs, there would be no screening the last few inches or would you add some screening or will it matter for the last few inches?
Any VFD manual will show the motor screen connected at both ends.
Generally it's okay to have the last few inches unscreened becasue somehow you have to get the individual cores into their respective terminals, but you could use something like this
30504 - WURTH ELEKTRONIK - SLEEVING, COND-NYLON, PER M | Farnell UK
Most people use Gremflex just to keep it tidy.
If screened cable is not going to be terminated into a special gland made for the purpose I like to use about an inch of heat shrink sleeving at the end, 1/2 onto the outer sheath of the cable and 1/2 over the inner cores, this keeps the end of the screen tidy and stops it fraying or straying. Mostly it's a good idea to solder a short piece of wire to the screen at the end, this joint is hidden under the heat shrink and makes for an easy way to terminate the screen.
Just to get this clear.
I have used CY 4 Core 1.5mm/2 cable from the VFD to the spindle, But I need to connect the screen to earth not just at the VFD but also at the spindle.
I will fit CY 4 Core 0.75mm/2 cable from the drivers to the stepper motors also the screen will be earthed at the driver end at a star end earth point and at the stepper motor end.
I will fit CY 2 Core 0.75mm/2 cable from the breakout board to the limit switches with the screen earthed at the breakout board, but the screen not connected at the switches.
I could use CY 4Core cable between the breakout board and the stepper motor drivers also the screen earthed at both ends.
All ends will be joined to a common earth point in side the CNC control unit.
Should I also run a earth cable between the control box and the CNC machine?
And I will get some sleeving to make the ends tidy, I like that idea.
YesQuote:
Originally Posted by Bush Flyer
YesQuote:
I will fit CY 4 Core 0.75mm/2 cable from the drivers to the stepper motors also the screen will be earthed at the driver end at a star end earth point and at the stepper motor end.
YesQuote:
I will fit CY 2 Core 0.75mm/2 cable from the breakout board to the limit switches with the screen earthed at the breakout board, but the screen not connected at the switches.
Yes if the diameter is sensible to do so.Quote:
I could use CY 4Core cable between the breakout board and the stepper motor drivers also the screen earthed at both ends.
Yes, The idea is to ensure there are no voltage differences between any of the screens so a star point is the best way to achieve it.Quote:
All ends will be joined to a common earth point in side the CNC control unit.
Yes the machine must be earthed for safety reasons.Quote:
Should I also run a earth cable between the control box and the CNC machine?
Like I mentioned earlier if you subsequently have any problems related to this you can always disconnect one end of a screened cable to see if it improves.
Hi EddyCurrent many thanks for taking the time to help with my simple questions, I can now sort this wiring with confidence now.
In addition any cables going to a motor, stepper or spindle, should be physically separated from the other signal cables as much as possible and it's not too bad if they cross at right angles, running them parallel is the worst. Of course this is difficult to do especially in the energy chain.
If you want to try a potential quick fix for false trips then try playing with de-bounce in Mach3 Config.
No substitute for correct wiring but it may get you going untill your ready to re-wire.?
Don't allow much pressure means voltage will be because of high voltages, this died.
Add capacitor.
Eddy (and others),
The topic of earthing and prevent loops is something, which I have struggled mentally with since I built my machine and thought I had it sorted until your extensive post on page 5 of this thread. Also what I have done may be correct for my circumstances, so just to check:
Firstly my machine is all metal and I have good conductivity right from the cutter tip to the bed (including through the spindle and bearing etc.). Initially when I built the machine I did think I needed to earth the driver/stepper CY cables back to the star point in my control box only (and from that to mains earth) with a separate earth strap from machine to control box star point and also to have the spindle earthed through the spindle cable shield back to the VFD earth point (and again from there to mains earth).
.
However I was getting a lot of spurious e-stops and when I disconnected the earth strap from the machine and essentially relied on the spindle to VFD earth they went away i.e. my machine is only earthed at one point in the VFD whilst all the stepper cables are only attached at the control box star point.
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In light of your post I'm questioning that again and would welcome an opinion especially as I also use a circuit making touch plate and cutter when setting tool height/z zero.
This also mentions plasma machine requirements, I'm not familiar with plasma machines.
CNCCookbook: Dealing with noise problems
This indicates you have some issue in some other area on the machine or in control box as doing this as just side tracked the problem not cured it.Quote:
Originally Posted by Washout
Noise is a bear to find You could try taking a earth wire from the spindle body back to Earth on the VFD this will ensure the gantry is earthed at least and probably the rest of machine if bearings don't isolate the rest of frame but still not create earth loop as it's not connected to Star point in control box.
Have you measured frame with a meter to see if it's putting out voltage.?
When you look about some people say connect the screen at both ends some one end this is why I mentioned earlier that if connected at both ends and there is a problem it would be easy to remove one end to see if it improved. VFD manuals show the motor screen connected at both ends but in addition an earth cable is also required, ideally this will ensure that both ends of the cable screen are at the same potential. Screens should not be used as earth connections, metal parts should be connected to earth at a star point for safety reasons. Loop currents flow because there is a difference in potential at each end of the cable, this is due to long cable runs and earth wires of minimum cross section. There is also the issue of earthing the negative side of DC supplies and also connecting them together, again some say this is good while others say it is bad.
http://ecmweb.com/content/avoiding-p...-cnc-equipment
The big issue is avoiding the creation of ground loops near control loop wiring.
There is also the issue of distinguising between earthing, and grounding.
If you look at commercial machines, they usually have seperate earth and ground points. All sheilding goes to earth, with ground being your negative power supply point.
.
I know that on my old lathe, the stepper wiring is unsheilded, and the only issue I got was when I connected the spindle sensor shield to the star point. I cut the wire to the sheilding, and never had a problem since (other than the usual usb SS communication issues!)
On my new lathe, I've kept it mostly as it was. All sheilds/earth points go to the earth terminal block, with all the power grounds going to the relevant ground bar. However it also uses 24V sensors/switches with differential encoders, so it should be very interference proof anyway. The mill will also be using the same setup once I get around to getting it going.