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Message |
    
Gerald_D
Registered
Username: Gerald_d
Post Number: 946
Registered: 11-2005
| | Posted on Tuesday, February 20, 2007 - 01:08 pm: | 
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Proper grounding/earthing is essential in a computer controlled machine. A couple of points can be discussed in this thread.
We use single point grounding to prevent ground loops. The main ground "gathering" point is the alu heatsink under the Gecko's. This plate is convenient because it is big, conducts well, is never painted, and easily screwed into. (Do not use a hard-anodised plate - that anodising is a good insulator).
From the marked point on this plate........
.....a thick cable is run to the table...
.....from the table to the gantry.....
.....from the gantry to the y-car....
.....from the y-car to the z-slide....
The ground cable is the green/yellow one with the yellow crimp lugs on the ends. Use a heavy gauge wire for minimum resistance/impedance. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 949
Registered: 11-2005
| | Posted on Tuesday, February 20, 2007 - 01:21 pm: |
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To get a good connection to the painted metal, first remove the bulk of the paint at that spot and then install a serrated washer between the crimped lug and the "dirty" metal:
These "star" washers are also used at the alu ground plate in the control box. Alu also needs something to break through its "dirty" layer. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 950
Registered: 11-2005
| | Posted on Tuesday, February 20, 2007 - 01:32 pm: |
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When using a sawdust extractor, and having the sawdust rub along the inside of a plastic pipe, huge voltages are generated and the static electricity must be drained to ground. Don't underestimate the havoc an un-grounded dust hose can cause! (fire is another consideration - seriously!)
Proper industrial grade dust hoses have a spiral wire in them for 1. keeping their shape, and sometimes, 2. for grounding. Their plastic grade is may be chosen for allowing the static electricity to drain to the wire. (If you can see a spiral wire in the plastic, it does not neccessarily mean the pipe is anti-static - the plastic may be insulating the electricity from the wire. A special "plastic" needs to be used) If your hose is of unknown grounding quality, run a bare copper wire along the inside of the hose.
The wire in a dust hose is normally not connected to the MechMate's ground system - it is connected to the dust extracting machine's (fan's) ground. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 951
Registered: 11-2005
| | Posted on Tuesday, February 20, 2007 - 01:59 pm: |
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Why must the ground cable be so thick? I am not expert on this but I believe it is because a second ground path (loop) does exist via the v-rollers as well. In cases where there is chance that a bearing may be conducting, we put a very low resistance path parallel to it and hope that the electricity flows via the cable instead of via the balls & grease in the bearing. |
Gerald_D
Registered
Username: Gerald_d
Post Number: 953
Registered: 11-2005
| | Posted on Tuesday, February 20, 2007 - 03:00 pm: |
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Some light reading:
Networked Machine Shop/Manufacturing Plant Learns the Value of Proper Grounding
How four years of bad advice kept an innovative company from realizing the potential value of its networked CNC-CAD/CAM systems |
Gerald_D
Registered
Username: Gerald_d
Post Number: 954
Registered: 11-2005
| | Posted on Tuesday, February 20, 2007 - 03:07 pm: |
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Another resource:
http://www.mikeholt.com/technical.php?id=technicalgeneral#Grounding |
Stephen Hull
Registered
Username: Oliver2257
Post Number: 13
Registered: 01-2007
| | Posted on Tuesday, February 20, 2007 - 08:12 pm: |
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Gerald,
Excellent grounding articles. Personal experience with these issues, now when there is an electrical problem, first thing I check for is proper grounding, loose connections, etc. I have spent time, $ and frustration replacing parts only to isolate the problem as poor ground or loop or a cold solder joint. Your suggestion of crimp connectors, large guage wire, star washers and clean metal is sound. Often I have seen sheet metal screws only used to secure the ground lug and they can work loose and make poor contact. I now use bolted screw with star washer where possible. I also use high quality contact cleaner. Thanks for your continued excellent support.
Stephen |
60. Cable Management & Wiring