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Proper shielding of iGaging DRO USB cables and installing stainless steel flexable conduit

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I just purchased and received 20 feet of stainless steel flexible conduit to use on my iGaging DRO USB bables. Its 7MM OD and 5MM ID. I figured the solid conduit was better than the automotive grade plastic split conduit since it doesn’t protect the wires from cutting fluid and chips very well. I need to run the cables through the conduit so I am going to have to cut off one of the ends and then refasten it to the cable. I also figured, while I’m at it I might as well make sure that the cables are properly shielded.

My question is, to properly shield the cable I need to make sure that one end of the shielding is connected to the ground and the other is not? Do I have that right? And which end should be connected to the ground?

Any recommendations on which end of the cable to cut off for inserting it throught the conduit.

If anyone is curious as to where I got the conduit, here is a link. It was only $30 and it is made very well.
https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/272396574044
 

Comments

#2
I used essentially the same flexible conduit on my I Gaging install. I cut the end going to the readout and respliced the cut ends after running through the cable. My install is grounded at both ends as I made retaining fixtures for the conduit which are electrically connected to the lathe body. My primary reason for using the conduit was to prevent damaging the wires. The conduit is not waterproof so you need to make sure the insulation on the I Gaging wires is intact. I had some problem with interference when the motor was turned off but that was coming through the power line. Adding capacitors to the I Gaging pickups cured that problem (at least, it hasn't resurfaced since the modification). Technically, to avoid ground loops, a shield should be grounded at a single point. I would guess that it would be best done at the pickup.

I have also seen advice not to ground the scales themselves. Mine are grounded, again, no issues with that. My I Gaging electrical circuitry itself is floating with respect to the chassis (lathe). I use a 12 volt brick for powering the Arduino circuitry with a simple voltage divider to drop the voltage to the pickups.

A blow by blow description is here: https://www.hobby-machinist.com/threads/another-lathe-dro-install.34106/
 
#3
Stainless steel is usually a waste of money. SealTite (flexible) or even EMT would work just as well. You seem to have gotten a good price for the stainless though. It is true that the shield should be grounded at one point, usually at the source of the problem. And I'm thinking of a wood structure. SealTite would be fine, but EMT would be out.

On the other hand, physical protection only for shielded cable would be another matter. Most any conduit would do. The shielding alone does the necessary and should only be grounded at the source end. EMT or even water pipe would do well enough as conduit to physically protect the cable.

Whatever conduit you choose, the NEC allows only 80% fill. As an old school electrician, I would highly recommend no more than 50%. But that's based on length, and there's not much of that here. Again, stainless conduit is like using a howitzer for a fly swatter. Most cable today is oil and water resistant. The usual protection is against physical cuts and blows and kinking or twisting resistance. Most any pipe would do the job. The big issue is to keep the cable shield insulated from the conduit except at the intentional ground. Even a section of old water hose would work, albeit not so pretty. The NEC types would fail that. But, for a home shop... ...
 
#4
My conduit is 1piece. There is no chance for any oil to seep into it.
I love your idea on terminating the conduit. It looks very professional. I think I will do something similar. Also at the end of the conduit I was thinking maybe an ‘O’ ring that tightly fits on the cable and inside the conduit would help against abrasion of the cable. I too have 12” and 24” iGaging scales on my Sieg 8.5x20 lathe. Somehow on the X axis DRO mount I designed it with enough clearance that when I made my tapered gibs later on they fit with plenty of clearance. I did my cross-slide scale differently because I did not want to loose any tailstock travel. I mounted mine out behind the crossslide because my splash shield sits way further back, probably about 16”.

How again did you ground the scales using the conduit? Is the shielding from the cable somehow attached to the conduit? I didnt see this mentioned in your thread. Also, not sure that it matters but I am using the Blu-Dro controller.
I hope this conduit does not cause any interference. I will cross my fingers and if it does I will have to install these capacitors that you speak of. I was asked to post a picture of my reader head board a while ago because I had inquired about doing this mod to them but never got around to it. Apparently some scales have different boards. I havent had any glitching issues yet and I am still using the power supply that came with the Blu-Dro. I do have wall wart 12V power supplies for the mill and the lathe Blu-Dro’s but havent hooked them up yet because I havent had any major issues.

I used essentially the same flexible conduit on my I Gaging install. I cut the end going to the readout and respliced the cut ends after running through the cable. My install is grounded at both ends as I made retaining fixtures for the conduit which are electrically connected to the lathe body. My primary reason for using the conduit was to prevent damaging the wires. The conduit is not waterproof so you need to make sure the insulation on the I Gaging wires is intact. I had some problem with interference when the motor was turned off but that was coming through the power line. Adding capacitors to the I Gaging pickups cured that problem (at least, it hasn't resurfaced since the modification). Technically, to avoid ground loops, a shield should be grounded at a single point. I would guess that it would be best done at the pickup.

I have also seen advice not to ground the scales themselves. Mine are grounded, again, no issues with that. My I Gaging electrical circuitry itself is floating with respect to the chassis (lathe). I use a 12 volt brick for powering the Arduino circuitry with a simple voltage divider to drop the voltage to the pickups.

A blow by blow description is here: https://www.hobby-machinist.com/threads/another-lathe-dro-install.34106/
I used essentially the same flexible conduit on my I Gaging install. I cut the end going to the readout and respliced the cut ends after running through the cable. My install is grounded at both ends as I made retaining fixtures for the conduit which are electrically connected to the lathe body. My primary reason for using the conduit was to prevent damaging the wires. The conduit is not waterproof so you need to make sure the insulation on the I Gaging wires is intact. I had some problem with interference when the motor was turned off but that was coming through the power line. Adding capacitors to the I Gaging pickups cured that problem (at least, it hasn't resurfaced since the modification). Technically, to avoid ground loops, a shield should be grounded at a single point. I would guess that it would be best done at the pickup.

I have also seen advice not to ground the scales themselves. Mine are grounded, again, no issues with that. My I Gaging electrical circuitry itself is floating with respect to the chassis (lathe). I use a 12 volt brick for powering the Arduino circuitry with a simple voltage divider to drop the voltage to the pickups.

A blow by blow description is here: https://www.hobby-machinist.com/threads/another-lathe-dro-install.34106/
 
#5
My conduit is 1 solid piece. It could be submerged in oil and wouldnt get a drop on any of the cable except for the ends if they were not sealed.
I think I am lost in regard to SealTite, EMT, and NEC. I dont know what any of this is or what is filled 50 or 80% ?
So you are saying that if my readout is glitching then I should ground it where? My lathe is steel. I am not sure where wood would be used.
Stainless steel is usually a waste of money. SealTite (flexible) or even EMT would work just as well. You seem to have gotten a good price for the stainless though. It is true that the shield should be grounded at one point, usually at the source of the problem. And I'm thinking of a wood structure. SealTite would be fine, but EMT would be out.

On the other hand, physical protection only for shielded cable would be another matter. Most any conduit would do. The shielding alone does the necessary and should only be grounded at the source end. EMT or even water pipe would do well enough as conduit to physically protect the cable.

Whatever conduit you choose, the NEC allows only 80% fill. As an old school electrician, I would highly recommend no more than 50%. But that's based on length, and there's not much of that here. Again, stainless conduit is like using a howitzer for a fly swatter. Most cable today is oil and water resistant. The usual protection is against physical cuts and blows and kinking or twisting resistance. Most any pipe would do the job. The big issue is to keep the cable shield insulated from the conduit except at the intentional ground. Even a section of old water hose would work, albeit not so pretty. The NEC types would fail that. But, for a home shop... ...
 
#6
Bill, the conduit is for signal wires from the pickup to the DRO controller. The wires are maybe 30 AWG at most. The entire cable is maybe 3mm in diameter. The voltage is 3 volts. Given the application, electrical codes shouldn't apply.

Z28, I would double check on the seal integrity of the cable. I have four different types of stainless flexible conduit and one made of aluminum. None of them are sealed. A simple test is to pull on the cable. If it expands and contracts like a spring, the joints are free to move and it w3on't be sealed. Another test would be to add some WD40 or alcohol to a small drip loop. Or you can plug one end and apply compressed air to the other. I put mine in a tub of water and it would make a great aquarium aerator.

My conduit is grounded to the lathe through my terminations. My scales are also grounded via the scale mounts. There is no physical connection between the conduit and the pickup head. My objective for using the conduit was to provide protection for the rather fragile cable in what could be a harsh mechanical environment. I don't use coolant on my lathe so there is no danger of an electrical short. On my Tormach mill, I used the same conduit for the optical homing system and for the same reason. I do use flood coolant there and to make my wiring coolant proof, I ran the conduit inside a length of oil resistant PVC tubing with custom made connections on the end to ensure seal integrity.

I believe that I just used several pieces of heat shrink tubing rather than an O ring as you are thinking But my conduit ends and exposed cable do not move in normal use so the chance of any wear is minimal. My Arduino setup was rather crude compared to the Blu DRO controller and the power supply for the scales may have been improved. If not, the addition of the capacitors to the pickups was fairly simple and it seems to be effective.

I thought about mounting my cross slide scale behind the lathe but I didn't want to have to give up the backsplash. As it is, I only have about 1/8" clearance when the cross slide s full to the rear. I lost about 1" of tailstock travel which would only impact me when I use a dead center and then only minimally.
 
#7
It is not possible to pull the cable and stretch the coils. It can only be compressed. It sure is air tight. I really dont think it matters much if it is or isnt. Its better than automotive wire loom and I purchased it to pretect the cables from sharp coils of swarf.

If I understand, you mounted your scales directly to the lathe with material that is conductive and in no way isolates them from the machine. I would assume this means you used aluminum or steel as the bracketry to mount them to the machine. This is how I mounted mine as well.

Bill, the conduit is for signal wires from the pickup to the DRO controller. The wires are maybe 30 AWG at most. The entire cable is maybe 3mm in diameter. The voltage is 3 volts. Given the application, electrical codes shouldn't apply.

Z28, I would double check on the seal integrity of the cable. I have four different types of stainless flexible conduit and one made of aluminum. None of them are sealed. A simple test is to pull on the cable. If it expands and contracts like a spring, the joints are free to move and it w3on't be sealed. Another test would be to add some WD40 or alcohol to a small drip loop. Or you can plug one end and apply compressed air to the other. I put mine in a tub of water and it would make a great aquarium aerator.

My conduit is grounded to the lathe through my terminations. My scales are also grounded via the scale mounts. There is no physical connection between the conduit and the pickup head. My objective for using the conduit was to provide protection for the rather fragile cable in what could be a harsh mechanical environment. I don't use coolant on my lathe so there is no danger of an electrical short. On my Tormach mill, I used the same conduit for the optical homing system and for the same reason. I do use flood coolant there and to make my wiring coolant proof, I ran the conduit inside a length of oil resistant PVC tubing with custom made connections on the end to ensure seal integrity.

I believe that I just used several pieces of heat shrink tubing rather than an O ring as you are thinking But my conduit ends and exposed cable do not move in normal use so the chance of any wear is minimal. My Arduino setup was rather crude compared to the Blu DRO controller and the power supply for the scales may have been improved. If not, the addition of the capacitors to the pickups was fairly simple and it seems to be effective.

I thought about mounting my cross slide scale behind the lathe but I didn't want to have to give up the backsplash. As it is, I only have about 1/8" clearance when the cross slide s full to the rear. I lost about 1" of tailstock travel which would only impact me when I use a dead center and then only minimally.
 
#8
It is not possible to pull the cable and stretch the coils. It can only be compressed. It sure is air tight. I really dont think it matters much if it is or isnt. Its better than automotive wire loom and I purchased it to pretect the cables from sharp coils of swarf.

If I understand, you mounted your scales directly to the lathe with material that is conductive and in no way isolates them from the machine. I would assume this means you used aluminum or steel as the bracketry to mount them to the machine. This is how I mounted mine as well.
The scale mounts are shown in the photos 6, 9, & 12 in the thread that I linked to. Aluminum was used for all the work except for the cross slide scale cover which is stainless.
 
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