Is it possible to shield a cable?

[Brenck]

Hi guys,

I'm wondering if I can make my stepper motor wires a home made shielding... I was thinking on get the 4 wires together and wrap around with aluminium foil. And then cover with a heath shrink tube so the alum. doesnt unwrap from it. Will that work? Will I actually have a shielded cable after that? Is there a special kind of aluminium foil for that or the ones you use to cook use will work?

Thank you all

[Al_The_Man]

What are you trying to protect the motor wires from? Or radiating to?
If they are twisted pairs this should be sufficient?
Al.

[bobsch]

Yes you would have a shielded cable, if you include a bare wire in contact with the foil and connect it to ground at one end only (don't want ground loops!)

Regular aluminum foil will work fine.

[Brenck]

Hi,

I'm tryng to make them not go crazy with the spindle wire, witch is a Kress motor.

I had all of them ( 3 motors ) together with the spindle cable on one of thoose spiral wire organizers, and that made it loose and add steps, people say that brushed motors make that happen a lot.

I now have all the steppers together but no spindle cable inside the spiral thing. It works perfectly but I have the spindle cable loose and does not look organized at all.

When you say have a wire inside and connect to ground you mean ( - ) of the power supply or like the physical ground? ( I'm getting confused because if I translate here the terms for negative and ground or land is the same word ).

Thanx guys

[bobsch]

Originally Posted by Brenck Hi, When you say have a wire inside and connect to ground you mean ( - ) of the power supply or like the physical ground? ( I'm getting confused because if I translate here the terms for negative and ground or land is the same word ). Thanx guys

Connect one end of the shield to the (-) of the power supply. Make sure the other end of the shield is not connected to anything.

[Al_The_Man]

However you should have a separate bonding (ground) conductor from the central ground point to each motor and spindle frame etc.
See post#8
http://www.cnczone.com/forums/showthread.php?t=105993
Al.

[wildwestpat]

Hi Brenck

Yes you can make your own but I have to ask why bother. The heat shrink tube will cost more than using commercial cable. For example 4 Core - SY Multi Flex Cables is about $2 per meter and is reasonably flexible. There are also 3 and 5 core versions available.

I have made multicore cable using heat shrink outer case and the problems are:-

1. Getting the cable to be flexible. This requires the cores to be twisted together BUT at the same time ensiring that individual cores do not become twisted. If the do the cable will be very ridgid and resistant to bending and the cores will snap if subject to a lot of repeated movements.

2. Threading the special twisted wires through a long length of heat shrink tube can be difficult. Suggest the innards are made up and clamps applied at each end. Then strip and twist all the conductors together and solder the resulting pigtails. This stops the individual cores untwisting or crossing over each other as you pull it into the outer jacket using an electricians tape or bit of fencing wire.

3. Coat the bundle of cores with french chalk or talcum powder. This helps prevent the heat shring sticking to the insulation on the cores.

4. Use a heat shrink that when full shrunk is only a little bit smaller than the over all diameter of the cores you have carefully twisted together. This helps to ensure the inner cores are not held too tightly. Also use a heat that does not melt or soften to flow point the inner cores insulation - obvious but it restricts the application of heat and choice of tube.

5. Use one of the neoprene heat shrink tubes as most of the others become very ridgid when shrunk. Also obvious but avoid those that have an inner coating of glue!

6. If the cores when twisted together do not form a neat flexible 'rope' with more than about five twists per foot then add extra cores or string to pad out the geometry to fill the circular cross section. Also consider using string as a center core.

Winding the cores together is ok done free hand for a few meters but longer lengths require some form of jig to ensure that the individual cable strands are not counter twisted as the cores are themselves twisted together.

I have used the outer braid from co-axial aerial cable as a shield and this avoids the problems you will encounter using cooking foil as the foil will fracture after several bendings when used under heat shrink outer. This is why commercial cable uses plastic film that has a thin metal coating and a bear bleed wire to ensure that the shield remains grounded.

Above all do not stick the four cores in a drill chuck and twist them that way. This will give you a very nice looking twist but one that is too ridgid for anything other than fixed wiring that is tied down to support cleats. To see what I am driving at take four bits of wire similar to the core you want to use - strip the ends and twist together. Hold the resulting pigtail in a vice take a piece of wood with four holes in it spaced at the corners of a 1 inch square. Thread one cable core through each hole - leave the free ends loose. Now gently rotate the wooden 'die guide block' and you will observe that the cores twist about as the four cores form a nice four core rope. Close observation will show that the die head is rotating and the cores are going the other way so that individual cores are untwisted just being wraped about a common axis with the other cores. The resulting bundle will be nice and flexible compared with a similar one made using a drill chuck to do the twisting.

I have made 100 meter lengths of upto 27 cores this way with a number of cores being coaxial and some twin core screened. The resulting jig was made of slotted angle. of the type used for shelving, and the cable reels were hung from the die head. Looked a bit like a drunk wind mill but it worked for prototypes prior to getting kilometers of cable made on a commercial basis.

Another approach is to use elecricians flexible metal conduit this is available in various sizes from 20mm upwards and used with special glands to ensure the metal connected correctly. The construction is similar to the flexible hand shower tube used in domestic shower cubicles. However the plumbing fittings are only 10 mm bore and limited to 1.5m long and some are stainless or brass beware that some are PVC with a chromed finish and they are not suitable.


Hope this helps _ regards Pat

[Brenck]

Thank you AL, great pdf

Pat,

Nice explanation, I wish it was easy to find shielded cables here in Brazil I would sure buy them but I tried to find AWG 22 with 4 cores and didn't have lucky at all. I can find 4 core AWG22 but without shielding

Thank you

[wildwestpat]

Hi Brenck

Just a thought have you tried searching for SY or CY control cable as these are used in the food industry for wiring to the machinery used in even small kitchens. Similar is the Canadian spec 'Unidrall 2100C'.

Good luck which ever way you go with this problem - regards Pat

[wildwestpat]

Hi Brenck

Just ordering some cable and I noticed that these people do a global delivery and sell cut lengths.

http://www.cse-distributors.co.uk/cable/cy-screened.htm

The Uk delivery charges are reasonable but you would have to follow the link above to get a quote.

Regards Pat

[mactec54]

Hi Brenck

Do not connect the shield to the (-) on the power supply as has been said in the above post, They should all connect to a physical Ground point.

If you need cable IGUS has some of the best there is

Your Aluminum foil will work quite well, but twist the wires before you wrap with the foil, you can twist the foil at one end of your cable & crimp a terminal on to it for grounding to your physical ground

If the foil is not strong enough at the mounting end, put a short piece of wire in the end, that you are going to ground, wrap the foil around the wire & crimp the terminal on to it

[Brenck]

Wow Igus sells cables to?

They have a company here in Brazil.

Thats it I'm buyng from them.

Thank you all