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Thread: DIY DT40 Galvo Cables

  1. #1
    Join Date
    Apr 2009
    Location
    North of Jackson Michigan USA
    Posts
    221

    Default DIY DT40 Galvo Cables

    In wiring up my latest build (story coming soon to a forum near you), I discovered the cables going from the DT40 amps to the galvos were a little short on one end. What to do?

    I found that my local rental places no longer had cable stretchers available, so step one: contact galvo vendor Dave at LSP. He contacted Dragon Tiger, who refused to supply longer cables, or even connectors and bare wire.

    Scrimping and crimping
    Dave was able to identify the Molex connector involved (a seven-conductor jobbie), which inspired me to build longer cabling. Below is one man's epic struggle to achieve length.

    Wires
    There are two cables heat-shrinked together here: a shielded 2 conductor and a shielded 3 wire.

    Here is a close-up of the business end of one of the original cables. I stripped the heat-shrink back to verify the drain wire was indeed the cable in the smaller heat shrink here.

    Click image for larger version. 

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    The two conductor wire was no problem; I have gobs of shielded 22ga cable left over from my recording studio days. Where to find 3-wire? I spent some time searching eBay and other usual suspects, but the only cable I could find was in 500-ft spools - not good. Finally I found some cheap 4-wire shielded cable at Jameco Electronics, URL below. $7.95 for 25ft - good. I snipped off the un-needed wire and was set to proceed.

    Wire Prep
    1) carefully measure the length of cable you need and then add an additional inch just in case.
    2) Trim the outer insulation back around 1 inch, and prep heatshrink to hold things together and look nice.
    3) Insulate the shield drain wire with teensy heat shrink (transparent, in this case, below - black is better).
    4) Trim the ends of the other wires back 1/4" or so and tin them with solder, then trim them back a bit more to have just an 1/8" exposed, even across the ends.

    This shows the cable on the right ready for crimping - the cable on the left needs a final trim.

    Click image for larger version. 

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    Crimping
    Once your wires are prepped, the crimping begins. You need the right tin connectors and an appropriate, expensive ($50), crimper. You might be able to get by with good needle-nostril pliers, but if you are going to be doing this a lot (and you will), you might as well get the right tool for the job (source below).

    Here is where some magnifiers will come in handy.
    The contacts a small, fiddly, but cheap. Buy extras because you will destroy some as you learn how to do this.
    The contacts have two crimp thingies: the front one (toward the round part) is for crimping the conductor, the back one is for crimping the insulation to provide support.
    First you crimp the front one - hold the contact in the pliers and gently insert the wire until the end of the insulation is up against the tool, as below:

    Click image for larger version. 

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    Gently squeeze down to make the connection. Then move the wire forward into the tool and crimp the rest of the wire, pinching down the insulation in the process:

    Click image for larger version. 

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    Your final assembly should look like this:

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    Here is the completed wiring, ready to slip into the shell:

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    Insertion
    The contacts need to go into the shell so that the barbed "back" of them engages with the holes in the back of the shell. Study the existing cable you have to see how this works. As you push the contacts into the shell, they will make little clicks as the barbs engage in their slots. Test this by gently pulling on the wires to make sure they are fully seated. Make sure you note the color of your wires and put the wires into the shell in the proper order. If you make a mistake, you can gently push the barb on the back of the contact in with a teeny screwdriver while pulling the wire out. Tricky to learn, but it can be done.

    Here is a shot of the final products, along with the original cables and the tools used to get the job done:

    Click image for larger version. 

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    Sources:

    644383 CABLE,SHIELDED, 4 CONDUCTOR 7.95
    https://www.jameco.com/webapp/wcs/st...gDrillDownView

    Contacts: WM2623-ND
    http://www.digikey.com/product-searc...=0&pageSize=25

    Shell: WM2617-ND
    http://www.digikey.com/scripts/DkSea...34962418502624

    Crimp tool:
    Molex PA-09
    http://www.ebay.com/itm/Engineer-Too...item3a8f88e4e4


    I haven't tested this yet: there is a small possibility that the slightly longer wires will screw up some delicate balance of dancing electrons twixt the amps and the mechanics, requiring a massive re-tune of the galvos. I doubt it, but we'll see.

    Big thanks to MondoDyne chief engineer Wayne Gillis for providing my crimper and instructing me on all this. And another thanks to Dave at LSP for his excellent service, prices, and continuing support. And a big Phhhhhbpt to DT for refusing to provide help in this.

    Hope this helps some PLer down the road.

    Lux Plus Esto...Mike
    Runs with Lasers

  2. #2
    Join Date
    Nov 2009
    Location
    Whanganui New Zealand
    Posts
    312

    Default

    Cool story bro. Great that you have taken the time to share.

  3. #3
    Join Date
    Feb 2007
    Location
    Fort Mill, SC USA
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    1,264

    Default

    Thanks for this well written post, Mike!

    David
    "Help, help, I'm being repressed!"

  4. #4
    Join Date
    Apr 2009
    Location
    North of Jackson Michigan USA
    Posts
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    Default

    In testing the cables, I saw no problems attributable to the longer lengths. Corners are crisp and everything checks out.
    As expected...

    HTH...Mike
    Runs with Lasers

  5. #5
    Join Date
    Feb 2008
    Location
    East Sussex, England
    Posts
    5,137

    Default

    It might be worth mentioning that you can buy a ratchet crimp tool that'll do it all (sleeve and wire crimp) in one squeeze of the handle for about 30. Rob Stanwax has them I believe but they're generally available. I use mine A LOT!
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  6. #6
    Join Date
    Apr 2009
    Location
    North of Jackson Michigan USA
    Posts
    221

    Default

    Ah, good to know.

    Thanks, Norty.

    ...Mike
    Runs with Lasers

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