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A String Winding Lathe

Discussion in 'Luthier's Corner' started by Bruce Johnson, Sep 17, 2017.


  1. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Another crazy contraption emerges from the Secret Underground Lab: A custom string winding lathe. Yep, it's a special machine made for making guitar strings.

    No, I'm not planning on getting into making my own strings.....This was a commission job. There's a small custom string winding company here in Los Angeles. They mostly make strings for the various Latin instruments, but they do some specialty guitar strings. All custom, hand wound, using specialized electric lathes. Hand wound means that the lathe spins the core, but the outer wraps are fed on by hand (like bare fingers!). An old craft requiring skilled technique. Fascinating to watch.

    They have several old lathes which were custom made probably 50 years ago. The old machines were starting to break down and be unreliable, and they were looking for help. Somebody told them about a wacko machinery inventor-type guy in town, and they found me. How could I refuse? Over the last few years, I repaired and improved each of their old lathes.

    Now the owner of the company is splitting off his own separate custom string winding operation, so he commissioned me to build a new string lathe from scratch. He gave me the basic parameters, and allowed me to come up with my own better design of the machine. Here it is.

    IMG_5175B.jpg

    Like a wood lathe, a string lathe has a headstock and a tailstock, on opposite ends of a long bed, or frame. The headstock and tailstock both have spindles that spin in bearings. Both are powered by the motor, and they both have to be mechanically synchronized together. Metal hooks thread into the inner ends of the two spindles, and the center core of the string loops on the hooks.

    IMG_5180B.jpg

    The tailstock spindle has a sliding shaft through the center. A big lever with a ratchet link is used to pull the string core up to tension. They actually take it a little higher than the tension it will see at normal tune on the guitar. The core stays at that tension as the outer wrap is wound on.

    IMG_5178B.jpg

    The headstock and tailstock spindles are driven, fully synchronized, through two triple-reduction timing belt drives, and a long countershaft that runs in bearings down the back of the frame. The belts, pulleys and bearings are all right out of McMasters stock. I machined up all the spindles, shafts, levers and other metal parts, and built the wood frame.

    IMG_5176B.jpg

    The tricky part of these string lathes is the speed. They run these spindles at 7200 rpm, which is fast. The old machines used single-reduction drives, with the long countershaft spinning at 3400 rpm. That caused all kinds of vibration and breakage problems. That's why I designed the triple-reduction drives on both ends of mine, to bring the countershaft speed down to 425 rpm. Much smoother and quieter and hopefully more reliable.

    I also made up the double foot pedal assembly which switches the lathe on and off, and "bumps" the spindles. The whole machine weighs about 220 lbs, and quickly disassembles into four main parts. I built the frame from wood to keep the cost down, and to reduce the noise. The bed is made from 3/4" Finnish plywood.

    A fun engineering and fabrication project. I spent about 65 hours building it.
     
  2. Very interesting. I'd love to be able to come down to your shop for a couple of weeks and just watch.
     
    kaoskater08 likes this.
  3. charlie monroe

    charlie monroe Gold Supporting Member

    Feb 14, 2011
    Buffalo, NY
    A number of years ago my brother (Master Tool & Die Maker) rebuilt an older winding lathe for the company Wyres.

    He got paid and I got a gross of medium gauge guitar picks :D
     
  4. That's pretty cool. 65 hours sounds like a lot, but I'm sure it would take me months to do something like this.

    So, people just call you up and say "Hey Bruce, I need this thing, but it doesn't exist yet. Can you make me one?"

    Thanks for sharing!
    -Jake
     
    andruca and Pbassmanca like this.
  5. Beej

    Beej

    Feb 10, 2007
    Vancouver Island
  6. Picton

    Picton

    Aug 16, 2017
    Reading, MA
    Nifty. Thanks for posting. It's interesting to get a glimpse into a side of the broader stringed-instrument industry that most of us never get to see.
     
    Westsailor likes this.
  7. But be honest, Bruce... did you think about it? Even for a second? ;)

    That's as really cool machine. It'd be really fun to see it in action. Do you think your client send you an iPhone video?
     
  8. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Well, start to finish, it was about 7 months, squeezing in hours here and there between everything else I have going on....

    It's more like "Somebody told me that you have a shop full of machines, and that you can build anything. Nobody else will touch my project. Will you help me please???"

    It can be hard to refuse, because I love technical challenges. That's why I'm constantly overbooked and behind schedule on everything.
     
    jchrisk1, andruca, VerryBerry and 6 others like this.
  9. rudy4444

    rudy4444

    Mar 13, 2012
    Central Illinois
    Teacher, HaphAsSard and Freekmagnet like this.
  10. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
  11. cazclocker

    cazclocker My social skills are rapidly dwindling.

    Oct 24, 2014
    Newton, Kansas
    That's fascinating... but what about tolerances... do you get variations or gaps in the outer windings from one end of the string to the other? All the lathes I've seen are made from heavy tool steel, and the stands they are mounted on are normally made from gray cast iron. Doesn't plywod change dimensions with the ambient humidity? I'm just curious - I'm not a luthier at all, but I have operated plenty of steel-cutting and wood-cutting lathes.
     
  12. fhm555

    fhm555 So FOS my eyes are brown Supporting Member

    Feb 16, 2011
    Nice! I've always been of a mind that nothing is impossible, it's just that some things take longer than others to bring to fruition.

    You said the winding is fed by hand, is there some sort of hand held tool/device used or do you just feed and hope you don't get a coil jump off the spool and wrap around your hand while the thing is spinning up at speed.
     
  13. Picton

    Picton

    Aug 16, 2017
    Reading, MA
    The beauty of plywood is that it's dimensionally stable. The problems you mention would definitely be a risk if the lathe were made of solid wood, unless it was very carefully oriented during construction.
     
    cazclocker likes this.
  14. cazclocker

    cazclocker My social skills are rapidly dwindling.

    Oct 24, 2014
    Newton, Kansas
    Ahhh... makes sense to me! Thanks for indulging my curiosity. Any chance you could post a video of you making a string on your string lathe?
     
  15. Ross W. Lovell

    Ross W. Lovell

    Oct 31, 2015




    I'm impressed and i fabricate machinery!

    Long ago a luthier friend dispelled my concerns with making that out of wood. Seen too many things that did not need metal.

    Be honest, you're a luthier and prefer working in wood?

    That is amazing work and your time invested, is minor, considering the complexity.
     
    cazclocker likes this.
  16. 74hc

    74hc

    Nov 19, 2015
    Sunny California
    Did you consider using extruded aluminum for the frame rather than wood?
     
    cazclocker likes this.
  17. Beej

    Beej

    Feb 10, 2007
    Vancouver Island
    Bruce hasn't chimed in here yet, but if you think about the loads involved with winding strings, it's nowhere near what a metal lathe goes through for example. This string winder has to deal with tension between the mounting points, but there is no load from in to out like there would be on a lathe. I think what you have here with the plywood (he said finnish, so probably birch?) is more than enough for the task it's being asked to do... :)
     
    T_Bone_TL likes this.
  18. T_Bone_TL

    T_Bone_TL

    Jan 10, 2013
    SW VT
    Wood also has ADVANTAGES - vibration was mentioned. Aluminum extrusions would be far more likely to have vibration issues (or need extra work to avoid them) than a wood frame. Load-wise, "the strings are tensioned a bit higher than they are in use" - so if my thin plywood upright bass can handle 4 strings, I'm not the least bit concerned with this thing built from 3/4 baltic birch and one string at a time on it.

    The only reason I'd consider valid for going with a metal bed here would be cost-effectiveness - if it did not make Bruce's custom modifications more difficult (and thus time consuming), a suitable used cast-iron lathe bed (which is overkill for this job) could be had for the price of not very many of the 65 hours he spent building this - so if modifying one of those was faster than building this, it might make sense. Come to think of it, my last cast iron wood lathe was free for the hauling. Structurally, wood is just fine.
     
  19. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Wow, a lot of questions and comments! Thanks! I've been busy in the shop all afternoon, machining up a batch of strap buttons.

    Some general answers:

    I know very little about the string winding process, and I've never even tried it myself. All I know is from talking to Gabriel and Jacob and the crew, and watching them demonstrate it a few times.

    It's a hand winding process. They are literally feeding the outer wrap wire between bare fingers and thumbs, applying light pressure as it wraps onto the core. Getting the wraps tight and even is a result of feel and practice. It definitely takes some skill. The basic technique goes back centuries.

    To me, it looks dangerous, but Gabriel says it isn't really. The wire is smooth and slippery, and they don't really cut or burn their fingers, as you might think. The biggest worry is if the core snaps, they don't want to get whipped by the flying wire. They have highly developed reactions to jump back and to the side, and not to try to grab the flailing wire. Stand back and let the lathe come to a stop. A big reason for the big foot pedals.

    Because it's a hand winding process, the lathe itself isn't really a precision machine at all. All it does is pull the core wire up to 30-40 lbs of tension and hold it at that tension while spinning it at 7200 rpm. There are no ground ways, sliding carriages, precision leadscrews, or any of that usual metalworking stuff. And there's very little load involved, other than the tension between the two spindles. And that's only 40 lbs. The motor is only 1/4 hp, and that's mostly used up driving the toothed belts. There's very little torque involved in winding the wrap wire onto the core.

    Deflection of the bed doesn't matter in terms of accuracy of the winding. But, vibration is a concern. They need the lathe to run smoothly at 7200 rpm to help them see and feel what they are doing. The old machines had serious problems with shaking themselves apart, to the point of bending spindles and sending metal flying. Most of the design issues of this machine are about keeping the spinning driveline smooth and reliable. And quiet, too. A quiet machine makes the workday easier.

    I went with a wooden frame for these reasons. Wood is good for damping vibration. Plus it's less expensive than a steel frame, easy to modify and attach things to, and lighter weight. The whole machine comes apart into four sections, and we had no problem loading it all into Gabriel's car for transport.

    I used 3/4" Finnish (aka Baltic Birch) plywood for the main bed. A long box beam with table/shelf underneath and the headstock and tailstock cantilevered off the top.

    The machine is back here in my shop right now to fix a few problems that showed up when Gabriel started trying to use it. One spindle bearing is rubbing when the string core is up to full tension. I hadn't noticed it because I was testing it without a string core in place. Duh. A few improvements to the tension ratchet mechanism. And I'd forgotten that he needs a reversing switch on the motor. When he does a two layer string, the second layer gets fed on in the opposite direction. All part of getting a custom machine going.
     
    BritFunk and andruca like this.
  20. this is great fun to read. I use GCS strings. They make a great string and I'm happy to see that they will have new tools for many years to come.
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Nov 26, 2020

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