Saturday, October 21, 2017

Experiment With a Bow Lathe

I've never done any turning before, either motorized or human-powered.  I've been thinking for a while about building some kind of human-powered lathe.  But I don't have the space for a free-standing spring pole lathe or flywheel treadle lathe, so I'm trying to figure out how to build one that uses my workbench as the "ways" of the lathe.

One very small solution is the bow lathe.  In this style lathe, the rotational motion of the stock is produced by a bow and string.  The string is attached to two ends of a stick and wrapped around the stock in between.  My left arm is the motor.
The bow, with string wrapped around the stock
On the far end, the string has a knot in it and rests in a V-shaped cutout.  On the near end is a similar V-groove, but I also sawed a little notch out of the side of the stick to help lock the string and keep it from loosening.
The near end (the end I hold on to) with V-groove and notch
Close-up of the locking notch
The two "puppets", the uprights with protruding pins that hold the stock, are 2x? scrap boards with hanger bolts in them.
The movable puppet is attached to the vise's movable jaw.
The vertical piece is glued to a horizontal piece that is bolted to the movable jaw.
The other puppet is a board screwed to a plywood base, fastened to benchtop with holdfasts
The pins are 3/8" hanger bolts with the wood screw ends filed to a point
The machine screw end goes through a hole and is fastened with nuts and washers on both sides
The stock to be turned is held between the two points
The tool rest is a piece of T&G 2x6 glued to a base that can be clamped to the benchtop
Tool rest in place, ready to turn
I have the string wrapped around the stock so that the stock rotates towards me on the pull stroke.  I started with a scrap piece of maple about 1" octagonal(ish).
Starting to turn the maple - it was rough going
I'd never turned anything before, so I looked at a couple videos (of powered turning) to get an idea of how to hold the tools and how to present them to the wood.  I have four crummy turning tools that I found at a garage sale last year and I sharpened them before starting.
The lathe tools - 2 gouges and 2 skew chisels
The author using the bow lathe
After using this lathe for a few minutes, I saw a need for three immediate improvements.  First, the bow hurt my hand, so I rounded all edges, cut it down in size and sanded it.  Second, the points were not filed very evenly and they were quickly widening the holes in the ends of the stock.  This would make the stock a little loose.  I could bring in the movable jaw, but I just kept making the hole larger and eventually it needed to change.

My solution was to change from the hanger bolts to 5/16" (because that's what I had) all-thread.  I filed off the last 1/4" of threads, then chucked it in a drill and ran that bald end over a file to get a reasonably cylindrical 1/4" rod.
The new points with 1/4" rod end
Drilled 1/4" holes in the ends of the stock to accept the new points
So far, this is working far better.  As a note, both ways of doing this required a drop of oil on the points to minimize vibration and noise.

The third problem I had was with the tool rest.  You really need a smooth top of the rest for the tool and your fingers to slide smoothly and my T&G board was quite rough.  So I sawed off the tongue, planed it smooth and glued on a piece of hardwood.
The upgraded tool rest with smooth top and rounded edges
And how are the results?  Well, not so good.  I can remove a little material, but getting any reasonably consistent diameter is not happening.  Also trying to get any shapes is a joke.  Without a second hand to stabilize the tool, it tends to dig in and stop the works.

At this point I don't know if my tools are bogus, my technique is bogus, or the lathe is bogus.  But I'll keep working on it.  Rome wasn't built in a day.


  1. Not a lathe expert but it seems to me that you aren't generating enough RPMs. I've seen videos of Indian turners using their feet to hold the lathe but the lathes were motorized. If I find the video again I will send you the link

    1. Hi Ralph. I've seen some videos (from Marrakesh?) where the turner is holding the turning tool with a foot and one hand, a bow in the other hand to turn the workpiece. They get plenty of RPM from the hand-driven bow. But the workpiece is typically very small, so you get more RPM from that than if the piece was larger.

  2. Hey Matt,
    Very clever use of the bench as the lathe bed. All you need is to continue refining. One thing that will definitely help is getting a metal surface on your tool rest, perhaps a piece of pipe? Tools need to be able to slide along with little friction.

    The other need is to gain better control of the turning tools. I can't offer any advice on how to control the tools with only one hand. The angle of tool presentation is so critical that only a few degrees change causes big differences in how the tool cuts. That's why we always see turners using two hands to control the tool; the hand at the end of the tool manages the very subtle angles.

    Maybe if your tools were long handled enough to let one end rest against your hip and then raise and lower your hip for control?

    Or, you could do like the guy in the video that I think Ralph was thinking of, a Moroccan who sits in the street and uses one hand and one FOOT to control his turning tool.


    You're on your way. Keep on refining.

    1. Thanks, Bob. Would a metal tool rest be better than a smoothed and sanded piece of hardwood? I worked with various ways of holding the tool, trying to control it better, using subtle shifts in hips or shoulders to change the angles. I got a little better at getting the tools to cut, but it was largely uncontrolled.

    2. I've tried both wood and metal tool rests and like the metal better. Yet, that's just personal opinion.

      However, the more important factor is having good control of the turning tools. You really, really, really need two hands for that. ... or a hand and a foot. :)

      Freeing up a hand by using a spring pole and foot pedal, as in the Maquire bench top lathe, would get you there.

      Keep havin' fun.

    3. Got it. Thanks for the follow-up, Bob.

  3. Have you seen Richard Maguire's bench top lathe:

    1. I remember seeing that before, but I think I'll review this stuff again. I think it's exactly what I'm looking for. Thanks Sylvain.