Roy Underhill’s Double Spring Pole Lathe

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From the August 2016 issue, no. 226

Wood turn on a lathe for spring rod concerns reciprocity, all back and forth. For example:

D: “Don’t you get tired of standing on one leg?”

A: “Of course, but if you try to work the pedal with both legs, you fall.”

or:

D: “Bet you can’t wait for electricity!”

A: “Well, this is an alcohol lathe!” (He said as you took a drink from your big colonial mug.)

or:

D: “It’s much safer than an electric lathe.”

A: “Unless it leans too far forward!” (He said tilting his head in the path of the downward spring pole.)

But quick bounces won’t win anyone by your side on the spring lathe. The answer that makes a true believer win is this: “Here, try it!” (He said as he passed the heel that turns into the interrogator’s hands.)

Adapted from an ancient German technical encyclopedia, this lathe is precise, portable, powerful, adjustable, adaptable and autonomous. The two dead centers do not allow any play in the piece and the direct transmission of the cable wrapped around the wood does not lose power in the transmission, friction or vibrations. The great virtue of this particular lathe is that it uses two wooden springs, connected by a sliding collar, to make the tension immediately adjustable. The raised barbell lengthens the tension of the springs and positions the control cable exactly where it is needed.

Just as important in this project, however, in addition to how rewarding the lathe to make and use is, is how accessible the materials are. I based the whole project on easily available pine construction lumber and you can practically build the entire lathe from a single 12 × 2 × 12 long up to the actual required 4 “and 7” widths.

Form the frame

Almost there! A single 12 ′ board of 2 × 12 nominal will give you most of the wood you need.

Start with the three horizontal rails, choosing the two most suitable for the upper pair (the “ways”) of the lathe. Keep parts in order by marking them with triangles.

Matching signs. As with any frame construction, start by grouping all the horizontal (or vertical) members and defining the lines through them as they are clamped together.

Place the upper pair together on the work surface, the narrow edges upwards and draw in pencil a triangle, which points towards the front (towards you) overlapping the two upper guides. The lower guide gets a single triangle on the upper edge, which points again towards the front of the lathe.

These 4 ′ long rails can be slightly irregular in overall length; the important thing is to have an equal span between the shoulders of their tenons. Hit your shoulders across the three rails at least 4 “from the ends to leave enough force in the protruding tenons for the wedges that attract them.

Tear it well. I tear off the long-grain cheeks of the tenons before cutting the shoulders. This reduces the cut needed to clean up a rift caused by a wobbling of the powerful circular saw.

Now write the thickness of the tenons on the upper guides (1 “) with the marking indicator held against those that will become the internal faces. These are single shoulder tenons on the two upper guides, with the shoulders facing outwards – towards the the front and rear of the lathe. Single-shoulder tenons are less stable than a two-shoulder version, but, since they are arranged in opposite pairs on the two rails, they cancel each other’s tendency to twist the deadly pole. Without a companion to counter it , the lonely lower track is best cut with a standard two-shoulder tenon.

Bored and more. Trench in both faces of the mortars through the posts will help guide the boring and chisels that follow.

In the same way as before, arrange the height of the mortises in the two poles and the shoulders of their tenons for the feet. Again, mark their front edges with the overlapping triangle. With the gauge working consistently from the triangle edges, write the 1 “widths of the mortises across the posts. Mark each indicator setting on both sides of both messages before adjusting the indicator again to mark the next line .

These mortises are simply rectangular tunnels quickly excavated after making accurate and clean entrances on opposite sides. Cut these tunnel entrances with repeated grain chisel cuts, leaving 1/4“- deep trenches to record the positions of the cochlea and the chisels that follow. Mount the auger lips in this trench and dig halfway from both sides, meeting in the middle. Clean with the most solid chisel.

Now you have your first chance to lift the lathe frame and see how fun it is to put six mortises and tenons together at the same time. Call me when you’re done.

Spring lathe cutting list

No.Item size (inches) Material Comments

t w l

❏ 1 short post 11/2 7 45 Pine 31/2“Double tenons

❏ 1 Long post 11/2 7 66 Pine 31/2“Double tenons

❏ 2 feet 11/2424Pine

❏ 1 Lower guide 11/2 4 48 Pine 1 ″ -thick TBE *

❏ 2 Upper guides 11/2 4 48 Pine 1 ″ -thick TBE *

❏ 1 barbell 3/4 21/248Pine

❏ 1 pedal 3/4 21/2 48 pine cone at the end

❏ 6 Wedges per frame 3/8 1 9 Pine Taper one end

❏ 1 Short elastic rod 1 1 43 Hickory to octagonal plane

❏ 1 Long elastic rod 1 1 49 Hickory to octagonal plane

❏ 1 Tool rest 11/2 63/4 12 Pine 1/2“Chamfer, front

❏ 1 Tool rest support 11/2413Pine

❏ 1 Lower part of the tool 3/4 4 6 Pine

❏ 1 Tail kick 3 5 173/4Pine tree

❏ 1 tail wedge 3/4 11/4 12 Pine Tapered at one end
* TBE = Tenon at both ends

Elevation

LONG post and foot profiles

Support surface for resting tools

Tool rest elevation

Tail kick elevation and profile

Tail kick elevation and profile

short posts and profiles of the feet

Wedge fang tenons

Wedge problem. Trace the wedges on the cheeks of the protruding tenons. Ream and chisel their mortises, easily adapting to the sides and adding additional space to the back.

The wedges through the tusk tenons at the ends of the rails look large and firmly lock the frame. To work, however, the wedges need that extra play on their back side so that they can push harder against the stakes as they are tapped down, rather than getting stuck in too precise a mortise.

From sturdy wood, tear off six,3/8“-Thick wedges, 9” long, 1 “wide at one end and taper 1/4“At the other.

Cove drill. Secure the blocks of the feet together and pierce their intersection to leave nice creek cuts for the ends of the relief cuts to follow.

With the frame assembled and the guides that fit snugly behind them, place one of the wedges against the cheek of a protruding tenon as it will sit when driven at home. Draw the sloping edge of the wedge on the tenon’s cheek, then draw a second line on the cheek that runs flush with the pole.

Remove the guide from the pole and bring the lines drawn by the wedge around the edges of the tenon. On the back, the one that was flush with the pole, add that extra game – 1/8“Or so. Set a mortice indicator to perform a hit 3/8“-Large pair of rails to guide your auger and chisel, then cut the mortises.

On your feet

Divide. The double tenons bent on the poles begin as a large, wide tenon. In this case you may first see your shoulders and then go back to the line.

You can enjoy a nice trick before you start cutting the joints to connect the feet to the poles. To give them more of a pedestal shape, the top and bottom of the feet are relieved 1/2“Or so. These cuts end in creek cuts, promptly made, two at a time, with the same auger that you used to make the mortises in the frame.

Fasten the feet together (base on base) and pass them both, positioning the lead screw exactly where the two pieces meet. Ream until the lead screw protrudes from the other side, then turn the joined pieces upside down and restart the auger at the passage point. Continue the boring to connect with the other side.

Restore the feet with the other edges tightened together and drill the second pair of holes. This process leaves four half-cylindrical cuts in each foot which make the shoulders smooth and rounded at the ends of the saw cuts.

Ogee! Set the compass to half the length of the baseline. Hit the short arches from the midpoint and from one end of the baseline. Place the compass at this intersection and hit a bow forming half of the ogre. Repeat on the opposite side. So cut it.

The joint that connects the foot with a pole must be of broad base for stability, but must not excessively weaken one component or the other. The double curved tenon on the pole does the trick by leaving an intact wood section in the middle of the mortise.

Start with a broad, centered, 5/8“- thick tenon, then cut out the intermediate wood with a circular saw. Instead of cutting the cheek of such a large tenon, here you may want to see your shoulders first and then split and shave to the final thickness.

Do an exploratory division halfway between the waste to get the grain run before you start working closer to the tenon. When you finish the tenon, spread it on the foot and trace it around to find the mortises to match.

The 14 ogee shoulders in this design go a long way in making the lathe look right. The ogre is the ancient wave-shaped recurve (arranged with a compass), as you can see in the illustration of the foot.

On the feet, the ogee curves are large enough in proportion to the thickness of the butt that easily take shape with a circular saw. The smaller nails on the frame, and in particular those on the thick tailstock, are best cut with a gouge and a chisel. While arranging the oge, you may reflect on the mechanical relationship of the rotating tools: the compass, the augers and the lathe (the machine you are building with them).

Spring poles, barbells and a magic ring

Continue to be a great one! The light pine balance requires a metal bushing to prevent it from coming loose.

Robust frame made, now integrated into the moving parts. Considering that for the frame we wanted heavy wood for strength and stability, we now need a light but rigid rocker that does not dampen the action with excessive inertia.

The barbell rotates to a 1/2”Iron rod with inserted sleeve bearing to protect softwood. The rod and sleeve usually hide somewhere in the section many small drawers-write-the-number-on-the-bag of your hardware store. You will need to cut them to size with your hacksaw.

The barbell rotates into a U-shaped slot in the top of the tall column. Find the top center of the tall spindle and draw a line directly from it to the center of the space between the tenons of the rail. This becomes the center line of this 3/4“Slots all over the world.

Use the barbell itself as a layout guide for lines across the top, fine grain of the pole, keeping it in line with the guides below while tracing along the sides. Bored on 1/2“Holes for the tree through the pole as accurately as possible, using a square and an assistant to check the work.

Oooo brilliant! Wrap a copper strap around the spring poles and drill through the overlap. The rivet and washer come from a farm shop where they are sold for the repair of the harness.

Ash, oak and hickory are good for spring poles, but whatever hardwood you can find will get you started – if necessary, cut the mop handles. Fast growing hickory or oak is stiffer than slow growing wood with many tight growth rings. Bring the poles down to 1 “square, then pull the knife and flatten the corners to form an octagonal section. The lower pole should fit completely inside the frame, but the longest one should reach about 6” through the slot in the pole tall.

The magic of this lathe is centered on the movable ring that connects the two elastic rods. Sliding the ring from left to right changes the strength of the combined spring from weak to wow, allowing you to combine the piece’s inertial resistance with a spring force that keeps the turning action lively and fast.

A simple knotted cable would make for the ring, but a copper band gives a little glow. I have seen a scrap length of 1/2“Copper tube halfway along its length and flatten one half in a sturdy strip. Bend it to easily fit the two rods, pierce through the overlap and rivets to close it.

One more step and you can try the spring action. I connect the spring to the rocker arm with a heavy wire rod (but I am still looking for a better looking light wood or metal connecting rod). Avoid anything that can be elastic and dampen the energy of the spring poles.

Tail, tool rests and centers

Make it often. Glue the tail butt from two layers of board. The small or deep shoulders of ogee are better combined with a chisel and gouge rather than cut with a revolving saw.

If you can get thick stuff for the tailstock, excellent. But in keeping with the mandate for readily available material, I use two good 18 “lengths of the glued plank.

Prepare the wedge for the tail kick in the same way as the fang tenons on the rails, but 3/4“Often and with enough protrusion in front and behind to facilitate the blow with a hammer. This wedge becomes very useful as you adjust the pinch of the two centers.

Depend on the rest of the tool for proper rotation, so don’t overlook it. A wobbly tool holder makes good work impossible and the whole concept of spring turning could be to blame.

The tool holder must be quickly loosened for adjustment, but just as quickly locked in place. It must be wide enough not to require frequent left and right movements, but not so large as to be unstable. The T-shaped under-piece keeps the 7 ″ -long, 3/8“The carriage bolt (secured with a mudguard washer and wing nut) centered between the rails and the L-shaped grooved upper half allows you to position the rest adequately away from the turning wood. A one inch wide metal strip screwed on the upper edge, it has a smooth and narrow fulcrum for the turning tools.

Smooth moves. A metal strip makes the bearing smooth for the turning tools on the rest. Build the rest of the tool with strength!

This tool holder does not have a ready height adjustment (you can do it with shims), but I found it satisfactory if the upper edge is level with the centers. Let the instrument rest first, check it by level, then use it to find the positions of the centers on the opening and closing credits.

The centers must be perfect, polished cones or they will constantly widen their seat in the end of the rotating piece and allow it to swing.

I have my students buying cheap # 1 cheap Morse tapered dead centers for their lathes, but if you’re ready for more metalworking, the rest of the 1/2“The rod used for the barbell can be turned into the lathe centers.

Don’t worry about the lack of screw adjustments on the centers. Like a wooden surface, you can perfectly adjust the pinch of this lathe with the taps of a hammer or, more often, with the handle of the turning tool.

How boring. Ream the seats for the centers with the brace carefully aligned with the axis of rotation of the lathe. The tapered centers fit well into an 11⁄4 “7⁄16” deep hole followed by a 3⁄8 “concentric hole.

Like centers, the transmission cable is a demanding part of the lathe. A natural fiber cable rubs very quickly from rubbing against itself, but will get you started. The best cable is the 3/16” for 5/16“Round leather belts used for pedal sewing machines. Pass the upper part of the cable through a hole drilled in the end of the tip of the barbell and stop it with an elevated knot. Run a length of 6 ‘and attach the end to the tip farther than the foot pedal.

I have never made a pedal more elaborate than a simple four-foot stick for this lathe, probably because I was so eager to try it that I looked for the fastest solution. Spring loaded pole lathes commonly have suitable pedals, usually a triangular series of sticks with one side hinged to the floor. Whatever you use, make the pedal light enough not to fight its inertia, but stiff enough to keep the turning action lively and decisive.

attachments

What is a lathe without attachments! Clockwise from left: spindle and head to make the wood too slender to work directly with the transmission cable. (One end of the thin wooden spindles in the square socket and the other turn the dead center in the tail kick.) A pointed spindle to turn the bowl. A chase of thread to make bench screws. A central hollow tail, made with a sharp brass hydraulic system, for boring grooves and the like. A constant pressure at constant rest for thin pieces. A scraper placed on an example of spherical joints and grip that helps to do (it is mounted in the rear kick).

– RU

turning

Find the weak point. A correct oblique cut with the gouge leaves a spiral finish while the bevel rubs on the wood. The control cable runs around the work on the side facing the turner.

You could turn the dried wood into the oven, just as you could only eat crackers, but the full flavor of wood turning is only found in the cooler things. With wedges, ax and switchblade, roughen some fresh turning material up to a 3 “diameter cylinder (a pretty nice cylinder for the first time out) about 18” long. Find the approximate centers on both ends and dig a small hole with the tip of a chisel that rotates at an angle.

Rub some wax into the holes, wrap the lathe wire around the butt so that it passes over the front and pinches the butt between the centers. Tighten the centers by touching the rear kick and driving in the wedge. You will have to tighten the pinch several times during the turn as the centers find their final place.

Place the toe on the pedal about a foot from the anchored end and push down. The stock should rotate towards you from above (if it moves away from you during the descent, the cable goes to the wrong side).

Adjust the tension of the spring by sliding the ring to the left or right to make a lively rotation during the ascent. You can make further adjustments by moving the positions of the connecting rod on the protruding pole and on the rocker arm. Note that the smaller the diameter of the point where the cable wraps around the workpiece, the faster the wood will rotate with each stroke. The large diameter equates to slower speed, more torque. Small diameter equals high speed, lower torque – just what you want.

Now for the turning point and the question: “Do you have to pull the tool back on the return stroke?”

No, you don’t, but you should certainly look for the best turning practice. It is not enough to put a gouge in the rotating stock and scrape your way of modeling. When the leg muscles and not the power plant do the job, you have a constant incentive to find the most perfect cut.

Start with your left hand by anchoring the gouge on the center of the tool rest and slide the skimming cuts from left to right for a length of 2 “until you have reduced to a clean cylinder at the right end of the butt.

Now try a correct rotation, making sure that the bevel of the gouge or chisel rubs the wood while the cutting edge makes a cutting cut through the grain, leaving a spiral shave. Always work from the largest to the smallest diameter.

The only specific concerns for the spring lathe are:

Don’t cut the cable with your gouge!

Raise your foot high enough to get more rotations of the kick with each stroke.

Keep the centers by pinching the wood (a hissing sound means you’re free).

Be generous with the people you care about!

The latter is so important. Some may find muscle power machines challenging for their world view, and if they make fun of you, you may be tempted to react. For example, to the question:

“Hey! Where’s the switch?”

You may be tempted to answer, “Right here!” (He said as he picked up a walnut stick and slapped the interrogator’s legs.)

But it wouldn’t be nice. PWM

Roy is the guest of “The Woodwright’s Shop” on PBS, the longest how-to program on television.


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