From Log to Curtain Pulls

Woodturning on my Taig lathe

Part of the Making Stuff collection
by Douglas W. Jones
THE UNIVERSITY OF IOWA Department of Computer Science

Mulberry Wood

Freshly split mulberry logs
illustration showing wood
In the spring of 2008, not long after the sap began to flow, the beavers along the Iowa River in my neighborhood began to selectively cut mulberry trees near the water. One tree they cut was large enough that after it fell, they gnawed off the branches to haul away, leaving behind the tree trunk. I noticed that the heartwood of the freshly cut mulberry stumps was a bright yellow, but that after a few days of sunshine, it turned a rich brown color.

The trunk looked interesting enough to me that I hauled it home and cut it into lengths that would just fit the bed of my Taig lathe, then split the logs into quarters. By splitting the wood immediately after cutting into lengths, I hoped to reduce drying stresses, end checking, and related problems. To a large extent this worked. Before starting work, I split a roughly square chunk of each log quarter, again using a hatchet.

Splitting wood instead of sawing it means you know exactly where the grain goes. In the case of mulberry, one immediate lesson is that even when the outside of the tree is straight, the wood inside isn't necessarily straight. Look at the second log from the left in the photo for a good example.

My initial goal was to make a set of decorative curtain pulls, althoug I ended up with enough wood to give blanks to others and contemplate other mulberry wood projects.

Roughing the Blank

Using a draw knife
illustration the wood in a vise with a draw knife
One end of each wooden blank needed to be round so it could be held in the lathe chuck, and any parts of the blank that protruded far enough to bump the lathe carriage or toolpost needed to be shaved off. I did this using a draw knife.

Mulberry wood is quite hard, significantly harder than sugar maple, a little harder than hornbeam and a little softer than black locust. Even so, so long as you take only thin shavings, a draw knife works very well on it.

Rough Turning

Setup for turning
the blank mounted on a lathe
In mounting my blank on the lathe to begin turning, I found that it was too large for my 3-jaw chuck, so I used a set of steel pins that fit snugly in the holes in the aluminum chuck jaws. The hand-carved round end of the blank is far from perfectly round, so to get the most secure clamping, it's useful to lightly clamp it, then wrench the wood in the chuck to find the loosest position before fully tightening the jaws.

I held the far end of the blank with a dead center — more about that later. The wood is hard enough that I had to use a hammer to drive the center into the wood before mounting the center in the tailstock.

Roughing half done
half of the blank is now cylindrical
For rough turning my blanks, I used an ordinary metalworking lathe tool, running the lathe at 1375 RPM. With a roughly shaved blank that's close to 2 inches in diameter at the largest, this may seem fairly fast, but at this speed, the vibration of the still eccentric blank is managable.

Just about any sharp pointed tool will suffice for rough turning wood, and it will work fairly quickly. I ended up mounting the tool twice, once pointing right, as shown in the photo, with the toolpost in the rightmost T-slot on the cross-slide while I cut as close to the tailstock as the tool would reach, and again facing left, in the left T-slot, so I could cut as close to the chuck as was safe.

Parting off the ends
half of the blank is now cylindrical
The final step in cutting my blanks was to part off the rough ends. I used an off-the shelf Taig parting tool. This has a shoulder that limits its depth of cut, so I couldn't part all the way through at this point, but the grooves helped me align the blade of a handsaw to make much cleaner ends than the chainsawed blanks.

Parting off the ends of the blanks at this point serves two purposes: It gets rid of the ends that I couldn't turn to size because they were out of reach of the toolpost, and it gets rid of the small end-checks that have developed while the blank dried.

On some of my shorter blanks, I only parted off the end by the tailstock, leaving the roughly-rounded end in the headstock unchanged until later.

Drilling

A hollow dead center
the dead center with a drill stuck through it
I wanted to make some decorative curtain pulls. To do this, each blank needed to be drilled from end to end with a hole just over the size of the curtain string. I used a 3/16" drill for this, since the string was about 1/8" in diameter. Since my blanks were all just under the roughly 9" capacity of the lathe, this qualifies as deep hole drilling. Holes with a depth to diameter ratio of over 10 to 1 are officially a deep holes; the depth-to-diameter ratio for a 9" by 3/16" hole is 48 to 1.

Gunsmiths have long used gun drills through a hollow tailstock center in order to bore the length of a gun barrel, and this technique has also been used in the woodworking community for well over a century. Here are some patents that illustrate this, one old, one more recent:

I made my tailstock center from a scrap chunk of 1/2" steel. I drilled it on axis using the lathe, with a 3/16" hole drilled from what would be the working end and a 7/32" hole from what would be the tail end. The difference in diameters is so that any small misalignment where the two holes met would not cause any hangups when drilling through the resulting hole.

After drilling the dead center from both ends, I turned a hollow point around my hole on the end. I made no effort at precision, but the angle of the cone around the hollow center is approximately 60° and I also made a very small chamfer on the inside edge of the hole at approximately the same angle. The photo shows the center mounted in the tailstock, with a very long twist drill poking through the hole.

Drilling through the tailstock
midway through drilling the blank
I mounted my extra-long drill in the jacobs chuck that came with the lathe, using the chuck as a handle. With the work spinning at 1375 RPM, I began drilling. I learned that if you drill aggressively, the drill does wander, but if you peck at it, drilling no more than one or two drill diameters before you pull the drill out to remove the sawdust, the drill stays very close to perfectly on center.

This technique is called peck drilling for a reason! You feel like you're pecking away at the hole, pulling out the drill, poking it back in, and pulling it out, over and over and over. I think one important thing about this method is that the drill is stiff enough that, if the hole begins to wander just a bit from the axis, the drill cuts to the side just a little bit each time you pull it out and push it back in, correcting any eccentricity that developed during the previous peck cycle.

Drilled Through
showing the drill all the way through
This photo shows the finished hole from end to end. Standing the drilled blank on end balanced on the chuck, you can seel how well the drill stayed on center. The drill chuck is at the end of the hole that was out by the tailstock when drilling. There, of course, the hole is naturally on center. Any error is at the end that was originally the headstock end.

At this point, the wood is only about half-dried, so it is not done shrinking. It's a good idea to let it finish drying before doing the finish turning. From this point onward, the hole through the center of the blank is our reference for the center.

Finish Turning

Tooling for finish turning
detail showing the finish turning tooling
Rough turning with whatever sharp tool was handy, I noticed significant tear-out in the wood surface. This led me to investigate better tooling. Looking at conventional woodturning, it looks like the best finish is achieved with a skew chisel. The skew chisel is held so the blade meets the wood at about 45° from being parallel to the axis of the piece being turned, and the chisel edge has from a 25° to 55° included angle (steeper angles for harder wood). In use, a skew chisel does not scrape the wood surface; instead, it is supposed to take shavings from the workpiece, not unlike the shavings from a plane.

I ground a tool I can fit in my toolpost that meets the wood in much the way a skew chisel is supposed to meet the wood, and it was a success, as you can see in the photo. The photo shows the finished end of one of my curtain pulls. I used a parting tool to define the surfaces perpendicular to the axis, and used my toolpost-mounted skew for the parallel cuts. The finished surface is mirror smooth to the touch, with no grain tear-out at all.

The fine shavings you see in the photo are from the final finishing passes, while the coarse curls are from the quick and dirty rough cutting passes. Even the fine dust is actually in the form of little curls. Unlike the dust you produce with a scraping tool, these curls settle out of the air quickly, and they tend to stream off of the tool edge into a fairl well defined and orderly pile on the lathe bed instead of flying all over the place. In sum, this is a really nice way to work with wood.

I ground the tool so it could be mounted for both left-hand and right-hand use. Whichever way you are cutting, always adjust the tool so its point of tangent contact with the workpiece is near the center of the cutting edge.

On an unrelated note, because I was working on a drilled workpiece and using a hollow tailstock, both drilled to the same diameter, I did the finish work with a piece of drill rod pushed into the workpiece and I oiled the tailstock. Technically, it's still a dead center, but I didn't drive it tightly into the workpiece, I merely mounted it so it gently brushed the end, and when I cut the flat finished face on the end, I even backed the tailstock off enough that I could use a parting tool all the way up to the drill rod.

Also, I did all of the finishing work at the tailstock end, reversing the workpiece in the lathe after finishing one end so that I could finish the other end. This way, all of the finish turning was concentric with the hole down the center of the workpiece and none of the finish turning was done with reference to the outside surface, a surface that was cylindrical before the wood finished drying but was no-longer a perfect cylinder by this point.

Finishing

Mulberry wood curtain pulls
two curtain pulls hanging against their final home
I drilled a 3/8" diameter hollow in the bottom end of each curtain pull using a spade bit. This served as a place for the knot at the end of the curtain string to hide. I sanded the pulls on the lathe using 400, 600 and 800 grit sandpaper. This is very hard wood, and it really did profit from sanding with such fine paper.

I finished the pulls with walnut oil and left them outside in the sun for several days. The UV in the sunlight both served to brown the wood and to help the oil polymerize. Unfortunately, it rained one day, and this raised the grain on the wood, so I re-sanded them with just 600 and 800 grit paper, and then added a second coat of oil and put them out in the sun again. The result was very nice, as shown in the photo.

The photo shows these pulls against the outside of the ornate wooden chest that they are now part of. Their permanent home is inside that chest, working the curtain that is inside the door of the chest. The design of the pulls, with a flange on each end, is intended to reflect the design of the wooden door hinges on the chest.

I should have left the pulls out in the sun to get a bit browner so they'd be a better match for the mahogany of the chest, but they do their job, and except when you're actually groping for one of the curtain pulls, they're out of sight inside the chest.