Monthly Archive for July, 2011

Lathe spindle lock with Pinecone handle – 1

Published on July 31, 2011 in Tool making and Woodturning. Closed Tags: , .

I teach woodturning classes at The Sawdust Shop, where they use 12″ Jet lathes. These lathes lack a spindle lock, which I need when unscrewing chucks and faceplates from the spindle. Jet supplies a screw-in tapered pin for spindle locking and indexing, but it’s a separate little piece. You probably know what happens to separate little pieces in a workshop full of wood chips. Now imaging how fast it happens in a public shop.

The result is that every time I teach a class, i have to go looking for a 1/4″ bolt to serve as an impromptu spindle lock. I decided to make my own, and make it big enough that it wouldn’t get lost in the chips. I also wanted to have some fun with the idea, so I turned the handle out of a pine cone. That decision posed some interesting technical challenges.

You can’t turn just any cone (unless you first want to cast it in plastic). You need one that hasn’t started to open up. That means harvesting it from the tree at an early stage. Mine came from a branch broken by a winter storm.

Cone reversed and mounted by its tenon

There’s no reference surface, so I started by mounting the cone between centers and turning a tenon on the end I though would show the most interesting pattern—the base (to the right in the top  photo). Then I put a chuck on the lathe and mounted the cone in it using that tenon.

As I started turning, I discovered an off-center hole in the cone that would cause a problem as I drilled a hole to mount the brass spindle locking rod, so I filled the hole with epoxy.

Epoxy to smooth the end of the cone

The epoxy was just to give a smooth surface so I could get a centered hole started. I planned to turn it away. However, if the epoxy is to be left for show, it’s important to get rid of any bubbles that get entrained when mixing it up. I used 5-minute epoxy, which I mixed and slathered onto the end of the cone, filling the hole. To eliminate air bubbles, I briefly blew air from a hot air gun onTo the glue. That makes the air bubbles rise to the surface and pop.

Starting the tool hole with a center drill

Once the epoxy had set, was time to drill. To insure a centered hole, I chucked a large center drill in the drill chuck, mounted it in the tailstock, and bored a pilot hole, a little smaller than the final 1/4″ hole. That let me drill an accurately-centered hole for the brass rod, right down the center of the cone.

Next, the special challenges of turning a cone.

Turning a Shaving Brush—part 3

Published on July 7, 2011 in Uncategorized and Woodturning. 2 Comments Tags: .

Cutting internal threads with a machinist's tap

The brush blank was already mounted in the chuck, so this was a good time to turn the outside profile. I could see the brush tuft hole in the end, so it was a simple matter to create a nice shape with adequate wall thickness around the hole. Because this Dymondwood is so tough and abrasive, I had to sharpen several times. The saying in turning is, “if you even think that maybe, possibly, you should sharpen, you should”.
Now it was time to cut threads in that 5/6″ hole, so I could turn the brush around and remount it. Getting taps to cut straight in is always an issue. If the tap’s a thin one and you start at an angle (easy to do if you’re holding the tap in your hand), you’ll often break the tap. The 3/8″–16 tap won’t break in the Dymondwood, but it would easily strip out the threads it’s cutting if I went in off-axis. So I used the lathe to help me.
In the photo you see the tap in a home-made tap wrench (the knurled handles sticking out to each side. That gadget to the right of it is key to the job. It’s a spring-loaded tap guide, held in a Jacobs chuck in the tailstock. Taps often have a slight depression in the tail end, centered on the axis. If you align the spring-loaded center with the tapping axis, put its point into the end of the tap, and bring up a little spring pressure, that will hold the tap on axis as you begin cutting threads. Every few turns you can bring up the spring pressure again as the tap advances into the workpiece. It’s less than $10 and has saved many a threading job for me.
Once the tapping was done, I screwed a Beall Collet Chuck onto my lathe spindle, pushed a piece of 3/8″-16 threaded rod through a collet, and clamped everything securely. Then I screwed the brush blank onto the stub of threaded rod and snugged it up tight against the collet face. Notice, in the photo, the little bit of blue shop towel sticking out around the left end of the brush. That protects the finished rim from the metal collet.

Finishing the end

Once the brush was remounted, it was a simple matter to clean up the end. That’s when I realized it was a little too plain. Fortunately, a friend had given me a little bag of 1/4″ mother-of-pearl dots, the kind luthiers inlay into the necks of guitars. You can find them at Stewart MacDonald, a luthier supply house. I drilled a shallow 1/4″ hole with a Forstner bit (for super clean edges), epoxied the dot in place (slightly proud of the surface), and leveled everything.
I wet-sanded to #12,000 with 3M MicroMesh, which left a high-gloss, waterproof surface. Then I finished by epoxying the brush tuft into place.
I’ve been using the brush for three weeks now, and I really like it. This is a good, fast project that yields something really useful. Now my son is asking for one.

Turning a shaving brush–part 2

Published on July 4, 2011 in Woodturning. Closed Tags: .

Drilling the mounting hole

I hope you all are enjoying this beautiful (and hot) 4th of July weekend. I’m taking a break from all matters corporate and enjoying friends and a little recreational writing.

So, the problem is how to mount our shaving brush on the lathe. We can’t turn it between centers because we don’t want to wind up with a visible hole in the end  from the tail center. We need to mount it from one end, and there are a couple ways to do that. One is by leaving it in the chuck as you see it here, turning everything, then parting the piece off and hand-finishing. But this Dymondwood is HARD, and the prospect of finishing the parted-off stub without power assist wasn’t appealing. So I hid the mounting hole in plain sight.

Once I’d drilled the hole for the brush tuft, I drilled a 5/16″ hole right in the middle of it, about an inch deeper than the bottom of the main hole. 5/16″ is just the right size to accept a 3/8″-16 tap. That tap cuts threads which will screw onto a piece of 3/8″ all-thread, and that’s the stage-two mounting strategy. If this were a softer wood, I could use the mounting screw to cut its own threads, as wood screws normally do. But this stuff is much harder than natural wood.

Cleaning up the rim

With both holes drilled, I cleaned up the rim and trimmed it perpendicular to the turning axis. Now’s the time, while the piece is thick, to do this, as there’s always a danger of pushing a splinter off either the inside or the outside wall when you run the tool across the rim. With material to remove on both inside and outside, I could clean up any problems so no one would ever see them.

Rough-sizing the hole

Now it was time to make the hole fit the brush tuft.

Tufts never seem to be an exact size. The knot of epoxy that binds the hairs together is usually slightly irregular, and it was bigger than my Forstner bit (intentionally). So I trimmed out the inside of the drilled hole to rough size.

Some people do this with a scraper, but Dymondwood is so abrasive it takes the edge off a scraper in seconds. I used a Viking tool, by Soren Berger, which is designed just for hollowing end grain. I got the top of the hole to final size with that tool, stopping frequently to check the hole against the brush tuft. It’s easy to take more wood out of the hole, but a lot harder to put it back, so a go-slow approach pays dividends here.

Scraping the hole to final size with square inside corners

Finally it was time for the scraper. I used a 1/2″ tool with an 80º corner ground on the left side. This way, I can put that point right into a 90º inside corner in my turning and cut either the side or the bottom individually. That makes for a much more controllable, less grabby cut. Since the top of the cut was already the right size for the brush tuft, I just had to extend the walls down to the bottom cleanly. The scraper did it in seconds.

Next comes turning the outside, tapping the hole, and remounting to finish the piece.