Woodworking in the great white north.

Marble Tower – down the drain – part 1

I mentioned in earlier posts that I was ‘stuck’ at various points and procrastinated a lot.  THIS, was the biggest cause of it.

Why was I stuck? 

  1. First:  I did not like the design of the spiral ‘funnel’ in the plans.
  2. Second:  I knew I wanted to turn a funnel, but wasn’t sure how I was going to do it.
  3. Third:  Once I’d made the funnel I couldn’t decide how to attach it.

The process of getting from the xylophone through to attaching the funnel was probably days of work, but months of elapsed time.

Part 1:  What to do instead of the planned spiral funnel?

The plans called for a piece of plywood cut into a spiral with the center pulled down and the whole thing attached to a block of wood spanning the width of the tower.  I thought this was kind of ugly and I had other ideas about turning a funnel instead.

Have you ever seen those charity coin funnels?  The ones where you drop a coin down a slot and it rolls around and around the funnel, gaining speed as it goes lower and lower until it reaches the bottom and is really whipping around before it drops out?  I figured I could do something like this for the marbles too.  I even went so far as to look up the physics involved in these funnels and try to figure out what the curve needed to be to get the most out of the funnel.  In the end, I found that the slope of the curve was going to be limited by the blank I was using and my turning skills.

Part 2:  How to make the funnel?

I wanted to make the funnel out of ash to keep it in harmony with the rest of the tower, so I settled on trying out segmented turning.  I had a couple of ash boards available still to use on this project, so I took one and started cutting segments at about 30 degrees each, giving me 12 segments to make up a circle.  This was very much design on the fly.  I cut enough segments to make up two 3/4″ thick ‘plates’.

My plan was to take the two plates and cut rings from them and stack the rings to make up the funnel blank.  I figured out that if I cut a ring from one blank, then staggered the next ring from the other blank, and so on, I would have enough overlap between the layers to turn the funnel.  Before gluing up the two ‘plates’, I realized that I would have a hard time cutting rings out of them once they were put together.  I ended up making four half circles instead and cutting the rings on the band saw.

I”ll interject here that I’ve never done segmented turning before (so, I get a check mark for challenging myself with a new technique) and only did a little bit of research on it before diving in.  I learned a few things in the process:

  • cutting the segments precisely in the first place is easier than trying to shave one segment down to make it all fit nicely
  • cutting the segments precisely in the first place makes the glue-up go much more smoothly
  • ensuring the glue-up is completely flat makes assembling the rings go much more smoothly
  • glue is not a substitute for a good joint
  • inserting accent strips between segments would be a good idea to hide the glue line – or choose your glue with glue lines in mind
  • once glued up the entire blank is a heck of a lot more stable than you’d think

I will probably try segmented turning again, but I’ll plan better and spend more time on it than I did with this one.

Once it was glued up, I put it on the lathe and decided to keep the outside ‘stepped’ to show the rings used.  The inside I tried my best to turn into a rough hyperbolic funnel.  I stopped a few times during the turning to try out a marble and was pleasantly surprised by the positive results each time.  In the end, I don’t think the shape of the funnel makes too much difference, what really matters is that the marble come into it on a tangential angle and have as much speed as possible.

I did experience some tear-out and the very bottom section was the worst for this.  In the picture above you can see that I lost a few small chunks in the process of turning it.  So be it, I did a bit of repair and once the hole was drilled into the bottom it was not as noticeable.

Next up, more going down the drain as I figure out how to mount it.

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2 responses

  1. Wow. That’s a beautiful turning. As a non-turner myself, I must say I’m impressed how you took the plunge into segmented turning.

    August 16, 2010 at 8:59 pm

  2. You’re too kind….just don’t zoom in too much or you’ll see the tearout. Apparently ash isn’t the best for turning end-grain…or maybe it’s just me. 🙂

    Next time I do a segmented turning I’ll document it with pictures/video….it’s a neat process. I’m allowing myself to gloss over my errors in this one.

    August 16, 2010 at 9:32 pm

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