Turning A Thick Walled Two Piece Hollow Form

Turning A Thick Walled Two Piece Hollow Form

Brian McEvoy

Turning A Thick Walled Two Piece Hollow Form

In this article Brian shows you how to turn a thick walled, two piece hollow form that you can further modify with pierced carving or decorative painting.
 
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Here are some photos of Brian's work to help inspire you.

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Some additional photos of Brian's new work with a painted theme.

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These stunning pieces are made from Cocobolo.

For relatively new turners in particular, one of the scary parts with these bowls is that the turned pieces can be large, but only 3/32" thick. The thinness is due to the fact that in most cases I pierce my work, so being thin is critical. I thought I should share one of my other favorite two piece hollow form designs. It is modeled after a South West Native seed pot that was traditionally clay. I embellish most of these forms with some sort of relief carving so thickness is required. For the one we're going to turn in this project, I have intentions of beading similar to Native woven baskets and the beads will be a full 1/4" deep, so I'll be turning the hollow form 5/8" thick. 
 
I prefer the two piece hollow form method rather than the one piece for a number of reasons:
 
  • Even if you're a novice you can complete this project with whatever tools you now use to turn a simple bowl.
  • You can turn most any size and not have to worry about reaching a long way over the tool rest.  I've turned these forms up to 22".
  • Thickness is not an issue; with simple calipers for measuring you can turn to a delicate 1/8 inch or any wall thickness you desire. And you can do it safely and accurately.
  • You can finish the inside so when friends or customers poke there finger in the opening (as they all seem to do) they will be impressed by the finished quality.
  • Probably the most important advantage using this method is the safety issue.  Though there are a number of wonderful hollowing tools on the market, in my opinion, none of them work with the simplicity of the two piece method.
The results of this exercise can be stunning and they make great gifts, sell well, and you should have a blast creating them. 
 
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Choose your timber wisely. Completely dry timber is imperative; this 6" x 10" piece was originally cut in the nineties and then in 2006 I cut a number of them in half and book matched them, so they are as dry as they'll ever get. Most of you won't have the timber prepared as I'm describing and I'm sure you don't want to wait 4 or 5 years to give this a go.  Another alternative to achieving this form with dry timber is to use a slab of 3+ inch lumber of the appropriate width. Cut two pieces off the slab and lay them end to end with the same side up, as in the second image. Draw equal size circles using a compass to mark your center and cut them round with your bandsaw.

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Mount your faceplate dead center. I like to use a faceplate with a center hole so when I fasten the center screw it automatically centers my faceplate in the compass mark at center. Delta makes these wonderful little faceplates. They only are available with 1 x 8 threads so you may need to use an adapter as I do.
 
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Mount the top of the piece on your lathe and proceed to turning into a classic bowl shape. Be very careful not to reduce the diameter of your piece. Remember the two halves will have to match up quite closely.
 
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At this point you want to determine how large you will want your opening. This will probably be governed by the width of your chuck jaws. On these seed pots I like to turn the top in a little. I find it makes it a little more esthetically pleasing.

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I like to turn a dovetail recess to accommodate the chuck.  I find the use of a dovetail scraper very handy and it ensures accuracy.  Once this has been established, keeping in mind that this recess will become your opening, be careful to leave a ridge to seat the chuck jaws against, then turn your recess a further distance, leaving the ridge intact.  The reason for this will become apparent when you turn out the inside of the form. 

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Reverse the piece on your lathe and carefully proceed with turning the inside. The vital part of this step is to not turn off more of the top lip than is necessary. Determine the thickness you desire and remove some of the meat from the inside; just enough so you can comfortably lay a straight edge across the top edge.

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Please don't be scared off by all of these steps. Though it may seem rather complicated, once you understand the basic concept, these forms are incredibly easy to create. I can comfortably do a half dozen in a day. When I demonstrate the method, I'm usually allowed 1-1/2 hours to complete the project from start to finish, and much of this time is taken up answering questions.

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This is a very critical step to ensure your glue joint is tight and true. In many cases, if care is taken at this step, the glue joint is barely visible. I use my bowl gouge to true the edge as close as possible, and then I lay a straight edge across the top edge to determine the high and low spots. I then use a skew on its side, acting like a scraper, to refine the edge. You'll be surprised how easy this is, but good light is important and if you're in doubt, magnifiers can also help a great deal. The bottom line is that you don't want any gap between the straight edge and the top lip of the form. 

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Now the real fun begins. Turn out the interior as you would any bowl you've turned. The fun part comes when you break through the bottom deliberately (not by accident as most of us have done). Keeping a consistent thickness, work your way down to the bottom until the recess you turned earlier appears. On most occasions you will hear a higher pitch when you're getting close. Note the disk flying free as I reached the critical stage. 

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Now that you have the consistent thickness you were after, sand the interior to finished quality. Be very careful not to sand the top edge - you don't want to be rounding off the flat surface. 

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Now that you've completed the top portion, follow the exact steps for the bottom half, with the exception of breaking through as we did on the top. I also sand the bottom to finished standards as I won't easily have access to this part once it's mounted in the chuck. Remember you want to turn the bottom half pretty close to the exact size as you did the top. When you're turning these thick walled pieces, the exact size isn't as critical because of the width of the glue joint. On the other hand, if you are going to be turning very thin then you have very little wiggle room. 

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Once you've sanded the inside of the bottom half, I like to give it two or three quick shots of Deft semi gloss spray lacquer. With the lathe running, buff the sprayed portion between coats. 
 
This whole process only takes a few minutes and when people look inside they see a nicely finished product. If the opening is small enough, this is of no concern. Obviously you can use whatever finish you're comfortable with.

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With the bottom still mounted in the chuck on the lathe (this is why we did the top first) move the tailstock in position with a cone live center to position the top. I use the Oneway live center that comes with a perfect cone. If you don't have one of these, just turn a wood cone to slip over your live center. I've done this many times with my larger pieces with a large opening. The beauty of this technique is that the cone in the tailstock automatically centers the top half to match the bottom, and acts as a clamp to ensure a good glue joint.

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After a dry test run where I mark the best position to achieve the book match I'm after, I mark the spot with a pencil. This way, once I have the glue applied to both sides I can automatically place both halves in the correct position. I then apply carpenter's yellow glue to both halves, ensuring full coverage.
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Place the two halves together in the predetermined position and gently move your tailstock cone into the center of the top portion. Apply firm pressure until both halves are perfectly flush with proper glue squeeze out  Let this set up for 1/2 an hour or so.
 
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Note the perfect glue joint.

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Sand the whole form down to finished quality. Though the opening will be a little rough from the dovetail you turned for chucking purposes, a minute or two with 80 grit usually does the trick.

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I can't emphasize enough how much fun these are to turn and the possibilities are endless. My favorite two piece hollow form that was actually 13 sections was a pagoda that I turned 7 or 8 years back. I'm truly looking forward to trying my hand a David Nittmann basket design on this piece we just turned. I'll be sure to share the results when it's complete.

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The Two Piece Hollow Form DVD we offer through our website takes you through this whole process in very easy to understand steps. It certainly makes a great gift for you or a friend.
 
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Brian McEvoy