The Two Piece Hollow Form
This article is a companion piece to our Two Piece Hollow Form DVD. If this tweaks your interest you can find ordering information at the end of this newsletter .
Please understand this lesson in most cases does not show the actual tool position for making the cuts. You must be able to turn two very similar shallow bowls to be successful. How you achieve this is not important.
There are many methods and tools used when turning one piece hollow forms. I have tried most, with some degree of success.
I prefer the two piece method for a number of reasons:
- You can easily complete the process with whatever tools you now use to turn a platter or a bowl.
- Wall thickness is not an issue. You can easily turn a delicate piece to 1/8" or less.
- You can finish the inside so when your friends or customers poke their fingers inside the opening (as they always seem to do) they will not get a sliver.
And lastly, for me the most important reason is the safety factor, especially for the larger pieces. Hanging a gouge or scraper over the tool rest for a long distance is always risky, especially for beginners.
I have completed hollow forms over 20 inches in diameter and only 4 inches deep. Because I pierce much of my work I have turned most of these to less than 1/8 inch thick. The resuIts can be stunning, and I am not sure this would be possible with any other method.
Because of the simplicity, I can comfortably turn 3 or 4 of the 10 to 12 inch forms in a day, and they are good sellers. Give it a try. You will have a blast and make a little extra cash.
Select a very well seasoned piece of timber. It is very important that your wood is completely dry.
A good size to use is 3" x 10 to 12". I have turned two piece flying saucer bowls as large as 4" x 22" The larger they are the more challenging they become.
Cut the blank in two. I always bookmatch the pieces.
Cut them round and attach faceplates to what will become the inside of the saucer. Turn the top first. Select the best or most interesting section for the top.
Be careful not to reduce the diameter of either the top or the bottom pieces. Remember they have to match perfectly.
Finish turning the outside of the top section to whatever pattern you choose. Note the deep recess where the opening will be: �" to 1" deep should do. Be mindful of the screws.
Turn a dovetail inside the top hole to receive the chuck jaws for reverse turning, just like you would a regular bowl. The top outside is complete for now. It is not necessary to sand at this point.
Essentially repeat the last few steps to turn the outside of the bottom section of the saucer.
At this point, turn the foot with a �" recess for rechucking, in order to turn out the inside of the bottom section. The main difference between the bottom and the top pieces is the depth of the recess. Sand the foot, inside and out, to finished standards. The outside of the top and bottom sections are now ready for faceplate removal. It is not necessary to have two faceplates.
Mount the top section into a four jaw chuck. I prefer the extended jaws, finding the extra room a little easier to work with, but any regular jaws will do.
If your piece is the slightest bit out of round, gently re-turn the surface in order to true it up. Remove as little material from the outside edge as possible.
Square the inside edge. Only remove the wood that is necessary to square the edge. You do not want to lose too much in diameter.
Remove enough materials in order to get a straight edge across the full diameter without hitting any high spots.
It is imperative the outside lip be perfectly flat. Note this edge is not flat. A skew on its side works well for the final truing. Remember this is going to be your glue joint. Once you are sure the edge is perfectly flat (a 1/4" glue joint is fine) start hollowing the inside.
This piece will be turned to 1/8" thickness so remove the wood in 1" stages, starting from the outside edge. Achieve proper thickness in this 1" segment before moving further into the bowl.
Use calipers for accuracy. This piece will be pierced so the thinness is necessary. Feel free to leave it as thick as you want. Keep removing material in 1" steps. Remember you turned a deep recess in the top piece that will become the opening in the top of your hollow form.
Eventually you will break through. This is now the inside of the top opening. Clean this up nicely, being careful not to hit the chuck jaws. 1/16" to 1/8" of wood before the jaws is perfect. This will be sanded away later. Sand this to finished standards. Remember everyone will be feeling the inside so do a good job. The top is complete for now.
After removing the top half from the chuck, mount the bottom half and repeat steps from the top portion. Remember to true the �" lip perfectly. This will also be a glue joint.
Do a dry test. Tweak if necessary. A slight variance, for example 1/16", in the diameter of the two sections is okay. A final sanding and finishing will take care of this.
Finish turning the inside of the bottom section until you are satisfied with the thickness. Sand to finished standards.
While still on the lathe, apply whatever finish you use to the inside bottom section. Be careful not to get any on the edge glue joint. Leave the bottom half on the lathe. Do another dry run. Find the best bookmatch position and mark both pieces with a pencil. This will make things easier when you glue the two halves and want them to be bookmatched.
Apply glue to both halves. Clean up the excess.
Using a cone centre, line up the pencil marks and clamp the two pieces, using the tailstock to apply pressure. If a cone centre is not in your arsenal, turn one to fit your live centre and the opening on the top section. The cone will centre the top half to match the bottom. Just exert enough pressure to squeeze the glue out. Clean up the excess and let dry for 15 to 20 minutes. Remove the tailstock. I use 80 grit sandpaper to clean up the opening. I like the foam backed Swiss paper. Using either power or handheld, finish sanding both the top and bottom. I generally sand to 500 grit.
Completed two piece hollow form ready for decorating, if you like, and finishing.
Finished hollow form. Embellished with finely pyrographed grouse feather, braided leather collar and pierced using a dentist drill. My finish of choice is spray lacquer. |