Vine Maple Goblet

On Wood Central’s Turning Forum Steven Lewis asked about turning goblets from green wood. I decided to give it a try using the alcohol drying method. The only green wood readily available to me is vine maple.

The limb was about 2 ½" in diameter. As you can see the limb was not straight so I expected the stem would warp when drying.

Bowl thickness is about 3/8"

The roughed out goblet is about 2" in diameter and 6" long. and the stem is ½" in diameter.


The piece soaked over night for my convenience. An hour or two in the alcohol would have probably been sufficient. After removing from the soaking container the goblet is wrapped in paper leaving the bowl uncovered.

The goblet is weighed.

Placed upside down on a rack for drying.

Weight in Grams.
11/20 - 1000 - 143
11/21 - 0830 - 117
11/22 - 0700 - 110
11/24 - 2130 - 106
11/25 - 1230 - 106
11/25 - 2100 - 105
11/26 - 1300 - 106
11/27 - 1100 - 105

At 10:00AM November 20th the goblet weighed 143g. Four and a half days later it weighed 106g. By the 27h it hadn’t lost anymore weight so I finished turned the goblet.

The bowl did not distort very much.

Since the pith was in the stem I figured the stem would warp and I was not wrong.

With the tool rest set at the center line I adjusted the goblet to have the stem centered.

Bottom and stem are rounded.

After further refinement of the stem the pith is revealed.

Tenon is glued into a waste block mounted in the chuck.

Steady rest provided stability for finishing the inside.

Goblet is stabilized with a wooden plug on the live center.

Unfinished goblet stands straight and tall.

After two days and two coats of Rocklers Gel Polyurethane the goblet stem remains straight.

Yew box.

This yew wood came from a tree that had died during the previous summer. Recently cut down the wood was wet but not as wet as a live tree freshly cut. Other turners got to the tree first so I am left with smaller limbs to work with. A box was hollowed from a limb section.

The top portion roughed out to 1/4" wall thickness. The inside is rounded to a center thickness of approximately 3/8. The bottom portion roughed out to 5/16" thickness. The inside rounded to a center thickness of approximately ½".

The pieces soaked in alcohol overnight for my convenience. An hour or two in the alcohol would have probably been sufficient.

After removing from the container the two pieces were butted end to end with the box interior exposed on each end.

This procedure for wrapping boxes was instigated by Ron Sardo, or was it Phil Duffy, shortly after I published the alcohol drying procedure in November of 2004.

Wraped and on the drying rack.

11/20 - 1000 - 126
11/21 - 0830 - 111
11/22 - 0700 - 109
11/24 - 2130 - 108
11/25 - 1230 - 108
11/25 - 2100 - 108
11/26 - 1300 - 108

At 10:00AM November 20th the box weighed 126g. Four and a half days later it weighed 108g. By the 26h it hadn’t lost anymore weight so I finished turned the box.

No degradation and very little warping.

In retrospect I should have turned the sap wood away when rough turning to reveal the rich colored heartwood. I will do that with the next box I turn from a yew limb.

Determining Alcohol Percentage

Calculating alcohol concentration by weight.

The phenomenon of miscibility is key to drying wood by alcohol soaking. Miscible liquids will reach a uniform concentration when combined in a container. An example is a bottle of wine which maintains a uniform consistency of alcohol and water no matter how long it sets undisturbed.

When a piece of wood is placed in an alcohol solution the phenomenon of miscibility will cause the water in the wood and the alcohol in the solution to migrate until they reach equilibrium. The final alcohol concentration in the wood will always be less than the starting alcohol concentration of the soaking solution.

Replacing water in wood with alcohol is the key mechanism for drying wood faster. Alcohol readily moves through cell walls and has a lower vapor pressure than water. As the concentration of alcohol in the wood goes down the drying time increases. Therefore, it is useful to know the alcohol concentration of the soaking solution.

A hydrometer is one way to measure alcohol concentration. To be more accurate the temperature of the solution needs to be measured to correct for density changes due to temperature. The easiest way to measure temperature is to use a hydrometer with an integrated thermometer. Hydrometers are expensive and breakable. Since a scale is needed to track the drying of wood pieces a method of determining alcohol concentration by weight would utilize existing equipment and minimize cost.

Knowing that alcohol and water have different densities I concluded that the alcohol concentration of a solution could be calculated by a ratio of weights. I contacted Professor Shawn Bearden in Pocatello, ID and ask him if he could help me devise a procedure. Shawn developed the graph and table used in this procedure.

The procedure requires the following:

A scale capable of measuring a minimum of 1 gram(g) increments.

A see through container with a narrow neck to increase the accuracy of the sample size to be weighed.

A copy of the Alcohol Percentage Graph and Table

 

 This water bottle has a color change near the top which is used for the measuring line.

1. Select a narrow neck vessel for weighing the samples. I prefer to use plastic since I am sure I will drop it sooner or later. A salad dressing bottle or water bottle make good sample vessels.

2. Draw a line about an inch below the top of the sample container. The line needs to be narrow enough to accurately measure each sample.

3. Weigh the empty container and record the weight.

4. Fill the container to the line with water.

5. Weigh the sample and record the weigh.

6. Empty the container and fill it with soaking solution to the measuring line.

7. Weigh the sample and record the weight.

Calculating the weight ratio.

The ratio is calculated by dividing weight of the water by weight of the solution. To be more accurate subtract the weight of the empty bottle from water and solution weights.

(Weight of water) - (weight of bottle) /(Weight of solution) - (weight of bottle)

Empty bottle weight equals 23g. 

Water sample weight equals 632g.

Solution sample weight equals 550g.

632g - 23g /550g - 23g

609g /527g = 1.155597

The resulting quotient is the ratio and will be a number greater than 1.

Rounded to 4 dismal places, ratio = 1.1556

Converting the quotient to percentage of alcohol concentration.

Using the graph find the ratio on the horizontal or X axis. Read the alcohol concentration on the vertical or Y axis.

Using the table find the ratio and the corresponding alcohol concentration.

After calculating the ratio round the number to 4 dismal places. The first two decimals correspond to the numbers on the chart and graph. The third and forth decimals are used to interpolate the concentration between the values given.

The first 3 numbers of the example ratio 1.15 correspond to the number on the chart for 62.20% alcohol concentration. The next higher ratio is 1.16 which corresponds to 65.79% alcohol concentration.

The last two numbers are used to interpolate between the ratios 1.15 and 1.16. Treat the last two numbers as a percentage of the value between 62.2 and 65.79. In the example the last two numbers become 56% (0.56) of the difference between 65.79 and 62.20.


65.79 - 62.20 = 3.59

3.59 x .56 = 2.01

62.2 + 2.01 = 64.21

Add the difference to the lower number which yields the alcohol concentration.

For alcohol soaking purpose it is not necessary to do the math to determine an exact percentage of alcohol concentration. A ballpark number is good enough.

Experience has shown that higher concentrations of alcohol in the soaking solution will produce the best results of faster drying times with less degradation of the piece. Therefore it is recommended that the starting alcohol concentration be greater than 60%.

Wood can be successfully dried with lower concentrations but the advantages of soaking in alcohol are diminished. Drying time will increase. Because there is more water in the wood, which does not migrate out of the wood as easily as alcohol, more stress will develop across the walls of a piece which increases the probability of cracking.

It is only necessary to weigh the water once as long as the same bottle is used for weighing the solution sample. The water weight for the bottle used in the example will always be 609g. For subsequent test it will only be necessary to weigh a solution sample.

After weighing the solution rinse out the bottle with a small amount of alcohol and add it to the solution container. Compressed air blown into the inverted bottle will insure it is dry.

Alcohol Percentage Graph and Table is available in JPG format. Print a copy of the chart for your convenience.

Order your shirts before they are gone.

There are only a few alcohol soaking shirts left. At the present I do not plan to order more shirts unless there are a large number of requests. The shirts are $14.95 plus $4.50 shipping and handling to United States addresses. You can order the shirts here.

As of Saturday evening November 4th the remaining number of shirts:

Time is Fine
6 - Large
2 - Medium

Don't Turn
1 - Extra Large
4 - Large
3 - Medium

Shirt sales have been the main source of financial support to offset the cost of testing and perfecting the alcohol drying protocol. I continue to refine the process and disseminate information as time permits. Thanks to all the people who purchased shirts and supported my efforts.

Several people have suggested I produce a video on the alcohol drying process. At this time I have not been convinced that sales of a video would yield enough return to justify the cost. Please take the time to email me your thoughs on the issue.