by Jo Miller
Glenn Schmitt – Green Wood Turning – from Log to Bowl
Glenn is an active member and director of the CMW board and, after serving as an assistant instructor at the John C Campbell Folk School for a few years, he was scheduled to teach his own classes in 2020 and 2021. Hopefully COVID will allow students to take advantage of his expertise in the coming year.
Glenn’s demonstration focused on taking a green log through cutting, bowl turning, and reshaping the bowl after drying.
Examining the green log:
Remember that wood will shrink on average every wood species is different, about ½% vertically, ~8% Transverse (think of it as parallel to the growth rings so around the tree) and 4% Radial (perpendicular to the growth ring so out from the center). These different stresses in the wood is what causes bowls to warp and logs to crack. Thus, the initial size of the green bowl will need to take this into account. If you want to finish a round bowl and you are starting with green wood you must account for these changes in movement, warpage by turning your green bowl thicker. A good rule of thumb is 10% of the overall thickness. The book “Understanding Wood” by R Bruce Hoadley is a great reference tool to learn about the properties of wood drying and shrinkage.
Glenn cuts a tree up into 4 foot lengths (this fits into his truck), and anchor seals each end. He covers the logs with a tarp under the hemlock trees to keep the logs out of direct sunlight until he has time to cut them into bowl blanks. When cutting the green log, cut a length of the log at least an inch longer than the diameter of the log. Draw a line through the pith incorporating the natural crack extending to the outside of the bark. This allows you to adjust your cut so that all the crack lines are vertical to the log. When cutting indoors he uses a 13” electric chain saw from Harbor Freight for his cuts. Never use a gas chainsaw in a closed space. He starts by making a notch on each side at the cut lines as a reference mark used to line up the chainsaw bar from end to end, cuts from one side ~ 85% down through the log along the pith line. Next, determine your blank thickness, mark the log for that thickness, then draw more reference lines parallel to your first chainsaw cut. Start cutting down through the log on the outer most reference cut lines making the pith cut your very final cut. – cutting all the pieces you need, then if the log was longer than your chainsaw, turn the log around to finish cutting from the other side. Again, start at the outside making the pith cut your final cut. He uses several aids for cutting the wood
A support rack made from scrap wood with notches
Plastic tree felling wedges from Northern Tools to keep the wood from binding on the chain saw blades. Plastic is better than metal wedges since plastic won’t hurt the chain saw blades when it comes in contact with the wedge.
Template for drawing the circles. He uses clear plastic bathroom sheets (4×8) and has cut circles with diameters from 4-24 “. Put a nail hole in the center to allow you to mark the center of the bowl blank and see if you are making a symmetrical circle.
Once the blanks have been cut with the chainsaw to length and width staying ~1/4” away from your drawn circle, remove the corners with your chainsaw, then remove the bark with a screw driver.
Turning the green bowl:
Place blank between centers:
Use a 4-prone drive center – since a 2-pronged center is more likely to split and dig into the wood as you’re turning. To drive the center into the wood, he uses a 7” long scrap of ¾” ID steel pipe (Lowes will give you left over pieces), puts a pipe cap on it and uses this to pound in the drive. It’s important that 2 of the prongs line up with the grain while the other 2 prongs go across grain.
Glenn has taken the pin out of the live center to make balancing and adjusting the bowl blank easier. The pin will make a dent in the wood and a live center with the pin will want to go back to that initial spot when you are trying to make slight adjustments.
Line up the blank so you get the “X” centered at the bottom of the bowl. Check on both sides of the blank to make sure the Grains line up at the level that will become the inside bottom of the bowl. Glenn like to mark that point on the end grain, both sides, this is his reference points for balancing the blank. You can use a laser on the tool rest to help with this as the blank is adjusted. Since the pin has been removed from the live center, the blank can be more easily adjusted. After balancing end to end look at the end grain of the blank. If you’re not seeing the grain curve at the center of the bowl for your reference marks. Your “X” will be off. Adjust the position on the live center to balance the curve in the center. Be sure to check both ends and make adjustments to balance differences. Now check the end grain mark again to ensure you didn’t change it when making your other adjustments. Now use both hands to tighten your live center into your blank.
Turning the blank:
The first step is to ALWAYS turn your lathe speed ALL the way down before starting the lathe. Step two is ALWAYS put your face shield on! Standing out of the line of fire should there be a problem. Turn on the power and slowly increasing the speed safely. Using a slow speed and a 5/8th bowl gouge with the flute only open slightly. Think about a clock face as references to turn the flute of your gouge. Your gouge would be pointing between 12 and 1, round the blank going from headstock toward the tailstock about ¾” deep. Next Cut in and face off from the drive center area outward until you have smooth wood. Look for cracks and take out as much as needed. This will determine the size of the bowl top.
On the bottom (tailstock side), rough shape the bowl and the location of the tenon. Initial cuts are easiest accomplished for Glenn by pointing the gouge at 11:30 or between 11 and 12 on the clock. After the uneven surfaces are roughed off Glenn starts to cut gliding on the bevel with the flute pointed at 10 to shape the bowl and tenon. Since the wood will move when drying, remember to make the tenon oversized- both in depth and diameter. Shoot for ~15% greater than the smallest size of your chuck. He doesn’t recommend making a recessed tenon since it is more likely to split the wood. On green wood, compressive force is stronger than expansive forces. Once the tenon is formed and bowl round, you can increase the speed of the lathe. Take your time and cut the tenon with a spindle gouge to ensure you have a very clean cut and a clean inside corner for the chuck to fit. He is avoiding torn end grain which can cause the blank to wobble when rotated and placed in the chuck. Continue to look for cracks or flaws that may become dangerous. You may have to change the shape of your bowl as you go to accommodate these. If you are making a functional bowl, you will want the base to be ~40% the size of the top diameter.
Once you have the shape you want, reverse the blank and put into your chuck. Line up end grain with your chuck jaws since the end grain is denser. Thus, the end grain is positioned so that there is the same amount of end grain and side grain in each jaw. To start put the bowl in the chuck and just barely tighten the jaws against the tenon. Glenn uses a golf ball with a 3/4 inch hole to slide onto the ¾ threaded live center. The golf ball allows the wood to adjust itself as he is applying pressure on the bowl pressing the tenon into the chuck by turning the hand crank on the tailstock. Then loosen the chuck jaws to allow the bowl to properly seat itself, then tighten the blank in the chuck. Once the blank is secured, he removes the golf ball from the tail stock and again puts the live center into the bowl blank to support the trimming of the outside and top if necessary. Turn your lathe speed ALL the way down before turning on the lathe. This is a standard practice every time a piece of wood is mounted on the lathe, safety first!
Hollowing out the bowl:
Once in the chuck, check to make sure your bowl is running true. Adjust if necessary. Your final thickness of the green bowl should be ~ 10% the diameter of the blank – i.e. a 13 ¼ bowl should have a wall thickness of ~ 1 3/8thinches. Flatten off the top of the bowl. Then use a pencil to mark your 10% thickness line inside the rim. Hollow the bowl keeping the thickness even – remember that the bottom of the bowl is flat. Glenn uses a relief three step grind on the back edge of the gouge to prevent bruising of the wood – especially important with Cherry. Glenn also prefers using spring-loaded calipers to check the thickness. Once finished, he uses a shear cut to take off any imperfections. You want the final cut to be as clean as possible.
Drying the blank and returning:
Wood dries at ~ 1 inch /year, thus a 1” thick bowl would take ~ 6 months to air dry (the wood is drying from both sides). To speed up the process, you can use a dehumidifier set at 50%. Turn it on intermittently – ½ hr on then 1 ½ hr off for a total of 2 hours/day.
Reverse chuck the bowl using suede leather in the bowl pressed against the chuck you will be putting the trued up tenon in. The leather will significantly reduce the slippage of the out of round dry bowl and eliminate the creation of marring or friction burn marks. Make sure the jaws are fully closed before mounting to reduce vibration. Glenn gets his scrap leather and saddle padding cut-offs 5/8thinch thick for padded jam chucks from Jackson Western Wear in Asheville.
Turn the lathe speed ALL the way down. Put your face shield on and then start the lathe, slowly increasing the speed to a fast but safe level. Turn the tenon first by shear scrape the bottom lightly until it’s flat, then use a spindle gouge to true-up and recut the warped tenon. Rough cut the outside of the bowl minimizing the amount removed and avoiding going right to the top edge of the bowl (remember you still have to cut the top flat and then the inside after mounting in the chuck).
Reverse the bowl and secure in the chuck. Again, balance the end grain and side grain in the chuck jaws. Use a cone Center on the live center to support the bowl until the weight is even all around. Go across the rim first and cut it flat. True up the outside of the bowl if necessary. Remove the cone and finish turning the inside of the bowl to the desired thickness. Then sand the inside and outside. Then remove the tenon. For a functional bowl he finishes with Mahoney’s Walnut oil, 2 coats applied 24 hours apart.