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| Instant-setting cyanoacrylate (CA) glue and a glue block give you a secure assembly. This lets you get the most out of each turning blank. |
Glue blocks are a great method of attaching a bowl blank to your lathe. There are other methods, such as double-face tape and chucks - and a knowledge of all these options will help you decide which technique is best for specific circumstances. But here, I'll focus on only the the glue block method.
Starting Out
You will, of course, need a face plate. Unless you are turning a very large bowl blank, you will need only a small face plate. Something that is 3" to 4" in diameter is big enough for turning a 13" or 14" diameter bowl.
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| Screw the glue block to the face plate (the screw must not prenetrate too deeply), then true up the assembly on the lathe to insure the glue block is equal thickness and flat enough to glue to the blank. |
Glue blocks can be made from 2" fir, maple or poplar. Make sure that the glue block is uniform in thickness and that one side is smooth and flat for gluing. The glue block should be at least 1" larger in diameter than your face plate. For larger turnings, make the glue block even larger to give additional holding power. A note of caution: don't use plywood here as the layers can separate!
Select a solid piece of wood for the glue block, then cut out a circle, using your band saw. You will use screws to attach the glue block to the face plate. The screws should fit the face plate holes nicely. If they are too small, the glue block could slip sideways on the face plate during the turning process, especially if you get a dig-in. Of course, you may never get dig-ins, but I still do! The length of the screws should penetrate into the glue block at least 3/4". Leave enough of the glue block free of screws so you can part through the glue block to remove the turned bowl when you are done.
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| You can use a piece of paper to find the center of the bowl blank. Draw a circle the same diameter as the blank, then cut it out.
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| Fold the paper circle in half. Fold in half again to form a cone. Cut the tip off the cone. That's the center.
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| Place the paper over the bowl blank and mark the center of the blank.
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| To register (center) the glue block properly onto the bowl blank, scribe a circle on the blank that is just slightly larger than the diameter of the glue block. |
Use good quality screws. I like to use screws with square-drive heads. Pre-drill pilot holes for the screws and watch for cracks in your block. Use at least three screws. Use more if your turning assembly will be large and heavy. Be careful, though. If you use too many screws, your glue block could split along the grain. After the screws are fastened, check the assembly to make sure the face plate is tightly and firmly attached to the glue block. It's very dangerous if there is any gap in between the glue block and the face plate. It's imperative that the glue block is securely screwed to the face plate.
To ensure that the glue block is centered to the face plate, thread this assembly onto your lathe, then turn the sides of the glue block. Doing this will center the glue block on the face plate. At this point, you can also test to make sure that your glue block is of uniform thickness. If it isn't, turn the face of the wood to true it up. Now you're ready to attach the bowl blank.
Getting Centered
Make sure that the side that will be the bottom of your bowl is flat enough to ensure a good glue joint. Do this by hand-planing the bowl blank or by sanding it on a belt sander. Be aware that if you use a belt sander, you should blow the sawdust out of the pores of the wood. Otherwise, the glue joint might be compromised.
Now you need to find the center of the bowl blank. If you have a large enough center finder for circles, use that. Otherwise, use a compass to mark "X's" near the center, where they will intersect at the center. My preferred method is to cut a circle out of a piece of newspaper the same diameter as your bowl blank. Fold the paper circle in half, then in half again to create a cone. Cut a very small piece off the point, and that is your center. Place the paper over your bowl blank, then mark the center.
With the center marked, use a compass to draw a circle that is just slightly larger in diameter than your glue block. This will allow you to glue your bowl blank to the glue block/face plate assembly and have everything centered!
Type of Glue
You can use yellow glue, but because that requires clamping, I find that gap-filling cyanoacrylate (CA) glue is more efficient with this method of mounting. Since I do not like to use the accelerator for CA glue, I use moisture. CA glue sets up with heat and moisture, so spread just a bit of water onto the glue block and rub the area to create a bit of friction heat. Apply gap-filling CA glue to the turning block inside the circle you've drawn.
Use a liberal amount of CA, but not so much that it will squeeze out when the glue block is attached. Make sure that there is glue in the center area of the glue joint. Put the glue block and face plate onto the turning blank, rub the two slightly together to spread the glue, then hold the assembly together, applying pressure, until the glue sets. If the glue is working properly, this should take less than a minute. I usually wait at least 15 minutes before I attach this assembly to the lathe to insure that the glue will hold. You could test the glue joint by banging the bowl blank on the table or floor, just to be doubly safe.
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| Put CA glue onto the turning blank, make sure there is glue in the center and also that there's an ample amount, but not too much. Apply pressure - by hand - to the assembly until the glue is set: less than a minute.
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Turning the Bowl
Turn the bowl as you normally do. I turn the inside first, but I find that many people would rather turn the outside profile first, then turn the inside of the bowl. Either way works fine. If you turn the outside first, don't turn the bottom of the bowl to a small diameter yet. You will need that surface area glued to the block for stability when turning the inside of the bowl.
Turn and finish the inside of the bowl, then most of the outside of the bowl. If your bowl will have a small diameter bottom, turn and sand that area last. You can now turn away part of the glue block to reach the bottom area of your turned bowl.
A word of caution: if you leave only a small area glued to the auxiliary block and you have a dig-in at this stage, you could knock your bowl off the lathe. Also, exerting a lot of pressure when sanding can loosen the glue block when it's only minimally attached. This is where you will be glad that you have taken the trouble to prepare your wood for a good, strong glue joint, and put enough glue in the middle of the circles!
Removing the Glue Blank
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| When the diameter of the glue block is small and the parting tool gets "grabby," then cut the remaining diameter of the glue block with a thin Japanese saw. |
When you are finished turning and have sanded your bowl, it is time to part into the glue block so that you can remove your bowl. For this, I use a sharp parting tool. Place your tool-rest as close as possible to the auxiliary block, then part as far into the glue block as is comfortable for you. It can get a bit grabby, especially if you have used hard maple for a glue block. When you have parted in as far as you feel comfortable, saw through the rest of the auxiliary block. Use one of those small Japanese saws and be careful not to mar the bottom of your bowl.
Another method is to use a chisel and mallet to part the bowl from the glue block. Do this off the lathe; it's not a good idea to be pounding on your lathe's drive shaft.
With this method of mounting a bowl blank, you will end up with either a flat bowl bottom or one that is almost round. Sand this area by hand or remount the bowl to turn the bottom.
Over the past 30 years, I have turned hundreds of bowls of many different shapes and designs using this method. It is quick, safe and allows you to get the most out of every turning blank.