Kevin's Woodturnings

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Centering Donut Chuck for Reverse Turning
Half-Ring Trim Jig
Bowl Wall Thickness Calipers
Segment Ring Press
Lathe Sanding Hood
Table Saw Blade Angle Vernier Pointer

Centering Donut Chuck for Reverse Turning   Donut chucks and cole jaws have both been around for a long time.  I decided to combine them to make a new version of a donut chuck that centers the turning.  A donut chuck is used to hold the turning reversed so the bottom can be turned.  One problem with a donut chuck is that it doesn't center the piece very well.  Cole jaws are used to grip and center a turning, but they only work well if the turning's chucking diameter is much wider than the turning height, like a salad bowl or a platter.  For example, cole jaws could only be used with vases if the lathe tailstock was used to secure them.  

Almost all of my turnings are glued to a faceplate, so when I part them off I need to finish turn the bottom.  I decided to not completely reinvent the wheel so I combined a donut chuck with a Nova chuck.  With this fixture, cole jaws in a Nova scroll chuck are used to center the turning (the turning lip must be flat).  The cole jaw's buttons do not need to be very tight against the bowl lip, just tight enough to center the turning.  The turning is held tight against the cole jaws with the donut chuck framework.

For turnings with small lips, there is no reason why the standard steel Nova chuck jaws could not be used rather than cole jaws.  Although, I would recommend softening the steel jaws with tape so your turning isn't marred.

This reverse turning fixture is designed with minor turning in mind, such as a recess in the bowl base.  If you are doing major turning of the bowl base, you should should consider using your tailstock to secure the bowl for the majority of the turning, then remove the tailstock to turn the remainder of the recess.  Also be aware of the RPM limit recommendation of the cole jaws.

This centering donut chuck was made from two 15" diameter disks of 3/8" baltic birch plywood and can accommodate a 12" diameter bowl.  I chose 15" diameter disks because that is 4" larger that the largest diameter of the cole jaws (11").  If you have larger cole jaws or wish to accommodate larger diameter bowls, just made the disks larger. 

The four 10-1/2" threaded rods were cut from a 48" length of 3/8" allthread.  Depending on the height of your bowl, you will likely need several different lengths of threaded rods for different bowls.  Four 3/8" t-nuts, twelve 3/8" nuts and twelve 3/8" washers were used as well as a 12" length of 3/4" clear plastic tubing.   

Click on the picture for an enlarged view.


This is a photo of the centering donut chuck with a bowl mounted.  This bowl is about 6" tall with a 4" diameter lip, so it couldn't be turned just using cole jaws.  Also the bowl does not have a graspable lip.  


This photo is another view of the centering donut chuck.


This is the rear clamping disk.  The center hole is my headstock thread size (1-1/8").  The four all-thread holes are evenly spaced at 13" centers.  Three holes (and threaded rods) might work equally well. 


This is the front clamping disk.  The inner hole was made 5-1/2" diameter (because that's a good size for my bowls).  I didn't lay out the all-thread holes on this disk because I drill holes in both disks at the same time using the rear clamping disk as the template.


A forstner bit was used to drill the headstock thread hole in the rear clamping disk.  A board was used to back-up the drill bit to prevent tearout.


The same forstner bit was used to drill a starter hole (in the front clamping disk) for jigsawing the 5-1/2" hole.


The front and rear clamping disks were clamped together and the 29/64" holes for the t-nuts were drilled using a standard drill bit.  Again, a board was used to back-up the drill bit to prevent tearout.  Note I have made a pencil line on the side of both disks to index the holes.


A jigsaw was used to remove the 5-1/2" center hole in the front clamping disk.


A sanding drum on the drill press was used to round the center hole in the front clamping disk.


The sanding drum was also used to bevel the inside edge of the center opening of the front clamping disk.  The bevel makes it less likely that the plate could mar the turning.


A piece of 3/4" clear plastic tubing (from Ace Hardware) was slit and fitted to the center hole of the front clamping disk.  The hose help protect the turning from the clamping plate 


A spindle extender might be needed for extra headstock clearance and can be purchased from:   

Install the rear clamping disk onto the headstock threads.

Tightly screw the cole jaw chuck onto the headstock. The allthread holes in the rear clamping disk do not need to line up with anything on the cole jaws. 

Put masking tape on the cole jaws to protect the bowl lip. The rubber buttons are actually One-Way cole jaw buttons, not Nova cole jaw buttons.  I like the One-Way cole jaw buttons a lot better than the Nova buttons (they are interchangeable).

With the front clamping disk hole bevel facing down, hammer the 3/8" t-nuts into their holes.


Install the threaded rods into the t-nuts in front clamping disk.  The ends of the allthread should be slightly recessed below the top of the t-nuts.  

I used a nut and washer on the backside of the front clamping disk.  Tighten the nuts securely.

Run a nut (with washer) partway onto each threaded rod.

Hang the front clamping disk loosely on the rear clamping disk.

Make sure the index parks on the clamping disks are lined up. 

Note that a nut and washer are run partway down each threaded rod.

Adjust the cole jaws just barely snug on the bowl lip. I think this will center the bowl better than tight jaws.

Engage all the threaded rods and loosely run on the four outside (rear disk) nuts.

Start snugging the outside nuts, equalizing the gap between the clamping disks.  

Don't tighten the inside (rear disk) nuts until the outside nuts are tight and the gap between the clamping disks is equal.

When the disk gaps are equal, tighten the inside nuts by hand.  I don't think you should use a wrench to tighten the nuts.

The threaded rods shout not hit your headstock anywhere.  Give the chuck a manual spin just to make sure.

Set up the tool rest so there is clearance between the tool rest and the t-nuts.  Give the chuck a manual spin just to make sure.

Again, make sure there is clearance between the tool rest and t-nuts.

Be aware of the spinning t-nuts at all times.  They don't stick out very much, but they will hurt if they hit your knuckle.  Don't try stopping the chuck from spinning by hand.




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Half-Ring Trim Jig   This table saw jig trims the ends of segmented half-rings so the half-rings fit together into a perfect ring.  Alfred Mirman first mentioned this great idea to me.  As you might know from my website, the way I glue segmented rings is that I glue segments to make two half-rings.  Then I sand the ends of each ring straight and square, using my 12" diameter disk sander, so the half-rings fit together perfectly.  Most of my segmented rings have a small enough diameter so that I can sand the half-ring ends, but some rings have a greater diameter so I needed to have another way to true up the ends.  The half-ring trim jig is the easiest way to perform this task for rings up to 18" diameter.  Also, for those segmented woodturners without a disk sander, this may be a great alternate method for making perfect rings.

The half-ring trim jig sliding platform is made so that when the jig is pushed past the table saw blade for the first time, the left edge of the platform is cut to zero clearance with the blade.  After that, anything that overhangs the left edge of the jig will be cut off by the amount of overhang.  To use the jig, clamp a segmented half-ring onto the platform, using the holddown, so that the minimum amount of material from both ends of the half-ring will be cut off.  Cut the other half ring the same way.  You might cut one half-ring face up and the other half-ring face down just in case your table saw blade is not perfectly vertical.  

Click on the picture for an enlarged view.

A large diameter segmented half-ring has been clamped into the half-ring trim jig.  Any half ring material that overhangs the left side of the jig will be cut off.

Another view of the half-ring trim jig.

The underside of the half-ring trim jig, showing the runner.  The runner must allow free movement in the miter slot but not have a sloppy fit.

I have glued sandpaper to the underside of the jig holddown so the segmented ring won't slip while cutting.

Bowl Wall Thickness Caliper   I have made a number of special-use wall thickness calipers. Some are for deep or unusual-shaped bowls. I originally tried to buy thickness calipers but none of them were exactly what I wanted. Either the calipers in the catalogs weren't shaped right, didn't have a measurement scale, or maybe couldn't be used one-handed. 

These calipers are made from 1/4" baltic birch plywood. I used an old pair of tin snips for my handle design shape. The caliper jaw shapes came from my imagination and from the calipers intended use. The scale doesn't need to be too big for general bowl thickness use. The scale reads 1" to 0" by 1/16ths of an inch.

Each caliper starts out as an outline drawn on construction paper. Next I trace the five caliper component sections onto the plywood and cut it out using my bandsaw. Then I rough-drill the handle holes using forstner bits. Next I glue the 3-piece scale section together and install a pivot screw. I sand the parts smooth with a sanding drum chucked into my drill press. The scale pointer, made from a handy wood scrap is then installed with a small screw so scale zero can be adjusted if necessary. I calibrate my caliper scale by closing the caliper jaws on known thicknesses, then marking the caliper scale. Caliper calibration needs to be done this way because, since the distance from the caliper's pivot screw to jaws is usually larger than the distance from the caliper's pivot screw to scale, the 0" to 1" mark width of the caliper's scale will usually be less than 1 inch. I calibrate my calipers using the jaws of a dial caliper, but it could also be done by careful use of a ruler.

Click on any photo to enlarge it.

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The long caliper was made for a deep jar, like #454 on my Lidded Jars webpage. The shorter caliper was made for short bowls, like #622 on my bowls webpage.

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The small caliper.

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The long caliper.

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The construction paper outline of the small caliper.

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The construction paper outline of the long caliper.

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This photo shows the rough sawn 5-piece small caliper sections.

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I photographed the long caliper construction paper outline against 1" x 1" graph paper.

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I photographed the small caliper construction paper outline against 1" x 1" graph paper.

Segment Ring Press   This ring press works great and it doesn't involve any welding.  You can buy the metal cut to length at a "metal-by-the-foot" outlet.  I would like to thank Jeff Crews for the idea of using an anti-twist plate to reduce the screw's twisting action on the glue-up and also locating a good source press screws.  These are pretty standard presses and are made primarily from 3" steel channel and 1" threaded rod (3/4" threaded rod works well, too).  I have seen these ring presses made entirely from wood and, if made strong enough, should work fine.

Ring Press Photos updated 8/25/12 - Click on the photo for an enlarged view:

The updated Ring Press uses small spring clamps instead of the lower nuts. The other change is using cheap lathe faceplates instead of the upper nuts.  These upxdates speed up clamp height changes.

A closer view of the spring clamp and faceplate.

Lathe Sanding Hood   I made this lathe sanding hood to fit my 24" Vicmarc lathe.  I think it will work on a bowl up to 23" diameter but I haven't tried it on that size yet.  If you make one of these, the side panels can be straight instead of having a curved cutout.

The plastic part where the dust collector hose attaches is called a "universal dust hood".  Here is a link to this part at Highland Hardware: click here.  A piece of chicken wire was sandwiched into the duct opening to screen out dropped sandpaper.   

The angle of the back is 15 degrees, which is optional.  The angle of the sides are 30 degrees, which I think is necessary to properly funnel the dust into the collector.  The angle of the top is 15 degrees, which is probably optional.  The top, back and base are made from 1/2" baltic birch plywood.  The sides are made from 1/8" baltic birch plywood.  Feel free to make material substitutions.  When I constructed the hood, I assembled the top, back, and bottom (screwed together, not glued) then used these pieces to make an outline for the sides.

To attach the lathe dust hood to the lathe bed I used six 1" diameter magnets (the pack contained six). Here is a link to this part at Highland Hardware: click here.

Click on any photo to enlarge it.

The sanding hood attaches to the lathe bed using magnets so it can be moved around and removed quite easily.

The front of the sanding hood top should be moved very close to the turning while sanding.  This traps the most dust.

A chicken wire screen prevents sandpaper and other bad things from being pulled into the dust collector.

The sanding hood has a factory-made dust port. My 4" dust hose uses a quick connector I bought at Woodcraft Supply.

I used six rare earth magnets in this pattern.

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Table Saw Blade Angle Vernier Pointer   This is a photo of a blade tilt angle pointer I made for my Delta table saw. I replaced the original cheap tin blade angle pointer with this vernier scale pointer. I used the original blade tilt angle scale, which is graduated in degrees. The vernier pointer divides each degree into tenths of a degree, so the vernier pointer makes it possible to accurately move the blade tilt by tenths of a degree so table saw blade tilt angle can be set to within 1/10th degree accuracy. After the table saw blade has been adjusted exactly square, the vernier pointer is adjusted to zero on the table saw's blade tilt angle scale. That's all the calibration necessary.

Click on any photo to enlarge it.

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The vernier scale pointer exactly replaces the original cheap tin pointer.

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I have removed the blade elevation handwheel to show more detail on the vernier pointer.

The scale is scribed into the back side of 1/8" plexiglass using a compass foot needle. I used the back side of the plexiglass because it was very close to the front side of the saw's angle scale and this would reduce parallax angle errors.

I got the idea for making this vernier pointer from my friend George "Sonnie" Sharrar, who made a table saw compound and frame miter-cutting sled that featured a vernier angle scale. His sled was very well-designed and I was impressed with his vernier scale accuracy, so I borrowed his idea.

The lines on the vernier scale are not every 1/10th degree, they are every 9/10th degree. I scribed the zero-to-ten degree segment of the blade angle scale from my table saw onto the piece of plastic, a tick mark for zero and a tick mark for ten degrees. Then, a friend of mine used a CAD program to print radius lines on a piece of paper, like spokes on a wheel, every degree for 360 degrees. I matched up the plastic 9 degree arc with 10 of the paper radius lines so that the 9 degree saw scale arc was divided into 10 sections. I then scribed the 10 marks into the plastic. Now, every division on the plastic would be 9/10th degree.

I mounted the plastic vernier scale over the table saw scale, replacing the old tin angle pointer, so that the 9-degree saw scale could be seen through the 10-section plastic vernier scale, and the vernier scale move with the blade tilt mechanism. I adjusted the vernier scale by lining up the zero tick marks of both saw and vernier scales exactly. So, the first tick mark on the table saw scale is 1 degree, and the first tick mark on the vernier scale is 9/10th degree.

The way the vernier works is, when the saw blade is tilted so the first saw scale tick mark and the first vernier scale tick mark line up, the blade has been tilted 1/10th degree. So, when the saw blade is tilted so the second two pointers line up, the blade has been tilted 2/10th degree, etc.

Of course, the scribe marks need to be layed out fairly exactly or the new vernier scale won't be very accurate. You should be able to visually judge if the vernier scale is accurate when it's installed for the first time.

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