How to cut mortise for chuck

[Joe Adams]

I'm fairly new to turning and am trying to figure out the best way to cut a mortise in the bottom of a plate so that I can hold it with a chuck.

I know how to cut a tenon for a bowl but this has me scratching my head.

I assume it's accomplished with a plunge cut but what's the best tool for the job?

FYI - I have a Oneway Talon chuck with #1, 2, & 3 jaws and a Jet 1236 lathe.

My blank is 6x2" figured maple.

Thanks!

[Ken Fitzgerald]

Joe,

I have been turning nearly 4 years but have been doing little the past 8 months or so.

What I'd probably do is center and hot glue a block to what will become the top of the plate. Using screws, attach the block to a faceplate.

Now turn the bottom of the plate. Turn the mortise using a gouge and a scraper like you'd turn the inside of a bowl but make a mortise that will fit on your chuck.

Put the jaws you intend to use on the chuck and open it to it's widest position and get the max diameter of the jaws. I'd make the diameter of the mortise about 75%-80% of the jaw diameter. The mortise should be deep enough that the ends of the jaws don't touch the bottom of the mortise. I would want the shoulder of the mortise resting on the shoulder of the jaws and not on the end of the jaws.

While turning the bottom of the plate and the mortise, use freshly sharpened tools and very light cuts so the hot glue joint will withstand the pressure.

Once the bottom of the plate and the mortise are turned, attach the plate to the chuck via the mortise.

Pry away or turn away the glued-on block and turn the top of the plate.

I'm getting ready to do the same thing and this is how I plan on doing it.

I'm sure someone with more experience will jump in soon.

Good luck!

[Thom Sturgill]

I diagree with Ken on two points - the mortice is shallow, I have seen the pros use as little as 1/8". The bottom needs to be very flat as the end of the jaws DO rest there. The shoulders of the jaws are not machined to be true the end is. I only use dovetail jaws for mortices.

The other point is that your jaws need to be as nearly closed as possible to maximize the area of contact. Use large jaws and close them tight. Size the mortice to that diameter just barely able to set in the mortice.

[Joe Adams]

Thanks for the feedback guys! Keep it coming.

I watched Jet's YouTube videos on plate turning after posting last night and the instructor used a Bedan to cut the mortise. That's one tool I don't have but am willing to buy if it's the best one for the job.

I noticed he used a fairly shallow mortise as well.

I'm trying to learn the right way to do things from the beginning so I can keep safety first!

[Alan Trout]

I agree with Thom. However I almost never use a mortise, I much prefer a dovetail tenon. It is much easier to split a bowl or vessel in expansion mode verses contraction mode of the jaws.

I also agree with Thom that the tenon does not have to be very big. I just did a hollow form that was about 7" in diameter and used #2 Nova jaws in contraction mode and the tenon was about 3/16" long. The most important part of any dovetail tenon or mortise is to have it the correct diameter. I size my stuff where I can see about a 1/16 space between the jaws when contracted on the tenon or expanded into the mortise. This insures I have full contract between the jaws and the wood.

I will use a skew as a scraper to set the shape as the skew angle is the correct angle for the dovetail tenon or mortise.

Good Luck

Alan

[Cyril Griesbach]

I agree with Thom. However I almost never use a mortise, I much prefer a dovetail tenon. It is much easier to split a bowl or vessel in expansion mode verses contraction mode of the jaws.

I also agree with Thom that the tenon does not have to be very big. I just did a hollow form that was about 7" in diameter and used #2 Nova jaws in contraction mode and the tenon was about 3/16" long. The most important part of any dovetail tenon or mortise is to have it the correct diameter. I size my stuff where I can see about a 1/16 space between the jaws when contracted on the tenon or expanded into the mortise. This insures I have full contract between the jaws and the wood.

I will use a skew as a scraper to set the shape as the skew angle is the correct angle for the dovetail tenon or mortise.

Good Luck

Alan

Alan has nailed it here IMHO. You can also use a parting tool if you must go the mortise route.

[Dave Rudy]

Bedan works great for this job. I have one angled at the correct dovetail angle which just fits the bill.

But you don't need to buy a bedan just for this. A parting tool works, and a skew works particularly well. As long as you're turning bowl-grain (face-grain) you're sticking the skew into long grain, not end grain. Use a narrow skew and cut straight into the bottom, at the desired diameter. When the blade of the skew is flat against the bottom of the cut (perpendicular to the lathe ways) you have a perfect dovetail.

[Reed Gray]

I use a recess/mortice exclusively, except for end grain turnings, and use a tenon there, as a recess will tend to split along the grain lines. The only problem with a mortice blowing up a bowl is if you make a very narrow shoulder, and then over tighten. I have dedicated dividers (two pointy ended compass) that is super glued to the exact diameter of my chuck jaws closed. After the bottom is flattened, I mark the size of the recess (note, only touch the left side/downward rotating side of the bowl blank) by marking smaller than needed, then moving the mark outwards till it is perfect. Dove tailed jaws will give the best hold. I have a dedicated scraper for this, available in the catalogs. You can use a bedan, a skew chisel, or even a small spindle gouge. Main thing is to make the angle match as closely as possible. This is easiest with the dedicated tool by lining up the shaft of the tool with the ways of your lathe as you make the cut, especially if the angle on the tool matches the angle of your jaws, and mine do (Vicmark chuck). Make first cuts inside the line, then make the final cut by just barely taking the line. This final cut is a whisper cut, where you just barely let the tool make contact with the wood. This helps make remounting more accurate so there is less wobble in the bowl when you reverse it. Also, remove any shavings and dust no matter how small the particles are. 3/16 inch deep is fine for bowls up to 16 inches, but if you feel better, make it a bit deeper, but 1/4 inch is almost too deep, and more than that is actually worse for holding power. If you want to go beyond 16 to 18 inches, get bigger jaws. My large chuck is 2 5/8 diameter, and my small one is 1 1/2 inch. A 12 inch bowl should have a shoulder (area around the outside of the recess before the transition to the sides of the bowl) in the 3/4 to 1 inch range. You could get away with 1/2 inch, but that is minimal, especially if you are coring and rough very aggressively. You do not need a death grip for a recess. In fact if you over tighten, you can blow the shoulders out, or put so much stress on the wood that if you do have a catch, it will fail at the point of most stress, the shoulder. To properly tighten, snug it up a bit, then rotate your chuck to the next key hole and tighten a bit more. On larger pieces, I will rotate the chuck around a couple of times and tighten a bit each time. Never will I really armstrong it. I make a recess in the top of the bowl by using a big Forstner bit to drill a recess. No face plate needed.

robo hippy

[Mike Peace]

When the blade of the skew is flat against the bottom of the cut (perpendicular to the lathe ways) you have a perfect dovetail.

IMHO, this assumes that the angle of the skew matches the angle of the dovetail on the jaws. Yours may match but I would be cautious in advising that all others will.

[Dennis Ford]

As you can tell, there are several ways to get there. Here is one more; I ground the the center point off a cheap fostner bit and used that to drill the mortice. This is not my usual method of work and there are some disadvantages but it worked for me. If you do this, clamp the piece to drill press table before trying to drill the hole. It is not safe to use the modified bit on anything that is not clamped to the drill press table. The drilled hole has straight sides instead of dovetail shaped, so this method is for smaller platters and light cuts. I used the technique to make a batch of saucer sized plates from 3/4" thick stock. I drilled about 1/8" deep and had no problems with either hard or soft wood.

[Ryan Baker]

IMHO, this assumes that the angle of the skew matches the angle of the dovetail on the jaws. Yours may match but I would be cautious in advising that all others will.

Most of the time, the skew angle will not be right for the dovetail, unless you have reground your skew to that angle. It still works with the sharper skew angle, just make sure the angle you cut matches the jaws.

And since Joe mentioned having a Talon, assuming you have the normal profiled jaws, you need a straight recess, not a dovetailed one. The dovetails may hold better in this application, but only if you have the dovetail jaws. (That was probably obvious, but just in case...)

[Joe Adams]

And since Joe mentioned having a Talon, assuming you have the normal profiled jaws, you need a straight recess, not a dovetailed one. The dovetails may hold better in this application, but only if you have the dovetail jaws. (That was probably obvious, but just in case...)

I was starting to wonder if I needed to buy OneWay dovetail jaws. The platters I have in mind will only be 6 to 8" in diameter. I'm trying to make change dishes for Christmas gifts.

[Leo Van Der Loo]

Joe you don't need Dovetail jaws, the #2 jaws on your Talon will do just fine, like Reed Gray I also use the recess most times (not always), use your cutoff tool to make the groove for your chuck jaws, or you could make the recess with your scraper, just make sure that the recess is square and clean, that is important, just have a look at this album that has a bunch of pictures that show the making of a large bowl that is held with a recess only while being hollowed, have fun and take care.
Leo Van Der Loo

http://homepage.mac.com/l.vanderloo/PhotoAlbum26.html

One picture here from a bunch of large bowls all with a recess but one :)

133518

[Dave Rudy]

Most of the time, the skew angle will not be right for the dovetail, unless you have reground your skew to that angle. It still works with the sharper skew angle, just make sure the angle you cut matches the jaws.

And since Joe mentioned having a Talon, assuming you have the normal profiled jaws, you need a straight recess, not a dovetailed one. The dovetails may hold better in this application, but only if you have the dovetail jaws. (That was probably obvious, but just in case...)

All good points. I missed the Talon reference.

1. My skew is reground (there is no magic in the amount of "skewness", so it still works fine as a skew;

2. I use only dovetailed jaws (Vicmarc and occasional Nova). I assume from the geometry that they hold better, especially in expansion (recess) mode, although I don't know that anyone has ever published testing on the subject.

Thanks for the clarifications.

[Keith Harrell]

You have the same chuck as I do. One of the mistakes I made was making the tenon to big when using a bowl that size. I thought I needed a #3 jaw and learned that the foot or base really determines what shapes you can do. I try to stick now with the standard #2 jaws with a tenon about 2"-2 1/4 and don't hog out as much wood in a single pass now. Broke a few tenons before I learned that. I wondered about the dovetail also but haven't pulled any out yet using the standard jaws. Dovetail I'm sure is better but either will break off if you try hard enough I learned.
Also make sure you are beyond the bark(into good wood) on the tenon.

[Mike Minto]

joe, teknatool make a small tool just for cutting dovetailed mortises that works great, and it's only about $15 - i won one in a contest, and use it when turning in this manner.

[Joshua Dinerstein]

I have been turning nearly 4 years but have been doing little the past 8 months or so.

Whoa Ken! What happened?!!? Don't tell me you found a way out of the vortex? That's just not right!

Joshua