tenon length to hold bowl?

Re: tenon length to hold bowl? *LINK*

Jennifer@Indy.USA

>Hi Ken,

A good rule of thumb that I've been told and still try to follow is to make the tennon long enough to fit the depth of the jaws. You want it sitting all the way down into the jaws until it bottoms out. The only time I don't follow this rule is if I'm turning something smallish and am not worried about it coming out of the chuck....or if I simply don't have enough thickness from the blank to make a longer tennon. I'm not familiar with the chuck you have but if the jaws are ribbed you can get away with a shorter tennon more often. Here's a link to the Oneway instructions for your chuck....I couldn't get it to open on my computer though?

Hope this helps.

Jennifer


Oneway Chuck Instructions

Re: tenon length to hold bowl?

Jim Pugh in Elyria, OH

>Sorry Jennifer, but I disagree. The tenon should not sit in the bottom of the chuck because this can lead to the piece rocking when being turned. Make the tenon shorter than the jaw depth, (typically 1/2" on Oneway chucks), and make the tenon transition at the bowl bottom square and flat. This provides a much larger surface for the bowl/piece to seat against and makes a very stable platform while turning.

Back to the original question....my tenons usually are between 1/4" and 3/8" long, depending on the size of the bowl. However, if you have a very thin piece to start with, such as a platter blank, you can get by with 3/32" to 1/8" long tenon. Just don't get overly agressive.

I like to make the tenon diameter at about the midpoint of the chuck capacity so if the bowl is being rough turned and the tenon goes slightly oveal, it can be trued up and still fit the same jaws.

Re: tenon length to hold bowl?

Jim Pugh in Elyria, OH

>I just looked at the Oneway link and item 4 on page 14 specifically says not to have the end of the tenon toucbing the bottom of the jaws.

The only exception I ever make of this is when I am turning in spindle mode and the blank/piece diameter is too small to allow a shoulder. Then I grit my teeth put it all the way to the bottom of the jaws. An example would be when making a goblet from a smallish limb.....

An Alternative....

Wally Dickerman at Green Valley, Az.

>Ken I suggest that you consider using something other than a chuck, especially for a blank with only a 2 inch depth. Most of my turnings are done using a glue block, and I recommend it. When I turn platters, and your 12 x 2 in. blank would be a platter, I use double faced tape. No wood is wasted using either method. If you're interested I can give you pointers on both.

Many new turners seem to be under the impression that using a 4-jaw chuck is the only way to turn a bowl. Well, the 4-jaw didn't even exist before about 1990. We did just fine before that.

Wally

Would love pointers!

Ken Platt (Granby, CT)

>Wally -

I'd appreciate pointers, especially details on using double face tape. I had considered using a waste/glue block, but with my limited shop time I was trying to omit another step if possible. Also, I was worried about my ability to get the surfaces flat enough for a good tape or glue bond, so any tips there would also be appreciated.

My last "bowl" was a platter, and the dovetail recess I used for rechucking made it necessary to leave the base thick, and as a result it came out looking and feeling unbalanced. Didn't want to do that again.

Ken

Re: tenon length to hold bowl?

Ken Platt (Granby, CT)

>Thanks, Jennifer. I downloaded the file and saved it. It appears to be an updated version of the booklet that came with my chuck, also better diagrams in color.

Ken

Thanks Jim

Ken Platt (Granby, CT)

>Those numbers give me an idea where to start.

Ken

Double Faced Tape...

Wally Dickerman at Green Valley, Az.

>There are three keys to sucessfully using double faced tape. Paper tapes and carpet tapes won't do the job. I use Permacel cloth tape. I get mine from Craft Supplies. The wood surface must be true and flat just as though you were going to make a glue joint. When the tape is applied it must be clamped for 2 or 3 minutes to let it set up.

When I'm using tape to turn a platter, I mount the blank using a faceplate or screw chuck on what will be the top of the platter. I turn the foot, truing the surface, and sanding it down to 600 grit. I also partially turn the bottom of the platter. I then apply the faceplate, with tape, to the blank, which is then removed and clamped for a couple of minutes. I Remount the piece and finish turning the platter.

Using this method, the blank is very secure, but don't leave it mounted on the lathe overnight. It may be on the floor in the morning.

To easily remove the finished piece, turn a 1/2 inch thick plug that fits into the threaded opening in your faceplate. Install the plug, mount the platter on the lathe. As you thread it on, the plug easily pushes the finished platter off.

Wally

I stand corrected....

Jennifer@Indy.USA

>I stand corrected. Thanks Jim....I'll have to change my method. Lord only knows the aggravation I've been causing myself.

Jennifer

Re: Double Faced Tape...

Wally Dickerman at Green Valley, Az.

>Ken, you can turn a device that will help center the faceplate when mounting it on the platter.

Using a 2 x 2 blank about 5 inches long, turn one end with a morse taper to fit into your tailstock. At the other end, turn the blank so that it'll just fit into the opening of your faceplate. Turn this about 1 inch long with a shoulder for the faceplate to snug up against. While the platter is still mounted on the lathe, put the device on your tailstock, mount the faceplate, with tape, and slide the tailstock so that the faceplate is mounted on the platter, then back the tailstock away. The faceplate will be accurately mounted. Remove the platter and clamp it.

Wally

Re: tenon length to hold bowl?

Bill Grumbine, Kutztown PA

>Ken, I will add to Wally's post on fixing a blank without the use of a chuck. I have chucks, and I love them, but there are times when they are not practical, and not everyone has them, so I teach without them at times. I learned a very good method from a Canadian turner, but you may have to invest in some extra equipment. That extra equipment is a second hand electric frying pan.

I use hot melt glue sticks in the frying pan. Once you do this, you are committed to using this pan for nothing else but, but they can be had for nothing or next to. Melt a bunch of sticks into the pan, and turn a waste block on a faceplate. Dip the waste block into the melted glue, and press it down on the center of your blank. It is a good idea to have the blank trued up as well as the waste block. In a matter of a few minutes, the glue is set and you can go on to turning. When you are done, the block can be parted off, knocked off, or turned away, depending on how big it is.

NOTE: This method will not work with a typical hot melt glue gun. These guns cannot provide the volume of glue needed in the time you need it for a good bond.

Bill

Re: tenon length to hold bowl?

Bill Grumbine, Kutztown PA

>Jim, I have been doing a lot of thinking about this lately, the notion that the tenon should not bottom out in the chuck. Now, I have been practicing this myself for years, but on occasion I have bottomed a tenon out and then some.

The standard wisdom is that the top of the jaws should index the shoulder of the tenon and not the bottom of the jaws because, as you write, the bowl can rock around in the chuck. But why? The bottom of the jaws are machined to the same level of quality and accuracy as the top of the jaws. To say that the area bearing against the bowl is larger is true, but is it significantly larger? I.e., is it large enough to make a real difference?

This is what I am really beginning to wonder about. If we can cut a shoulder accurately, why can we not true up the bottom of the tenon to the same level of accuracy? I think we can. If we can then we can free ourselves from the tendency to make the foot of the bowl the same size as our chuck jaws, something that has been brought up in other discussions. In other words, are we limiting our creativity and our options by adhering to the standard wisdom? I know I have been doing it this way, but like I say, I have begun to "question authority" as it were.

I am not taking aim at you or what you have written, since I have taught this way for a long time myself. But, you have provided an opening for yet another dialog on the things we do and why we do them, and now we can discuss, do we really need to do them this way, or are we all in a giant rut together on this? I think I am going to experiment on this one a bit.

Bill

Re: tenon length to hold bowl?

Wood Spinner

>Ken

As you become a better turner it all comes together. Time and wood shavings make it all happen. You never bottom the tennon. When you cut the botom and make the tennon be sure the piece has a flat ledge for the jaws to set on. On most pieces 1/4 is adequate but on large I cut to almost the depth ov the jaws. If the wood is a little soft or unstable use thin CA around the tennon where it meets the base. After the CA clean up your cut and then mount.

Good turniong and be safe

Bill

One More Thing...

Wally Dickerman at Green Valley, Az.

>Double faced tape won't work on wet wood.

Wally

Thanks Wally..

Ken Platt (Granby, CT)

>

Re: tenon length to hold bowl?

Mark Kauder, Phenix City, AL

>Ken,

One thing not mentioned (and I am surprised because I may have learned it from either Wally or Bill G.) - the modern 4 jaw chuck is one of the worst impediments to good bowl/platter foot design. Way to many people feel that using a scroll chuck is a necessity, and it using it, compromise the design of the bowl/platter to fit the chucking requirements. I have a chuck, and though I am finding after nearly 4 years of ownership, I am only now that I have a bigger lathe, starting to use it much. In the past I used faceplates attached to waste blocks. Now, I still use waste blocks, but now turn tenons on them to accept my scroll chuck jaws.

The wasts block allow a little more standoff of the wood from the chuck, and allow you to turn the foot down to whatever size is appropriate for the bowl/platter shape.

Years ago, standard practice for poorly done bowls was to put felt on the bottom to cover the screw holes from the faceplate. These days, way too many feet on bowls are just poorly disguised chuck tenons.

Just my opinion - your mileage may very.

Mark

Re: tenon length to hold bowl?

Glenn Hodges

>Bill, the reason I do not let mine bottom out when they are roughed out is because after they dry, the bottom is sometimes uneven. When attached back to the lathe to do the finishing work on some wood this warp will cause problems.

Nashville, Ga

Re: After the bowl is dry and warped,

Al Crandall

>After the bowl is dry and warped, don't you re-true the oval tenon before chucking the piece to make the finish cuts? Couldn't you cut the end of the tenon to make it flat again at the same time?