Turning tennons for a chuck... [Archive] - Sawmill Creek Woodworking Community

Ray Bell

12-10-2010, 3:19 PM

Rick, I am probably one of the least qualified to help you, but I almost always use a 3" face plate on the spindle end to begin with. Turn the outside of the bowl, and add a tenon to the bottom. After the outside is formed, and sanded, I install the chuck with tenon. It is a good idea to use one of the tapered, threaded inserts in the tail stock to mount the bowl in the chuck while reversing the bowl. Install chuck/bowl on spindle and turn the inside. I know this is probably overly simplistic, and one of the experts will be around shortly to explain this better.

Enjoy!!

Sean Hughto

12-10-2010, 3:26 PM

I'd make you a video with my flip, but I'm guessing you can find dozens on youtube already. If not, I plan to turn at least one bowl over the weekend.

What sort of scroll chuck do you have?

Jon Prouty

12-10-2010, 4:19 PM

comments from a new turner - take with a grain of salt.

I drill a hole in the blank (the part that will be hollowed out) and use my chuck supplied "screw" and screw the "screw" into the hole by having the chuck mounted on the lathe and rotating the hand wheel and screwing into the blank. That was a long runon sentence. Then bring up the tailcenter and form the outside of the bowl and tennon. I will back off the tail and smooth out the tennon. Unscrew from the chuck and remove the "screw". Chuck up the tennon and take care of the inside.

I realize the words sound dumb but that is the process I use.

Jon

Thom Sturgill

12-10-2010, 4:28 PM

I was taught to start between centers, but you have to be careful to get the blank well balanced. Flatten the bottom and mark the diameter of the tenon based on the closed (or nearly closed) diameter of the chuck jaws. Turn off enough material to create a tenon and a flat that the jaw faces will rest against. THIS MUST BE TRUE. The tenon should either be square to the flat (for serrated jaws) or slightly undercut for dovetail jaws.
Cut a 'secondary' step or tenon back from the main tenon leaving enough width at the flat for the jaws to sit. Turn the outside of the bowl/hf. The secondary step is to allow you to visualise the curve through to the bottom after the tenon is removed. I got this from Mike Mahoney's video . (http://www.youtube.com/watch?v=zz_0jHdjdh0)

Placing the blank between centers provides a true center mark that will be used later. If you start with a face plate or screw chuck, still bring the tail stock into play to make this mark - it will pay off later.

Mount the bowl/hw in the chuck loosely and use the tail stock to ensure that the center is still aligned and then tighten the chuck and remove the tail stock.

Hollow.

When reversing to remove the tenon, whether using a vacuum chuck, jamb chuck, doughnut, or whatever, the tail-stock should be used with the dimple created earlier to return the piece to true center.

I'm sure others will chime in, but that's how I work. Hope it helps.

Sean Hughto

12-10-2010, 4:32 PM

As far as mounting your blank at the beginning, I pretty much always use a faceplate with multiple steel screws. On some smaller blanks, I've also used a screw chuck.

Steve Campbell

12-10-2010, 4:36 PM

Rick I find it a lot faster and easier to just mount the rough blank between centers. Shape the outside, along with the tenon. Then you can mount it in the chuck and finish turning the inside.
Hope this helps a little.

Steve

John Keeton

12-10-2010, 4:37 PM

Rick, I don't turn many bowls, but I do it like Jon has stated - except for removing the tailstock and "smoothing out the tenon." I am interested only in having the tenon true, and a "register" against the bottom of the bowl. I am not concerned about a flat spot for the face of jaws to fit flat against - just that there is a definitive surface contact all around for the jaws. I usually use a tenon that is about 3/16" deep. If the wood is soft, my tenon is usually not dovetailed. If it is hard wood, and will not compress without the chance for cracked fibers, then I will dovetail the recess slightly to fit the inside of the jaws.

As Thom has said, try to have the tenon the size your jaws will be when "almost" closed. That will give you the most metal/wood contact.

Sean Hughto

12-10-2010, 4:37 PM

How large a bowl do you do this with? What do you use for the center on the drive side?

John Keeton

12-10-2010, 4:44 PM

Sean, if the question is to me, my swing is limited to 12.5", and I have done 12" with this method with no problems. I use the wormscrew in the chuck and the tailstock for support.

I don't recommend this, but on small HF blanks that are uniform in thickness, I have simply marked the center for the tailstock and jammed the blank against open chuck jaws with drawer liner for friction. It is easily enough for me to get a tenon on the bottom. I wouldn't attempt to do much else like that, though!!

I never use a faceplate.

charlie knighton

12-10-2010, 4:46 PM

only thing i can add is that the tendon does not bottom out in the jaws, also the amount of waste wood between tendon and bowl gives you leeway in whatever design you choose, much prefer 4" blank than 2" blank

Sean Hughto

12-10-2010, 4:51 PM

Thanks, John. I was actually asking Steve regarding "just turning the rough balnk between centers." But I think that's the question you were answering anyway, right?

Don Geiger

12-10-2010, 4:57 PM

Hi Tom:

I whole heartedly agree with your approach. Well said! I learned the benefits of starting between centers from Ellsworth years ago and have use this method of starting all my pieces this way. It enables me to adjust the piece so I can get the results I want without getting locked in, which is what happens if you start by screwing a faceplate on or drilling a hole and screwing a screw center in from the git go.

If you are going to use a chuck with compression jaws, making a second step beyond where the jaws are resting is critical. When doing this be sure the transition from the curved surface and the step is crisp or your eye gets distracted and it's hard to predict the curve past that point. This technique also enables you to continue the curve to foot instead of ending up with the curve terminating into the shelf and having a large flat bottom on the bowl or hollow form.

In re-centering the piece against a jamb chuck or vacuum chuck, I use a different technique. Come see me at the Florida Symposium and I'll go over it with you.

Don Geiger

I was taught to start between centers, but you have to be careful to get the blank well balanced. Flatten the bottom and mark the diameter of the tenon based on the closed (or nearly closed) diameter of the chuck jaws. Turn off enough material to create a tenon and a flat that the jaw faces will rest against. THIS MUST BE TRUE. The tenon should either be square to the flat (for serrated jaws) or slightly undercut for dovetail jaws.
Cut a 'secondary' step or tenon back from the main tenon leaving enough width at the flat for the jaws to sit. Turn the outside of the bowl/hf. The secondary step is to allow you to visualise the curve through to the bottom after the tenon is removed. I got this from Mike Mahoney's video . (http://www.youtube.com/watch?v=zz_0jHdjdh0)

Placing the blank between centers provides a true center mark that will be used later. If you start with a face plate or screw chuck, still bring the tail stock into play to make this mark - it will pay off later.

Mount the bowl/hw in the chuck loosely and use the tail stock to ensure that the center is still aligned and then tighten the chuck and remove the tail stock.

Hollow.

When reversing to remove the tenon, whether using a vacuum chuck, jamb chuck, doughnut, or whatever, the tail-stock should be used with the dimple created earlier to return the piece to true center.

I'm sure others will chime in, but that's how I work. Hope it helps.

Jon Prouty

12-10-2010, 6:26 PM

I like the between center way too but you gotta be sure to get a good bite on the headstock end.

Regarding turning the tennon as small as possible to the chuck jaws... I like to go a bit oversized on the roughout. If I go to close to the closed size in roughout, when I re turn to bring the tennon back to round the tennon could get to small to bite down on. darnit.

Jon

Rick Markham

12-10-2010, 6:41 PM

Thanks guys, I am trying to digest all of that. Sean, I'd like to see a video of how you do it, there are actually very few complete videos on youtube about turning the tennon, they all cover part of it, or assume you already know part of it.

As for centers on the drive side, I have a face plate, a steb center and the "woodworm" on the SN2. The first blank I want to turn is only 6" in diameter (rounded) and 4" in depth, but I have a couple larger blanks for later.

Steve Campbell

12-10-2010, 6:47 PM

Sean I am a new delta owner so I am limited to 12 inch. I have done a couple of 10 inch plus bowels this way before. I normally round my blanks somewhat on the bandsaw so they are not too far off. I use some hardboard discs that I made. find the disc that seems to fit the blank the best. I then use an old nail set that I ground to a point to hold the disc on the blank while I cut it on the bansaw. When I'm done cutting the blank I turn the blank over and use the same disc to mark the center on the other side. I just use the standard drive center that came with my lathe. Just use a wood mallet to set the center before mounting on the lathe.
I make the tenon a little larger on my rough outs. It doesn't have to be very much large. I did make the mistake once of cutting the tenon too small. Of course it had to be on a real nice bowel. I wrapped the too small tenon with tape and was able to return.
Steve

Richard Madden

12-10-2010, 6:51 PM

I'd have to say I pretty much do it the same as Thom described. I don't measure the tenon size though...just eyeball it.

Hilel Salomon

12-10-2010, 7:10 PM

Is it just me, or did you specifically ask how you cut the tenon in order to fit it to the chuck? I agree with most of the posts about how you mount it initially, but you also mentioned that you have a worm screw and faceplate as well as an SN2 chuck. I've had much better results using a faceplate, although I have used the screw and-on occasion- even mounted the piece with a sorby steb center, and a revolving steb center. Either way, you will need (if you use the SN2 chuck) to make a tenon which is dovetailed (tapered) to fit the chuck neatly. You should also leave a flat space where the jaws touch the bowl, but it isn't necessary to make the dovetailed tenon as thick as the jaws. Depending on the size of the bowl 1/4" or less of a tenon might do the trick. Now, about achieving the dovetail on the tenon:

Experienced turners can do this with an ellsworth/Irish/sweptback grind, but you can also do it with a parting tool, a bedan tool and anything that will allow you to cut the tenon at an angle. I often use a bedan tool straight into the tenon and then twisted in such a way as to create the dovetail angle. Alan Lacer and spindle turners will disapprove of this, but a lazy way (and I am ever lazy) is with an angled skew. The angle gives you an automatic dovetail on the tenon. You might want to use calipers to determine the size of the tenon, so that your jaws will go almost (but not completely) around the tenon. The closer they are, the more holding power you will have, but if they are completely around, you stand the risk of losing the piece.

I feel silly giving these instructions in light of the fact that many of the respondents are infinitely better turners than me. I think though that many of them lost sight of your query.
Regards, Hilel Salomon

Rick Markham

12-10-2010, 8:36 PM

Hilel, your right I needed both parts. But mounting the blank definitely came first ;) I watched a small portion of Mahoney's video available on Youtube (I need to order his videos) where he used his skew just as you described. That was my plan for cutting the dovetail.

Thanks y'all for all the information so far... I'm anxious! :)

Bernie Weishapl

12-10-2010, 9:25 PM

Rick the video I got when I first started turning was Mike Mahoney's From the Tree To The Table. I have pretty much used his methods ever since.

Peter Lamb

12-10-2010, 9:31 PM

While you are ordering videos get tBill Gumbine's!! They will be very helpful to you.
Peter

Rick Markham

12-10-2010, 9:33 PM

Thanks fellas! they are duly noted!

alex carey

12-10-2010, 10:16 PM

+1 to keeton, I usually use a woodscrew or just friction.

If its something quite large that needs immediate roughing ill use a 6" faceplate.

John Keeton

12-10-2010, 11:05 PM

Regarding the cutting of a dovetail for the tenon, for what it is worth, Teknatool DOES NOT recommend a dovetail, but a parallel spigot. This is from the chuck manual -

Make the spigot as parallel as possible to maximise the efficiency of the clamping action. Only approximate sizing of the spigot is necessary, as the jaws will accommodate a wide range of spigot diameters within the spigot limits stated above. The 50mm standard jaw has a thin lip or shoulder at the front face. This is designed to bite into the timber as the jaws are tightened. DO NOT CUT A RECESS FOR THE LIP TO FIT INTO, AS THIS WILL REDUCE GRIPPING POWER.

Notwithstanding this, if the wood is very hard, I do create a slight dovetail, but with softer wood (most of it) I do not dovetail the tenon. I do dovetail recesses when used - as instructed.

Sean Hughto

12-11-2010, 7:22 PM

Sean, I'd like to see a video of how you do it...

Here ya go.

http://www.youtube.com/watch?v=WD1Dw1D4OU8

It's a rather crude little bowl made from a scrap, but it's hard to make a nice piece I found with a Flip taped to the front of your face shield. ;-) I ended just showing my whole process. The tenon stuff starts about a minute in. Oh, and sorry about my singing.

The one at the front with the scoop is the product of the demo:
http://farm6.static.flickr.com/5168/5252554450_3dc6e60e79_z.jpg

Hope the vid is of some use, or at least amusing. Cheers.

Lee Koepke

12-11-2010, 8:18 PM

Here ya go.

http://www.youtube.com/watch?v=WD1Dw1D4OU8

It's a rather crude little bowl made from a scrap, but it's hard to make a nice piece I found with a Flip taped to the front of your face shield. ;-) I ended just showing my whole process. The tenon stuff starts about a minute in. Oh, and sorry about my singing.

The one at the front with the scoop is the product of the demo:
http://farm6.static.flickr.com/5168/5252554450_3dc6e60e79_z.jpg

Hope the vid is of some use, or at least amusing. Cheers.thanks for the video .... ( i had the mute on so I couldnt hear any singing .. ) i havent turned a bowl yet, but am scheduled to take a bowl turning class at Highland WW tomorrow .... at least I have a decent idea with to expect. appreciate taking the time to do that.

Ray Bell

12-11-2010, 8:26 PM

Question...is a spigot the same as a tenon?

John Keeton

12-11-2010, 8:57 PM

Question...is a spigot the same as a tenon?Yes. Keep in mind that Teknatool is from New Zealand, and I believe spigot is a term used in Britain and other countries, as well as earlier on here in the states. But, I am pretty new at this, so I could easily be wrong on the derivation of "spigot."

Rick Markham

12-11-2010, 9:07 PM

Sean, Thank you very much! That actually answered a whole lot of questions that I had. Will you do me a favor and take a picture of your spear point tool for me? I also didn't expect ya to have to tape your flip cam to your faceshield, that's above the call of duty! Beautiful little bowl too. That is the first video on youtube now that has the process from beginning to end that I have seen. Thank you so much! Your shop looks a bit like mine too, hehe.

Just to give ya guys a brief update, on what I have done, since some time has passed with the forum update. I turned my first bowl last night, I cut the tenon largely the same was as in the video, I used my skew to true up and shape the tenon (I made a template for max opening of the jaws and minimum opening and that helped a lot) I had good success with the shape of the bowl, and the tenon. I unfortunately chose Spalted sycamore (it was really pretty, I know I never take the easy way in the beginning, but what fun is that?) When I was hollowing the inside, it was quite punky and most of the fibers came apart instead of shearing off (gouge was very sharp.) I am sure my touch was a little heavy too. It was a good learning experience, so I am going to move forward and try something not spalted, and take it as a learning experience. I will come back to the other spalted sycamore blank I have later, when I am more experienced.

Michael Mills

12-12-2010, 9:27 AM

To quote from John Keeton
Regarding the cutting of a dovetail for the tenon, for what it is worth, Teknatool DOES NOT recommend a dovetail, but a parallel spigot. This is from the chuck manual -

Make the spigot as parallel as possible to maximise the efficiency of the clamping action. Only approximate sizing of the spigot is necessary, as the jaws will accommodate a wide range of spigot diameters within the spigot limits stated above. The 50mm standard jaw has a thin lip or shoulder at the front face. This is designed to bite into the timber as the jaws are tightened. DO NOT CUT A RECESS FOR THE LIP TO FIT INTO, AS THIS WILL REDUCE GRIPPING POWER.

If you are using the supplied SN2 50mm jaws and you open them full and glance at them it does appear both sides are dovetailed.

I took these pictures with a machinist square clamped to the sides of the jaws.
The outside is an obvious dovetail from top to bottom.
The inside is straight up for about 2/3 of the way. Then there appears to be a slight dovetail (what Nova calls a lip?). I tried to measure it and it seems to be about 1/32 inch wide, it is probably 1mm wide. This is all that will bite into the wood.
If you cut a full dovetail, Point B on the wood must be crushed by the jaws before Point A of the jaws ever makes contact.
You will also note there is a small bevel on the top of the inside of the jaws.
I’ll do like John and go with the Nova guidelines.

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As far as mounting the blank I use most methods depending on the hardness of the wood and the size of the blank. The larger, the more I go to a faceplate (8 inch or larger). Smaller I go with a standard 4 blade spur or for punky or soft wood the 2 blade spur. I will have to learn to use the worm screw, I have never tried it.
The steb center I only use on dry wood as mine tended to drill itself into the wood but that could be from catches :D.

James White

12-12-2010, 2:29 PM

John,

Thank you for pointing this fact about the Nova jaws out. I have had a few pieces let go from catches. I am sure it was due to this as you could see the wood crushed at the peak of the dovetail. Lesson learned.

James

Rick Markham

12-12-2010, 3:16 PM

Thanks Michael, I will definitely do this in the future. Thanks for breaking out the engineer's square, I have a few, and should have used them. I've been working on a Cherry bowl (It keeps getting shorter and shorter) due to my "learning curve" when I cut the tenon on it, I cut it very shallow, as I noticed there isn't much of a dovetail in the jaws, looking at the square in there it is mostly an optical illusion. I will definitely cut them square on hardwoods from now on. Thanks for all the input!

Thomas Canfield

12-12-2010, 10:27 PM

In the past I normally would use the worm screw in chuck to mount a rough blank. I use a 2 3/4" Forstner bit to get a flat spot for the chuck face, leveling up the rough blank on the drill table before spotting the face. Recently I saw a demo where it was recommended to use a 1" spade or Forstner bit to form a recess for a 1" 2 prong spur drive and start the rough piece between centers. With the 2 prong spur, you can easily adjust the piece on the lathe by shifting the tail stock, and the recess prevents the spur coming out. The use of the tailstock is needed, but you can shape the outside and make a tenon for mounting in a chuck to do the interior. I still like the process on some of the larger sections (25 pound or so up)of leveling out the piece and using the 2 3/4" Forstner bit and worm screw or a 2 1/2" faceplate to get a firmer hold on the piece, still using the tailstock to rough out the outside. It is easier for me (damaged left arm) to screw a chuck or faceplate on than try to hold up a piece and try to get it between centers.

Wally Dickerman

12-13-2010, 12:00 PM

Rick, you've received a lot of information on tenons. If you don't mind my saying so, you are making a bigger deal out of this than is needed. It's really pretty simple. I have several chucks, all Oneway Talon and Stronghold. I had one of the original Nova chucks but that went with my last lathe when I sold it.

Cut the tenon with straight sides. Cut it so that it doesn't bottom out in the chuck. The machined top edges on the jaws should fit snugly against the shoulder of the cut. To get the "perfect round" contact, the jaws should be level with the body of the chuck. They are designed that way. However, a little larger or a little smaller makes little difference. If you haven't already found out, the protruding jaws are real knuckle-busters. Before you remove a piece from the chuck, make a pencil mark on both sides of one the jaws so that when you return the piece to the chuck it goes on exactly as it was before. I use the #4 jaw.

Wally

Scott Hackler

12-13-2010, 12:18 PM

Rick,

For me the only way I like to turn the tenon (and the outside roughing) is to mount a faceplate ring to the top of the blank, bring up the tail stock, rough the whole outside and turn the tenon. The I flip it around, take off the faceplate ring and bring up the tailstock for support as I true up the outside and turn to final shape and sand. The with the tailstock still in place, I will hog out all I can reach before going without the tail stock. Unless, of course, the blank is small and semi-dry.

Now on smaller stuff, where I need a tenon, I will use my stub drive and turn between centers until I have the tenon turned.

Prashun Patel

12-13-2010, 1:23 PM

To beat the proverbial dead horse: I prefer to use a faceplate. It just seems to hold better than the worm screw for me. Also, after the outside and tenon are turned, I install the chuck, and put on a tailstock adapter that allows me to screw on the faceplate to the tailstock. This allows me to get the bowl centered properly. I leave it on until I've hogged out a good portion around the rim.

I've never been scientific about the amount of slope on my tenon. I do stop the lathe every now and then to make sure it's tight.

Lately after I remove the faceplate during hollowing, I've taken to using a spade bit in a drill chuck in the tailstock. This does 3 things: 1) allows me to plunge to the right depth, 2) removes that annoying nub in the center that develops during hollowing, 3) Every now and then I turn off the lathe and plunge in the spade bit to the bored hole to recenter the blank.

Rick Markham

12-13-2010, 1:37 PM

Yes Wally it has become a much bigger thing than I expected! But I would have missed your little tidbit about marking both sides of one jaw so the piece gets returned exactly. I've now made two bowls and look forward to showing them off soon. Now I just need to finish up a self portrait for class, and make a donut chuck so I can turn the tenons off. Thanks guys for all the help you have given me.

Rick Markham

12-13-2010, 1:40 PM

Prashun, I need to get a drill chuck for my tailstock. I know it will make finding the final depth much easier.

Scott Hackler

12-13-2010, 2:25 PM

Lately after I remove the faceplate during hollowing, I've taken to using a spade bit in a drill chuck in the tailstock. This does 3 things: 1) allows me to plunge to the right depth, 2) removes that annoying nub in the center that develops during hollowing, 3) Every now and then I turn off the lathe and plunge in the spade bit to the bored hole to recenter the blank.

A SPADE BIT????? Boy that is about the roughest way to drill a hole. Seems a bit dangerous as well. You should think about buying a set of forstner bits. very smooth and a lot less change of a accident if you hit a knot or something real hard.