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Tenon Consistency Challenged

Randy Anderson

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I've made hundreds if not thousands of tenons in making bowls and vases. It's my primary mounting method. I seldom have an issue with one that I can't get to true up after taking it off the chuck but sometimes as you likely know, once you take it off it can be a bit tricky to remount it to spin dead true. It might take a bit of fiddling to get it true on a second mount.

My challenge has been with making sets of dinner plates lately. Something I don't do very often and where spinning true is critical for detail work and curves / plate faces that match and are clean. I put a shallow tenon on each side of the blank so that I can flip it back and forth a few times as I work through the production steps for each plate. In my recent plate work I could not get a consistent mount from one face to the other. I would create a tenon, not very deep, make sure it was as clean and true as I could, flip the blank over, and put a tenon on the other side. As I flip the piece over to perform a step on the other side the piece would not spin near as true as I expected and the tenon now on the tailstock side would be off center a bit. Sometimes barely, sometimes a lot. I fought back and forth for a long time trying to figure out what was wrong and finally just muscled my way through. It's the only thing I turn where I have a tenon on both sides of the piece for a while.

Maybe I'm expecting too much from a 2 1/2" tenon? I have a oneway chuck so the jaw grooves do bite into the wood a bit. Maybe that little bit depending on where in the grain they bite makes the difference? Maybe I should shift to a mortise mounting method for something like this? I also have a Nova chuck with dovetail jaws and a single inside ring for the tenon mount. I found it would be a bit more consistent but still not a fix. Yes I cleaned the jaws, chuck, checked all was tight for the thread insert, clean headstock screw face, etc. Just looking for some experienced folks that might have some insight.

My hunch is that a good sized mortise mount is the right way to do things like this.
 
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Don't know if I have any insight into why this particular work piece went wonk. But I can tell you what I do in an attempt to maintain alignment. As a general rule I try not to release one mount until the next mount is secured.
I use two chucks. I make the new tenon then mount the second chuck on an adapter & live center on the TS. Bring the second chuck onto the tenon and tighten the jaws. Now I can release the first chuck and remove it. The second chuck and work piece are then transfered to the HS.
I do the same for recesses, Cole, Longworth. And something similar with the vacuum chuck.
 
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Randy if I have to remove and remount, I will mark the recess/tenon with a pencil between the #1 and #4 jaws.

It does help to grab it at the same place and it will turn more true, and yes make sure you have it sit right against the jaw faces the firs time it is mounted or else you won't get that right the next time.

I also will set the toolrest right close to the rim and rotate by hand after remounting it, to see if the piece is turning true, a small mallet can persuade if needed ;)
 
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@Randy Anderson
I haven't turned plates so I was wondering why it's necessary to create tenons on both sides of the blank? In my mind, creating a plate doesn't seem that much different from a bowl; just shallower and a different shape. I read what you said, namely that "I put a shallow tenon on each side of the blank so that I can flip it back and forth a few times as I work through the production steps for each plate." Can you explain this?

Also, I agree that marking Jaw #1 on the tenon gives a more consistently true remount, but this is applies to the one tenon on a bowl or hollow form. If this was done with both tenons, I think there would at least be much less wobble when remounting unless there is a significant period of time between mountings or the wood is wet to begin with and it just dries out quickly. I generally have more trouble preventing wobble when either of these two scenarios exist.
 
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Randy Anderson

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Randy, for one plate you're right. One tenon mount and a jam chuck or longworth to finish and could be done. When doing a set of 6 I do the same step to each one as I move along. Production mode so to speak. I don't completely finish one then move on to the next. I shape the dia, the lip, the inside, etc to be sure I have 6 that are the same, or very very close. Then flip and do the same for the bottoms. I found for me doing the same activity on each one gives me a much better ability to be consistent and compare as I move along.

There have been times when as I get to plate 4 or so I may change my idea (or the wood does) a bit and I need to go back to the previous and adjust them. I can then flip, work the bottom for each in turn, flip back to turn the small tenon off the top, sand, flip back to sand the bottom, etc. I then end up with 6 that are very close to each other. If you put them all out on the bench and walk around them you can spot things that might need tweaking so your options to redo are still there. I leave the bottom tenon on to apply abrasive paste and then jam chuck to get rid of the small tenon on the bottom. All I have left to sand and finish is the small area where the tenon was on the bottom.

I know, may be more steps than an experienced platter turner would need for sure but for me it really helps with the consistency. If you do 6 inside shapes all at the same time they tend to be more alike, for me anyway.
 
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The advice to mark where the jaws contact the tenon is my best thought. There is one part of the process where we have very little control - as has often been repeated - wood moves. Not just seasonally, but with the relief of internal stresses as well. Few woods that I have access to will run perfectly true when turned from two mounting sides. I’ve come to the conclusion that we get as close as possible and point out that turning wood is not the same as machining.
I’ve found some woods - mostly exotics like African Blackwood and cocobolo that get closer to turning true with multiple mountings. Some of the California Black Acacia I’ve turned also comes close. But the big leaf maple, madrone and alders that are local here have a mind of their own.
 
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@Randy Anderson - I haven’t turned sets of plates, but have turned several plates and platters. I like your idea of ‘production mode’ for consistency as well as efficiency.

I’m still not sure why you need two tenons, help me with my thought process. I would first mount flat face pushed against friction drive, pushed by cup center in tailstock. With this mounting I’d put a shallow tenon on the bottom and turn the foot - out and lip on the bottom. Do this for each of the set. Then mount each in the scroll Chuck and touch up lower side if needed then turn the whole rim and inside, sand back (foot - out) and top. Set aside and do the same to the rest. Then mount each in Cole jaws or such (using cup center mark to recenter) to turn the foot-in on the bottom and remove the tenon.

I think this allows turning each step in multiples without rechucking. What am I missing?
 

Randy Anderson

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Ron, I'm sure mechanically speaking there is a much more efficient way to do what I do. I don't like doing tool work in between the piece and headstock so want the ability to have it facing out when turning whatever side I'm focused on. Net is I want to keep my options open as I move along. I'm pretty good with a gouge and scraper but still want the option, if desired, to back up and change. I actually did that on a batch of 4 I did yesterday for my daughter. After I had them about done I set them on the bench and just didn't like the curve from the lip to the bottom. Didn't look quite right so mounted them back up, changed the curve a bit and done. Being able to remount and have them spin true (or not) was part of my frustration and reason for the post.
 
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For me, the dovetail profile on the left make for better rechucking concentricity and less "out of plane" (?) wobble. The jaws on the right have ridges that have a tendency to shift the platter. Didn't like the ridges so I ground them off.
I use a recess for platters and have, on occasion, used a recess on both sides for initial shaping. Most of my recesses for plates are cut a light 1/8th inch deep, with the diameter barely large enough to fit over the jaws. Might not seem deep enough but I've never sent one flying. If, after rechucking, there is a bit of wobble, loosen the jaws slightly and shift the plate 10° or so, tighten and check for wobble. A few shifts will usually get the plate (or platter) running true.
These jaws are for a Stronghold, not sure what the # is but the outside diameter is ≈ 4 7/8th.

Reshaped jaws.jpeg
 

Randy Anderson

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Clifton, I suspect your use of a recess for platters is where I need to go for my next batch. I did find that the Nova chuck jaws with the dovetail profile were a bit easier to get to spin closer to true after a remount. We get set in our ways I guess. I default to tenons for all I do and I don't do plates and platters very often. Certainly not sets. Thx.
 
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I also tend to use recesses rather than tenons when making plates and platters, although I’ve never done a production run. One advantage of a recess is that when you’re ready to make the last cut (for me, using a friction drive on the inside of the plate, with tailstock support, or even a vacuum chuck, it’s an easy matter to just shave the edge of the underside undercut into a perpendicular or open curve.
 

hockenbery

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Maybe I'm expecting too much from a 2 1/2" tenon? I have a oneway chuck so the jaw grooves do bite into the wood a bit. Maybe that little bit depending on where in the grain they bite makes the difference? Maybe I should shift to a mortise mounting method for something like this? I also have a Nova chuck with dovetail jaws and a single inside ring for the tenon moun
I have found the dovetail jaws work better for me in remounting. Matching many grooves is less repeatable. Crushed fibers can fill a groove and push the tenon off center when closing.

With dry wood a tenon close to the true circle will remount more positively. Try 2” tenons.
At true circle most jaws will have an 1/8” gap from fully closed.

ONEWAY sells dovetail jaws. If you have real dovetail jaws on the Nova they should work..
I don’t use the bird beak Nova Jaws. Real dovetails are much better in MHO. Some folks like the bird beak and they may work for you.
 

hockenbery

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One other issue with the ONEWAY jaws is they don’t work well with shorter tenons.
If the tenon face lines up with a tooth ring it will often push it up instead of biting in.
Tenon taller than the last tooth you get great holds.

If you don’t get catches a 1/8” tall dove dovetail will hold a 14” platter just fine and recenter well.
My wife does that often and some platters she remounts after working on it off the lathe.
 
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I also tend to use recesses rather than tenons when making plates and platters, although I’ve never done a production run. One advantage of a recess is that when you’re ready to make the last cut (for me, using a friction drive on the inside of the plate, with tailstock support, or even a vacuum chuck, it’s an easy matter to just shave the edge of the underside undercut into a perpendicular or open curve.
I use a shallow recessed tenon. 1/8" depth is plenty. I've recently made a couple 16" diameter 'plates' with a 1/8" recessed tenon using 4/4 stock. Stronghold chuck and profiled jaws
 
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I prefer a recess on plates and platters in order to maximize the available wood, and because the shoulder of the recess can become the foot quite easily. Most of the plates I made were from 4/4 boards. Except for the facing off, with a recess, every bit of the wood thickness is usable. The large diameter jaws used are very stable, too.

AFAIK, all the Nova jaws have a true dovetail on their outside surface. The 'bird beak' on some sets is just on the inside.
 
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For me, the dovetail profile on the left make for better rechucking concentricity and less "out of plane" (?) wobble. The jaws on the right have ridges that have a tendency to shift the platter. Didn't like the ridges so I ground them off.
I found the same problem with that ridge on my OneWay chucks so since I had made an adapter for my LaBlond metal lathe to mount 1 1/4-8 woodturning chucks for threading I was able to accurately turn them off. The process is to close the chuck on the wood worm screw then set the top slide for the angle and and turn the ridge off.
 
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A little over 11” dia.
And if you measure any ceramic rim plate of that size the bottom rim that sits on the table is around 7”.

Agreed, It’s a great idea to mark your jaw position so that you have an aid in re-chucking the piece accurately. Even so, chances are that you will not get it exactly. There will probably be a small variance. With a 2.5 inch tenon that small variance amplifies at the 11” rim and so does the out of round amount. If you choose to re-chuck, then I would try to reduce the amplification of the error. If your tenon is 7” inches there would be very little runout after re-chucking. I learned about this concept from Glen Lucus patter demo at the 2010 AAW Hartford Symposium. I bought the vicmarc chuck and the 7,8; and 9 inch jaws and never looked back. If one needs to see the math and geometry to prove that this works and why, I’d be happy to provide it. I usually make 7” dovetails very shallow say 1/8” for the hold and trim, finish round them up with a recess just like a real plate. I dislike the Aesthetics of a woodturner expansion chuck platter bottom.
 
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Large jaws on a vicmarc chuck has really opened things for me. That big mount is so stable and strong, and has allowed me to incorporate the foot inside the tenon on even the largest bowls. No loss in blank height from tenon removal.
 
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Well, I always use a recess, even when turning dry wood, which isn't often. One thing I found that helped get a true mount was to use a NRS to fine tune the shoulder that the top of the chuck jaws seat against. With a gouge, there is always a tiny bit of bounce from going uphill/downhill/uphill/downhill on each revolution. The NRS will take off the high spots so I get a more true surface. When I get 2 identical pieces, it is an accident, and I never worry about pieces matching 'exactly'. This would eliminate any variable mounts if you just finish turn, reverse, and finish turn. Some times rotating 90 or 180 degrees can make a difference. I have had, more than once, found that the set screws on the jaws can get loose and that is what causes a bit of extra wobble. While I turn more bowls than platters, it seems that platters are more prone to vibration/wobbling near the rims as I turn. I am guessing that the bowl shape is less prone to that, but not sure.

robo hippy
 

Randy Anderson

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Thanks all, some good info and tips that were likely causing issues for me. I have a blank left that I plan to test a bit on today. I believe going to a larger shallow mortise mount and using my Nova chuck that actually has dovetail jaws will help plus conserve material for me. I also don't care for the obvious turner mount recess to be left on the bottom of my work so should be able to finish it up into the foot nicely. I likely have a couple more sets of plates to do, I have two more daughters.
 
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I've always wanted a metal lathe but that's a wholenother rabbit hole... I spun the chuck on the lathe and with the judicious use of an angle grinder took the outside ribs off. Might be a "don't try this at home" moment. This was before oneway made smooth jaws. The larger jaws definitely help with reducing the out of alignment error.
Here is about a 16th inch recess on a 15 inch platter.
15 inch platter.jpeg

Close up of one of the jaws. The "teeth" seen are the inside ridges as these are modified profile jaws.
The outside dovetail portion is smooth.
Shallow recess 15%22 platter.jpeg

I hope you let us know how the experiment goes.
 
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The dove tail angle needs to be sharp and 'crisp' to make this work. I saw Mike Mahoney do a walnut platter maybe 14 inch diameter, and had a recess about 1/16 deep. With new chuck jaws, that would work fine. With old beat up jaws with some dings from my McNaughton coring tools, I wouldn't attempt that....

robo hippy
 
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I spent a week with Richard Raffan one year in Utah and one of the things I learned from him was that a 1/16" dovetail tenon or recess was more than enough to hold your work. That has worked especially well with my Nova chucks with the 2" jaws as that birds beak is a dovetail and works very well with that 1/16" tenon. Mike Mahoney whether it was here in my shop or at a symposium someplace showed doing dinner plates using large jaws with a very small tenon or recess. From that I bought 8" Vicmarc jaws and that is what I use in conjunction with a 1/16" tenon for dinner plates. 95% of my work is done with tenons and once in a while I'll use a recess. Again this works for me and your results may vary.
 
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Randy if I have to remove and remount, I will mark the recess/tenon with a pencil between the #1 and #4 jaws.

It does help to grab it at the same place and it will turn more true, and yes make sure you have it sit right against the jaw faces the firs time it is mounted or else you won't get that right the next time.

I also will set the toolrest right close to the rim and rotate by hand after remounting it, to see if the piece is turning true, a small mallet can persuade if needed ;)
I do the same, although I tend to make the tenon the foot and finish it completely and sized to match the jaws as close as I can. If I am concerned about the foot giving way, I will run CA around where the foot joins the bowl, let it soak in and go hard.
 
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