Would appreciate advice for the initial steps in beginning the "second" turning of a twice turned bowl. About one year ago, I "wet" turned three black walnut bowls each about 10" diameter leaving a wall thickness of 1" and a generous sized tenon (first time for me using the twice turned technique). The bowls dried and as expected ended up with an oval shape (and fortunately with no cracks). I mounted the first bowl securely using a jam chuck with tail stock support and re-turned the tenon round with a dovetail for my VM chuck. While still in the jam chuck I turned the outside of the bowl. When I reversed the piece using the chuck to turn the inside, the external surface had a fair amount of wobble and I needed to re-turn it round. My question is should I have re-turned the tenon, reversed it and then turned both the outside and the inside of the bowl? If I did it this way, would the proximity of the chuck to the outside bottom of the bowl restrict access for my gouge to turn the outside bottom of the bowl? I haven't started the second and third bowl yet. Are there other options for this initial process? Thanks in advance for your suggestions.
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"Second Turning" Advice Needed
- Thread starter John Husokowski
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I used to experience that - However I learned the first thing I do is to true up the outside of the bowl and form the foot, and then very gently and carefully true up the tenon to "perfect circle" dimension, making sure there's a true square flat for the shoulder of the chuck jaws to register on when gripping tenon - That usually takes care of the worst of the runout - (wobble) I will often sand and finish the outside before turning it around to do inside - if there's only a slight runout on the outside then it isn't a lot to worry about except when you plan to turn the bowl thin for some reason which is when slight variations in thickness caused by aforementioned runout become glaringly obvious - but usually I can get the bowl outside finished and a trued up tenon that when turned around and re-chucked (I often will mark tenon with a dot for "top" that lines up with #1 jaw of chuck too, so I can register it in the same spot into the chuck jaws) , the bowl typically runs nearly perfectly true (You couldn't see any wobble, but might feel a slight bit - a thousandth of an inch or so) However, if you plan your bowl properly and the bottom and foot are high enough off the tenon, you can usually do some shear scraping from the foot to a bit outside where you can true up outside (or just continue the shear scrape cut - this is where the ellsworth or jamieson or Irish grind can excel)
I do what you have done, but instead of a jamb chuck I find it easier to use a 4-5” disc chucked in my 4jaw as a friction drive (I use a piece of rubber drawer liner between the disc and inside of the bowl). Sometimes I find a little bit of wobble when turning it around. Just yesterday I twice-turned a 9” cherry bowl and had this, it didn’t take much with a negative rake to even out the outside before I turned the inside. Then I reversed again onto Cole jaws to turn off the tenon.
I put the rough bowl between centers using a friction drive ( wood chunks of different diameters, threaded to go directly on the spindle, sometimes I just use a chuck/jaws, I dont worry about padding anything, the ID will be cut).
True the tenon, and out from the tenon for an inch or so. The bowl is put into the chuck and turned. If warped significantly I round the ID to about 75% 1st, then finish turn the OD. I’ve found that not removing some of the ID results in a warped OD when the ID is cut.
True the tenon, and out from the tenon for an inch or so. The bowl is put into the chuck and turned. If warped significantly I round the ID to about 75% 1st, then finish turn the OD. I’ve found that not removing some of the ID results in a warped OD when the ID is cut.
John
I do all of my bowl turning outboard with no tailstock involved, so the following may be irrelevant to you this time, next time and probably to most other forum members anytime.
* I add an internal dovetail recess when I'm green turning and remount on that with deep jaws when I'm 2nd turning. At the green turning stage I leave a tenon on the foot should I have to true/reform the internal tenon, but that is mostly not needed.
* Mounted on the internal dovetail recess I re-turn, sand and polish the outside to the finished stage.
* I then reverse and hold the piece by the recess that I formed in the foot while turning the outside and re-turn, sand and polish the inside while held in expansion mode in the chuck jaws.
* The piece is finished at that stage and ready to be removed from the lathe.
* A downside of this method is that I have to have many dovetail jaws sizes to allow for the appropriate foot size to suit each individual piece.
* for me, everything else about this method is an upside...
I do all of my bowl turning outboard with no tailstock involved, so the following may be irrelevant to you this time, next time and probably to most other forum members anytime.
* I add an internal dovetail recess when I'm green turning and remount on that with deep jaws when I'm 2nd turning. At the green turning stage I leave a tenon on the foot should I have to true/reform the internal tenon, but that is mostly not needed.
* Mounted on the internal dovetail recess I re-turn, sand and polish the outside to the finished stage.
* I then reverse and hold the piece by the recess that I formed in the foot while turning the outside and re-turn, sand and polish the inside while held in expansion mode in the chuck jaws.
* The piece is finished at that stage and ready to be removed from the lathe.
* A downside of this method is that I have to have many dovetail jaws sizes to allow for the appropriate foot size to suit each individual piece.
* for me, everything else about this method is an upside...
The tenon on any bowl I make always has a finish cut on it before I turn the bowl around. When you remove stock the wood moves to a degree. If you made the tenon first and the removed stock from the outside I feel the tenon is not in tune with the outside of the bowl so the last cut, a finish cut on the tenon trues it to the outside of the bowl.
I haven't twice-turned a lot of bowls, but I'm wondering if the wobble was just from your tenon. I used to use a scraper and even ground one to my dovetail angle. I've since learned to make the diameter match the nearly closed jaws, and I cut them very cleanly with a sharp spindle gouge. No more fuzzy tenons and no more jaw corners digging in. (and a lot less wobble when I mount it in the chuck)
John H.,
I agree with your concert about problems with lack of clearance near the chuck after reversing and think it's better to shape the outside and tenon first.
In addition to the good advice so far, especially that to, when truing up the tenon, make a good flat contact ring on the bottom for the chuck jaws to bear against, make sure the tenon is not so long that it touches the inside bottom of the jaws when reversed. You probably already do this, but just in case...
Also, in general, make sure the "corner" between the flat and the tenon is clean with no stray fibers. Before mounting the chuck for reversing, Chris Ramsey when turning a cowboy hat carefully cleaned the threads and the mating surfaces of both the chuck and the lathe spindle so no dust or debris would prevent the chuck from running true. That could cause a problem with a bit cowboy hat!
It's also useful to use plenty of pressure by hand when tightening the chuck on the cleaned up tenon - I sometimes rotate it a bit just before and while tightening.
And as Darryl mentioned, it's best to size the tenon diameter so it is very close, just slightly larger, than the diameter of the jaws when closed. If the tenon diameter is too big, the eight "corners" of jaws will contact the wood first and as they compress the wood they can indent the wood unevenly, and the curve inside the jaws may not even properly contact a too-large tenon - this could make a lot of wobble.
I think someone already mentioned that the dry wood can move, even the outside is perfectly turned. Assuming the wood is perfectly dry, when wood is removed anywhere stresses in the wood can cause the wood to move. (I had one case where internal stress relieved it self rapidly with a loud "crack" I heard from across the room!) If you have the time, maybe true the tenon and turn the outside shape, then give it some time to "rest". That's the way I learned to turn twice-turned lidded boxes where even though dry well dried, the wood can move. For those, when turning the roughed box to approximate final shape I let it sit in the chuck for a few hours, or even better overnight then true up everything again before continuing.
The only other thing I can think of is if the dovetail angle you made was too steep the jaws might close first on the end of the tenon rather than securely at the base. As discussed recently in another thread, I mostly quit making dovetails on a tenon (and a recess) and just let the ends of the jaws bite into the base of the cylindrical or nearly cylindrical tenon. If the tenon is well sized for the jaws, the holding power is not compromised.
Are you a member of a club? Many have mentors with a lot of experience who aren't afraid to help! Maybe someone could come and take a look when you are about to reverse your next bowl.
JKJ
For the second turning, if the bowl is not overly deep (less than 5 inches), I reverse mount it between centres using a normal spur drive. Before turning, I rotate the bowl by hand to make sure it is as close to true as possible. Sometimes a minor adjustment is required as most bowls will warp during drying. The tenon is then trued and the outside is turned and sanded. The bowl is then chucked on the outboard so the interior can be turned and sanded.
For deep bowls, I will mount it on the outboard by the bottom tenon and turn a recess on the bowl’s interior near the rim. I can now reverse mount it in the mega jumbo jaws in expansion mode. This allows me to turn the tenon true along with the exterior of the bowl. Then it can be mounted by the tenon for interior turning.
For deep bowls, I will mount it on the outboard by the bottom tenon and turn a recess on the bowl’s interior near the rim. I can now reverse mount it in the mega jumbo jaws in expansion mode. This allows me to turn the tenon true along with the exterior of the bowl. Then it can be mounted by the tenon for interior turning.
Thanks for the gouge mention, Brian. I always start between centers to prep a holding method, wet or dry. For me that is a faceplate or glueblock. Then Yes, the swept back wing is designed for the sheer scraping on the outside of the bowl to sneak up on the wobbling surface.
I turn mostly bowls so all mine are second turned unless it’s a natural edge or hollow form. I have several sizes of jam chucks and select the one i will use in relation to the size of the bowl. I use a 6-7” jam chuck for 12” or smaller bowls and a plate type chuck for any larger bowls.
Smaller bowls I will first flatten the tenon and clean the foot area up, determine the size of the foot and turn complete the outside of the bowl and usually sand to 120 grit. I will then finish the tenon adding the dovetail, flip the bowl and finish the rim and turn the inside. Getting the foot flat and the tenon as near perfect as possible. You may still get some wobble but it should be easily taken care of with some shear scrapping. If there is a lot of wobble then it is usually caused by the tenon not seated properly in the chuck or the tenon was not cut properly.
For larger bowls I use a plate type jam chuck and do the same process as with smaller bowls but only turn about a third of the outside of the bowl, finish the tenon, then flip the bowl, true up the top rim, and finish turning the outside. I can shear scrape the bottom third if needed. I don’t like the wobble when flipping a large or small bowl and this method works for me. I end up with a bowl running true with this method. This also helps if you are adding some embellishments to the outside of the bowl, like a band where you need to define the band with a skew cutting a small grove, which is harder if you have a wobble. I have also used this method when turning smaller bowls and needed to cut a groove for a band that was dyed or used pyro on.
Most of my bowls are 1/4”-3/8” thick depending on size and I have made a few thicker depending on style or use. When turning the inside, for me, it’s always easier if the outside is running true, I establish my thickness at the top inch or two of the bowl and on my final cut I will have a couple of fingers bracing the outside of the bowl to prevent any flex, harder to do if there is a wobble.
I continue the inside turning about 1-1/2” of depth at a time. Usually by the time I’m 3/4 of the depth of a bowl some stress is released in the wood and you end up with a wobble by the time the bowl is finished with some species of wood.
Smaller bowls I will first flatten the tenon and clean the foot area up, determine the size of the foot and turn complete the outside of the bowl and usually sand to 120 grit. I will then finish the tenon adding the dovetail, flip the bowl and finish the rim and turn the inside. Getting the foot flat and the tenon as near perfect as possible. You may still get some wobble but it should be easily taken care of with some shear scrapping. If there is a lot of wobble then it is usually caused by the tenon not seated properly in the chuck or the tenon was not cut properly.
For larger bowls I use a plate type jam chuck and do the same process as with smaller bowls but only turn about a third of the outside of the bowl, finish the tenon, then flip the bowl, true up the top rim, and finish turning the outside. I can shear scrape the bottom third if needed. I don’t like the wobble when flipping a large or small bowl and this method works for me. I end up with a bowl running true with this method. This also helps if you are adding some embellishments to the outside of the bowl, like a band where you need to define the band with a skew cutting a small grove, which is harder if you have a wobble. I have also used this method when turning smaller bowls and needed to cut a groove for a band that was dyed or used pyro on.
Most of my bowls are 1/4”-3/8” thick depending on size and I have made a few thicker depending on style or use. When turning the inside, for me, it’s always easier if the outside is running true, I establish my thickness at the top inch or two of the bowl and on my final cut I will have a couple of fingers bracing the outside of the bowl to prevent any flex, harder to do if there is a wobble.
I continue the inside turning about 1-1/2” of depth at a time. Usually by the time I’m 3/4 of the depth of a bowl some stress is released in the wood and you end up with a wobble by the time the bowl is finished with some species of wood.
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Dave Landers
Beta Tester
This is how I normally do it. I call it a friction chuck (the bowl isn't jammed into anything, just friction between something in the headstock and the live center). I finish and sand the outside before reversing it into a chuck.
Yeah that can happen. A few reasons:
Wood moves. Even tho it's "dry", removing wood will release tension and it'll move. The difference between between-centers pressure and "flying free" in a chuck might do it. Sometimes, if I feel things are moving too much, I'll do a pass on the outside and inside, then set it aside, then turn it a third time after a few days.
Maybe you didn't get the tenon as good as you thought. The flat is more important than the tenon angle - that's where the alignment happens. I usually true up the tenon first thing (just in case something happens, I can always mount it in a chuck) - but then t's a good idea to touch it up right before you reverse it, in case things moved while you were working the outside.
If it's wobbling just a tiny bit, you can probably ignore it. If your wall thickness varies by like 1/16" due to the wobble, nobody's gonna notice.
The first turning when the wood is green the tenon must be made oversized so that there will be enough material to true it up to the diameter needed for the best grip. That is why I like the profile jaws on the OneWay chucks because the tenon diameter can be larger then the minimum diameter and still have a firm grip. The use of a recess can be the correct diameter on the 1st or rough turn and as it drys it will shrink and then can be re-turned back to the correct diameter.
You all came up with some great advice and very helpful pointers. Truing up the outside and foot then forming the tenon or if the tenon is formed before the outside to go back and re-true it as it may have been knocked off center. Being precise when forming the tenon in regards to the dovetail angle degree, sharp angle where the dovetail meets the flat, depth, "perfect circle" diameter and making sure that the shoulders are dead flat. Looking out for tension release changes and maybe waiting a day or two to finish the bowl. I do try to be compulsive when forming my tenons not only to prevent wobble but also to prevent a bowl flying at my face. I did make some wooden "angle finders" that match the angles on my VM chucks and a cheat sheet for my different jaws when planning a tenon (below). My first turned bowls have a pretty wavy rim and not sure if a disc type friction chuck would work well but I did see on Kent Weakley's online video about twice turned bowls that he used a disc with two different depths that he attributed to Glenn Lucas to accommodate the waviness of the rim (
View: https://www.youtube.com/watch?v=2qor9wes5zk
). I have not used tenons on my bowls yet but do use them on my plates. I do belong to my local turning club and will also seek advice there as well
I will incorporate your group advice when I turn my 2nd and 3rd bowls.
Thank you all for your input. Greatly appreciated.
). I have not used tenons on my bowls yet but do use them on my plates. I do belong to my local turning club and will also seek advice there as well
I will incorporate your group advice when I turn my 2nd and 3rd bowls.
Thank you all for your input. Greatly appreciated.
Attachments
Picture perfect tenons, thank you.
John, the friction disc doesn’t touch the bowl rim. It’s small enough to fit inside the bowl. Put a piece of leather, thin rubber mat, or even paper towel over it. The rim of the disc applies friction to a circle inside of the bowl to drive it with pressure from the tailstock.
Ron, Got it, I misunderstood. Thank you.