Small tenon + large vessel = vibration?

[Prashun Patel]

For the life of me, I have been unable to make finishing cuts on vessels that are larger than 8-9". I get a lot of vibration around the rim, particularly on the inside.

It occurred to me that despite my improving technique, perhaps my tenons are just too small. I use the stock 50mm jaws with my Nova G3 chuck. My tenons are almost always about 2" in diameter.

So, the question is, would a larger tenon (4"?) reduce the vibration?

Do larger tenons also make it easier to reverse the vessel and have it turn concentrically? I also find that devilishly difficult when re-turning: (I true up the tenon and outside first, but when I flip and remount in the chuck to finish the inside, it's almost always out of center.)


Any help appreciated.

[charlie knighton]

is this on dry roughed out bowls or green wood bowls? at what speed are you turning to do the finishing cuts? can you feel vibration at that speed on the lathe?

[Thom Sturgill]

Yes and no. A larger tenon WITH LARGER JAWS would probably help (especially on a heaver chuck like the SN2). Nova publishes limits for each chuck/jaw combination for each configuration (face or spindle - expansion and contraction). The standard jaws are probably the worst set they sell. Many if not most of their jaws require a dovetailed tenon - those want a straight tenon but do not have serrations (like the 'powergrip' jaws) to grip with.
The tenon should be the size of the jaws when nearly closed to give maximum contact between the jaw and the wood, too large and only the edges dig in.

Other issues include the fact that you should finish as you go - never come back after you have hollowed about 1" past an area. After that you will have lost the internal support of the wood and it may have moved, or may flex to the pressure of the tool.

I recently watched Lyle Jameison demo turning a HF and he says he avoids the problem by going old school and using a faceplate. Doesn't need a steady rest either. Even a small faceplate gives both better diameter and better length limits than a chuck will. You do lose a bit more wood, but as they say - that stuff grows on trees.

[Steve Schlumpf]

Prashun, to answer your question about a larger tenon solving the vibration issue... I would have to say not necessarily. There is something else going on here. In addition to Charlie's questions, I would be more concerned with how well the chuck jaws are mating with the tenon. It is critical to have the correct grip; anything off and you will introduce vibration.

There are two types of tenons; those that use a 90* mating surface and those that use a dovetail. In my case, I use a Oneway Talon with the number 2 jaws for almost everything. I used to have problems when reversing forms but upon closer inspection found that when the chuck jaws were closed all the way, the edges of the jaws protruded just a bit, most likely the cause of when the pieces were made. I closed the jaws and used a file to smooth off the faces of the jaw set. That made a huge difference!

One other thing, in addition to the correct mating junction (in my case, 90* where the tenon/form intersects), I also use a pen to mark the slight gap between the # 4 and # 1 jaws. Always aligning those marks allows me to remove and replace the form as often as needed without causing an out-of-round condition.

[Prashun Patel]

Thanks, Guys.

I turn mostly green wood. It's when I re-turn the dried roughout that I have problems. The lathe is not perceptibly vibrating; it's just that I get chattering during the finish cuts near the lip.

Thanks, Thom, for those insights. I always find it hard NOT to want to come back to the rim. Takes a lot of restraint to try not to improve it incrementally...

[Prashun Patel]

Ok, thanks, Steve. I'll check those things. I do notice that when I put my tenon in the chuck, the bottom of the vessel sits flush, but as I tighten, I can NEVER get all 4 jaws to stay mated to the bottom; there's always a little space that gets unevenly tweaked between the jaw and the vessel bottom. I'll check them for being coplanar. THANKS!

[Thom Sturgill]

If you start between centers so that you have the dimple on the bottom of the tenon, you will find that useful for reversing. Start the re-turn by reversing and truing the tenon and base which should have been slightly oversized while green. This should make the item turn truer when re-mounted in the chuck.

Down here in Florida, we often turn to finish while green due to the nature of the local woods and the local temperature/humidity - otherwise they often mold while drying - and not the pretty spalting type mold either.

[Sean Hughto]

Does it vibrate from the start of the re-mounting? If so, you may want to make yourself thicker rough-outs. I do stuff like 15" diameter at at least 2" thick in rough. Tenons are usually 3 to 4" diameter and 1/2" deep- and a Oneway Stronghold is my chuck. I true the tenon with the rim pressed by the tailstock against a rubber shelf lining covered plywood disk at a slow speed - ya just need to round that oval. Once mounted in the chuck, I do the outside working from the base to the rim - it's a little weird working on the headstock side, but you get the hang of it. At this point, the thick rough is still providing plenty of support, even at the rim and even if the wood was really wet and ovaled 3/4" or whatever. Finally, I attack the inside, and like the others have said, once I get past the rim, I don't tend to go back unless I want to use the 80 grit gouge to smooth the chatter. Perhaps this is all stuff you know and do, but for what little it may be worth ....

Good luck!

[Richard Coers]

No mention of wall thickness that I can see so far. What thickness gives you trouble? I steady thin walls with one hand and make the cut with the other. It will settle down a little after you get in the first inch or so. I always resharpen before making the last cuts. Too much pressure on the heal of the bevel will also set up vibrations. Lift the handle a little. Too agressive at thinner walls is not good either. I've been doing larger work around 16" dia, 6" tall, in soft maple, with 5/16 walls green. I use a 5" tenon on these.

[John Keeton]

For whatever it may be worth, I never use anything other than the 50mm jaws for my HF turnings, and I nearly always make inside finishing cuts as well as outside finishing cuts after completely hollowing the form. However, I have either a steady rest on the form, or tailstock support. I would add that the bottom of the form is often much less than the tenon - sometimes 1", depending on the form.

I rarely turn and return, although Schlumpf does that most of the time. The few times I have done that, I still don't have the problems you describe. I think it is an issue of lack of support in your case.

As to re-centering, I do as Steve does and mark the tenon. I don't see how a larger tenon would aid in that situation. I would, however, true up the tenon, and remount the piece in the chuck before truing up the outside. I think that sequence is bound to cause some concentric issues. Then, when you true up the outside, and then do the inside, you will have even wall thickness.

[Reed Gray]

Well, it could be a bunch of things. First, the tenon, or recess which I prefer. Dove tail jaws do give a mechanical advantage, a locking wedge joint. If the bowl is climbing out of the jaws a tiny bit, your tenon is most likely not square/flat, but even if it is off by a tiny bit, it shouldn't be much of a problem. If your tenon is too deep, which I don't think it is, then that makes for more problems. A tenon should be in the 1/4 to 1/3 the diameter of the bowl, so a 2 inch tenon on a 9 inch bowl is a bit minimal, but it can be done. The only time that amount of run out is a problem is if you are trying to turn to less than 1/8 inch thick walls. When you reverse, there is always some run out. If you are running with 1/16 inch of run out, that is +/- 1/32, which is really close. As long as the jaws are tight enough, there should be little problem with the mounting. These are the basics, which you most likely have figured out.

Next would be solving the problem of a bowl that has been hollowed out. The problems are mostly on the inside of the bowl, same as when roughing, or green turning to final thickness. There is more mass before you hollow, so vibration is not a problem. As the walls get thinner, this is where the saying 'the bevel should rub the wood, but the wood should not know it' comes into play. Also, 'Hold it as you would a bird. Too tight and you kill it. Too loose, and it flies away'. When the vibration starts, we tend to clamp down on things. The more you clamp down, the worse the bounce gets. Your left hand only rests on the tool, it does not hold it down on the tool rest. The left hand does not rest on the tool rest either. It took a long time for me to learn not to clamp down like this. I think it was Chris Stott who did a demo for our club and started the cut on the inside of the bowl, then dropped his left hand to his side, turned to face the club and was chatting merrily away as he continued the cut. This is a handy skill to know about, though a bit nerve racking to practice at first. If you check my bowl turning clip on You Tube I show this. You do not need to totally remove your left hand from the tool, but keep it very gently floating on the tool. This is where you learn to 'feel' the wood cut. I have never used a steady rest. I learned to do it with my left hand. Tool/bevel rub pressure = hand pressure. If your hand is getting hot, you are pushing too hard. Some times smaller tools help. If you are rigid, the shock/vibration goes two ways, one is into the wood, and the other is into you. If your arms can become like shock absorbers, you are getting there.

The wood does 'adjust' as you cut. Part of this is because the wood cuts differently through end grain and side grain, and uphill/down hill, so there will always be some run out. It is almost impossible to come all the way back to the top for one continuous finish cut. Here is where blending in the stop and start points is done with a shear scrape.

I hope this makes some sense, but it really is all about feeling the cut.

robo hippy

[Jim Underwood]

What Reed says is accurate. I've seen Stuart batty turn thin bowls from rim to bottom and never get chatter. Chatter is caused by too much tool pressure. It's a tricky thing though. I've not mastered it but I've had enough success to know how to begin correcting the problem.

[Joe Meirhaeghe]

I turn lot's of vessels of all sizes from 3" to 30" long and use about the same size tenon on all of them. I use the standard size jaws with about a 2 1/4" to 2 1/2" tenon. I also use a steady rest on all of them regardless of the size of vessel. Never had any vibration issues.

[James Combs]

I turn lot's of vessels of all sizes from 3" to 30" long and use about the same size tenon on all of them. I use the standard size jaws with about a 2 1/4" to 2 1/2" tenon. I also use a steady rest on all of them regardless of the size of vessel. Never had any vibration issues.
What Joe said except I haven't done anything larger then about 12".

[robert baccus]

All good advice. One way to square the bowl when tightening up is to use a oneway tailstock with the3" cone reversed. Put a little pressure on the bowl as it seats. You could improvise one as well. I very seldom use a tenon for the reasons you mention. My go to is a 3" faceplate with a screwed on glueblock of very stout wood---no wasteblock crap. I like them 2-2.5" thick and it will last for many bowls. Face the glueblock square when mounted on the lathe and square the blank between centers. A generous amount of thick CC and bring up the tailstock for pressure. Piece of cake to reverse this way--a cone in the faceplate hole and a friction block to drive it. Leave the bowl mounted through the finishing--it will always remount true in remounting. Don't sweat the strength--I do pieces of 100#+ this way. Especially good on end grain pieces (vases)--screws hold crappy in soft green endgrain and you lose no expensive wood.

[Prashun Patel]

Thank you for all the responses. I will try to refine my tenon forming technique. I will also try a faceplate. Appreciate the responses.

[robert baccus]

I never figured out if you are irish grind cutting or nose cutting. Most turners have ignored nose cutting the last few years. I use both but on a thin finishing cut I find it much easier to do a nose cut with a 3/8" honed DB gouge with the bevel just touching. Might try it.