Is there a guide for tenon size?

[Bill Wilcox]

Hi All!!
I know that I have yet to post any of my work. This will be rectified soon as I am meeting a person who has a Gallery in my small town and I will be showing him some of my work.
I am in the process in turning a spalted Silver Maple bowl. The dimensions are: 10 1/2" X 4 1/2 deep.
I began turning the bowl with a faceplate mounted on the pith side of the blank. I turned the bowl and was considering making it a salad or popcorn bowl. I want a foot on the bottom and turned a 3 1/2" foot. I also turned a 1 5/8"X 3/8" tenon for the chuck. The wood on the foot was a bit spalted but it seemed quite firm. I removed the faceplate and installed the chuck and tightened it down. While I was hollowing out the inside of the bowl (lathe speed:345RPM, using a freshly sharpened 5/8 bowl gouge) the tenon sheared off sending the bowl to the floor after bouncing once on the ways. I was doing a pull cut from the center to the outside because I was getting bad tear out in the spalted area cutting from the outer portion to the center.
Should I have made the tenon lager in diameter?
Should I have made the tenon thicker? ( The paperwork for the chuck says to make the depth a minimum of 3/16" and to make the depth as small as possible.)
Are there any guidelines as to size of tenon in relation to the size of piece someone is turning?
Since the wood on the bottom is slightly spalted, should I think of using a screw chuck to hold the piece on?
I will be remounting the piece once I figure out this problem.
Thanks,
Bill

[John Keeton]

Bill, you will probably get all kinds of comments, but I will start out. Keep in mind that I have limited experience with doing bowls.

I would probably have been using a little more speed, and I rarely will attempt a pull cut coming out of a bowl. Seems they are very prone to a catch. My guess is that had as much to do with this event as anything, but I wasn't there. Is there evidence of that on the inside surface?

[Steve Schlumpf]

Bill - this is one of those times that photos would really help us out.

Just me, but I would have used a tenon around 2 1/8" to 2 1/2" in diameter and made sure that the shoulder area was at 90* so the chuck would seat properly. Make sure your tenon is not bottoming out in your chuck - again, no idea what chuck you are using , so a photo...

I will agree with John - a pull cut on the inside of a bowl is going to result in a catch - unless you have been turning for a long time and know what you can get away with. Most likely it dug in and that's what pulled the blank out of the chuck.

I would put the blank between centers, turn a new - larger tenon, and try again.

Good luck with this! Hope to see some of your work real soon!

[Allen Neighbors]

Bill, I would not attempt a bowl gouge, pull cut from the center out, if I was near completion. I might try shear cutting that direction - very carefully, making light cuts, with a higher speed. Or I might reverse the lathe, and try a reverse bowl gouge cut, from the outer rim toward the center...
But trying a cut with a bowl gouge from the center to the outside, nope. I'd catch it, everytime. I shake a lot, but it is a dangerous cut for anyone, because you're cutting uphill, or against the lay of the grain, and the bowl is thin, by this time, and it will flex against your cut, even with a decent bowl steady.
I'm sure that someone else may have some other suggestions, but these are just my opinions... if it was 2 cents worth, you'd have change coming. :)

PS: For tenon size, I turn the tenon down to about 1.75 to 2" diameter x just slightly less than 3/8 thick, that way my normal jaws are just nearly a true circle, when clamped on the tenon. Got to have a square shoulder for the jaws to rest on, also. If the wood is soft or punky, I re-enforce the the tenon with CA diluted with Acetone, so it permeates the wood.

[Keith Burns]

First, I agree with the others on the pull cut.

The tennon size could have had something to do with it as well. I submit sizing your tennon to fit the size of your jaws when the are almost totally closed. This allows more surface contact between the tennon and the jaws.

[Wally Dickerman]

Bill, a 1 5/8 in. tenon is way too small for a 10 1/2 bowl. For 2 reasons...It just isn't a secure as a larger tenon would be, and a larger tenon give more mass so that your cuts are more solid. You say you plan on a 3 1/2 in. foot. Why not make the tenon that size? As for tenon depth, make it as deep as you can without bottoming out. That is, the end of the tenon shouldn't touch the chuck. The tenon shoulder should sit firmly against the chuck.

The chuck jaws should match the size of the tenon for best results. The more you open the jaws, the more they are out of round and aren't holding as well. The best position for the jaws is if they are flush with the body of the chuck. The jaws are round, and aren't sticking out at a knuckle-busting position.

I'll second the motion that 375 rpm is way too slow for bowl turning. You get faster, better cuts at higher speeds. Experienced turners have greatly different opinions on turning speeds. In most cases I would be hollowing a 10 inch bowl at probably 1100 or 1200 rpm.

I'm assuming that your bowl is face or cross grain. This means that you should be cutting from rim to bottom when hollowing. Otherwise you're cutting against the grain, which can give you all kinds of problems.

Wally

[Bill Wilcox]

Thanks for the reply everyone. Here are more details.
1. I was using a Barracuda-2 chuck with #2 jaws.
2. Outside gripping diameter for #2 jaws are: 1 1/2"- 2 5/8".
3. I was just starting the hollowing process and was facing off and establishing my wall thickness. I had just used my parting tool to mark my wall thickness and was at the most 1/2" deep from the lip.
When I mounted the chuck I made very sure the face of the jaws were flush to the foot before I tightened the jaws.
I usually do hollow from the outside to the center but while I was facing off I was getting some drastic tear out and wanted to get past the spalting and into some harder wood.
In Wally's statement of having the jaws as close to closing because if the more open the jaws are, the more out of round the piece can be.
Maybe I need to move up to the #3 jaws since the outside gripping diameter is: 3 1/16 -4 3/8".
I will post some pictures in a few minutes.
Thanks,
Bill

[Leo Van Der Loo]

You got all good advice here, I will just give you my way of doing it, but first why did the bowl come out of the chuck ??.

Well you were using a pulling cut, it does exactly that, you are pulling on the wood while it turns and vibrating from cutting, any give here, and we talking wood, that is also spalted on top of that, and that wood will move into the pulling direction and yes out it comes, more holding power might have prevented this (different chuck jaws, and larger tenon/recess).

Your foot size is about the normal size for bowls, about 1/3 of the diameter, (nothing chiseled in stone though) now I would have used a recess and my Oneway chuck with jaws that have better holding power both on a tenon or in a recess (yes that my opinion) by having the foot 3 ½" I can have a 2" recess to hold the bowl and the wood of the foot being larger than the recess opening sits against the jaws and will give leverage to the full size of that foot, it's like having a 3½ tenon in your chuck.

You do still have the spalted wood problem, and this is never as strong as sound wood, so some CA added to soak into that wood would make it a little stronger.

As for the lathe speed, you can turn at that speed, I might use a low speed like that for roughing, but I would use something like 1000 rpm for a bowl that size.

A conventional grind bowl gouge would probably give you a better cut and in a pushing-in direction, just a thought on the tool to use

Just remember, there's not really a wrong way, any way that works for you is the right way, nevermind what I or anyone else says :rolleyes:, it is just what works for me/us :)

[Bill Wilcox]

Here are the pictures of the piece.
Leo, I was considering using a recess but I just used what I am used too.
Also Leo the piece just didn't come out of the chuck. The tenon sheared off and the tenon remained in the chuck. The gouge I was using was sharp and had a conventional grind. I do think I am going to try some CA on the tenon.
Thanks for all the advice,
Bill

[Bernie Weishapl]

Bill most time when doing bowls over 10" to 12" I use the Oneway #3 smooth jaws. Used to hold large platters or bowls these jaws will grip from 3-3/8'' to 4-1/2'' round stock. I have never had a problem with the tenon. I also use these to hold HF's. On smaller bowls I make sure the tenon is just slightly bigger than the #2 jaws of the chuck fully closed.

[David E Keller]

Good advice here so far. On the CA glue, I apply thin CA to the tenon then touch up the tenon before reversing. That's probably self evident, but I didn't want you to try and chuck up a lumpy glue tenon. Also, the CA will soak into the wood which may affect the finish later if you get it onto/into areas that won't be turned away later.

I'll bet increasing your turning speed will help considerably with the tear out. Light cuts and a sharp tool are essential for soft wood. Looking forward to seeing the finished piece.

Also, I'm not sure how you would pull cut with a conventional grind gouge. It seems as though the wings would catch every time.

[Leo Van Der Loo]

Here are the pictures of the piece.
Leo, I was considering using a recess but I just used what I am used too.
Also Leo the piece just didn't come out of the chuck. The tenon sheared off and the tenon remained in the chuck. The gouge I was using was sharp and had a conventional grind. I do think I am going to try some CA on the tenon.
Thanks for all the advice,
Bill

Bill sorry for mixing the reason it came off up, I actually did read that the tenon did break off, but by the time I had read all the other replies that had slipped my mind, so this means that we have to mostly blame the size of the tenon and the wood strength.
Looking at picture #5 I see you have not drilled the center out, it is something I recommend you do, take away that difficult to turn center where it can grab your tool and twist it around.
Also then hollowing the bowl start at the center and push your tool in towards the headstock, that way all you forces are towards the chuck or faceplate, rather than away from it.
I'll ad a picture of how hollowing from the center out would be better IMO, as like I said you cut towards the center and headstock, HTH :D

154654

[Bill Wilcox]

Leo, I took your advice and have turned a recess of 2 1/8" and a depth of 1/2". I am also going to coat the inside of the recess in CA to harden the wood. I normally do drill out the center however I have been able to set my tool rest so that it cuts the center pretty darn well. but I will go back to my standard way and drill the center out.
David, I have been doing quite a bit of practice with my gouge and I watched a video on Rude Osolnik and watched how he uses his bowl gouge. He orientates his gouge to where he is cutting just on the first 1/16" of the gouge just off of center. He also make very smooth and light cuts. Since doing my practice I have found that I am able to control my gouge to where I am cutting just off the center of the gouge. I also watch to make sure when I want to do a "conventional grind" shear cut I make sure that the flute is well over to the side. I really practice a lot and I am always watching videos making sure to see how the person is rotating and moving his tool.
I find that if you really watch the persons hand that is holding the tool handle you can learn a lot.
Thanks Leo and everyone for their assistance,
Bill

[Richard Madison]

Bill, Looking at your last picture I see nothing wrong with making a pull shear scrape cut from the center outward with a traditional grind bowl gouge. I do it on every bowl, in the center area where the bottom is flat or nearly flat. Then push in from the outer edge as Leo shows with swept back bowl gouge. May continue this cut across the bottom or not. Alternate between the two cuts to form the interior of the bowl.

There is a chunk missing near the center that suggests a catch of some kind may have happened.

[Bill Wilcox]

Richard, no catch happened. All I felt was that the piece was feeling and sounding like something was coming loose and then the bowl went boom off the lathe. Good thing I checked everything because I found that when the bowl spun off the ways, it hit the tighten lever for the head stock. The marks are from when I was doing some center cuts and then was cleaning up the very outside of the inner bowl where I had used my parting tool to establish my wall thickness.
The other issue I have is that since the time of the incident, the pictures and re-mounting it on the lathe, the outside of the bowl had started to check like crazy. I have had pieces that were greener than this out on my lathe overnight with now problems. One of the fun things I like about turning is trying new ideas. I have been reading and watching videos of Ron Kent. I see that he places his bowls in liquid dishwashing detergent before, during and after turning. He even keeps a bottle of his mixture of LDD/H2O at his lathe to keep the piece wet. So... I have tried it with a White Oak bowl that is green. I soaked it overnight, during the turning, and for one day after turning before I placed it in a oil bath. The bowl has been in and out on a 12 hour cycle now going on a month. There has been very few checks and so far am pleased with the process. So for tonight the Maple bowl will rest in a nice LDD/H2O bath till morning.
Has anyone else tried this method? If so please let me know how it has gone for you.
Thanks,
Bill

[Dave Ogren]

Bill,

Sorry to read about your problems. I always use a recess (with a slight taper) 2 5/8"+++ diameter by 3/16" to 1/4" deep for everything up to 20" dia bowls. Have great sucess, never lost one. Also, using Vic Marc chucks.

The LDD soak process use it all the time with almost no failures.

Another thing to consider is the plastic wrap around the lip. I have used that and am really happy. See Reed Gray (aka robo hippy) posts on the subject. He has posted several times about that. The wrap can be purchased from Lowes for around 7 bucks.

Good Luck,

Dave

[Bill Wilcox]

Dave, I see now where you are talking about. I think that it happened when the piece sheared off. To be honest I didn't feel a thing LOL. I saw the piece go flying and moved away and shut the lathe down.
What I ended up doing is installing my #3 jaws and clamped the chuck on the foot/tenon. I tried this morning to use the recess on my #2 jaws however when I was tightening the chuck down, the force I used was too much and the recess cracked. This bowl will now have a flat bottom rather than a foot. I also drilled the center out like I always do.
When I get close to the bottom I will be using Jeff Nicols drill bit tool. It really works slick for finishing up the inside.
Thanks,
Bill

[Allen Neighbors]

Has anyone else tried this method? If so please let me know how it has gone for you.
Thanks,
Bill

I had very good luck with the Soap Solution. I used Ivory Concentrated Dishwashing Detergent, so I mixed it 1soap/2water. It just got too expensive for me, and I began to soak in clear water. I think it's working pretty well, also. One month in water with changes every week.
Keep turning!!