Thread: Bowl turning mistake

It happens.

Is the spigot bottoming out in the jaws? Are the jaws resting on the base of the bowl? The spigot looks a little long for the jaws. This could be a contributing factor.

If I was turning that size bowl, the spigot diameter would be a close to 50mm by between 4 & 6mm long.

Originally Posted by Pat

It happens.

Is the spigot bottoming out in the jaws? Are the jaws resting on the base of the bowl? The spigot looks a little long for the jaws. This could be a contributing factor.

If I was turning that size bowl, the spigot diameter would be a close to 50mm by between 4 & 6mm long.

Nah It may have been close to bottoming out the jaws,I. Do have larger jaws I could try next time that are ribbed internally.

Ok I’ll try a larger a larger spigot tomorrow see how that goes.

When I got my first chuck, I adhered to Nova's G3 50mm instructions about keeping the tenon at the diameter where the chuck jaws form a circle. About 1 in 15-20 forms would break off at the tenon. I decided to increase my tenon OD to 2 1/4". Since then, my loses are about 1 out of 100 maybe.

I know that Nova and any other manufacturer making woodworking tools have to establish safety protocols not to protect us, but to protect them. If using your jaws in the wide open position is unsafe instead of their recommendation of a smaller tenon OD, then why did they design the jaws to open a lot wider than what they consider safe? ................. Jerry (in Tucson)USA

Your problem is your choice of tenon position. Tenons must be founded in solid wood, not the sapwood as shown. The structure of wood has defined zones. from the outer, the bark, cambium layer, sapwood, then heartwood or "true wood" as some call it.

Photo 2 clearly shows the grain as "branch wood" with the pith visible, growth rings etc. Photo 4 shows the shear plane as being between the bark and sapwood with almost no heartwood visible.

The successful bowl images show that your tenon was placed in heartwood.

All very good comments, sound advice. So I will throw my 2 bobs worth in as well

I turn a few of these bowl thingys and have come up with a few things that work for me and they may work for you.

I finish the outside of the bowl or vessel to its final shape or form completely right down to applying the first coat of finish whatever it is and generally its some sort of oil here to bring up the grain, this also helps to prevent any discolouration/stains etc due to handling etc. It then gives you a clear idea of what the internal form must take. The foot is turned with an eye for the aesthetics and to what jaws I have to hold it by without damage. So my 'tenon' is highly controlled and usually no more than 6-8mm thick and the most common shape is a bead.
The bead is perhaps the weakest part of process at this point, so I run CA or super glue around where the bead meets the bowl and let it harden. The hardening wont be instant so go and have a cup of coffee etc, but you will have a tenon now with its best chance of survival.

Now at this point it should run pretty darn true in the chuck and depending the timber , size or dia etc you may want to add your steady to the bowl. I routinely use my steady here and by doing so rarely have any failure, in fact I cant remember when I had a failure here.

I have made my own steady set up using either roller blade wheels or skate wheels, either way, the tyres on the wheels must have some give so they wont mark the bowl. I then pedantically set up the steady with an equal amount of pressure on each wheel. That gives a small amount of compression that holds the bowl in a firm grip but not so tight that it will distort the bowl when you bring it to its final wall thickness. Always imagine here it will distort, this will prevent you from over tightening the steady wheel grip.

During turning listen, listen, listen. Its rare that you wont have some sort of warning before the tenon breaks, spontaneous breaks generally occur when you have a fault within the blank its self and often they are not apparent. But even they will give you some sort of a hint as you hollow it out. If they are minor but still potentially dangerous use CA to strengthen. If they are large and on a incredible blank use Araldite or similar but always give it time to go off. What you may find much of this sort of strengthening will be turned away in the process and the CA filled ones will largely blend into the form and not be noticed.
But above all else drop the speed, I routinely turn on difficult blanks around 500 rpm or less . The idea that you must turn at some mind boggling speed is bulldust. The real idea is produce some thing of beauty on an amazing and difficult blank that you're proud of. .

Quite interesting thread as I had the exact same possibility happening turning the same wood. I've found a few ways to get good results, first and foremost I try to have a very wide (or large) spigot with jaws of the same or very close diameter of the spigot.

With this timber it compresses and will rip/tear easily, so being gentle with sharp tools certainly helps. I also turn this somewhere around 500rpm for something that size and slightly faster for a smaller piece.

I generally use spigot sizes of 60mm or 88mm using Vicmarc VM100 jaws of 100mm or the two step 70mm jaw sets for this stuff if one can make a good spigot on reasonable timber. In your case I would make, or consider making a sacrificial block that I glue to the blank. I tend to make the sacrificial block as big as possible to spread the load, so far almost no issues with iffy material.

Below is a small finished bowl of the same timber, a blank of the same timber which will be going onto the lathe in the next few days and finally one of my iffy timbers with an attached sacrificial block adhered to it ready for turning. The spigot size for reference, is approximately 60mm in diameter and is matched to the larger jaw of my two step 70mm Vicmarc VM100 chuck jaw set.

Mick.

Mango_20221122_104922.jpg

Originally Posted by Mobyturns

Your problem is your choice of tenon position. Tenons must be founded in solid wood, not the sapwood as shown. The structure of wood has defined zones. from the outer, the bark, cambium layer, sapwood, then heartwood or "true wood" as some call it.

Photo 2 clearly shows the grain as "branch wood" with the pith visible, growth rings etc. Photo 4 shows the shear plane as being between the bark and sapwood with almost no heartwood visible.

The successful bowl images show that your tenon was placed in heartwood.

Ah this is a great point, generally im aware of heartwood and sap but for some reason when im selecting a piece from the stockpile i am consumed by thinking where the first mount will be to get it into the lathe to then start turning as this is guided from the arborist cut the pieces for me. Ill consider this from now on. Thanks

Thanks so much for all the responses so much experience here. I guess each piece would need assessment as to how best mount it. Think I’ll refer to the raffan book on turning I’ve got buried in the bookshelf ha

no no please keep this running, ie can others show their stuffups and mistakes, then others can provide answers, options, remedies so we can learn.

I have plenty of blanks to get through so I expect plenty of failures to present here for assessment ha. Best way for me to learn

Also I could hear and feel by my 3rd gouge cut internally was feeling a bit different and since I backed away a little it came off in a fairly gentle manner, don’t remember the RPM but wasn’t full speed that’s for sure but I aware it was occurring

Lots of useful tips in this thread.

Thanks
Nathan

Wouldnt you know it I had one come out of the chuck today Luckily the tenon was over size 46mm it is now 36mm the right size. I should have taken an image but its still in/on the screw chuck, will post one tomorrow. Its a very small piece in Redgum 4 x 3 small as its for a swap and is going to the Texas. Oh and it will have convex spirals, they love em over there.

Here we the small Redgum on a screw chuck with backing plate, EEE applied and just about to to be turned around to finish the open and hollw

If I am using a spigot (I do when green turning) I make it at least 1/3 the diameter of the bowl. Using that ratio I've not had a tenon snap off, well not in the last thousand bowls... or off how many I have turned before that...

Like everyone else, I have the occasion green blank escape the jaws, but that is no drama at the green stage.

Nathan, looking at the smallest diameter of your tenon it appears to be close to 1/5 the diameter of the piece. That would be too small for me.

I think I can also see some spalting in the first photo of your piece, which means the wood will be weaker in and around those areas. If that is the case, extra steps like a CA application to those areas is needed, especially if in or near the tenon.

Managed to turn some new bowls without them flying off today was a good day!

Larger tenons or spigots whatever they’re called and enjoyed making a larger bowl this time around around 300mm starting diameter. Reached the limits for my jaws so I now see why a larger set of jaws could appeal for these sizes

Did take a while to core out the centre for the larger bowl but really enjoyed having a cut start right at the edge and carrying it through smoothly to the centre was satisfying. I’m enjoying the intuitive feedback you get from the tool to know when your cuts going well or not

Anyway having fun making a mess for some gifts before Xmas. Need more experience so I’ve got plenty more blanks ready to go

pleasure watching your progress, gives my dreams hope.

what type of wood are you using and I presume its 'green' if so then how long to dry it out or is that microwave job?

I am so looking forward to retirement No 3 this time its final then we need to move house, rebuild my workshop and hers, then replace my ute with another Falcon ute but my plans for it are awesome.
Dont think I will be sitting around.