Thread: Bowl turning mistake

Originally Posted by NeilS

If I had the jaw size I'd be using a spigot close to 4" on a 12" green blank that I was coring, especially with that amount of spalting.

There is always another jaw size you need and then a chuck for every size... it's a slippery slope...

Aint that the truth

Originally Posted by NeilS

There is always another jaw size you need and then a chuck for every size... it's a slippery slope...

Originally Posted by hughie

Aint that the truth

Tell me about it. Then change over Chuck Manufacturers . . . The collecting jaw sets begins again.

Just to throw the veritable cat amongst the pigeons (just to see what happens!) - I rarely if ever turn bowls on a tenon - always use a recess, sometimes only 3 or 4mm deep depending on the timber, and use the jaws in expansion mode. Have only ever lost one bowl which I turned too thin (sub 2mm) and I use the 'rim' that remains to carve the feet from.
Now going to duck and dodge the abuse from all the nay-sayers!

Originally Posted by TTIT

Just to throw the veritable cat amongst the pigeons (just to see what happens!) - I rarely if ever turn bowls on a tenon - always use a recess, sometimes only 3 or 4mm deep depending on the timber, and use the jaws in expansion mode. Have only ever lost one bowl which I turned too thin (sub 2mm) and I use the 'rim' that remains to carve the feet from.
Now going to duck and dodge the abuse from all the nay-sayers!

I also only use recesses when final turning my bowls. Done that forever, on countless bowls.

But, I do use a tenon at the green turning stage and when coring.

I find it easier to re-grip a tenon when it comes to re-turning a bowl that was previously green turned in the event that I can't immediately get a satisfactory grip on the recess left inside the bowl. More adjustment is possible with an irregular tenon than with an irregular recess for positioning the bowl for re-turning.

In the case of coring I just find it easier to know the depth of the core with a tenon. I reckon that there is also more of a risk of hitting the jaws with the coring blades if a bowl blank is mounted with a foot recess.

Otherwise, I'm recesses all the way, even with hollow forms. And, once the outside of a piece is turned, sanded and polished I just use the completed recess to hold it for finishing the inside of the piece, at which stage it is all done. I never go back to touch the foot.

So, no abuse coming from this direction...

Originally Posted by Tonyz

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.

I have a big stack of mango from an arborist that chopped it down so I’m cutting into manageable sections to rest for months. It’s still a little wet but the bowls ive turned from it I’ve given away locally and haven’t cracked or moved much as it’s same climate.

Today I tried a different technique for the base that I saw on YouTube. I much prefer this method to mount going forward and I think I’ll pick up a larger 120 chuck also.

This was from a she-oak blank from WA and was an absolute gem to turn. Really enjoyed it, my finishing needs work but still came out nice I think





Cheers
Nathan

Originally Posted by TTIT

Just to throw the veritable cat amongst the pigeons (just to see what happens!) - I rarely if ever turn bowls on a tenon - always use a recess, sometimes only 3 or 4mm deep depending on the timber, and use the jaws in expansion mode. Have only ever lost one bowl which I turned too thin (sub 2mm) and I use the 'rim' that remains to carve the feet from.
Now going to duck and dodge the abuse from all the nay-sayers!

This is what I’ve tried on my most recent bowl that I just posted above. I agree and really enjoy this technique, I’ll certainly try to do this again in future bowls

I personally prefer tenons, due to a variety of reasons, but if mortices float your boat, go for it.

WA She Oak is very nice to turn.

Delbs, if you come across some radiata pine in a suitable size for a bowl, turn that. That will teach you about tool control, as when you get a good finish off the tool in pine, you are going to get a good finish in 99% of timbers.
(Grey Box Burl, I am looking at you!)

I have had less failures using a recess than a tenon. That said every bit of wood is different so have a good look and a think.
Regards
John

PS I often use this chuck that only goes a about 5 mm deep with a recess. I think its only spun off one time in many years of doing bowls.

So, I'm late to the party and it looks like you have things pretty much under control, but I did notice a couple of things in the photos of your first post that have me wondering.

No-one else has mentioned 'em, which surprises me a bit as they're what I think of as common mistakes and I'm sure we've all had experience with 'em when we first started turning.

So, perhaps I'm completely off base and just seeing things that aren't there... but I'll offer these up as likely causes.


Firstly, that's a fairly 'steep' dovetail and looking at the marks it looks like the edges of the jaws bit deeper into the bottom of the spigot than at the tip of the jaws. Ideally, for maximum grip, the dovetail angle should closely match the inside of the jaws, so that any jaw marks left behind are pretty much parallel. So I suspect the main culprit was too steep a spigot angle.

If I'm right, then a good catch could've caused the spigot to skew over just a wee tad in the jaws, making the blank unbalanced and causing things to skew over even worse... until 'twas over as far as it could go and suddenly stopped short. This'd happen in a split second at turning speeds and with a heavy(ish) blank the sideways load can be equivalent to good sideways whack with a sledgehammer! Ripping at least part of the spigot off is pretty much par for course.


Secondly, what I take for the jaw marks appear to be widely separated. Were the jaws nearly closed when the piece was mounted or did you have large gaps between each jaw? The spigot & jaws should be sized so that the jaws are nearly circular (normally @ nearly closed) when fully tightened. That way the whole length of each inside jaw face is in contact with the spigot, rather than just the edges biting hold.

It looks to me like you had a poor size match between the two... of course, I could be way off base.


Shall I shut up now?

Originally Posted by Skew ChiDAMN!!

Firstly, that's a fairly 'steep' dovetail and looking at the marks it looks like the edges of the jaws bit deeper into the bottom of the spigot than at the tip of the jaws. Ideally, for maximum grip, the dovetail angle should closely match the inside of the jaws, so that any jaw marks left behind are pretty much parallel. So I suspect the main culprit was too steep a spigot angle.

If I'm right, then a good catch could've caused the spigot to skew over just a wee tad in the jaws, making the blank unbalanced and causing things to skew over even worse... until 'twas over as far as it could go and suddenly stopped short. This'd happen in a split second at turning speeds and with a heavy(ish) blank the sideways load can be equivalent to good sideways whack with a sledgehammer! Ripping at least part of the spigot off is pretty much par for course.


Secondly, what I take for the jaw marks appear to be widely separated. Were the jaws nearly closed when the piece was mounted or did you have large gaps between each jaw? The spigot & jaws should be sized so that the jaws are nearly circular (normally @ nearly closed) when fully tightened. That way the whole length of each inside jaw face is in contact with the spigot, rather than just the edges biting hold.

It looks to me like you had a poor size match between the two... of course, I could be way off base.


Shall I shut up now?

Mate your spot on. I didn’t realise this at the time but the angle on the tenon is what I was trying to match for the jaws because I do have a set of actual dovetail jaws.

Then in a brain fart moment discovered the thread adapter m30 was installed in a chuck that had a default set of jaws not the dovetail set, I tried but couldn’t get the adapter swapped over so I thought the jaws that could fit would be fine. Your right I can now see how it wouldn’t be gripping the tenon all the way around and putting too much pressure around it.

Then to compound it further perhaps my bowl gouge wasn’t as sharp as I’d like it to be or I was taking to deep of a cut with poor angles and made it come off. It was too small a tenon also

Very good feedback thanks mate. All lessons learnt I’ve tried to overcome in subsequent bowls, have had one come flying out or break since but still get vibration when coring/hollowing out the bowl at certain parts.

I might take photos of my my bowl gouge also to see if it can be improved angle or shape on the tormek.

Learning as I go bit by bit

Merry Xmas everyone

Originally Posted by orraloon

PS I often use this chuck that only goes a about 5 mm deep with a recess. I think its only spun off one time in many years of doing bowls.

Snap!

IMG_2233.JPG

That's the one that I also first used in recess mode. I don't use it anymore but continue to use recesses to hold and complete all pieces for final turning.

A recess is stronger than many realise. Recesses as shallow as 2 to 3mm will suffice on smaller pieces. In most cases I have a foot ring and the only challenges there is getting that wide enough to hold and for it to still work as a design feature.

Here is a cross section of a foot showing about a 2.5mm recess and the supporting foot profile. Note: this is just the remaining foot area of what was a larger bowl that was turned off for another purpose. Some turners who use a recess bury them in the base of their pieces, but using recesses doesn't preclude having a well defined foot...

Recess foot cross section.jpg

Recesses do need to be correctly formed and the diameter needs to be very closely matched to the jaw size used. The downside of that is having enough jaw sets for different sized pieces. I'm still waiting for a manufacture to bring out a 65mm jaw set to save me making my own of that size.

It's just one method and likely to suit some more than others. Perhaps not the first thing to try if a new turner, but at least an option to try later at some stage.

Originally Posted by NeilS

Snap!

Recesses do need to be correctly formed and the diameter needs to be very closely matched to the jaw size used. The downside of that is having enough jaw sets for different sized pieces. I'm still waiting for a manufacture to bring out a 65mm jaw set to save me making my own of that size.

The closest I know of is the Vicmarc two step jaw for the VM100 chuck. I have one and it is possibly my most used jaw set, for internal use I can get away with 70.5mm if I'm really careful, the jaws when fully closed measure 70mm. Mostly though 71-72mm is what happens.

These jaw sets are the perfect jaw set for the recess for clock making, at least for the mechanisms from Timberbits. For their USA made clock mechanisms, they are perfect.

Mick.

Originally Posted by Optimark

The closest I know of is the Vicmarc two step jaw for the VM100 chuck. I have one and it is possibly my most used jaw set, for internal use I can get away with 70.5mm if I'm really careful, the jaws when fully closed measure 70mm. Mostly though 71-72mm is what happens.

Nova also has 72mm jaws.

The nearest to what I need is the VM120 standard jaws, which are 68mm on circle. My thought at this stage is to turn those down to 64mm on a metal lathe. I would only do that for about half of their 12mm depth, which will leave the metal as manufactured where the jaw meets the screw plate to retain its strength in that area.

Neil, I had totally forgotten about the 120 jaw sets for this size; I'll try to keep that useful information in my porous brain for future reference.

Mick.