• We invite you to join UKWorkshop.
    Members can turn off viewing Ads!

Bottom thickness!

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

Chris152

Established Member
Joined
26 Apr 2017
Messages
2,370
Reaction score
154
Location
Cardiff
Following on from Clive's yarn bowl thread, I got to wondering about base and lower side thickness. I tried once-turning some green cherry bowls thin so as to avoid cracking and all seem ok, but they took a lot of effort on my part, removing the bowls from the lathe to check thickness and on some stopping too soon. But the truth is that the ones that worked ok are not as stable as bowls with thicker bases and lower sides.
Is it just turners that like thin bases and lower sides on account of the skill it requires and in reality, from a user's perspective, a heavier base is better (more stable) in most circumstances? Fruit in bowls (for eg) is rarely balanced in terms of weight.
 

Phil Pascoe

Established Member
UKW Supporter
Joined
29 Jan 2012
Messages
21,180
Reaction score
1,549
Location
Shaft City, Mid Cornish Desert
Sometimes what seems great to turners isn't necessarily great to everyone else. I used to get marked down in competition for boxes, pots etc. with lids a fraction loose - it was better apparently to have them fit just tightly, so that when you lifted the top the bottom stuck until it fell off and hit the floor. It was common then for people to moan that the base had gone out of round and the top no longer fitted anyway. I could never quite see the sense in making them so tight - if I wanted airtight, I'd use a Kilner jar. :D
 

CHJ

Established Member
Joined
31 Dec 2004
Messages
20,130
Reaction score
73
Location
Cotswolds UK
Chris152":214kgyfv said:
...Is it just turners that like thin bases and lower sides on account of the skill it requires and in reality, from a user's perspective, a heavier base is better (more stable) in most circumstances? Fruit in bowls (for eg) is rarely balanced in terms of weight.
Rarely would the off-set weight of fruit in a bowl be sufficient to topple a thin based or narrow based bowl.

This one has never toppled in the 14 years it has been in use.
fb.jpg


I think wall/ base thickness aesthetics are more to do with the form of the article than any rule of 'must be'. once due attention has been given to the risk of splitting due to relative wood movement with humidity changes.

The only time I personally feel happy with a piece that does not appear balanced in the hand due to uneven distribution of wood thickness is in Vases intended for dry flower arrangements where the heavier base and internal reduced depth aids in is practicability.
 

Attachments

CHJ

Established Member
Joined
31 Dec 2004
Messages
20,130
Reaction score
73
Location
Cotswolds UK
phil.p":mp44igth said:
Sometimes what seems great to turners isn't necessarily great to everyone else. I used to get marked down in competition for boxes, pots etc. with lids a fraction loose - it was better apparently to have them fit just tightly, so that when you lifted the top the bottom stuck until it fell off and hit the floor. It was common then for people to moan that the base had gone out of round and the top no longer fitted anyway. I could never quite see the sense in making them so tight - if I wanted airtight, I'd use a Kilner jar. :D
I have always tried to engineer the fit between base and lid on my pieces intended for practical use so that any subsequent slight wood movement would not prevent a usable fit without obviously exposing obtrusive gaps due to ovality or binding etc.

Piston fit lids that are going to remain practical can rarely be made without ultra seasoned wood subjected to subsequent staged seasoning through rough and then finished turning.

Even then with the majority of wood species, the fit in my experience is likely to vary between tight squeaky & a loose fit depending on season and location.

I once made the mistake of putting a couple of my 50+ year old swiss file containers on a tool rack held on with terry clips, a moments inattention clipping the lid instead of the body of one saw the files end up on the floor a few days later when the lid-body interface changed dimensions.
 

Alpha-Dave

Established Member
Joined
18 May 2015
Messages
330
Reaction score
120
Location
Durham
Is it art or functional? Thin walled is often more aesthetically pleasing, especially if pierced, however completely non-practical.

There is a guy in the woodturning club I go to who sells bowls and pots etc. He cannot sell bowls that are lightweight: he says that people are attracted to them and pick them up, then make a face that says ‘something is wrong’, then they pick up a thicker/heavier one and they buy it.

In my opinion it is possible to achieve practical and beautiful but examples are rare.
 

MikeG.

Established Member
Joined
24 Aug 2008
Messages
10,158
Reaction score
661
Location
Essex/ Suffolk border
Chris152":102ctbn1 said:
........ removing the bowls from the lathe to check thickness......
Why not measure from a known point on the lathe? In fact, if you screwed together a base board that rested against the motor housing, say, or the tailstock, with an upright and then a horizontal pointer set to the centrepoint of the bowl before the bowl was placed on the chuck, all you'd have to do was offer that up to the work every so often and look at the gap from the end of the base board to its reference, and that would be the thickness of the bowl base.

Now, I'm feeling slightly dizzy and nauseous. I've gotta get outta this sub-forum quick...... :)
 

CHJ

Established Member
Joined
31 Dec 2004
Messages
20,130
Reaction score
73
Location
Cotswolds UK
Chris152":1xd7vj01 said:
…... removing the bowls from the lathe to check thickness ..
Normal practice is to measure blank thickness with callipers before you start, adjusting for any spigot or socket that is formed.

Then check depth of hollowing with a depth gage as you go.

Like this: -
depth guage.jpg
or a simple home made equivalent.
depth guage2.jpg

Or drill a hole from the front face when mounted to a controlled known depth and don't cut deeper than this.

No need to remove from lathe which in most instances is undesirable.
 

Attachments

Chris152

Established Member
Joined
26 Apr 2017
Messages
2,370
Reaction score
154
Location
Cardiff
Maybe I'm just a clumsy fruit-bowl filler - quite likely, I tend to go for the most 'economic' (lazy) ways of doing things around the house.
My preference overall is for wider rims that reduce to normal-thickness sides and base, but that kind of variation's not good for green turning apparently (different rates of drying). So no real options if i want to once-turn green.

Concerning checking base thickness, I felt a bit dizzy trying to picture your idea, Mike! The only constant I can see is the location of the base (and the tenon can be shallower on some than others in my turning, so it's the depth from the bottom inside of the bowl to the tenon that's at issue), the variable is how far the inside of the bowl (opposite from the headstock) is reduced in relation to that? Maybe a fag-packet-type drawing would clarify but don't expect you to design it for me. :)

I'd not seen that device before, Chas - I might look out for one, tho the bowls I'm doing now are from half logs so it's all a bit variable and imprecise at the outset.
But both your comments have reminded me of a rusty set of calipers that I got with my lathe - they've got to help with establishing the thickness of the sides toward the base, and therefore with the base (the sides run smoothly into the base). The reason I'd forgotten them is my preference for thicker rims - I can remove them as far as the rim but they won't come off the bowl.
Can you get turners' calipers that register a measurement that you can read before removing them from the part being measured (if that makes sense)? I've searched but not found.

Thanks all for your thoughts.
 

Chris152

Established Member
Joined
26 Apr 2017
Messages
2,370
Reaction score
154
Location
Cardiff
Brilliant - thanks Chas.

edit to add - one of the things I really like about woodturning is that you don't need that much kit, once you have the basics. But it's also apparent that in keeping my head down and trying to get better at basic turning, I'm missing a few tricks - first the negative rake scraper in Clive's thread (which I reground today, and very happy with how they work), now a depth gauge and external thickness calipers - I'd not seen either before. I really appreciate the advice I get on here, brilliant forum.
 
Top