Reaching the limit of diameter

[Dr.Al]

After all the experimentation with the duplicator, I wanted to get back to more conventional turning for a little bit longer before I hang the lathe from the ceiling again.

I recently bought a couple of big bowl blanks. One of them is destined to be a new fruit bowl and is big, both in diameter and thickness. Turning a bowl of that diameter is going to be a bit challenging, so I thought I'd try with the slightly thinner one first (for which I have no particular target in mind).

It started off looking like this:



If you're eyesight is good enough, you'll have figured out it's Brown Oak and 280 mm diameter, 50 mm thick. If you look closely at the left-hand edge, you'll see the wax has been removed a bit - that's where I clearly didn't get the face plate quite central and had to hand plane a little off to get it to rotate without hitting the bed. The theoretical maximum diameter for my lathe is 281.4 mm, but I think we can realistically call it 280 mm max.

Turning the outside shape was quite straightforward and, with all the practice I had last year, I didn't have too much problem turning the inside either. With that all done, it looked like this:



So far, so straightforward. However, in order to maximise the thickness of the part, I'd hot-melt glued a bit of Sweet Chestnut on the bottom and that's what was held in the chuck:



That needed to be removed and there was zero chance that I'd get this in the Cole Jaws so a different approach had to be used. I did wonder about just soaking it in Isopropyl Alcohol (which will defeat a hot melt joint), but getting enough into the right places struck me as next to impossible without removing most of the Sweet Chestnut anyway, so I decided to remove as much as possible on the lathe.

In November I went along to a meeting of Gloucestershire Association of Woodturners and the demonstrator there handed out some cubes of foam. The foam came from the company for which he worked and is typically used for insulating sea kayaks if memory serves me correctly. After cutting it to size to fit the kayaks they have a lot of off-cuts and he'd brought along a box full for anyone who wanted a block to take away.

I cut the block in half and used Gorilla Glue to stick it to a bit of oak. Once the glue had been left to set, I skimmed the outside round, leaving a slightly rough finish, but it's foam, so that doesn't really matter.



One of the rarely but occasionally handy accessories I've got for my lathe is a live centre with an M33 thread on the end. When I'd removed the bowl from the lathe after doing most of the turning, I'd left it in the chuck and just removed the whole lot. I mounted the chuck on the M33 live centre and put that in the tailstock. I could then push the tailstock up against the foam block, compressing it rather a lot:



The foam block provides the transfer of the motive force, the chuck in the live centre keeps everything concentric, at least until I cut all the way through the Sweet Chestnut block at which point I would expect the bowl to go flying across the workshop!

I took it quite gently, stopping every now and again to see what it was looking like:



I'd mostly finished the bottom surface before gluing the Sweet Chestnut on, so in an ideal world I'd just remove the Chestnut and glue and leave an immaculate surface, but I'm not that good at turning! Has anyone on here ever tried turning a bowl with a sacrificial base held on with a couple of layers of masking tape and some superglue? It'd be quite easy to get off of course, but I'm a bit nervous about whether it'd hold well enough for hollowing out the inside of the bowl.

A bit more progress - you can see that a downside of this holding method (rather than just using a live centre into a centre dot) is that the chuck stops the rest from getting close, although it didn't seem to be too much of an issue:



This is the point that I decided to stop:



I took it off the lathe and used a Dozuki to saw off most of the sacrificial block, leaving this much:



Most of that got removed with the 80 grit sanding disc on the lathe spindle (visible in the background of the photo). The last bit got removed with a random orbital sander, using a bit of plywood as a temporary work surface:



I've found my Mike's Magic Mix now so I used that for the finish. It's had one coat so far:



Side view:



I found the process of turning away the sacrificial piece without the Cole Jaws a bit daunting but it worked quite well all things considered. Perhaps next weekend I'll psyche myself up to turning the big Ash blank into a fruit bowl.

 

[Woodbloke]

Hot glue is incredible stuff but I'd never use it for this sort of spinning application. Instead I use a bit of paper sandwiched between the sacrificial chunk what goes in the chuck and the bowl; simply glue with your fave PVA, clamp and leave overnight to fully cure (slightly important!!) and you're ready to go in the morning. On the face of it, you might think that a paper bond will fail but it will 100% hold for turning on the lathe. To remove, lock the headstock with the job still in the chuck, hold the bowl firmly and just twist or use a chisel to act as a wedge on the glue line. It'll come away easy peasy and will leave next to nothing to clean up in the Cole Jaws; try it and see - Rob

 

[AndyP]

The ends justify the means Al, nice looking bowl.

I’ve often read but have yet to try Rob’s paper and PVA technique. Is the type of paper important?

 

[Dr.Al]

Hot glue is incredible stuff but I'd never use it for this sort of spinning application.

I'm curious, why would you never use it? Just because of the hassle of turning it away? I'm using it based on a recommendation from our resident turning expert, @CHJ. It certainly seems to hold very well.

It does have the enormous (in my opinion) advantage over paper and PVA that you can turn the bowl in one "sitting". It's quite common that I have an afternoon in the workshop and then the next one will be a week later, so anywhere I can avoid leaving things overnight is a big win from my point of view.

Taking this brown oak bowl as an example, I turned it in its entirety and applied the first coat of finish in an hour or two yesterday afternoon. I'll probably be able to spare 5-10 minutes tonight to add another coat of oil, but if I'd used PVA then I'd be turning the inside on Friday.

 

[Woodbloke]

I'm curious, why would you never use it? Just because of the hassle of turning it away? I'm using it based on a recommendation from our resident turning expert, @CHJ. It certainly seems to hold very well.

It does have the enormous (in my opinion) advantage over paper and PVA that you can turn the bowl in one "sitting". It's quite common that I have an afternoon in the workshop and then the next one will be a week later, so anywhere I can avoid leaving things overnight is a big win from my point of view.

Taking this brown oak bowl as an example, I turned it in its entirety and applied the first coat of finish in an hour or two yesterday afternoon. I'll probably be able to spare 5-10 minutes tonight to add another coat of oil, but if I'd used PVA then I'd be turning the inside on Friday.

Agreed yes, you can turn the bowl in one 'sitting' but quite often, I don't...I come back to it over an extended period when I feel the urge to do a bit more on 'the Dark Side'. I use hot melt glue for quite a lot of stuff as, for example, it'll stick polythene to polythene where other adhesives won't but the thing I don't like is that it has a 'thickness' for this turning application.

The other, and highly important factor is that being a parsimonious soul, the paper and glue method means that the sacrificial bit doesn't get destroyed and can be used over and over again - Rob

@AndyP - the paper is vital as it allows the glue bond to be easily broken as indicated above. Without the paper, the joint is permanent and you'd need to turn off the sacrificial chunk to release the bowl.

 

[AndyP]

Sorry Rob, just edited my post. Should have read “is the TYPE of paper important”. Newspaper? Printer paper, Thickness?

 

[Malc2098]

Back in the 60s at school, me and the WW teacher always used the paper method, no problems at all, and we turned quite a few items and I made quite a bit of pocket money. Anyway, the paper we used I think was known as cartridge paper, the sort of thickish paper you had in your art book, if that makes any sense.

 

[Woodbloke]

Sorry Rob, just edited my post. Should have read “is the TYPE of paper important”. Newspaper? Printer paper, Thickness?

As Malc says above, thickish paper or very thin card. Best not to try it with loo paper - Rob

 

[Pete Maddex]

I have used newspaper I turned a 19mm dowel split down the middle and it separated easily.

Pete

 

[Lurker]

I use newspaper too.

 

[Dr.Al]

I've done a bit more turning this weekend and made yet more bowls. The end game was to make a new fruit bowl out of a big lump of Ash. However, I thought it would be interesting to see whether the masking-tape-and-superglue trick would work on a turned bowl so I started by turning this simple bowl out of a lightly spalted bit of beech:



It was held onto its sacrificial base using two layers of wide masking tape and some superglue and superglue activator:



Once I'd finished turning the inside, I applied some firm wiggling force and peeled the masking tape off, leaving it looking like this with zero underside finishing required:



Buoyed by the success of that, I thought I'd have a go with another Spalted Beech blank, this time a bigger one (but not as big as the to-be-fruit-bowl Ash blank). The two sides looked very different, with one looking relatively plain:



and one looking really quite stunning:



With the normal sort of shape I'd typically turn a bowl, I was worried about losing that pattern so I contacted the venerable @CHJ for advice. He suggested turning it with a fairly flat bottomed shape and an undercut inside (helpfully illustrated with a picture he shared with me). It seemed a bit of a daunting prospect but I gave it a go.

As with the first bowl, I used two layers of masking tape held together with superglue:



After turning the tenon, I could mount it in the chuck:



Here we go...



Looking okay so far:



This is how far I got before the masking tape gave way:



Rear view:



As you can see, the masking tape's attachment to the sacrificial piece didn't withstand the cutting forces. With hindsight I could possibly have just used a single layer of masking tape (taped to the bowl). That side has a stronger bond purely as a result of the bowl being bigger than the sacrificial piece. The superglue would then be gluing wood to masking tape rather than masking tape to masking tape.

Anyway, thankfully I'd turned enough of the inside of the bowl that I could grip it with the Cole jaws and hot-melt glue a new base onto it:



That one worked fine for turning the rest of the inside of the bowl (and cleaning up the outside a little where I'd made a slight dent as the masking tape gave way).

Having finished making that bowl and experienced the masking tape giving way, I decided to err on the side of caution and use hot melt glue for the big Ash blank. The blank was ordered online as a 280 mm by 75 mm bowl blank. After ordering I was told they didn't have any 280 mm ones in stock but they had a bigger one so they sent me that for the same money. Unfortunately, 280 mm is already stretching the limits of my lathe, so the first thing I had to do with the blank was make it a bit smaller:



After screwing on a face plate, I could then tweak the outside with a #5 until it rotated freely:



Ready to go...



That made quite a mess!



Removing the (hot-melt attached) sacrificial base was done exactly the same as the Brown Oak one in the earlier post so I didn't bother with any photos of that bit of the process.

After applying a couple of coats of Hard Wax Oil, I managed to do a photo shoot while the sun was still out:





Profile shots of the two bigger ones.





Thanks again to @CHJ for the invaluable advice.

I think it's about time to hang the lathe from the ceiling joists again and do something else (although I haven't decided what yet).

 

[Malc2098]

Nice.

 

[CHJ]

I would say that mastering the undercutting of the internal rim and inside takes the large spalted piece up a level in achievement of tool use/control.

 

[AndyP]

Undercutting the rim always adds a bit of class INHO and as you found can aid when gripping in the those cole jaws