Hollow Forms – More:
Richard Findley turns a more challenging hollow form.
Keeping in mind the areas I need to improve, the plan for this second hollow form is to turn a more enclosed shape, one that will require a tool with a crank in the shaft to reach into the inside shoulder. I now know the limits of the tools I am using much better due to unwittingly making my first form bigger than I perhaps should. I have also identified a couple of the tools that work well with my style of turning and I have become reasonably familiar with them since turning the first form.
I decide there is little point making a form with a tiny hole as this is very challenging, especially for only my second attempt. Photographing such a form for the article would be quite uninformative as you really can’t see anything on the inside. It is possible to turn a form with a hole on the side to show what goes on inside during the turning, but I feel this will add considerably to the level of difficulty so I decided against this approach. I also found during the turning of the first form that I’m still at a stage where being able to see what I’m doing is helpful to me. So I’m going to play it by ear a little and see how small I can comfortably make the hole while still being able to see inside and with it still working with my planned design, which ultimately is the most important factor. It needs to work as a finished hollow form.
Having made one, the theory and the practice have become closer together for me. This one should be easier, although I’m offsetting my new found experience by making a more difficult design. I think the biggest challenge will be using tools with a crank in them to reach into the corner, but otherwise this should be reasonably straightforward, but we shall see!
Now I know the limits of the tools, I know this form will not be as tall as the first. I also know I want a more enclosed form so probably a slightly heart-shaped piece would work best. As before, I make a couple of sketches and check my books for design inspiration. Once again, Mark Baker’s Woodturning Projects: A Workshop Guide to Shapes shows a few examples and the curve of one catches my eye. I’m not keen on the neck, but the body shape works well for what I have in mind. My sketch feels like it’s missing something around the hole though, so you’ll notice I have marked a rim detail with a question mark. I’ll see what works as I turn. This freedom is not something I’m used to with my production work and it feels a little strange, but I’m rolling with it.
Wood and tools
I am using more of the ash (Fraxinus excelsior) wood I got from my friend George Watkins.
He assured me that ash is a good timber to get into hollow form turning as it is quite user friendly and reasonably stable. I’m interested to see how much, if any, movement these hollow forms will produce. The two tools I got on best with the first form were the carbide tipped tool and the shielded ring cutter. It seems that a straight cutter can reach a surprisingly good way into the curved shoulder of a hollow form, but I will certainly need some degree of crank or swan neck to reach into the more difficult areas. The one piece of theory that I know about these cranked hollowing tools is that to ensure they work safely, the cutting tip should not protrude much past the straight shaft of the tool otherwise the twisting force produced can be potentially dramatic and uncontrollable. It will be interesting to see how this goes.
Making a start
As before, I mount the ash log section between my four prong drive and live ring centre and rough it down starting with my large bowl gouge and finishing with my big spindle roughing gouge. With the ends trued up I mount it onto my faceplate. I did consider using the alternative of holding the timber in my chuck, but as the faceplate method worked so well last time I see little point in changing my method here. Once secured to the faceplate, I once again mark out the blank with the area where the screws sit, a section for waste, the form itself and the final piece of waste, which is next to be turned away. I gradually develop the outer shape of the hollow form with my 12mm spindle gouge. This is just spindle turning so my main focus is on producing a pleasing curve to the profile. Although the final form will have a relatively small base, I leave the lower portion quite chunky for now so it can withstand the forces of hollowing. This does make it more challenging to visualise the final shape, but I will develop both the inside and outside further as I proceed.
The first step to hollow any form is to drill a central hole as most cutters perform best cutting on the side rather than on the end. I use the same 21mm drill I used last time mounted in my Jacobs chuck in the tailstock. As always when drilling on the lathe I go steady at a relatively low speed and clear
the flutes of the drill regularly.
With the hole drilled I pick the first tool. I like how slender the carbide tipped tool is at the business end, which allows the toolrest to be close to the work. Clearly this isn’t essential, but it feels more natural to me. I have marked with a pencil the size of opening I feel works best with the design. In the end it isn’t that much smaller than the first hollow form I made, but it is smaller and I have the challenging curved shoulder I originally planned for.
I decide to see just how much I can do with the straight tool and it is surprising how far round I can reach. I will definitely need some degree of crank to finish it off, but nowhere near as much as many tools offer. Having had success with the shielded cutter on the last hollow form, I reacquaint myself with it before adjusting the head to produce the required crank. I try a few adjustments of the links on the tool until I find just the right balance between being able to reach where I want to get to and being controllable. Oddly the
cutter is a good way beyond the line of the shaft and so theoretically should be quite unstable, but I find this works perfectly for me. I suspect, as I found when I first used this tool set up to someone else’s liking, this setting won’t suit everyone.
I gradually develop the inside of the shoulder regularly checking the thickness with my callipers, but I am so focused on cutting it perfectly and achieving an even thickness that I forget my earlier idea of leaving some thickness around the opening for a rim detail. It’s too late now though so I’ll have to just carry on and come up with something else to finish off the rim. I can’t shake the feeling that it’s going to need something.
Continuing to hollow
The lower quarter seems to take forever to get right. I am determined to get the flow of the shapes right while keeping the inside as free from tool marks as possible. I feel like I am removing a lot of wood and the evidence seems to back that up, by the shavings I regularly blow out of the form, but my callipers tell me there is still plenty of wood left. Eventually, with some work on the outside of this area as well, I am happy with all of the elements: the curves, the level of finish, the balance of the shape and the wall thickness. To check this I unscrew the faceplate and hold it up the right way. It’s amazing the difference seeing something the right way up or from a different angle can make. Fortunately, I am happy with my work so far and decide it is now almost time to sand.
Throughout the turning process I am thinking about the rim detail, or lack thereof. There isn’t enough wood to turn anything particularly decorative so I tidy the edge of the hole with the wing of my spindle gouge. It looks improved immediately, but still needs something. It occurs to me that perhaps just a simple cut line might be enough to give a little interest to what is currently quite a plain top surface. I draw a pencil line to see and this confirms that it should do the trick so I sharpen up my point tool and cut a small ‘v’-shaped groove, which I think works well. Simple, but effective and I like that.
Sanding the outside is straightforward and I take it from 120–400 grit without a problem. I realise that one
of the problems with my first hollow form were the few tool marks that remained on the inside. Usually tool marks like this can be sanded out with some coarse abrasive if you struggle to perfect it with the tool, but because access is restricted on the inside of a form it’s impossible to apply enough pressure to the wood with the abrasive to completely get rid of the marks. With the knowledge learned from my first attempt I made sure the tooling is much better this time so the sanding of the inside is easier and generally much more successful. As before, I sand as far into the form as I safely can with my fingers before switching to a sanding stick, which has Velcro attached and allows sanding in tricky places like this. Again I sand from 120–400 grit on the inside.
Happy with my sanding, I remove more timber from the base leaving just a small spigot attached to the waste on the faceplate and blend the sanding as much as possible before sawing the form from the waste and finishing the base by hand. I apply a coat of lemon oil to protect it while it settles and store it in my office along with the first form.
Four weeks later…
After leaving the forms on a shelf in my office to settle and fully season I take them down to the workshop to have a closer look. I am pleased to see they haven’t cracked, but they have moved as wood tends to do. They have gone from being round to slightly oval in shape when viewed from the top. They are also a little heavier than I expected them to be. This is an odd thing to say as wood loses weight as it dries so the forms will be lighter now than they were four weeks ago and I don’t remember thinking that when I turned them. They seemed quite flexible and almost fragile when they were fresh from the lathe, but as the moisture has left them they will have stiffened and they actually seem a little thick now. One lesson I immediately take from this is that you can go thinner than you think with green hollow forms. This doesn’t particularly take anything away from them, but it is something to bear in mind next time… if there is a next time!
I apply four coats of satin hard wax oil and they are finished.
Oval vs round
The technique I used here was largely based on my discussions with George Watkins, as this is the way he does his hollow forms – turned thin in one hit and allowing them to move. I am aware that an oval form may not be to everyone’s taste so the way to avoid this would be to turn the forms a little thicker and let them settle and fully dry out. Then remount on the lathe, preferably on a chuck, which avoids large chunks of timber, which are likely to crack during seasoning, and finish turn. This would ensure a perfectly spherical form when viewed from the top. I spoke to another friend of mine who does this and he explains that whole books could be (and probably have been) written on this subject, but when I push him, he recommends a wall thickness of 15–20mm if you want to re-turn them, although there are a lot of variables including species of wood, size and shape of the log it comes from and where on the tree it’s cut. This would be something to experiment with in the future, but for the purpose of these articles, this technique
of turning in one hit has been ideal as deadlines are always looming.
Despite my earlier complaints about turning green wood, I have enjoyed making these hollow forms. There is clearly a steep learning curve with the many techniques involved, but I was able to draw on my past experience to see me through to a relatively successful outcome. I am always my own harshest critic so all I can see with them is the many flaws, but on the whole I am pleased with the way they have turned out. Next time I would definitely make them thinner, perhaps 4mm or even less, and I might be interested to experiment with the techniques involved in turning them twice to achieve a more circular form.
My advice to anyone wishing to have a go at turning hollow forms would be to speak to someone with experience who can let you try out a couple of different tools before committing to spending a lot of money on what could be the wrong tool for you. I would also recommend sourcing good quality timber
as this could well be the key to success with this and with most types of turning.