I’ve had three emails about two-part hollowforms this week, each asking for more detail than the youtube videos provide. I’d have thought the videos were clear enough to be honest, but who am I to say.
The easiest way to add the detail was to turn one and photograph it, but as my shoulder is no better I decided to use the deep hollowing rig to make it painless.
Firstly select your log for potential interest and features, cut to length and mark the centres. The question of where to place the pith is a vexed one. Many prefer it central, others prefer it off centre. The choice is yours, but I have no preference and will work to the particular log. As this is Yew I had no concerns about this issue.
This is a largish log at 8″ by 10″, but it will enable better shots. Log safely mounted between centres, the 4-pronged drive well driven in with a soft-headed mallet.
The log has been roughed down, and the top two-thirds of the shaping done. This leaves a bulk of wood at the base to support the form during the considerable stresses of hollowing. A spigot was turned on either end, one to mount the body, the other to re-mount the top section for re-shaping. The top was parted off cleanly and put to one side. The top piece was mounted in a chuck and the edge turned true, cleaned up, and then measured accurately to mark the recess on the body section. The body was then re-mounted and a straight-sided recess cut to the measurement taken from the top section. Avoid damaging this recess during hollowing.
As I needed to photograph the process I opted for a large entry hole. It actually makes no difference in a two-part form, so better to provide yourself with plenty of room to get the tools in if you’re doing this for the first time.
If this is your first deep hollow, take care and do not underestimate the stress on the tool, the workpiece, and your body. They are considerable and potentially damaging to you and the wood.
The deep hollowing rig reduces the stresses on you and the workpiece by providing a captivated tool and a constantly online cutting edge. The cutting edge should be at centre and slightly canted to provide a sheer cut, which also results in less resistance to the cut, making the process less aggressive and so safer.
The top piece has been replaced, paying attention to grain positioning. Here I have then made a parting cut to the size of some solid copper wire, and copper wire glued into the cut, leaving it proud of the surface. You may have decided to make the neck from the same log, but here I have used a scrap of padauk that was handy. The neck section was turned in a separate chuck, and a spigot turned on one end, cleaned up and sanded. The body was then remounted (still in its own chuck) and a recess turned to take the neck. The neck was then glued and clamped until the CA glue was cured. The neck is then blended into the top of the body using a shaped plug over the revolving centre for support. At this point the copper wire can be gently cut flat using the wing of a 3/8″ long-ground spindle gouge.
As this is Yew, there were inclusions which I wanted to break through during hollowing. This often looks good on the finished form, but can present problems when refining the shape and whilst abrading. Don’t press to hard with the abrasive.
The form is now ready for final abrading, sealing and finishing, and then parting off. This can be a hairy process, and if uncertain part so far and then cut off with a handsaw. The form will then be reverse turned to finish the base. I’ll upload another image tomorrow when it’s completed.
I think I’ve answered the specific questions raised, and hope it helps. Sorry it wasn’t a longer explanation but time as ever is a factor.
If you have limited turning experience I would caution against attempting a hollowform. I cannot state the strains and stresses invloved to firmly. Take your time. Make sure all holding points are secure. Check everything three times. And take light cuts and stop and check what you are doing on a regular basis. And don’t start with an 8″ by 10″ log! Start small and work your way up.