Monday 9 July 2018
There are other options available when making hollow forms that enable greater access for the hollowing process. Another option for this is parting off the front of the form, which after hollowing is then reinserted into a recess slightly smaller than the diameter of the form itself.
This method is similar to the process for box making and enables a small hollow form to be made without the use of a dedicated hollowing tool. Within this project I have used a bowl gouge to remove the material inside the form. For a deeper form a hollowing tool should be employed due to the overhang of the tool tip from the toolrest.
I have designed this hollow form so that not only the need for a hollowing tool is removed, but also the sanding/finishing process is almost nonexistent. This is because texturing and scorching are used instead to add visual interest to the off-the-gouge finish, which is used here.
Adding to the presentation of the final piece, the form has been designed with a round base. It is placed onto a plinth which has a small concave recess turned into the top surface; this way the form can be articulated into different positions to give a sculptural feel. The idea can be adapted to include staining and other forms of texturing. By experimenting, design alternatives are possible.
Try different texturing effects such as using a stonemason's scutch hammer to mark the wood before scorching. You never know what new texturing ideas you will come up with. For this project I used an oak (Quercus robur) post measuring 120mm square x 170mm long and a piece of laminated kitchen worktop measuring 150 x 150 x 36mm. The project can be scaled down proportionally for 100mm square material.
32mm spindle roughing gouge
8mm spindle gouge
12mm bowl gouge
6mm parting tool
3mm parting tool
Mark the centre positions on both ends of the end-grain blank and mount between centres. Using a spindle roughing gouge turn the blank down to a cylinder and true up the front face using a bowl gouge. Once true, use the gouge to turn a spigot to fit the jaws of your chuck, then profile the outside of the form. Produce a flowing curve from the top all the way to the base
Reverse the form and tighten into the chuck and bring the revolving centre up for added security. Clean up the front face using the bowl gouge but stop short of the centre by around 10-20mm. On nearing the revolving centre, slide the centre back out of the way and continue by turning a rim for the opening. This rim/opening wants to flow up away from the front face
Using a 3mm parting tool, part in to a depth of around 6mm in from the outside of the form. The front face is going to be the rim of the form. Produce another cut next to this so that you have a recess of around 10mm wide from the front face. You now have the finished hollow form profile
Part down into the form from the shoulder you have produced, stopping around 10-20mm from the centre. Start parting 1.5mm from the left shoulder to leave a registration to work to when making the internal recess that will be used to fit the front face/insert back into the form. The form is now ready to be parted through
Using a bowl gouge remove/hollow the material from the inside of the form. Push the tip a short distance into the wood with the tool turned anti-clockwise towards the direction of the cut, which will be from the inside to the outside diameter. Angle the tool in towards the cut to an angle of around 20 degrees and as the cut progresses deeper into the form, rotate the tool further in an anti-clockwise direction until eventually the tool is rolled over and the left flute is almost horizontal. Remember to only cut on the lower wing of the tool. Hollow out the material until the wall thickness is around 10mm and don't forget you are going to turn concentric rings on the outside later
Using a skew chisel placed horizontally on the toolrest in a trailing mode take fine cuts with the toe of the tool from inside out, up to the registration mark left from the parting process. Stop half a millimetre short of the register line and produce a recess depth the thickness of the parted front face plus 2-3mm so that when the insert is glued back into place, it will sit lower than the rim surface by a few millimetres. Once to depth, open out the recess up to the register mark checking regularly the fit of the parted insert. Once cut, blend and create a gentle radius on the inside edge of the rim to break the harshness of the sharp edge
Insert the lid into the recess – do not glue at this stage – and bring the revolving centre back into place. Using a 8mm spindle gouge with the flute horizontal and the tool in a trailing mode, turn concentric lines approximately 1-2mm deep at equal spacing into the front face of the form. Do not cut into the shoulder of the opening
Remove the insert and scorch with a small blowtorch. I placed the insert onto a piece of brick and cleaned up all the wood shavings from the immediate area, ideally this should be done outside. Check your insurance and make sure you have an appropriate fire extinguisher nearby in case of any incidents. Scorch around the area in stages so you don't overheat the insert
Glue the insert into the form, bring the tail centre back into position and apply slight pressure while the glue cures. Once cured, use the spindle gouge with the flute rolled over facing you and the tool tip on centre height, drill out the centre of the opening by taking gentle cuts, then blend the opening so that it flows down into the form
Wrap a piece of 240 grit around a rod and use this to finish the opening with the lathe speed at around 100rpm. If you prefer, with late speed low, roll a piece of abrasive into a tube and use this, but keep lathe speed to a minimum to avoid potential binding
Turn a small piece of waste wood to fit into the chuck jaws and replicate the internal profile of the entrance hole of the form – this will be used as a friction drive. Place a small piece of tissue between this and the entrance hole of the form. Bring up the revolving centre into the hole left by the drive centre and apply light pressure. Using the 12mm bowl gouge blend the base of the form so continuing the profile into the base, reducing the spigot as you are doing this. Always remember to work from outside diameter inwards and watch the unsupported flute does not contact the spigot material. Turn the waste material down to around 10mm
Using the 8mm spindle gouge add the final grooves into the base of the form, stopping just short of the spigot. Once the grooves have been turned, cut the spigot carefully from the base of the form using a fine hacksaw blade. Clean up the shavings, then blend the base using 240 grit abrasive. The next step is to scorch the rest of the form. Once cool, spray the form with Chestnut Satin Acrylic Lacquer to seal the scorching onto the wood
Preparing the base
You can laminate wood together or use a solid piece of timber to create the plinth, but if using a laminated block remember, as with any laminated wood, the glue lines may fail so check the wood is sound before using. Cut the piece to size using a bandsaw, finish the edges on a bench belt sander and finish by hand using abrasive. Mark the centre of the base and drill a hole to suit the screw chuck. If you do not have a suitable screw chuck, then the base could be glued to a waste block
Using a 12mm bowl gouge turn a concave recess into the face of the plinth around 40mm diameter x 8mm deep, with lathe speed set to around 400rpm. Be mindful to make a note of how far the screw chuck protrudes into the base so not to turn into it. Add a ply spacer to the screw chuck if it is too long, but be aware that this may weaken its holding strength. Once to depth and the concave form is smooth, using 240 abrasive lightly sand the recess using a 50mm hook-and-loop arbor in a drill. Once complete, remove and finish the base with your desired finish before applying four rubber protectors to the base
The finished scorched hollow form in oak is now complete and situated on its very own plinth