Bowl Faults

Monday 9 July 2018

This month I would like to show you a few ideas for repairing and working with faults. The project features one of my rough turned bowl blanks which had dried exposing a split on one side and as I discovered, there were quite a few options available for working with the split.

I chose to open up the fault and add an additional fault on the opposite side and then made some steel staples to hold the fault together. I found that the wall thickness of the ash bowl needed to be fairly chunky to take these steel staples, but I was pleased with the overall effect that was achieved.

There are a number of other options available, including using thin leather strips to lace up the faults, using wooden butterflies to hold the fault together, and also filling some of the cracks with brass powder and then using a cyanoacrylate.


1 The finished bowl

2 Here is a roughed out ash bowl blank measuring 380mm (15in) by 180mm (7in) which had dried with a 50mm (2in) crack on the end-grain side of the bowl. The distinctive heartwood and growth rings show where the bowl is most vulnerable to cracking. Sometimes very fine hairline cracks go unnoticed at the roughing out stage and open up whilst drying. If the bowl blank was inverted you could see that it will have come from the centre of the tree

3 To save the bowl blank, I chose to make a feature of the fault and also add what will look like another fault on the other side. On your bowl blank, you will need to make a pencil mark on the opposite side of the bowl to mark where you are going to open up the original fault and add an additional fault on the opposite side of the bowl

4 Mount the roughed out bowl blank on the lathe and use a dome-shaped wooden disc mounted in the chuck. Ensure it is a good size and fit to the inside of the bowl. Place the bowl over the disc and bring the tailstock up to hold it firmly in place. If a blank has distorted and gone out of shape, it is a good idea to put the bowl blank in a chuck and take a couple of cuts out of the inside to enable it to sit nicely on the wooden disc. Start by cutting the dovetail with a 10mm (3/8in) spindle gouge (the plug in the middle will be left on). This will give the centre alignment for reverse chucking later, but ensure it is sufficiently small enough to sit inside the centre of the jaws. Lathe speed here should be around 700rpm

5 Next, make a shearing cut on the outside of the bowl. There is no bevel contact on this cut as the wood is making contact straight onto the edge of the 12mm (1/2in) bowl gouge. The important point here is to have the flute facing the wood and well over to the left hand side. Ensure to begin with the foot of the bowl working outwards towards the rim. Working in this direction should give the cleanest cuts as you are working with the growth rings of the bowl blank

6 Use the same 12mm (1/2in) bowl gouge but this time making a pushing cut with bevel contact. This is a very fine cut cutting at the tip of the tool. As you are starting with a roughed out bowl blank which will already be the desired shape, only a few cuts are needed to achieve a finish to the outside shape. Lathe speed is still around 700rpm

7 Usually, only a small amount of shear scraping is needed on the outside, starting first of all with the round nose scraper. This tool suits the curved shape at the base and is used at around a 45 degree angle to the wood straight from the grindstone with the burr left on. Lathe speed is about 600rpm

8 Repeat the same step here but instead use a straight edged scraper. The same angle of approach is required, leaving the burr on from when it was ground. I find this way works well for me

9 For this project, we are not going to have a dedicated foot as we will make a small 'V'-cut with the tip of a skew chisel. This will be darkened using a piece of wire to achieve a friction burn

10 Here is the burn line being added using a cheese wire which is a piece of braided stainless steel wire with two wooden toggles for handles. The wire needs to be held in one place with a small amount of pressure to allow it to get hot and to burn. Lathe speed is around 1200rpm

11 Next, power sand the outside to a finish starting with 120 grit followed by 180, 240, 320 and 400. If you wish you can use a finer grit, such as 600 or 800

12 Reverse the bowl and mount in the chuck. Having cut the rim flat, it is now time to make a few cuts part way down the side of the bowl, stopping just below the original fault but still using the long-ground 12mm (1/2in) bowl gouge. Lathe speed is about 800rpm

13 Keep an eye on the wall thickness using double-ended callipers. The wall needs to be fairly chunky to take the steel staples that will be added later

14 Cut down and open up the original fault using a coping saw. Use the spindle lock to hold the piece stationary

15 Draw lines on the opposite side of the bowl where it is going to be cut. This will enable you to get rid of the small faults, which will also be cut out with the coping saw

16 Use a die-grinder and work from the compressor to allow you to carry out the final shaping. Alternatively a dremel type flexi-drive or similar could be used

17 Next, use a small gas burner to scorch the inside of the cut-outs

18 To finish off the burning and to reach the parts the gas torch will not burn, use a hot wire pyrography machine. Ensure to use this at maximum temperature

19 Finish the gouge work on the first three inches or so then start shear cutting to allow you to clean up the edges after the cuts are made with the coping saw. Use the 32mm (1 1/4in) round nose scraper with lathe speed around 600-700rpm

20 Make all remaining cuts on the inside of the bowl with the 12mm (1/2in) short ground bowl gouge. The shorter ground bevel works better around the curve in the bottom of the bowl. Next, shear scrape once again with the 32mm (1 1/4in) shear scraper. Increase lathe speed to 1000rpm

21 The rim and inside now require power sanding with the drill and the sanding pad angled so that the two faults will pass the pad without pulling the sanding disc from it. Only the bottom of the pad should make contact with the wood. Lathe speed is around 500rpm

22 To make the pins use two 150mm (6in) nails, cut off the heads and beat them on an anvil to a hammered finish, using various tools to try and give an aged appearance. These can also be bent into shape to give the effect of a large staple

23 Offer the staple up over the fault, using a hammer to mark a reference point for drilling the holes. They will need pre-drilling, otherwise this size of staple into this wall thickness is likely to split the wood

24 Next, blacken the staples by heating them up with a gas torch (ideally to cherry red) and then plunge into old engine oil. Leave to cool off and then wipe clean

25 Drill four holes in the previously marked places and use the spindle lock to hold the lathe stationary. Then, knock the pins into place with a hammer

26 The only thing left to do is to reverse- chuck and to remove the dovetail. Mount the bowl on the lathe over a domed piece as wood, as before, but this time use a piece of router mat between the two and the tailstock and cut away the dovetail with a 10mm (3/8in) spindle gouge. The pip in the centre will be removed off the lathe with a skew chisel. Then, sand with the usual grits ranging from 120 to 400. Ensure to do this at a fairly low speed of about 500rpm and take great care. Alternatively you could use a vacuum chuck instead

27 It is now time to finish the piece, using Danish Oil. Once dry, apply a further two coats. Other finishes can be used if preferred, on or off the lathe, such as sanding sealers under oils or waxes, but this will depend on which finish you prefer

28 This is the finished bowl, with faults made into a feature using metal staples