Louie Powell
|
Mark
I think the situation you described wither the flaw was on the surface actually presented TWO potential problems.
1. How to fill the void while minimizing the tendency of the filler to spill out of the flaw 2. How to fill the void so that the resulting patch remains securely a part of the finished turning
As to the first issue, the short answer is 'patience'. The long answer is that the void needs to be filled in stages, and this could take hours if not days with the filler curing between applications.
You can't do anything about gravity, which means that if the void extends around the side of the bowl, the filler will tend to run 'downhill' around that side. One possible solution is to construct dams that holds the filler in place until it cures. Something like what you were trying to do with saran wrap, but possibly on a smaller scale. Fill a portion of the void, let it cure, remove the dam and if necessary construct another so that you work your way around the side of the bowl in stages. And yes, this is messy so work in an area where spillage won't hurt anything important. If you have to overfill the flaw, and get some runs, that's ok - just let the filler cure and return the bowl to smooth the surface.
Others have raised the issue that repairing a surface flaw is difficult because the patch is on the surface, and if it doesn't adhere tightly to the piece, it can fly off as you are turning and sanding. One solution is to use a rotary tool and burr to deepen the flaw in a way that provides a stronger bond to the underlying wood. Think about how the dentist grinds out a cavity before doing a filling.
If the flaw is very large, it could be helpful to add some reinforcing. For example, you could drill holes in the bottom of the flaw, turn some dowels out of the same wood and glue those into holes in the turning to fill some of the void, and then add the filler around the dowels.
Another idea is to do a 'dutchman'. A dutchman is a patch used in the flatwork world that is glued into a recess carved into the piece, and then sanded flush with the surface. Most often they are oval and both the recess and filler are made using a router with a spiral cutting bit and collar. You can use the same timber, but some people prefer to use a contrasting material to show off the craftsmanship. I was in custom fine furniture shop just yesterday that had a table that had been patched using brass dutchmen .
In the world of turning you can do effectively the same thing by drilling out the flaw, enlarging the hole, gluing in a dowel of the correct diameter, and then finish turning the surface. Theoretically, you could use a router to cut some other shape, but drilling is much easier when the piece is turned on a lathe. And if you drill at an angle, the patch will end up being oval.
If you do a search in YouTube, you will find some videos by Frank Howarth, an architect and turner in the Portland area who has a shop that is absolutely amazing. He has several videos in which he has turned bowls from imperfect wood, then used a bandsaw to cut out the flawed sections of the finished bowl, glued in a contrasting timber, and then returned the bowl.
Finally, it isn't always necessary to repair flaws, especially if they are natural artifacts in the timber.
|