Tuesday, September 30, 2008
Inlay and Rosette Tricks
I'm always looking for a quicker and more accurate way to inlay without visible gaps. Inlaying a straight-edged design does help, but as always, the room for error is basically a couple thousandths. In other words, not much. The inlay either fills the mortise right up to the edge or it doesn't. Lots of fancy inlay is done on darker fingerboards like rosewood or ebony. Filling gaps in these woods is easy. Just overfill with epoxy and let the dark wood hide the errors. Inlay in lighter woods like walnut poses a challenge, and inlaying soundboards of soft spruce calls for a light touch and extreme accuracy. My technique isn't unique. However, I do have a little trick I use that improves my results. I always tack glue my inlay to the substrate with a tiny drop of CA glue. It won't budge while I scribe with a #11 Xacto blade. And it pops off quite easily afterwards.
I route the majority of the mortise with a 3/32" spiral bit, then sneak into the corners with a 1/32" bit. These little buggers are really fragile, but they cut very smoothly and allow me to get into tight corners. I clean up the very tip of the corner with the #11 Xacto.
And here's where my little trick comes in. I use a highly polished jeweler's burnisher to compress and spread the aris of the mortise wall. 99% of the time this takes care of any iffy spots in the fit. If a particular area is off by more, I'll use some extra pressure and try to smoosh the wood fibers a tad more.
The burnished areas are visible around the perimeter of the mortise. These will get scraped and sanded flat after the inlay is glued.
A matching caul puts pressure evenly on the inlay.
This is ivory in walnut.
For rosettes with inlaid central calligraphy, getting the pattern on the blank in the correct position can be tricky. There is no room for error when the border of the inlay is a 2mm circle surrounded by 2mm walnut. Any deviation from the pattern will be obvious.
I cut some tiny windows into the pattern to line up exactly where the pattern should lay. Once I position it exactly I tape one edge to the blank, flip it over, spray with 3m Super 77, flip it back and press it down. The tape acts like a hinge, returning the pattern to exact spot.
This dark walnut rosette is made from several plies of alternating grain veneer, epoxied together and cured in a press. This plywood makes for easy, predictable cutting since the "grain" of the wood is the same in every direction. And obviously it makes the rosette very strong.
After cutting the pattern, but before removing the paper.
The finished rosette. Walnut and ivory.