Well, I was right – the back grooves took almost two hours to finish by hand. Some time ago I had thicknessed two strips of Walnut for the purfling. Today I slit one of them into five sections. My plan is to use solid Walnut for the purfling instead of the traditional three-layer black-white-black purfling.
This is the year that #9 will be completed! The body has been sitting on my bench, looking at me with a reproachful attitude. A couple of days ago I routed the purfling grooves, this afternoon I cleaned up the ones on the top of the body. That’s the easier plate done. I expect that cleaning up the ones on the back plate, which is Maple and Walnut, will take much longer.
This morning I trimmed the belly plate to a profile better matching the installed ribs. I had originally planned to trim it with a guided router bit. I even drove to Lee Valley to pick one up that I thought would do the job. Unfortunately the top bearing mounting is completely different from the other bearing bits that I have. Finally I decided to just do it with a sanding drum on the drill press. That took only a few minutes. Lesson learned: sometimes the simple and obvious answer is the best.
A few days ago I had drilled alignment holes and made brass pins to fit. They’ll need to be trimmed to length, but I think they’ll be a nice touch in place of the usual ebony ones. Another unconventional thing was to apply a layer of Livos finishing oil to the inside surfaces. Finishing techniques have come a long way since the days of Stradivarius and Guarneri.
Open time is usually a problem with hide glue. Even working as quickly as possible, it starts to set up by the time the clamps are on. I’ll take off the clamps tomorrow and see if I got everything adhered properly.
My original plan for this instrument was to eliminate the use of glued-in linings and machine shoulders with grooves directly into the plates. That worked fine for the bottom plate. Unfortunately the ribs aren’t all exactly perpendicular, so there is some minor variation in the profile where it was intended to fit into the grooves in the belly plate.
My solution was to plane off the shoulders, glue linings onto the ribs, and assemble in the traditional way. Unfortunately (there’s that word again!) that left shallow grooves visible, since I had machined the groove slightly below the plate inside. By the time I had sanded that all flat, the plate edge was under 2 mm. My solution was to apply a Walnut shim all around. Yes, it increases the weight. The belly plate weight went from 81 g to 99 g. But that’s with the Bass Bar in place in the latter measurement, so the wight gain was less than I had feared.
The tap tones stayed pretty much the same as before: Mode 5 at 349 Hz (F4) and Mode 2 at 152 Hz (D#3).
The linings are glued to the tops of the ribs. The alignment pin holes are drilled. I just need a router bit with a top bearing so I can trim the belly plate to the same profile as the ribs. Most of the perimeter is fine, but the C Bout areas have a bit of excess plate showing. I could sand it back manually, but a guided router bit will hopefully do a cleaner and more consistent job.
The back plate was heavy by about 7 grams, so I planed a bit off the left side where it was thicker. The graduation is now as it should be, and the weight is spot on at 121 g. That’s the usual target of 115 g plus an allowance of 6 g for linings. The belly is 81 g, 6 g over the target mass of 75 g.
The corner and end blocks are trimmed to size, but only approximately to height. I intend to make the plates non-coplanar, so I will adjust the block heights once the ribs are in place. The machined-in “linings” are trimmed back for the blocks.
Both the back and belly plates are graduated, scraped, and sanded. There’s no replacement for running your fingers over the surface to confirm smoothness and consistency!
Although I haven’t posted anything in a while, I do occasionally work on #9. Today I cleaned up the back plate inside. I have the upper plate profiled and cleaned on both sides. The back plate is now in the same state. I’ll still have to graduated the back.
Using the Veritas Pull Shave (regrettably, no longer in production), doing the initial gouging of the top plate was quick and easy. The back plate will be much more work. Then I’ll use finger planes in decreasing sizes, then finally scrapers, to get to the required thickness in each area. I’ll leave those details for later posts.
I used a 1/8″ CNC end mill in the drill press. I wanted a flat bottom, not little divots like what you get with a drill. I started setting the depth with the new caliper gauge I installed on the drill press, but after the 6 and 5 mm holes, I decided to use depth gauges instead for the remainder.
I also tried using a foot actuated operator for the drill press depth control, but that didn’t work very well. Holding the work-piece with my left hand and operatiing the drill press with my right is quite tedious. But over yesterday and today I got it done.
Over the past few days I’ve done a bit of work each day. Today I did the final rough shaping near the C bouts, then scraped everything end to end to reduce inconsistencies. The shapes are close to the templates. I’ll still do some detail scraping to satisfy the fine texture that only can be determined by running hands over the surfaces.