Posts Tagged ‘purfling cutter’

Home Stretch for the 14-inch Viola

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On the Home Stretch Now!

The 14-inch Viola is getting closer to completion!

When I last posted, the viola was still in the spool clamps. The back plate was installed, but that was as far as I got that night.

Viola in spool clamps

Lots of promise, but not much “grace” in this picture.

 

Spool Clamps Off: Lots of Work to Do, Preparing for Purfling

So…the next step was to remove those clamps, adjust the overhangs as needed, and get on with the purfling. That sounds pretty straightforward, but there is always more to anything than meets the eye.

front view, back plate installed, button needing shaping.

Looks nice, at first glance, but take a look at the neck button (where the back plate overlaps the heel of the neck.)

 

side view viola with unfinished back plate.

Side view of the same state of the viola.

 

Back view viola with unfinished back plate.

Back view: button hidden by my hand. No purfling, and no shaping done.

 

Purfling Groove

I marked the purfling groove, using what is frequently called a “Purfling cutter“, but which is actually a marker. It has two blades that simply lay out the sides of the groove, by scribing them a set distance in from the outer edge…which is why I want the outer edge perfect, before beginning purfling. I have modified my cutter a bit, to make it work more reliably, but the link above shows the type of tool I use. I don’t think I have that brand. I can only use the marker to get within an inch or so of the corners. I lay out the corners by hand, sometimes using a frnch curve to achieve some repeatability.

Afterlaying out the groove in pencil and scribe marks, I incise the lines with a small sharp knife, then pick the waste wood from between the cuts.

Here is the completed groove:

Purfling groove and button complete

Purfling groove complete. Notice that the button is taking shape as well. The neck, too is getting slimmer, and smoother. Lotsa work…

Here is a detail shot of the groove:

Detail of purfling groove.

Detail of the purfling groove.

 

The Purfling, the Channel, and the Finish Work.

Finally I can start cutting and installing the purfling itself. I use a wood purfling, which is very brittle when dry, but bends nicely with a little moisture and a lot of heat. Once the purfling fits correctly, I lift each stip out partway, and insert hot hide glue under it, then force the strip back into the groove. Afterward, I mark the crest of the channel, and cut the channel using a sharp gouge. Finally, I use a tiny plane as well as gouges and scrapers to bring the convex curve of the plate into a fair, smooth agreement with the concave curve of the channel.

The purfling is complete, the channel is cut, and the back curve faired into the channel.

The purfling is complete, the channel is cut, and the back curve faired into the channel.

 

Purfling detail

Purfling detail: look closely, and you can see the edge-crest line in pencil.

 

side vies of viola.

It is a fairly high-ribbed viola: 35mm. I think it will sound good.

And, it is looking more and more like a viola!

Viola nearly complete

On the Home Stretch!

 

What is next? Edgework, and final scraping; coffee stain, mineral ground, sealer, and varnish…and then fittings and set-up. (The outer edgework is not even begun on the back plate.)

This is definitely as far as I am going tonight, though…. Getting too tired.

 

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Cello Back freshly purfled

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One-piece Cello back purfling complete.

Narrow (violin-style) purfling, like the original

Today I completed the back plate purfling. Though this is a cello, I purfled it with violin-style purfling, as it was pointed out to me by Jacobus van Soelen that the original instrument (1712 Davidov Stradivarius) had narrow purfling, like a violin, not the wide purfling I used on my first cello (and which I actually like to use on violins and violas, as well.) I just like the eye-catching appeal of the larger purfling as a rule. In this particular case, I must concede that the wood is so beautiful that it really does not need additional “eye-candy”.

The job starts with layout and measuring

Last night I laid out the corners, and marked the whole purfling channel using a purfling marker (sometimes called a purfling cutter— but I only use it for marking– I use a knife to actually cut out the slot for the purfling).

Then cutting and fitting

This morning I incised the whole purfling slot, using a small, home-made knife, and then cleaned the waste wood out of it with a purfling pick.

While I fitted purfling into the slot, and carefully fitted the corner miters, the glue-pot was heating up.

Gluing the purfling

When all the purfling seemed to fit correctly, I tipped each center-bout purfling strip up out of its respective slot, so that it pivoted up and out on the two corner miters, but left the ends in the slots, unmoved. I slipped hot hide-glue (quite thin) into the slot, using a palette knife, brushed hot water to flow the glue, and pressed the purfling strip back into the slot, forcing it deep into the groove with a special tool. (Sometimes I use my purfling pick for that job. Today I remembered that I have a plastic wheel on a sturdy handle,  actually designed for forcing the rubber trim into screen window frames. It worked perfectly. :-)) Then I repeated the above process for the upper and lower bouts.

If I start toward the middle of a section of purfling, and work toward the ends, the glue is forced along under the purfling, and squirts out along the edges and, finally, out the ends, and the miters. The result is that all of the piece has adequate glue, even if some spots had been a little skimpy. Then I brushed more hot water to re-flow the glue, and wiped off the excess with a rag.

So– here is the completed back, ready for final arching, and for having the edge channel cut, etc. It will look pretty rough until the gouge slices along the channel, and trims that excess glue and damaged fibers off the top of the purfling strip. Then it will look very nice. (Purfling isn’t only for looks, by the way, on violins– it also helps stop a split from the edge from moving up into the plate…supposedly.) Anyway, this is how it looks for now:

Completed purfling on one-piece cello back, before carving the channel.

The channel still needs to be cut, but the purfling is complete.

Lower treble cello-back corner, freshly purfled

Lower treble corner, freshly purfled

The next step will be to mark an edge margin all the way around, locating the crest of the finished edges, after which I can use a gouge to carve the channel, and begin the final arching.

But, for today, I have a bow to re-hair, so this is as far as I am going with the cello.

 

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