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H.R.Fisher

C-bout lining mortise?

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 What  procedure do you use to cut the mortises into the corner blocks for the C-bout lining? This may seem like a trivial question but I have been trying various methods none of which I'm  very happy with.    I would  be interested in knowing how others do it. As always, thanks for your response.

                                                                                                                              Henry

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Henry, briefly, I cut the sides of the mortise with a single edge razor blade then cut the mortise ends and gradually excavate the waste with a 1.8 mm wide chisel (Hirsch).   Here's more detail:  I lay out the mortise size and locations with a 0.3 mm mechanical pencil using magnification to check the size.  I push the razor blade edges of the mortises just a little undersized because the wood compresses a bit and then swells back up when the linings are glued in.  This is nothing original to me-basically the method I was taught in school.

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I found in the Heron-Allen manual where he said it's o.k. to notch the lining if you need to.  I'd rather have more corner block than lining anyway.

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...but what if I only have a .5 mm mechanical pencil?

I appreciate you, Doug, and I know I don't know a lot. It's just a lining though. I really don't see why it has to be perfect. Your chisel is the right size, so why mark everything out with a pencil when it can be chunked out in 10 seconds and still look good? Heron-Allen is right here imo, notch the corner and jam it in.

Serious question: why should those mortices be perfect?

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I just jam my 2mm chisel in, little bites at a time, and the spruce just pops out along the grain.  Of course, using extremely low-density, processed spruce for the corner blocks makes this a bunch easier.

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I use a straight thin bladed whittling knife, and a chisel that started off at 2mm but got ground down to about the thickness of cello purfling.

 

I start by scratching a guide line from the tip of the corner roughly dividing the block down the middle.  I like to mortice my lining roughly to this line.  But not finicky about it.  I just quickly draw the line to give some guidance. 

 

Next, I hold the actually lining against the ribs and running over the block were it will be morticed in.  I press the knife along both sides of this lining to mark the mortice onto the block.

 

I cut the mortice by alternately pressing the knife deeper into the block along the marked sides, then clearing the wood with the chisel.  The back edge and bottom of the mortice are all chisel work, no knife.  I check the depth using the actual lining again.

 

The whole operation is very quick.   And I can see that with more experience it will get down to 30 secs or so.

 

 

I use willow blocks, so don't know how this would feel with spruce.  Works great in willow.

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I just jam my 2mm chisel in, little bites at a time, and the spruce just pops out along the grain.  Of course, using extremely low-density, processed spruce for the corner blocks makes this a bunch easier.

  I guess I need to invest in a 2mm chisel and jam it in!   sounds simple enough,I should have thought of that. :)

                                                                                                                                Henry

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My husband uses a razor blade (marked to the right depth) and he of course has a tiny chisel. I think it's a shade bigger than 2, but basically 2. The whole process is insanely fast. Those mortices look a ton harder than they are. Imo most procedures in violinmaking look exactly as hard as they are though.

Eta: the result is not Germanic perfection, and I understand that is, in itself, a satisfying goal, but he does all 8 in under 10 minutes for sure. (Added photo)

post-59554-0-08159900-1432344759_thumb.jpg

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Absolutely! I use my Dremel with the purfling jig, and a slightly larger diameter bit than the one used for purfling.

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I saw my lining mortises out, and leave them at a rough 45* angle inside, instead of chopped out square. That way I just have to saw down my lines and chop out the waste. I used to make them square, but realized this was faster, just as strong, and also looks identical from the outside.

The real trick is getting a chisel that is the right size. I bought one the right size for cello, and I made one for violin.

M

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The very available NIJI "hobby" knife chisel packs, which are actually pretty good for what they are, come with a variety of "flat chisels which are small, but not small enough to do the job, but they are easily modified with a dremel "cutting/grinding" wheel. where you can cut/notch into the stock NIJI chisel and make the cutting blade as skinny or fat as you would like to. You can make different widths for different dimension linings, you can make a "left or right" by cutting the notch on either side {so the flat back is "workable" from left or right cutting positions"} and as a bonus, the NIJI blade is much longer of a plunge that you would need which makes it so when you cut your notch you can also cut the notch not just for as wide as you need, but as deep also, the end result being a "depth" stop that is very handy for not plunging in too deep.
 

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A Stanley carpet knife (that I use for lots and lots of other stuff, an aluminium one that I modified a bit so the blade doesn't slip) and I ground a couples of old files to chisels that have the right width.

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I just jam my 2mm chisel in, little bites at a time, and the spruce just pops out along the grain.  Of course, using extremely low-density, processed spruce for the corner blocks makes this a bunch easier.

 

 

I do it just as i think Don Noon is describing .... there are a series of photos of me doing it here;

 https://www.facebook.com/146764275375079/photos/pb.146764275375079.-2207520000.1432359456./243379099046929/?type=3&theater

n

 

Really? only chisel and no lateral cuts with knife?

Interesting, I've never tried it, I will have to try next time.

For the moment, X-acto saw for the 2 lateral cuts (cutting at 45°), thin knife to deepen the cuts, 1.8 mm chisel for splitting off the wood.

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A Stanley carpet knife (that I use for lots and lots of other stuff, an aluminium one that I modified a bit so the blade doesn't slip) and I ground a couples of old files to chisels that have the right width.

The single beveled carpet blade is perfect for lining mortices.  I chip the ones I have into smaller blades.

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Or don't mortise them at all.

The argument that a mortised middle lining stiffens the body always seemed specious to me.

The reason I think the c-bouts are typically mortised and the others (more often than not) are not is to keep the lining from "springing" away from the rib.

No empirical proof, but seems reasonable to me.

A problem (if it ever really was one) solved with a well fit lining let into notches rather than a full mortise.

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The purist may frown on the following but maybe not.  Soak a block of the lining material in water for a few days.  Move chip breaker back on a #5 plane and adjust opening for slightly thicker than needed lining thickness.  Put block into vise, figure out the run of the grain, put on gloves and plane away.  Your new linings will come out naturally curved.  I needed 72 linings and this was the most efficient cutting method for me.  Form them while wet or leave them laying to dry.

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Or don't mortise them at all.

The argument that a mortised middle lining stiffens the body always seemed specious to me.

The reason I think the c-bouts are typically mortised and the others (more often than not) are not is to keep the lining from "springing" away from the rib.

No empirical proof, but seems reasonable to me.

A problem (if it ever really was one) solved with a well fit lining let into notches rather than a full mortise.

You are correct. A bent piece of wood wants to straighten out. Linings inside a curved bout will be held in place with a decent glue, but linings on the outside of the curve can have ends that will eventually work free and start buzzing. I remember there was a fad a few years ago to mortise all ends. That had a short life.

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2 cuts with a thin knife to form a V.

Cut the complementary sharp on the bent lining (you can even adjust the tip on a hot iron).

 

7.735 secs total per corner.

 

And nobody can see that it is a non-Cremonese job from the outside.

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2 cuts with a thin knife to form a V.

Cut the complementary sharp on the bent lining (you can even adjust the tip on a hot iron).

7.735 secs total per corner.

And nobody can see that it is a non-Cremonese job from the outside.

Right. But that is what Carlo Bergonzi did. See Roger Hargrave's contribution to Biddulph.

Eta: not suggesting you didn't know this, no doubt that's what gave you the idea. Just offering an interesting reference.

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Really? only chisel and no lateral cuts with knife?

Interesting, I've never tried it, I will have to try next time.

For the moment, X-acto saw for the 2 lateral cuts (cutting at 45°), thin knife to deepen the cuts, 1.8 mm chisel for splitting off the wood.

Exactly

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I believe it was Roger H in one of his articles on the cremonese method that suggested the purpose of mortising the mid bout linings was to provide additional strenght to the rib cage when undergoing the stress of bring removed from the inside mold.

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