Saturday 28 September 2013

Because You Asked: Making a Lute Mold (3)

Okay, here we go--the final push to get this mold-in-progress glued together.

So far, we've made a base plate and a lot of blocks that screw up to it, and we've transferred the plan, long section and cross section profiles from our drawing onto them.  Before we glue all this up, though, we've got to make sure that these profiles will be visible and usable to us as we carve the mold.

So set up your bandsaw and sharpen your chisels... we've got some work to do.

Cutting the Blocks
With all the cross sections traced, you're ready to cut away the excess wood from the blocks.  You can cut very close to the line here--no more than 1mm.  Be brave--if you cut much farther away, you're just leaving more wood to hog off when carving begins.

When you eventually glue the blocks together on the base plate, you will need to clamp across the blocks as well as along their length.  To provide a flat clamping surface across, I mark and cut cleats into the blocks as I cut out the cross sections.
Mark and cut out all the cross section blocks--then meet me at the bench for the next step.

Trimming the Blocks
With all the sections now cut out, it's time to trim down to the long and cross section lines that you've traced onto the blocks.

Start with the cross sections first.  Place a block in your vise, and then with a chisel held at a 45 degree angle, trim down to your marked cross section line.  It's important to trim at a generous angle, because this angle will allow us to see and use (i.e., carve down to) the cross section after the mold has been glued up.  (When you get to a cleat, you'll have to saw away a bit of it to get close to the line with the chisel.)
Sawing away a bit of the cleat...
... so we can trim right to the line.

When you've trimmed down to the line, draw the rib joint lines--in pen--onto the bevelled surface you've just made.  This is to ensure you'll be able to locate the rib joint lines after the mold has been glued up, in order to lay out rib lines during carving.
For long section lines, proceed as with the cross sections--using a chisel, at a 45 degree angle.  (You may need to do a bit more chiseling if you find yourself having to contend with a cleat.)
Here's a look at one of our blocks--this would be from the front section on the bass side, showing the long section and cross section trimmed in.
Here's a look at all of the blocks on the bass side with long and cross sections trimmed in.  And like magic--there's the whole longitudinal section!

Maybe here you can get a better idea of what I was talking about in my last post about drawing in the cross sections only on the 'uphill' side of the blocks.  It's not necessary to draw them on the downhill side, because that cross section is actually the 'uphill' side of the next block in line. 

Preparation for Gluing
All the blocks are now cut and trimmed down to their lines; all blocks have cleats cut into them for clamping across the sections.  We are now almost ready to glue up the mold.

Before we do, though, it's a good idea to do a dry run, screwing all the blocks to the base plate, clamping across all the cross sections and along the long sections.  By the time we've finished gluing there will be a forest of clamps attached to this beast, so it's a very good idea to know how all of them will fit together around the mold at one time.

When you're certain all the clamps will fit harmoniously, remove and set them aside, close to hand, in the order that you'll use them.  Unscrew all the blocks from the base plate and set them aside also, in the order in which they'll be glued up.

Leave the screws in the base plate, backed out, ready to screw up into the blocks. 

Gluing up
Begin with one side of the bottom section, and apply glue to the bottom surface only.  I use Titebond, and spread the glue with a putty knife.  You don't actually need too much glue on any of the surfaces of the blocks; once all these pieces are glued together, clamped and dried, there's little chance of a glued joint failing.  On the other hand, too much glue will present problems--there will either be a lot of squeeze out to clear away, or excess glue will distort the alignment of the blocks.

Apply glue, then screw up to the base plate (save time and wrist fatigue by using a power driver.)  There will be some squeeze out, which should be cleared away with a sharpened stick.

Now go on to the other block of the bottom section.  Glue goes on the contact surfaces: the bottom (against the base plate) and the side (against the other block).  Screw it up, then clamp across the two blocks.
Once these two bottom section blocks have been glued, the mold can be set upright on the bench, allowing easy access for screwing up the remaining sections.

Go on to the next section, first one side and then the other, spreading glue on all the contact surfaces, screwing up tight to the base plate and clamping across.  At this point I also like to clamp--temporarily--along the long section too, just to make sure I get good squeeze out.  Clamp tight on both the treble and bass sides, then remove the clamps, and go on to the next pair of blocks.
Temporary clamping on the long section

I do this temporary clamping on the long section for each pair of blocks I glue in.  It makes for a fair bit of clamping and unclamping, but it's important to do it as you go along.  If you wait until all the blocks are in place before clamping the longitudinal sections, you'll find that the glue has already set in the first joints you glued up--and it will be impossible to get a good squeeze out (and a tight fit) in those joints.

Here's something like what the finished gluing-up job should look like.
(My darling wife Julia calls a photograph like this 'clamp porn'.  I prefer to think of it as 'clamp erotica'.)

That is all for now.  Let the glue dry; don't even think about working with it for a day or two.  Take the weekend off--you have my permission.  The really difficult part comes with the carving of this beast into something resembling a lute body, and we'll turn our attention to that in our next installment. 

Thursday 26 September 2013

Because You Asked: Making a Lute Mold (2)

Hi there, and welcome back!  In our last exciting episode, we made a base plate and two big blocks of wood, and clamped all three pieces together.  So far, so good.

Before we go onto the next step, though, I'll just take a second to remind you of the main principle we're working with: to put together a mold with plan, longitudinal and cross-sections built in.  We've already traced the plan and cut the base plate to shape, so there's our plan section.  We've made two blocks, one on each side of the centerline, so we've created a place for us to (eventually) draw our longitudinal section.  Now we're at the point where we can insert our cross sections.  But how do we do that?

Answer: by very carefully marking the cross section points on the mold blocks, and then sawing the blocks at those points.  As you will see, by doing this we'll create surfaces on which we can draw in the cross sections from our plan.  After we put together all the pieces, our cross sections will be there, inside the mold, patiently waiting for us to carve down to them.

That part's down the road a bit, though.  First of all, we need to mark and cut apart these blocks accurately at the cross section points.

Cutting the Cross Sections
The logical place to start is at the bottom of the mold--the last cross section.  While you've got the base plate accurately clamped to the mold blocks, mark the position of that last cross section (you can see it on the edge of the base plate) on both blocks.  Then before you unclamp the base plate from the blocks, drill some pilot holes through the base plate into the blocks below that last section, so that you can screw the blocks accurately back onto the base plate.  (I use 2" #10 screws and big washers for this job).

Screw with washer, cross section marked
Unclamp and unscrew the pieces.

Now, find your cross section mark on the bottom of the blocks.  Use an accurate square to mark a line across the bottom, and to "wrap" that line all the way around the block.  Take the block to the band saw (which is well set-up, with the blade perpendicular to the table), and cut the block along the line.  Cut carefully but smoothly--and make sure that your saw kerf is on the outside of the cross section line.

When you've cut both blocks, return them to the base plate, and screw them up in position.  How are things looking?  Reasonably accurate?

Yeah, reasonably accurate...

Good--then clamp the remaining blocks into position tight against them.  (By the way, there should be no need to plane or otherwise true up the faces of the blocks you've cut--whatever little wiggles you made with the band saw will be the same on each side of the kerf, so the two pieces should fit together closely.)  Now do the same procedure--mark the next cross section point, drill pilot holes, unclamp, draw a line around the blocks, then cut with the band saw.  Continue until you've cut the blocks at all the cross section lines (all except the section where the top block will eventually fit up to the mold--we'll true that up later, during the carving process.)

It should be clear now why I said to leave the mold blocks extra-long, and that's because with every cross section line you cut, you lose about 1mm or more of length (the width of the saw kerf).  Added up over the length of the mold, you could lose a total of 6-10mm--so you need to plan ahead.

At this point, you should be able to screw all of the little blocks to the base plate, and if you've done your work well, they should all fit together tightly.  Here's what it looks like from the top side:

Look closely--all the cross sections have been cut.  Here's what things look like on the underside of the base plate, with all the sections screwed up into place:

A quick detail shot:

Drawing the Sections
Our next step is to transfer the longitudinal and cross sections from our drawings onto the blocks we've cut.  Let's do the longitudinal section first.

You now have all the blocks screwed up to the base plate, so while they're there, take a long clamp and clamp together, from bottom to tip, all the blocks on one side of the mold.  Let's make it the bass side of the mold (since this matches my drawing best).  Unscrew all the blocks on that side, and lay the clamped blocks face up on the bench.  Place the drawing of the longitudinal section on it carefully, and remember to account for the thickness of the base plate.

The longitudinal section on my drawing is a little faint in this picture, but trust me, it's there.  I'll just transfer the line to the block using my dividers set at 1.5mm (the thickness of the rib material), then remove the drawing and trace the line using a sharp pencil and flexible curve.  How's it look?  Again, it's faint--I've used a sharp, hard pencil to draw it--but it's there.

With the long section traced, I'll screw all these blocks back onto the base plate, and go on to the cross sections.  We'll work with the same principle, this time clamping across a pair of blocks, removing them together from the mold.  Let's begin in the logical place, with the bottom cross section.

Lay the clamped blocks face up on the bench, and carefully place your cross section drawing on the surface (again, remember to account for the base plate.)  With the drawing either taped or tacked in place, prick through it with your dividers set at 1.5mm (the thickness of the rib) to transfer the cross section to the blocks.  Also be careful to mark the exact locations of the rib joints.

Remove the drawing, and with a sharp pencil and flexible curve, draw in the cross section line and rib joints.  Here's what things should look like:

If everything looks good, unclamp the blocks, set them aside, and go onto the next pair.

By the way, unlike the bottom blocks you've just marked, all the section blocks from now on will have two sawn surfaces upon which could be traced two cross sections.  However, you only need to trace one cross section--the cross section that is the larger of the two (that is, the one that's on the 'uphill' side of the block.)   If that sounds confusing, don't worry--I'll show you pics at a later stage that will show just what I mean.

I think that will be all for now.  There's a lot of information here to digest, and for both of us it's already been a long day at the work bench.  Let's take a break--read a poem, go for a walk, enjoy what's left of the day.  I'll talk to you again soon.



Sunday 22 September 2013

Because You Asked: Making a Lute Mold (1)

I've had a number of requests for advice on how to make a mold for building a lute back.  Well, here goes.  This is a vast subject, and my own method takes a lot of explaining (I've found), so I think the best way to deal with it is in a short series of posts.   And let me just say at the outset, what I write here won't be a step-by-step, how-to explanation.  There will necessarily be a lot of details left out that you will have to work out on your own (just as I once did, and am still doing.)

There are plenty of ways to go about making a mold.  The first one I ever made was a very simple cross-shape, using a single piece for the longitudinal section and a single piece for the cross section, following instructions by Ian Harwood from a book on making musical instruments.  I also tried making a solid mold using the method described by Robert Lundberg in his book Historical Lute Construction, which is basically building up a big block of wood, then carving away everything that doesn't look like a lute back!  Lundberg uses external templates to give shape to the block, but I found this to be a very difficult method to use.  It was a great relief to me when I finally met Grant Tomlinson, and he set me on the path to mold-making righteousness.

My method is based on Grant's, and it differs from his in a number of details, but the fundamental principle is the same: to built a lute mold with the plan section, longitudinal section and cross-sections built into the mold itself, rather than to shape it using external templates.  It takes a bit of doing to put the pieces together, but once they're glued up, the basic shape of the mold is already in place.

To get started, you'll need two things: a good stock of wood, and a good working drawing of your lute.  The wood first: jelutong works very well for making lute molds.  It's relatively light and stable, and of a uniform density throughout, so it carves easily.  It's also readily available in dimensions that suit this job (2" stock that's 6-8" wide).

Next, a word about your drawing.  Whether you're using a museum drawing or a commercially available plan, you'll probably want to make your own accurate working drawing.  If you have a technical drawing of an historical lute, you'll want to rectify or modify the long, cross and plan sections to make a pleasing (and viable) shape; if you're using a commercial plan, you'll at least want to the check the accuracy of the sections you're given.  Before you even think about working with wood, make sure that all the sections fit together--you don't want to get halfway through the process only to find that your dimensions don't match.

Here we go.

The Base Plate
The first piece you need is a base plate, onto which the body outline will be traced.  The plate is made up of two planks edge-glued together (the glued joint then becomes the centerline).  The piece should be planed very flat and smooth on both sides, and should be a very even thickness throughout.  What the specific thickness is doesn't really matter, but later on you will need to know exactly what that thickness is.  I've found that somewhere around 20mm works well.
Your base plate will need to be at least as wide as the widest part of your outline, and a few millimetres longer, too.

Lay your outline drawing down on the base plate, aligning the centerlines carefully.  Tape or pin the drawing down securely.  Then with a sharp pin, prick through the locations of all your cross section lines through the drawing down onto the base plate.

You are now ready to transfer your body outline from the drawing to the base plate.   However, because your working drawing is a representation of the full-sized, finished lute body, you need to subtract the thickness of the ribs from your outline as you transfer it.  To do this, use a sharp pair of dividers set 1.5mm apart (the approximate rib thickness), and prick through the drawing.  When you prick through the body outline with one point, the pin line you create with the other point (1.5mm inside) will be the outline of your mold.  (Around the capping strip area there's a double thickness of wood, so this width will be around 3mm, blended in at the ends of the capping strip.)
After all the lines have been transferred, remove the drawing and draw in the cross section lines and body outline with a sharp pencil.  Use a flexible curve to help draw the outline.

On the bandsaw, cut close to the line, except at the very bottom and very top of the outline.  At the bottom, leave 2-3mm extra length--this is to account for the fact that many lutes have a longitudinal section that protrudes farther than the bottom of the belly (if you've ever seen the Vienna KHM's drawing of the Gerle lute, you'll know what I'm talking about.)  Leave about an extra mm at the top end too.  Shape to the line with a disk sander, or on the bench with a sanding block.
One other thing you can do at this point is to mark your centerline and cross-section lines on the other side of the base plate (you can use a small engineer's square to transfer the lines at the edges of the plate from one side to the other.)

With me so far?

The Mold Blocks
Now we need to make two long blocks, which make up the remaining wood of the mold.  Because these blocks will sit on each side of the mold's centerline, I think of them as treble and bass blocks, and I mark them as such to keep track of which is which as I go along.

The rough dimensions of these blocks are as follows: the width of each block is a little wider than half the base plate, while the depth will be a little deeper than the depth of the mold, minus the thickness of your base plate.  The length should be a fair bit longer than the base plate, maybe 20 or 30mm (I'll explain why this extra length is needed in a minute.)  Depending on the dimensions of the mold you're making, three layers of 2" jelutong should be more than enough thickness; cut the pieces to length, joint them flat, and glue them up.  When the glue is dry, true up the bottom and inside (centerline) surfaces with the jointer.  It's important that these surfaces be very flat and perpendicular to each other. 

To ensure that they are, I finally clamp the blocks together on the workbench, then flip the whole thing upside down so the bottom surface is facing up.  Using a jackplane, I flatten the whole bottom surface.

Do not unclamp these blocks.  The surfaces of the blocks are now very flat and close to perpendicular, and are ready to accept the base plate.  Align the base plate centerline with the centerline created by the blocks.  The ends of the blocks should overhang the bottom edge of the base plate by 3-5mm; the rest of the excess length of the blocks should extend beyond the top end of the base plate.  Clamp the base plate securely to the blocks.

I think I'll stop here, for now--this seems like a good spot for a cliff-hanger ending.  I hate long goodbyes.  Take care, and I'll post again in a little while.

Saturday 7 September 2013

(Old) New Work

Hi friends,

Hope you've all been well since we last talked.  I haven't posted in a while, but feel like I'm about to unleash a flurry, nay, a veritable barrage, of new posts, in the coming days and weeks.  I had a great summer, and I hope you did too, and I feel really recharged and ready to get back to work, both in the shop and on la blogue.  So here goes!

First up is a bit of old-ish business--some photos of a 13c lute that I finished late in 2012, in a group of two alongside the 12c lute that is the subject of my previous post.  This lute has a body based on the Paris Schelle, with an extension after Widhalm, just like the one that I built, and posted about, in 2011.

This lute has a back made of Honduras rosewood ribs and holly spacers, with ebony fingerboard, points and neck veneer; the extension is made of English sycamore, dyed black, with Castella boxwood pegs.  It was originally built for a European client who was, unfortunately, unable to take delivery.  The lute now belongs to Dr. Ken Lee of Vancouver, BC.

Incidentally, this set of photos is the inaugural one featuring my new digital SLR, a Nikon D3100.  My digital photography skills are still developing, as is my lighting rig and studio setup, but I think it's an improvement over previous efforts.  Enjoy....

That's most of the shots I've got of this one--there are a few others on my flickr page, if you want to check it out.  More stuff soon!