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First Cello Build

PostPosted: Tue Mar 26, 2019 12:02 pm
by Tom Griffin
I've spent most of my life as a machinist/fabricator/designer creating stuff out of metal and after recently retiring, have decided to spend more time working with wood. I started by building a Maloof rocking chair for my new granddaughter and am now focusing my efforts on building a cello. I played cello in a secondary instruments class back in high school and have always been fascinated by their sound and design, and now that I have the time, have decided to build one.

I started out by absorbing as much technical information as possible from the internet, books and acquaintances through my website. Once I had a handle on the technical aspects, I started building many of the specialized tools and fixtures. Of course that stuff is all available from luthiery suppliers, but I couldn't justify spending all that money on something I could make, when it'll probably only be used a couple times. I built 50 spool clamps from some of the Walnut and Ash left over from the rocking chair project, a number of wooden bar clamps to use when gluing the ribs to the corner blocks, a bending iron to form the ribs, and of course the form or mold itself. The pattern for the mold came from a book by Henry Stroebel, which has full size templates for a 4/4 and 7/8 cello. I wanted to use a poster published by the Strad of a Stradivari 'Davidov' 1720, but it's no longer in print and I was unable to locate one. From what I understand, the Stroebel templates are very similar in shape and size.

I just got started bending the ribs, so before I get too far into the project, I thought I would start a build thread to document my progress. I am definitely a novice in musical instrument construction, but not in craftsmanship itself, so I'm pretty sure some of my methods will vary from those traditionally used, but the result will be the same. I'll start the thread out by posting some pics of the tools and fixturing that I built, and then move on the the instrument itself.

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These are the 50 spool clamps that will be used to clamp the front and back of the cello to the rib structure. The going rate for ready made clamps is about $7 a piece or $350 for the lot. All I have invested in mine is $10 for the carriage bolts and wingnuts and a little bit of time.

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This is the bending iron that I built to form the ribs. It's basically a 3" x 5" x 7" chunk of aluminum made into an airfoil shape, with various radii to suit. It uses a PID temperature controller and solid state relay to power a couple of electric cartridge heaters with a type K thermocouple for feedback on the temperature. I had a vague idea what the temperature needed to be for use, so I designed it for up to 500ºF and hoped for the best. As it turns out, 350ºF was adequate so it's a bit over designed. :)

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Rough shaping the iron on the mill.

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After some time on the belt sander.

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The cartridge heaters, PID controller, solid SSR and thermocouple.

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Wiring. (Not one of my strong suits)

The mold was pretty much Mr. Stroel's design. I used 13 ply concrete form plywood from Menards because it was as flat as Baltic birch plywood, but less expensive. It's a three layer design with a center spine and removable outer plates to allow the addition of the linings around the edges of the ribs (for reinforcement). It's purpose is to provide a template for the form of the body and hold the corner blocks in position for shaping and for gluing the ribs to them. Once the rib/block/lining structure is complete, the mold is disassembled and removed.

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Creating a Mylar template for the mold.

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The finished mold.

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The cutout for one of the end blocks.

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The wood came from a variety of sources. The striped European Maple for the back came from Golden Tonewoods in Romania. The Sitka Spruce front came from Alaska Specialty Woods in yup, Alaska. The rough shaped fingerboard came from India ($30 shipped) because I was unable to find Ebony stock of the necessary size and quality at any price. The neck and blocks came from International Violin. The Tiger Maple boards for the ribs came from a guy in Ohio. I ran them through the planer, resawed them and took them to a friend who had a thickness sander to get them the the finished thickness of 1.7mm. I tried planing them to size, but the figure in the wood made it impossible. Even hand planing it didn't work very well.

The first step in actually building the cello was to temporarily glue the six corner blocks to the mold. I just used a couple dots of white glue on the center spine. The joint has to be strong enough to hold the blocks for shaping and assembly, but weak enough so they can be broken loose to remove the rib assembly when finished.

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The corner blocks glued and taped to the mold. Once dry, I used an oscillating spindle sander to shape the two middle blocks for the "C" shaped ribs.

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The bending procedure was a learning experience. Basically I both sides of the 1.8mm thick ribs with a wet rag, held one end against the flatter part of the iron to heat it up, and then gradually worked the end of the rib around to the part with a tighter radius and held it there until the water evaporated. I arrived at a best temperature of 350º. That was enough heat to form the wood without scorching it. At the advice of an actual cello maker, I thinned each end of the "C" wood to 1.2mm in the area of the tight radii and it worked very well. You have full control of the shape and can add or subtract curve by applying heat until the fit is perfect. I over bent the "C" ribs slightly so the clamps would force them out against the form and blocks when glued, for zero gaps.

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One of the finished "C" ribs. They are left a couple mm wider than the mold for finishing and a bit longer than needed for the clamps to bear.

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Trial clamping before glue.

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The first ribs glued in place. I have never used hide glue before so that was a leaning experience. I bought a bath heater used for waxing (as in hair removal) and used a beaker to mix the glue in. As it worked out, if the heater is turned all the way up, the glue reaches the necessary temp of 140ºF. I warmed the middle blocks with a heat gun, but still had to really hustle to get everything clamped up before the glue set. The rest of the ribs will be easier because none are curved as tightly as these and they can be glued to the blocks one end at a time.

Re: First Cello Build

PostPosted: Tue Mar 26, 2019 3:13 pm
by Brian Evans
I got two comments - you got one kick-ass shop there, I am jealous, and I really enjoyed your post! Nice job!

Re: First Cello Build

PostPosted: Tue Mar 26, 2019 4:30 pm
by Tom Griffin
Brian Evans wrote:I got two comments - you got one kick-ass shop there, I am jealous, and I really enjoyed your post! Nice job!


Thanks Brian,

It's actually more of a machine shop than a wood shop, but you'd never know it from the amount of sawdust on everything. The combination of sawdust and oily metalworking machines makes one hell of a mess. Can't wait until the weather warms so I can purge the place.

Tom

Re: First Cello Build

PostPosted: Tue Mar 26, 2019 11:46 pm
by Jim McConkey
Maybe your next build should be a dust collector! A DIY Oneida Dust Deputy, a bucket, and a small shop vac will build a fine one cheap.

Can't wait to see this come together!

Re: First Cello Build

PostPosted: Wed Mar 27, 2019 1:18 am
by Tom Griffin
Jim McConkey wrote:Maybe your next build should be a dust collector! A DIY Oneida Dust Deputy, a bucket, and a small shop vac will build a fine one cheap.

Can't wait to see this come together!


I'm actually in the process of building a new shop up north, and it will have a built in dust collection system. Up until the last year, I rarely cut any wood so it wasn't an issue.

Tom

Re: First Cello Build

PostPosted: Wed Mar 27, 2019 9:42 am
by Bryan Bear
This looks great! I can't wait to see more.

Re: First Cello Build

PostPosted: Wed Mar 27, 2019 12:09 pm
by Tom Griffin
Thanks Bryan.

I put a few hours in yesterday making the two upper ribs and gluing them on. The larger radii were definitely easier to work with, even at full thickness. The area where the curve reverses was a bit of a challenge getting it all to follow the form, but the curves can be moved around as much as needed without issue.

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There are way more provisions for clamps in the mold than needed, but I guess too many is better than too few. With a good fit on the form, it only took three. I decided to add the spring clamps to make sure the feather edge of the "C" ribs made good contact at the joint.

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I made the upper ribs in two pieces to get the best looking figure on top where it's the most visible. The joint between the to is irrelevant because the upper block will be mortised to receive the neck.

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I got to use my new Ibex plane to pare down the extra width on the ribs and it worked extremely well right out of the box. Should even be better with a good edge. I'll get it close with the plane and then switch over to sheets of sandpaper taped to a flat surface to get the entire surface flat where it glues to the front and back plates.

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The ribs were left purposely long to make it easier to work with and will be cut back to where the "C" rib feathers out.

Re: First Cello Build

PostPosted: Wed Mar 27, 2019 3:38 pm
by Bob Francis
This is a great thread please keep updating :)!

Re: First Cello Build

PostPosted: Wed Mar 27, 2019 4:16 pm
by Bryan Bear
This is inexperience talking and not, in any way, a critique. I have never used an inside mold so this may be a dumb question/observation but I would have guessed that the mold would be shallower than the intended rim thickness/depth to allow the linings to be glued in while still around the mold. At least for one side allowing the mold to be pushed out the other side. I suppose you could still do that by breaking the block loose before doing the linings.

I've only ever used an outside mold (not violin family instruments) so my only issue is making sure the mold is shallow enough to have room for the lining clamps.

Keep the posts comming!

Re: First Cello Build

PostPosted: Wed Mar 27, 2019 4:38 pm
by Tom Griffin
Bryan Bear wrote:This is inexperience talking and not, in any way, a critique. I have never used an inside mold so this may be a dumb question/observation but I would have guessed that the mold would be shallower than the intended rim thickness/depth to allow the linings to be glued in while still around the mold. At least for one side allowing the mold to be pushed out the other side. I suppose you could still do that by breaking the block loose before doing the linings.

I've only ever used an outside mold (not violin family instruments) so my only issue is making sure the mold is shallow enough to have room for the lining clamps.

Keep the posts comming!


Bryan,

It's a three part mold. The center spine and two removable outer plates. They can be removed one at a time to allow the linings to be added.

Tom

Re: First Cello Build

PostPosted: Fri Mar 29, 2019 2:31 pm
by Tom Griffin
It's starting to take shape. I made up the lower, one piece rib last night and got it glued on. This morning's task was to plane all of the ribs down close to the mold in preparation for sanding, and trim the four "C" rib joints to size. Next in line will be to glue up the upper and lower plates, and transfer the outline of the body to them. Once that is done, the linings can be added and the mold removed from the rib assembly. I made a trip to the Depot last night and actually found a piece of Cedar with enough knot free and straight grained area to use for them. Not musical instrument grade for sure, but adequate just the same.

Tom

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I glued and clamped the center joint first, then the lower corner blocks.

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Angling the lower clamps a bit before tightening them pulled the rib tight against the mold. I also made the radius on the ribs here slightly larger than the block so it conformed better to the block when clamped.

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We have the outline of a cello!

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The thickness of the feathered edge on these joints varied a bit, so I'll have some sanding to do to get them to look right. There is plenty of wood to work with there so I'm not going to lose any sleep over it.

Re: First Cello Build

PostPosted: Fri Mar 29, 2019 9:38 pm
by Rick Milliken
I love the mold set up, especially how versatile the clamping system is, brilliant! Off to a great start, watching with interest

Re: First Cello Build

PostPosted: Fri Mar 29, 2019 10:52 pm
by Tom Griffin
Rick Milliken wrote:I love the mold set up, especially how versatile the clamping system is, brilliant! Off to a great start, watching with interest


Thanks Rick.

I can't take credit for the mold design, it belongs to Henry Stoebel. I tossed around other ideas, but he pretty much nailed it so I used his. The clamps do work very well, but if I made them again I wouldn't use threaded rod for the bolts. The threads make it difficult to get them in the holes when you are hurrying to get everything clamped up before the glue sets.

Tom

Re: First Cello Build

PostPosted: Sun Mar 31, 2019 3:46 pm
by Tom Griffin
I mustered up enough courage to cut into the expensive chunk of Sitka Spruce for the sound board. The first task was to sand the ends so I could see the grain pattern and decide how to best orient the two quarter sawn pieces so the grain is as vertical as possible relative to the bottom surface. Then I planed the bottom surfaces flat and jointed the inside edge for the glue joint. I decided to use the rub method of joining them (no clamps) and it worked like a charm. I clamped one piece on edge and poured a line of hide glue along the joint, then place the other piece on top and rubbed it back and forth until the glue grabbed, then just let it set overnight. The result was a nice, tight glue joint. From what I understand, the technique only works on Spruce and not on Maple, so the back will need to be clamped.

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The pouring method made a lot of sense, because it kept the glue from cooling down as fast as it would have if brushed on. There was also no doubt that there was enough glue because it oozed out all along the joint.

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This tree must have grown in a pretty harsh environment with growth rings that close.

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The center line on the front was planed flat and the piece shimmed up along the outer edges before planing the back flat.

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I decided to just plane the blocks and ridges down the the mold instead of sanding it. I used the Rob Cosman method (YouTube) of sharpening my pane and the result was impressive. Even my jack plane cut the end grain of the Spruce blocks like butter.

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I laid the mold assembly on the backside of the Spruce front, marked the outline plus 4mm, using a washer and pencil, and sawed it out, staying just outside the line.

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There is a heck of a lot of wood to remove, both inside and outside, but at least everything is going in the right direction. I was thinking of adding a couple of locating pins to keep the front aligned with the ribs. Probably will locate them in the groove for the purfling so they are hidden when everything is finished.

Not sure whether to tackle the linings next or start the arching. I'm pretty much done for the day though, so I'll save that decision for tomorrow.

Tom

Re: First Cello Build

PostPosted: Mon Apr 01, 2019 7:26 am
by Karl Wicklund
I don’t have much to add here, other than a sincere thanks for posting.

Re: First Cello Build

PostPosted: Fri Apr 05, 2019 4:03 pm
by Tom Griffin
I used a Kutzall wheel on the mill to flatten the edge of the soundboard and it worked so well I decided to use it for the rough arching as well. It saved a heck of a lot of elbow grease. The drawings included contour lines so I transferred them to the wood and went to work. Still have a little more to do, but the heavy cuts are done. After this I'll make some templates for the arch at different locations and fine tune it using traditional gouges, planes and scrapers. My biggest fear right now is breaking off those delicate corners of the soundboard.

Tom

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Re: First Cello Build

PostPosted: Fri Apr 05, 2019 11:54 pm
by Rick Milliken
For what it’s worth, I have done rub joints on both spruce and maple with no issues. Admittedly only a few time, so not talking from depths of experience. The largest was for a archtop, so still smaller than cello, but worked fine.

Re: First Cello Build

PostPosted: Sat Apr 06, 2019 9:27 am
by Tom Griffin
I'll probably do a rub joint on the Maple, just because it works so well to spread the glue and eliminate the excess, then throw a couple clamps on for good measure.

Tom

Re: First Cello Build

PostPosted: Tue Apr 16, 2019 10:46 pm
by Tom Griffin
Spring chores have slowed the progress down a bit, but I managed to get a few things done on the cello. The arching is pretty close, but still a bit high because it was done before the 1.5mm deep channel was cut around the edges. The channel was a little scary because I had never used a gouge before and the grain changes direction quite a bit on its path around the edges. That and the outer edge of the channel is only a couple of millimeters in from the edge. I contemplated making a scraper to eliminate the chance of an errant cut, but sucked it up and used the gouges instead.

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I was surprised at how much time it took to get the arch established even after using a Kutzall wheel (a finer one) to rough it out. A convex plane with a toothed blade was the most useful. It did a much better job on the grain of the Spruce without tearing it out. A flat plane with a straight blade worked (will work) well to finish up using fine cuts with the grain, frequently switching direction for the best cut.

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Had to see what it looked like on the ribs. :)

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The channel is pretty much complete here, but needs some final finishing around the corners.

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Now that the channel is cut, there's a little more work to do on the outer part of the arching.

Re: First Cello Build

PostPosted: Sun Jun 16, 2019 10:28 am
by Tom Griffin
Not mush progress on the cello with summer in full swing, but I did manage to get the top and bottom profiles nearly complete. I thought they were farther along until the tool I made to mark topographic lines on them said otherwise. I haven't tried to correct any of the irregularities yet, but it shouldn't be that difficult with the lines as a guide.

I started playing around with scrapers, having never used one before, and was having difficulty creating much of a hook on the edge. Turns out the burnisher I was using was too soft. I tried an old lathe mandrel instead and the difference was like night and day. I think I have some hardened drill blanks somewhere that I'll make a new burnisher out of. That would probably be easier than re-hardening and polishing the old one.

Tom


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