Jim McConkey's Flood Mandolin Twins

[Jim McConkey]

Now that the thickness is calibrated, it is time to start drilling. Here is my rough outline for the thicknessing.

I drill a matrix of holes, spaced as close as I can get them. The islands in between often disappear on their own, of I can drill them vertically to minimize them. NO MILLING! Because of the depth stop, all I have to do is bottom out for each hole. Here is the plate after the 5 mm pass. The island in the center is because I don’t have enough depth on my small drill press to reach the center. It will be chiseled out later.

And again after the 4 mm section. There is no need to drill the 3 mm part, since most of that thickness comes out of the top surface in the recurve area. In any case, you want about he outer 15-20 mm to be flat for gluing.

The big island in the center and the remaining little islands between the holes comes off in just a few minutes with a chisel.

And finally, time to kill the fingers again with the little Ibex plane.

[Jim McConkey]

So now it is time to breakout my old thickness gauge. I need to rebuilt it one of these days, because the frame has twisted a little, but it still works fine. Just make sure the indicator’s plunger hits the stop, and zero the dial.

Then go around the plate checking the thickness. The center is thickest, at about 5 mm, thinning toward 3 mm at the recurve before returning to about 4.5 mm at the edge. It was actually pretty close after cleaning up the inside surface, and only needed to be tweaked.

[Jim McConkey]

And finally the inside is properly graduated and smoothed out. It still needs a little touchup and a good scraping. Two plates down, two to go…

[Arnt Rian]

Hi Jim, long time! I haven't been around the forums much lately, so I didn't even know there was a MIMF Birthday contest going on, these things are always a lot of fun. Not enough time and too much on the plate for me to join this time, unfortunately. Anyways, this project is great: Mandos, reclaimed or "alternative" woods, what's not to like? Keep up the good work

[Jim McConkey]

Hey Arnt, good to hear from you! I hope you are still building. I have to give you some credit for getting me to the point of being able to build again. A few years back you had suggested using a birch countertop from Ikea as part of a workbench, and that is exactly what my new bench is designed around. It worked out great, much easier than laminating a top, and looks MUCH better than plywood! So good, in fact, that I usually keep it covered with cardboard. I can't bring myself to mess up that nice top yet!

Your message also brings back very fond memories of the 2003 ASIA conference just down the road from me in Westminster, Maryland. I went. You flew over for that conference. Amy Hopkins taught an inlay class. Staffers Mark Swanson and Ellie Ericksen and too many other MIMFers to count all came. It was huge MIMF gathering and loads of fun for everyone. When the membership was much bigger, we used to have a bunch of local MIMF get-togethers, but there unfortunately hasn't been one in years.

[Gordon Bellerose]

I am watching this with great interest also Jim.
I really like the innovations used while carving the tops.

A great story to begin the whole thing too.

[Jim McConkey]

Thanks, Gordon! I am just trying to make a few mistakes here to help you out! (LOVE your tagline!)

My arch-carving methods are actually not all that unusual or innovative. Even my old Siminoff book from the early 80s suggests using a router to hog off the outside before carving. Bill Moll's MIMF violin making class we had years ago recommended the Safe-T-Planer, since that tool was becoming widely available (and still is, now, from Stew-Mac). A drill bit is commonly used for the inside, but I like the bigger, flat-bottomed mill bit a lot better, because there are almost no divots to plane out by hand. You can simply drill out most of the islands that are left between the holes and almost be ready to start planing when you are done drilling. Planing is minimal because of the flat-bottomed bit. If anything, others usually start with a formal topo map for the plates and try to make the terraced cuts a little more accurately. I will admit I am rushing and winging things just a bit too much here. Most professionals would use a CNC or router-based dupli-carver for the plates. The nice thing for us occasional amateurs is everything I have done here can easily be done on a small drill press, with no other special tools required other than the Safe-T-Planer and milling bit.

[Jim McConkey]

The shape will be determined by a form I built as part of the MIMF mandolin class years ago. Nothing more than 2 pieces of MDF glued together with a mandolin cutout in the middle. As usual, life got in the way, and I was never able to complete the class or get much beyond the form. One thing we didn’t talk about in the class (not that I remember, at least), was turning in the inside cutout into spreaders, like I saw on Siminoff’s web site. Thank goodness I kept the cutouts!

A couple cuts on the bandsaw removed the center portion. A 1” Forstner bit cut the cavities for the ends of the 5” (125 mm) turnbuckles, and a couple of 1/2” Forstner bit passes cut the channel out to the center, which only took a few seconds with a chisel to clean up. A 1/4”x1” screw and washer hold the ends of the turnbuckles in place.

This spreader can be used both for newly-bent sides while they dry and at the time of assembly. You simply spin the turnbuckles by hand, and the two cutouts hold the sides firmly in shape and in place. The gap in the middle gives plenty of room to clamp the neck and tail blocks in place.

While thinking ahead to the assembly, I was also perplexed on how to clamp the top to the sides while the sides are still in the form to keep their shape. I am well equipped with homemade spool clamps, but they are only like 1 1/4” diameter, nowhere near big enough to get around the form. So I drilled a series of 1/4” (6 mm) holes just inside the edge of the form. I have to disassemble the spool clamps, but I will be able to put them in the holes from the bottom, and add the top disks and wingnuts after the top gets glued on.

[Jim McConkey]

The neck and tail blocks are are oak from my demolished flooring. The grooves on the back of the flooring had to be planed off with the Safe-T-Planer and smoothed with my drill press sanding jig. It was more efficient and less wasteful to take off the top finish off with the sanding jig than to try to plane it off.

The tail block is just one piece, bandsawed and sanded to match the curve of the tail. The neck block had to be laminated from 3 pieces. They were glued with Titebond III, which is not normally recommended for lutherie because of its propensity to creep, but it made sense in this case for 3 reasons. First, it is waterproof, so that if the joint ever needs to be steamed apart, the neck block will not fall apart in the process. Second, I will be using Siminoff’s simplified V-joint (also highly recommended by Mario Proulx in our library), and this joint involves installing two vertical dowels after the joint is assembled. These dowels will lock the pieces together and not allow any creep. And lastly, I had it on hand, and did not have any polyurethane glue, which might have been a better choice.

[Jim McConkey]

The blocks are ready, but it seems the sides have relaxed a little since bending, requiring a quick touch-up. Before I can glue it up, I have to cut the sides to length. It is not necessary to fit the sides tightly at the neck end, because they will be cut away later when the neck joint is cut anyway. Using the neck block to temporarily secure the ends, the tail ends are marked and cut to fit as snugly as possible.

The sides are put back in the form with the spreader, the tail end is fitted and the spreader is tightened into place, keeping a good fit at the tail. You have to watch out here, the spreader tends to pull the tail joint apart. It is a good idea at this point to tap around the rim with a block and small hammer to make sure the sides are seated correctly before tightening the clamps. This mold was designed for a flat-top, so it is actually too deep for archtop sides, which are considerably shorter, so it was necessary to use a small block when tapping.

Once the sides are locked in place and the tail joint is tight, it is time to spread some hot hide glue and clamp. Clamping couldn’t be easier – one cam clamp to hold the tail block against the end, and the other to hold the neck block tightly in place. Time to put it aside and let it dry until tomorrow, when mando #2 gets its turn.

[Jim McConkey]

With the bodies starting to get glued up, I will be needing the necks shortly.

The heels were laminated with waterproof TB III glue (as explained before, so they won’t come apart if the joint ever needs to be steamed), with alternating grain directions in each lamination.

A flat-top mandolin I own was damaged in the same flood that destroyed my house. It is currently apart being rebuilt (new repair discussion coming soon), and its fretboard is currently off its neck, so I used it as a template.

I cut fretboards to match the template fretboard, with some modification at the end since the other mandolin is a flat-top and doesn’t have the extension common on archtops. The extension is exactly half the width of the fretboard, and the little corners at the bottom left were cut with a 1/2” Forstner bit and just cleaned up with a file.

Once the fretboards were cut to shape, I used them as templates and cut the necks to match. Time to find my microplane rasp and get to work shaping the neck profiles.

As I mentioned before, the heads do NOT have a veneer installed - that is the original floor surface! The desire to retain the original finish was the reason I chose this style of scarf joint. With the other possibility, only half the head would have the original floor finish.

[Jim McConkey]

With only one form and two mandolins to make, they obviously have to take turns. One rim set is done, and the other has been glued up. It is almost time to glue on the tops, so I better finish those while the rims are being glued up!

First, the already-glued rim can have the top kerfed linings installed. Its twin will get its after the glue dries from adding the blocks. Clothespins make cheap and effective clamps for linings. You might notice that some of them have been modified to have the spring further back to give a larger opening. I use these for repairs and other situations where I need to glue or reglue the bottom linings.

[Jim McConkey]

Next, the tops need their F-holes. I copied the F-hole pattern from Siminoff’s book and transferred it to mylar (laser transparency) with an X-acto knife and a Fiskars cutting surface. This almost proved to be pointless, because I can’t see the F-hole cutouts at all when the transparency is laid on the top! But the paper cutout worked. Well, almost. The pattern is actually for an F-style mandolin, so the spacing is a little different than for an A-style. The top holes of the Fs were too close to the edges, so I had to rotate them inward.

The key to layout of the F-holes is that the bridge should lie on the line connecting the two innermost points on the F-holes. The necks are designed so that the neck meets the body at the 12th fret. So it is a simple process to lay the fretboard on the top, with the nut end of the fingerboard where the neck will attach, and then just mark the position of the 12th fret to get the bridge position.

A small hole is drilled in the center of each F-hole. This will eventually be a starting place for the jig saw, but it also helps define the location of the F-holes on the INSIDE of the instrument. Siminoff recommends gluing a piece of surgical gauze tape over the position of the F-holes on the inside to reinforce the holes, but I didn’t bother. For complicated soundholes on other instruments I have used a thin piece of wood glued with the grain 90 degrees from the top, but that didn’t seem necessary here. The holes were cut with a hand jig saw and cleaned up with a violin maker’s knife and jeweler’s files. The little tube is Pro-cut, a wax for jig saw blades. I normally use it for cutting inlays, but it seemed to help on the wood, tool.

[Jim McConkey]

The tops also need bass and treble bars. These are much more like violin braces than guitar braces. They are shaped to fit a curved bottom, and thin to almost nothing in the recurve (thinnest) area of the top. They do not tuck under the kerfed lining.

I had a little wood left over from the tops, so I sliced some brace wood out of the most quartersawn part. It would have been nicer to have finer growth lines, but the wood is what it is.

The braces are cut to length and positioned approximately in position. Since the top is hollowed, this leaves the brace suspended by its two ends. In order to mark the curve of the top, I took a brace cutoff, cut a notch in the top, and put a piece of mechanical pencil lead in it. The marking tool rides along the inside surface of the top and draws the outline of the top on the brace. This has to be done for both sides, since they are both different.

This improvised marking tool did not work very well because the lead kept slipping or breaking. Siminoff uses a pencil stuck in a small block, same idea, but probably more reliable. I ended up using a divider to etch the line in the braces. And having just replaced a couple hundred feet of baseboard, I should point out that the same trick works for fitting baseboard to an uneven floor. What? You thought all houses were square and plumbed? Think again!

[Jim McConkey]

The braces are planed to the lines with a finger plane and violin maker’s knife. When the fit is getting close, you can put a piece of sandpaper on the top, and sand the brace with short strokes in position, much like fitting a bridge to an archtop.

Doesn’t fit too bad…

After heating the top and braces, and brushing on hot hide glue, two spring clamps hold the ends in place while a cam clamp holds the middle of the brace. My spring clamps wouldn’t reach the middle of the brace.

I will let the glue dry overnight and tomorrow the tops can go on the rims.

[Bryan Bear]

I'm really enjoying watching this unfold!

[Gordon Bellerose]

Yes. I am enjoying this thread also. Keep up the good work Jim!

[Jim McConkey]

The rims have their blocks and kerfed linings, so it is almost time to glue on the top. Well, not quite yet. It helps to shape the braces *before* gluing the top on. It can be done afterward, but it is trickier.

I needed to make sure everything is level so the top will sit flat when glued. The blocks were a little proud of the sides and had to be planed down, and the kerfed lining is rarely ever perfectly flat after gluing, but the finger plane takes care of that in no time.

It also helps to put a small brad in the blocks that will help keep the top in alignment while being glued. I used an alternative here. I put a staple in the block and cut off the legs close to the block. I lined the top up correctly and gave it a good whack with my fist, and the staples dug into the top, making it much easier to put back in exactly the same position after being glued.

[Jim McConkey]

I used the spreader to hold the rims slightly protruding. The kerfed linings also help it from slipping down. My spool clamps have been disassembled and installed in the new holes in the form, just waiting for the top.

After warming everything for a few minutes with a small hair dryer, I quickly put hot hide glue on the braces and top, realigned the top, and weighted it own until I could get all the clamps on and tightened. I get the ends and sides clamped first, then start adding clamps in between. It worked fine, but I am not crazy about this clamping arrangement. It would be a lot easier to have a form with outside slots, like on a solera, so that the clamps can be adjusted assembled to just a little too wide, then put on quickly and engaged with a turn or two of the wingnuts.

[Jim McConkey]

So now I have two half-mandolins. The end joints didn’t glue as cleanly as I would have liked. I may have to think about a stripe or wedge on the end. We’ll see if I have time.

Gordon, this is another mistake you don’t have to make for yourself...

Speaking of time, I had to go out last night, and in my rush to get the second body glued up after I got home so it could dry overnight, I quickly trimmed the top to match the rim out of the form, which was being used to glue the other body. Just to make life interesting, the body had elongated slightly out of the form, and when I went to glue it, the top wasn’t wide enough to get to the edges. I had to fudge the placement of the top a little to minimize the gap. I would have eventually routed a gap there anyway for binding, but this gap is almost twice as thick as the binding I had intended to use. I could use a thicker binding all the way around, or stick with the current binding and try to add a sliver of top material just at the widest parts. I’m not sure which way I will go yet, but the key to being a good luthier is learning to hide your mistakes.

Besides this screwup, I found that somehow the bottom of one of the F-holes got shifted a little to the side from where it should be. Oh well. Too late for that one. At least it doesn’t look too bad.

In any case, I was so rattled by such a major screwup that I took today off and took care of other stuff, despite being on a very tight schedule to finish by next week. The next step is to fit the neck, probably the most exacting part of the whole build. Just to make it more interesting, I have no experience at all cutting neck joints. I need a clear head before starting that, so I have been reviewing the process and the procedure, and triple checking my drawings and getting even more confused. My own full-scale drawing says I should be aiming for a neck angle about 4 degrees, but most other sources say 6 degrees. I have to think about that some more.