Roughing the re-curve

The central part of the cross arches can be accurately defined by the catenary arch on the inside. How close you make it to the edge will determine how close you come to a curate cycloid as your outside shape. The recurve starts out by figuring out where the line of inflection, and the low point is going to be. The low point is easy; look at the plans; or in my case where I'm making it up from scratch; come up with a number. I'm using 7 mm in the c bouts, and 9 or so for the rest. I'm putting double purling in; since I'm making it somewhat like a Maggini shape, so those numbers should work. Amati models may go in further than that, an other models may get closer to the edge. Now we have to find the inflection line, where the concave curve changes to convex. Turns out it is easy.

You know how a cycloid is formed. A disc is cut out with a circumference that will cover the distance form low point to low point in one revolution. A hole is placed 1/2 the height of the actual outside arch (height of the arch minus the thickness at the low point), a pencil is inserted, and the disc is rolled on the circumference. We don't need to make all that, we just use some simple trigonometry. Figure out how far the disc rolls in 15 degrees, find the sine and cosine of 15 degrees, and use those numbers to find where the pencil would mark at 15 degrees. Do it for 30, 45, 60 and 75 degrees, and you will have 4 points that define the recurve exactly.

I had to edit this part. I was trying to find the point of inflection, and forgot to add the width it rolled with the disc. DAH! So I did it over. For a normal Strad type arch it is about 66 degrees of rotation at the c bouts. For a slightly wider and shorter del Gesu arch, it is about 72 degrees of rotation. So, a Strad arch is about 75% convex, and a del Gesu about 70% convex. The upper and lower bouts will have even more rotation to get to the point of inflection. I draw out some of them, I picked 7 on this one, and I can pick and choose what sort of tool I will use to cut them. Here are my choices for concave curves:

And the recurves and the ones that will cut them:

Turns out, the recurve, even in the c bouts of this 5 string, use my three widest tools. The bottom of the lower bout even needs to be somewhat flatter. This is what I came up with doing one side of the belly and the back.

These are not finished. This is only to rough out the recurve for preliminary tuning. I also only cut the recurve part first, and didn't blend the central part of the arch in to it. I cut the recurve from the low point to the inflection line, or a little past it, and then use the thickness punch to put pin pricks on the inside to finalize the inside arch. It is only after that that I use the punch to do the outside.

This is what the inside looks like:

Well, those photos don't want to load. I'll put them in another time.

You have to be aware of how much the concave arch goes down from where the platform that you have is set. This one goes down just less than a millimeter in the c bout area, and less than 1/2 of that everywhere else. This means that for this one, I will end up having to cut the central area, without being able to use a full arch like I roughed it out with. What the maker does when this happens is up to individual style. They can just keep the thicknesses really thick, or cut them out with smaller cutters. They can make a hump, or a tiny radius, or any number of things.

This may explain, or confuse!

5 String Roughed Out

I had the plates roughed out. Now I filed and cut them close to the finish outline. I double checked the outside long arch, and inside long arch, and then the inside cross arches. Cut the edges down to about 5 mm thick, and blended the outside in some. They are still quite thick from 1/2 way to the edge. The center may be somewhat thick, but I've never done this before; nobody has; so I want to start thick and try to find out what works.

I bought a wall cabinet to put stuff in. Mostly varnish stuff, and that kind of thing; not tools. It works good.

These photos show the size of the beast I'm making. It is more of a 5 string viola with a violin scale than a 5 string violin. Hopefully it will roar like a beast. It isn't long, but it does seem quite wide.

The 5 string

Like I said, I'm doing a 5 string. I drew up a Maggini cello from 1600 that I think looks great. Turns out in 1/2 scale the stop length is the same as a violin. My brain went crazy and thought 5 string; so that's what it is. I had to change it some. The actual stop is right on center. Bruce Carlson said that is fairly typical for Brescian instruments. But they had the bridge low. Here it is:

It is a sweet thing isn't it? I lowered the f holes so they matched where the bridge was. Then I had to lower the lower corner because the cool f holes somehow lost some of their length. Not really, but it just looked that way. Then I had to lower the centerline of the lower bout. I ended up with this:

Once I get the outline on the roughed out plates, it won't take too long to finish up.

Projects

I have several projects going on. Three involve finishing up instruments. One is the Strad I did on this blog. My varnish job had problems; some of it didn't adhere well. I tried taking the parts off that didn't stick, and putting varnish back over. That was a disaster. My hats of to restorers. I have the Gagliano viola and Plowden to glue up, and finish. Necks are part done, ribs and plates are done, but need tuning up. Shouldn't be too much to do on either. Then my latest:

I really liked this Maggini cello I saw photos of. I drew it up, and noticed at 1/2 scale it had a 195 stop, with the bridge were it was set (the notches and f holes are on center). For some reason I thought 5 string, and that's what I'm doing. I just started gluing the ribs today. The plates are roughed out, and need to get the final outline from the ribs before I can finish them up. For the scroll I took the Gofriller viola scroll, and unfurled it one turn for space for the extra string. I like the results.

The back sides and neck are cherry, and for the belly I have a chunk of poplar. I had it glued up as a viola back. It is very light and resonant. I decided to use maple instead because the poplar was just so plain. But for a belly it may work. If not I have a nice set of old bear claw Sitka as a backup.

The varnish is off the Strad. Came off easy with isopropyl. Watch the alcohol, your varnish might just peel off! I had to take the belly off to fix a crack. This red spruce is very chippy, as seems prone to splitting. Sitka is looking better. I'm ready to glue it back together but I have an issue. What is this?



I had the back and belly in the garage, and on the deck for a while, maybe a month, and there are black dots on the neck. They don't just rub off. I tried water and a paper towel. Oil, tripoli and chamois. Neither one touched them at all. Mold? What to do?

I've been working a lot on my devotional blog. Reading and watching youtube videos. Lots of buzz about September 23. I don't know for sure about it, but I don't want to be stupid either. I'm always ready.

Oil for Varnish

I've been playing with oil for making some varnish. I can buy good varnish, but once you have tried to make it, and had some minor success; the process is stuck in you, an you want to try it again to see if you can do better. The same is true about violin making. The same is true about every aspect of your life; even the spiritual. I've been washing the oil, and then clarifying it in a pan until the water is all out. It gets it darker, but it is still clear. I'm trying to get it to go redder, buy washing it in different things. The oil is just boiled linseed oil from Home Depot. That is the jar on the right. As you can see it isn't the pristine stuff that you would put on a salad! It looks fairly nasty.

With some backlighting it show some promise though.

They are arrainged from light to dark on the left. When I look at them in the light, there is a difference in color, and darkness. The photos don't show so much.

The lightest.

The next lightest.

The second darkest.

The darkest one.

I have some raw pine resin, and fir resin on order, so once that stuff comes in I can cook some varnish up. I never know exactly how to measure the parts. How is the oil I have now measured? It isn't quite pristine; I'm sure it has less volume than it started at. Same with the resin. The hard resins are easy to weigh, but how much water is still in raw gum. I'll try the Keith Hill method for the raw gum.

Now, here is the plain oil out of the can washed with water, and sat overnight. The oil itself seems to be hydroscopic, it doesn't act like the nice oil on Tad Spurgeons site.

So, I have to cook it in a pan, and boil out the water. It made a lot of yellow foam, and bubbled like crazy for a while. I but it on the heat until it bubbles, then swirl the pan off the heat until the bubbles stop. They were pretty much ending and I took a measurement of the temperature. 260 degrees F. It looks like this:

With back lighting it is the lightest of all, but still redder than it was before.

I want a dark varnish in as small a thickness as possible. We will see.

Cello Cross Arch Design

I've been avoiding the basement; it's just too cold down there right now. So I planned out my arching. I did have it somewhat figured out. I knew my long arch, and I knew how the inside long arch would go. I roughed out the inside catenary, leaving it some ways in from the edge, so I could always widen it up if I needed to. Now I needed to see where I need to be.

I drew out the f holes on the inside of the belly. This way I can see how the f hole sits on the arch.

The area of the lower wing looks like it should work into a nice shape. I make that area outside of the f holes as their own shape. It fits into the rest, and starts as a continuation from above the f hole; but it terminates as it flows into the lower wing by the eye. The arch below the eye sweeps into the edge in a big curve. At least that is the way I do it. That's what I like. I don't know if it is anyones style, but it makes sense to me, and it works well with my method of making. This is how it looks on the viola. First the upper arch flowing into the lower wing.

And this is the treatment at the bottome end:

It's nice and sunny today. Everything is SOOOO much better when it is nice ans sunny. I drew up some archings the other day at work. It's really easy to do. I had the measurements of the width and height, and just went form there. I started 40 mm up from each block, and made them 30 mm apart. I ended up with 21 of them. The most interesting ones are the middle ones.

I stay quite a ways away from the edge. If you get too close to the edge, your arching will be more bolbous looking. I'm not trying to get that. I want it looking right. You can see how the catenary defines the center portion of the arch, but the recurve is a differnt thing altogether. It seems to me the recurve is where the aching templates would be the most useful.

Make some purling

I decided to make some purfling. I read all the people who wrote about making theirs. A big peice of stock, a big plane, and a big workout. I can deal with the first two, but I'm not interested in a big workout. I decided to do it differently.

I found a piece of maple in the wood bin at work. planed the side to see what I had, and sliced off two 1/2" wide pieces. I have enough left to get three more pieces. I sawed two strips to make three strips about 3-4 mm or so wide. That will be the height of the purfling. Then I started planing. I have no idea where the purple came from. Very strange.

It worked pretty good. The strips were are about .7 mm thick or so. I stopped for lunch. After lunch I read Michael Darnton's way he makes purling again, and noticed that he brushe the wood with hot water, and lets it set 20 seconds, and then planes it. I gave it a try, and it works great. Dry, it cut fine, but a little chatter; but that will just show up as handmade. The biggest difference is the curl. The first ones curled a lot, and with water they only have a gentle curl. I found a piece of wood to use as a brace to keep the bench from moving.

I kept planing over and over, and sawing the slots down when I got to where they disappeared. Next time I will saw them deeper, and stop sooner. When the wood is wet it is harder to saw; you end up with fiber, and it is harder to keep straight. If the groove was still 1/8" deep, it would be easier.

So now I have two piles: one to be the center whites, and one to get dyed black. I'll go through the whites to see if any are too thin. I need to get some chemicals to dye the blacks. Roger Hargrave uses ferrus sulfate, Pot. Hydroxide, and logwood chips. Darnton uses ferrus sulfate and tannic acid. Roger's method needs boiling, but appears to be a one shot deal. Darnton's method seems to be a repeat as necessary thing.

Does anyone have a preference? Have you tried either method?

Cross Archings

I had a question about re-curves and cross arches. My outside arches are very much like a curdate cycloid. I don't make templates for them, and I don't have to get them perfect. The arching is composed on the inside.

With at cyloid, the point where it switches from convex on the top to concave on the edges is mathematically given. It is 1/2 the width, plus on half of the arching height. For a c bout that might be 50/2=25, plus half the arch height so 16-3(edge thickness)/2=6 1/2. So, the point of inflection is 31.5 mm from the centerline. 38% is concave! Much more than you would expect. In the bouts it is even a higher percentage because the arch height is lower, and the width is wider. The one constant is that the inflection point is always one half of the arch height.

If you have a cross arch from a poster, it is a simple matter to draw the inside arch in. Then draw a line for the bottom of the plate, and hold the poster upside down, and use your chain to see where the width comes on the bottom. If you do this for all the arches given, you have a good idea of where the original catenary cross arches can go to, if you want to end up with a similar arch. If you have done this for a few, you can come up with your own discoveries.

Here are a couple of sketches that show some of my ideas on cross arches. It is easier to draw them, then to put it in words.

What do you think?

Roughed out Cello Belly

I have the belly roughed out; really rough. It is 8+ mm everywhere, and way big on the outside, but I may have to add a peice at the lower bouts as wide as the purfling, maybe. I don't know what I did, but I must have either measured wrong, traced wrong, or the joint was way off when I planed it on the lower half. I don't remember any of that, but we'll get to that when we have to.

It is surprising how fast it went. About 5 hours total after gluing it up. It is about double the weight at 880 grams. (I used the kitchen scale) and the tap tones are viola like at 360/180hrz. I don't know if th etones will drop in half when the weights drop in halve; but it does seem to me that at least the wood is in the ballpark.

Here it is this morning before cutting it out with a coping saw. It is much easier to saw spruce than maple. But, I bet you knew that.

I can refine it some before I have to build the ribs so I can finalize the outline.

First off, I will have to be sure that the bottom is still flat. It doesn't seem to have moved.

Then I will cut the eges down to about 6 mm. That should be plenty.

On the inside I can take the long arch out to the blocks, or close to them, and re-do the cross arches to match.

Then I can carve the ceter area of the front down to a smooth circle, and even out the thicknesses.

Then I can blend the cross arches into the edges. They will still be high.

That is about it. If I do the same with the back, I can arrainge things like arch height (I have some room on the belly, but not the back) and thickening, to get the plates to be close in pitch. I don't really know if it matters, but it is easy enough to do. THat is about all that can be done until it gets down to finishing.

Drill press work

I worked on getting the cross arches roughed in, and the long arch refined. Before I start drilling hole in the other side as a guide, I want to make sure that the inside arch is halfway decent. It took about an hour and a half.

Now it's time to drill the holes. I use a 1/4" or so drill in my drill press. It is nothing fancy. The bearings aren't great, and there is up and down slop, and it isn't exactly square, (I don't think) but it was $40, and it drills holes. I made up a little post that the plates sit on from stuff I had sitting around, and I set the drill above that. I use 5 mm for violins and violas; I'm using 8 mm for the cello.

It took longer than I thought to drill the holes. The drill press won't reach the middle, but there isn't a whole lot of stock there, and my thickness punch will reach the middle of the plate.

After that it is just hog away at it with planes until the holes dissappear. I still have work to do on it, but there is a good hard hour worth of work there. An hours worth of good work is enough at one time, We watched a goofy movie that we had never seen, "Princess Bride. What a corny movie! Well, we've seen it now! And we had fun watching it, and maybe my joints won't be as sore tomorrow.

Starting on the Belly

I glued up the belly yesterday when I re-glued the back seam. Today I started roughing the inside. My method is to rough the inside close, rough the outside a couple mm's or so thick, and then flatten the bottom. At that point I can start finishing. I figure that is the way the master received the job from the apprentice. I'm doing the grunt apprentice work now. With planes the work is very easy. Here is the first hour:

First I drilled 2 holes twenty mm's deep. I'm making a long arch based on two catenaries, kind of like a back, but with longer arches. I didn't want just a straight catenary, and I didn't want a Strad-like arch. It is more like a del Gesu. The arch is quite flat, so it should work.

It's hard to tell from the phot, but the long arch is all roughed in. I leave it a little short so if I have to take more off the bottom than a mm or so, the arch won't be undercut at the blocks. I write this like I've been doing it for years, but I just found in out when I was doing the cello back. At least I learned something. And I learned how to glue up a long crack.

As you can see the planes leave a big pile of chips in just an hour. But they are nice easy chips. I move the plane in a long motion, cutting the whole arch in one swipe. Sometimes I may have to work on an area to push it down; especially near the block where the arch rises quite quickly; but most of the time the plane bottom defines the cut, and make the job simple.

Now, I have to go to work. Tomorrow is Sunday and I'm off. I'll work on the cross arches then. It is supposed to snow. I've heard anywhere from 5-10 inches. Yuck.

Cellos are bigger

Cellos are bigger. You would think that I knew that right off the bat. I did notice that, but I didn't realize what it might mean. My back needed to be sawn, and that didn't go too bad. It cut straight, and even on both sides. The problem is that the outside of the board was only cleaned up in the middle from the plane, and the ends were still rough. I didn't think about how much off they were. I'm going to have to glue some shims on the ends of the back on the gluing surface to get it so they don't rock, and then we'll see if I need to do more after they are joined.

I'm trying for a 24 mm back. That's what I figured I could get out of the stock. It will go with a 27-28 mm belly. The pieces will make it, but only with the doubling. I guess that is the proper term for my wedgelike shims. If this happened on a violin, it would be an easy fix. Rub it on the diamond dust wheels that I have, and see where the low spots are, and glue on some stock. The cello back is not that simple. I don't have anything that big to grind it on, and it is hard to hold it in a way that keep s it flat all the time. One side I only needed doubling on one side to stop the rock, and the other needs it on both ends. Hopefully the ones I have glued on now will be enough so I can join them tomorrow after the glue dries, and I flatten them out.

I'll show pictures when I'm done.

I'm putting the purfling groove in the del Gesu violin today. The plan for it and the viola is to glue the belly on the ribs. Cut the recurve and tune them. Get the mortice cut, and get the neck set and glued in, and then glue the back on. I will cut the recurve, and tune the backs on my boards I cut out.

I'll have to get the scrolls done; I never did finish them, and rough out the radius by the botton on them.

And then they will only need to be strung up and tested, and then get finished off with some varnish.