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Making a double bass


Roger Hargrave

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sorry.... ribs ...I knew that. really, I did. :blink: my question was if the neck heal was formed concave to the rib curve, or vice versa. Thanks for the answer.....as per Andrea Guarneri. 

   My next question ...for a modern neck set, given the need to have a small gap between the top and the overstand /heal to prevent cracking of the top during it's life span ,and given that the majority of the strengh in the neck joint is in the button area, and having a top block  made of the same wood as the top and in a similar orientation as the top ..... would it make any sence to have the ribs butting the neck, but then having the spruce top block sidewalls fit a bit loose? I see some makers fit the mortice/tennon tight enough to support the body ,can't help but wonderif just a bit looser could be a good thing. not sloppy loose, just not tight tight.????? 

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Roger,

I have been helping a friend/bassmaker on an instrument in prep for varnishing.  He has a small shop so the probems escalate at that point. 

Our solution to tanning and drying is this: don't take the bass to the drying box, bring the drying box to the bass.

We are making four 24" wide plywood panels the length of the bass + handles at each end.   Six 18"/15W back lights per panel. 

The bass is on a cradle. The panels can be stationed beside, under and over the bass.  The top panel is on pulleys from the ceiling.  Pull them up at night, turn them on and go home.  In the morning they can be stored or retracted as necessary.

Great thread!

Joe

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Thanks for that Joe. I have been thinking along those lines. Panels rather than a box will also alow air to circulate more freely. I will be making some final decisions on this next week. 

 

Just to add a bit of colour, here are a couple of recent, almost finished portraits. My daughter (80cm x 100cm) and Michelle Wie (240cm x 140cm). But right now the workshop is too small with the bass here as well, so the painting will have to stop for a while. 

 

 

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 Koen sent me his experiments and I sent him my experiences with both his and my own experiments. Since his death people have been asking me what the constituents of Koen’s varnishing system were. Well the answer is that although I know something about his methods, I do not know exactly how he made his various products. For this reason I can only tell you how I make and apply my varnishes, and this changes from instrument to instrument. These changes depend upon what I am copying and my mood at the time. I have always tried to keep the process simple. I have never liked complex recipes and methods. So in the next weeks it will be my system (similar but not the same as Koen's system) that I will be describing. I will also try and say something about how I came to develop my present methods. In the meantime if anyone wishes to try the system that I will be using I suggest that they go out and purchase a kilo bag of simple 'Plaster of Paris. Don't get any fancy quick drying or high quality stuff that might have additives.    

 

I'm really looking forward to it. Roger I think this thread is by far the best one since I've been here. A heartfelt Thank you.

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So, when you get your 1 kilo bag of Plaster of Paris it will still be hot. (Meaning that when you add water it will set.) It will need all the fire taking out of it and here is how it’s done. Get up early in the morning and fill a bucket with ten liters of cold water. A plastic bucket is best. An old metal bucket might just transfer some iron into the mix. Next get yourself a smooth stick. Pour the plaster into the water and stir vigorously and keep stirring continuously until your arms are falling off. Depending on your state of health this might take ten minutes or half an hour. The longer you can keep going the better. When you need a rest let the plaster settle for a minute or two; not more and stir it again. Do this as often as you can for at least an hour. If you let it settle for more than a minute or two it will start to set and the particles will become too big.

After an hour of continuous stirring let it all settle again and as soon as it is possible pour off the upper layer of water. Even if the water looks clear, DO NOT POUR IT INTO A SINK OR A TOILET OR ANY FORM OF CLOSED DRAINAGE. It will eventually settle and set no matter how much water you follow it up with. If you have a compost heap pour it on that. It will add lime to the mix. As soon as you have done this fill the bucket again and stir vigorously. Keep stirring for as long as you can. The more you stir the finer the particles will be. Then you can stir vigorously for a minute or two and leave it for ten minutes. Do this until lunch time (about 4 hours in total). After a short lunch pour of the water again and refill the bucket with fresh water. Stir vigorously for a few minutes every half hour until tea time (4 more hours). In the evening leave the TV ever hour and give the bucket a stir. Last thing before going to bed… well you know by now. Next morning pour off the top water and fill the bucket again with fresh. For the next three or four days stir it vigorously every two hours and change the water each morning as before. Doing this for a week will achieve the best results. After a week you can let a small amount dry to see if it sets. It should not, but it still might. If it stays soft and friable like slightly courser talcum powder you are about right. BUT always wear cloves because it can irritate sensitive skin and even cause dermatitis. Keep the dry powder in a dust and metal free container.

Why we are doing this will be explained tomorrow or Friday. Good night.             

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One of Brian Hart's tools that really came in handy was the fret saw that he made for me. I had it made for cellos, but it works on bass soundholes as well as violins. I asked him to make one that turns in all directions and this is what he came up with; genius. I have also posted a picture of my V shaped board that features in my rasping the outline post. I use it for cutting out soundholes. (Unfortunately too small for the bass)

I think this saw will allow the blade to be at different angles.

 

www.knewconcepts.com

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I never realized this plaster job took so long!

Is the resting time very important for the plaster, other than to spare the luthiers arm and for changing the water?

Paul

 

If you were a kilo of plaster being stired by a crazy violin maker you might want a few minutes rest as well. 

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I bought one of these recently. While the smallest blade would work on a cello F-hole, the bow saw excels and cutting out plates. By the time it takes me to get to the garage and set up the band saw, I can have a violin plate cut out by hand.

 

old news to some, new to me!

 

Chris

 

I agree entirely! 

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While I am still enjoying a delightful numbness on my right arm from yesterday's plaster big stir up...

 

I got to the point that I could try out my new purfling cutters.

 

I was quite jealous of Roger's Jackson made toys, so I decide that I could just make myself my own version of the tool. Some maple offcuts, some steel for the plates and a rather simpler design. I have yet to spruce them up with shape and finishing off details, such as the obligatory stamping with my name, so they don't get confused with Roger's in 300 years time. 

 

Truth is, plain and simple, they do what it says in the can. 

 

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Strange minds think alike. I made a set last week too. I went the whole hog - made them out of boxwood and antiqued them!

 

I'm a bit scared to do a fiddle with them yet - I find I'm inclined to lose the line. I shaped the blades with a very slight radius on the flat side, a rounded tip with a long bevel. Perhaps I just need to practice more.

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Strange minds think alike. I made a set last week too. I went the whole hog - made them out of boxwood and antiqued them!

 

I'm a bit scared to do a fiddle with them yet - I find I'm inclined to lose the line. I shaped the blades with a very slight radius on the flat side, a rounded tip with a long bevel. Perhaps I just need to practice more.

Yep, I am finishing them off bit by bit,

the blades are now sharpened with a round tip.

 

I need a bit of practice as well, it is a different idea altogether, might want to use some scraps before butchering a nice spruce front... 

 

Also, the method outlined for producing purfling shavings works very nicely, by the way. 

 

Juicy thread, no doubt .

 

Jose

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While I am still enjoying a delightful numbness on my right arm from yesterday's plaster big stir up...

 

I got to the point that I could try out my new purfling cutters.

 

I was quite jealous of Roger's Jackson made toys, so I decide that I could just make myself my own version of the tool. Some maple offcuts, some steel for the plates and a rather simpler design. I have yet to spruce them up with shape and finishing off details, such as the obligatory stamping with my name, so they don't get confused with Roger's in 300 years time. 

 

Truth is, plain and simple, they do what it says in the can. 

 

attachicon.gifpurfingcutters.JPG

 

Nice! Sorry about the arm, but isn't that what your right arm is really for?

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Although, I have not yet described in detail the process of pre-coloring the wood before applying the ground; as promised I would broadly like to say something more about the bucket of Plaster and its purpose. Obviously I intend to illustrate my work on the bass as and when I do the work, this is just by way of a basic explanation.

 

I am pleased to see that some of you are already into the plaster slaking process. I am not a great one for chemical formulas; however, I believe that what we are making is fine crystals of a fully hydrated form of calcium sulphate.  Although it is slightly irrelevant, perhaps some cleaver person can put us right on this. All we need to know is that we are basically making a simple filler, (or an extender, depending on how it is to be applied). There are probably as many possibilities for filler/extenders as there are violin makers. These include; bolus (a kind of clay), powdered glass, chalk, marble dust, silicates of various types, mica, marine glass, and a whole bunch of natural and commercial fillers and extenders with various commercial names. Most of these products are available from companies like Kremer and Hammerl. You will need to try several with your particular varnish to see which ones work best for you.

 

Now it is important to say that these are fine powders and some, possibly all, are dangerous if breathed in. Mica and Marine glass are particularly horrid. Silicosis and pneumoconiosis are not just diseases that affect miners. Don’t forget that allergic and respiratory problems can already be caused by wood dust; we don’t need to aggravate the situation. Please wear masks and if possible work outdoors when using any of these substances.

 

I know that there are many people out there that already know a lot and I apologies if I am talking down to you, but perhaps it is better if I try to explain my reasoning as I go on.  Let me begin by saying something about the role of fillers or extenders in the violin varnishing process. At this point I should say that I will be varnishing the bass with an oil varnish. I have been using oil varnishes for most of my working life. However, fillers and extenders are also used in conjunction with spirit varnishes. Actually my paternal grandmother was a French polisher, (no David not that), and I can remember her using a fine white powder in the process. I don’t know what it was, but it must have been very cheap because she had to watch the pennies. Basically what these filler/extenders do is to block or fill the pores in the wood to stop the varnish from penetrating too deeply. There are two main ways that this can occur. The first is to apply the filler before the varnish and the second is to mix the filler with the varnish.

 

In the first process, the chosen powder is usually mixed with water or an extremely weak solution of animal glue. It is mixed into a muddy paste and is applied liberally onto the wood. (Although the plaster mixes well with the water, some fillers mix better with oil varnish.) Before it has chance to dry the mix is rubbed into and then off the wood with a lint free cloth. It is important to rub off any surplus, especially from all the nooks and crannies. I tend to do this one section at a time starting with the ribs. Next I do the back and the belly and finally the head and the neck. Clearly the trick is to avoid getting the whole thing too wet. Otherwise joints are going to start springing open. However, this is not a serious problem if you work quickly and efficiently.

 

Whichever method you choose to use for applying your filler/extender, there are two points to be aware of. When you make your instrument you need to avoid getting glue anywhere on the surface that is going to be varnished. This is my main concern when I mask off areas that are to be glued. (See posts #100 and #104.) It is possible that the Cremonese makers had fewer problems with this process if they used casein glue for the neck and back and belly to rib joints. Gluing with casein is a slower process and there is less need to apply larger amounts.  Either way Sacconi says that Strad cut off the surplus glue around the rib to back/belly joints. This makes sense to me, because washing it off will only spread it into the wood and seal the pores in a way that I personally do not want. If you choose to use the methods that I will describe here, any glue left in or on the wood will leave an unsightly white fleck. This applies to both methods of applying the filler/extender.  The second point is that any end grain areas need to be filled with extra care. On the belly these are the areas at either end of the arching and in particular the edges. If these are not sealed well they can turn almost black when the first full coat of varnish is applied. To a slightly lesser extent, the same goes for the end grain on the head and back.

  

Now a couple more explanations may be required here. The first time that I applied a Plaster of Paris ground I was shocked and horrified at what I had done. (I always had the bad habit of working on finished instruments rather than test pieces.) If you have done the work well the instrument will look as if someone has rubbed it all over with talcum powder, (also a useful filler). It will quite literally be white. This is OK, but what you do need to avoid is too much powder building up on the surface. This can also happen if you use too much animal glue and if you have not washed the Plaster of Paris long enough.  

 

The second explanation is about why such a white ground is going to provide a good undercoat for our varnish. Well this boils down to something called ‘refractive index’. The easiest way to explain this is to imaging a thin sheet of clear white glass. If we then take a hammer and break this sheet into tiny pieces, and then grind those pieces into a fine powder in a pestle and mortar, the glass will no longer be transparent.  However, if we then pour this opaque white glass powder into a glass of water it will again become transparent. This is because the powdered glass has a similar refractive index to the water. The closer the refractive index of the medium (in this case the varnish) is to the filler/extender, the more transparent the ground will eventually appear.  This is where experimenting with various fillers is essential because the closer the refractive index of the filler is to your varnish the more transparent the final product will be.

 

Those people that want to try what I call, ‘the extender method’, will have fewer problems with possible weakening of the joints, but the process is not quite so easy. Moreover, it wastes a lot more varnish.  Both methods will give you good results and I still alternate between the one method and the other. On this bass I will be employing the water method, precisely because it requires less varnish. Nevertheless I will briefly explain here how the extender method works.

 

In this case, varnish rather than water is mixed with the filler/extender until it forms a thick honey like substance. This is then applied directly onto the wood with a lint free cloth. Like the water method it must be thoroughly rubbed in and then rubbed off.  Here it is important to note that the mix needs to be applied very dry on all end grain areas. However, for the process to work (also with the water method) the molecules of varnish must eventually surround the molecules of filler/extender. Any areas that are not surrounded will remain white. The balance is not easy. If too much varnish is in the mix the end grain areas will go black; too little and there will be white patches from the filler/extender. With this method the resulting ground will be the color of the varnish, but it will appear matt.

 

With the water method, once the water has dried completely, the first varnish (ground) coat can be applied either with a brush or with a lint free cloth.  Like the extender method the varnish must be well rubbed in and then rubbed off. The end result will look very similar in both cases. I always use a small amount of dryer with this ground coat of varnish.  See also topics: Purfling mastic Filler #2 and #4; Driers #15

 

I almost forgot. Neil and I made a very nice filler from an Alum / Potash precipitate; the sort of thing that you fix a lake color on, but just made without the color. 

 

 

Photo 1 is the bass before I applied Koens (the last I had) 50/50 mix of primer I & II. Photos 2,3 & 4 are after the application. The bass still needs to be placed in the UV shed. 

Photo 5 is the viola with the basic color applied. This is a combination of UVA for two weeks, (I forgot to take it out) and eighteen months old rabbit urine, that was painted on before placing it in the UV box. If you don't let it stand it stinks for quite a while. The UV box is usually enough, but the urine does help to darken the wood even more. The first stages of the plaster application is in progress. 

Photos 6 7 8 & 9 are more images of painting the plaster onto and rubbing it into the wood. Extra care is taken to be sure that edges and end grain areas are well sealed.

 

Photos 10 & 11 show the plastic (perspex) scrapers that I use if I am mixing the filler/extender with varnish. Scraping off the surplus helps to prevent waste, because the excess sludge from one area can be used elsewhere. These are not really necessary for water based applications.

Photo 12 shows the belly (still damp) with the excess plaster rubbed off. When these surfaces dry out they turn white.    

 

Photo 13 shows the white look of the instrument once all the surplus plaster has been removed. It also shows the first application of varnish being applied to the ribs. Be careful not to apply too much otherwise it may be wasted. Any surplus can be saved and re-used by using the scrapers.   

 

Photos 14 15 & 16 show the first varnish coat being rubbed in and rubbed off.

Photo 17 18 & 19 show the final look before this Andrea Guarneri copy viola is placed in the UV box.  

 

 

 

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Next week, I will be sending to Ariane my STRAD article "Optical Effects for Luthiers". There, I discuss RI matching that Roger mentions. The important take from my article is that the RI's need only be close to work as Roger finds.

Stay Tuned.

Mike

 

I can't wait, too. I'll brush up on my Optics. :angry:

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