Hints to a achieve a proper soundpost fit


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I'm trying to adjust a new soundpost to my violin and it's becoming really difficult to perfectly adjust it to the top and back plates.

 

So far I've had no problems to chose the correct size of the post but can't achieve a perfect fit on both plates at the same time. Is there anything I could make to calculate the proper angles?

 

BTW I'm assuming the way to cut the post ends is with a very sharp knife?

 

Thank you!

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I feel I can get a perfect fit everytime because I do it the same everytime. I don't use a knife. I use a flat glass plate with 400 wet dry sandpaper to cut the angles. I use an angle finder to keep record and make adjustments. I use a dial caliper to keep tract of the length as I cut. And a starrett combination square to keep the ends square.

You will automatically get a feel for it after awhile. My lastest and greatest addition to fitting a perfect sound post is a Luthier Light. I used to think a mini maglight was sufficient until I bought one of these from Fiddle Doug. Get one trust me.

There is more to fitting it which I basicall do with a piece of business card and taking the post in and out. another great tool to have is a soundpost grabber. It makes things so much easier.

 

Here's my tools to fit a soundpost.

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Just use the old post to help you fit the new one. Look through the end button hole with either a light inserted through the f holes or a lamp over them and look at where things aren't fitting. Make sure to look at the back side with a mirror inserted through the f holes. Take note where things aren't fitting. Write it down if you have to. Feel how tight the post is with your soundpost setter.

Take the old post out and start cutting the new post. Make changes to the new post based on your observations and you have the old post right there as a reference. I use a small sliding t bevel to compare my angles between posts.

I also use a 1 inch chisel to cut the ends. I grip up on the blade and make slicing motions like a knife. I find it's easier to get a flat surface, but a large flat knife would do the same I suppose.

A few thoughts. Check the ends of your soundpost with a straight edge of some sort until you can spot flatness by eye. Usually when people have a hard time fitting a post, it's because they are doming the end. If you do this, the post wants to spin on the high spot of that dome when you are trying to put the post in. If the post doesn't want to right itself while you are pulling it into position, you most likely have something wrong with the cut. Usually it's rounded.

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In brief, the general proceedure is to start with a post that is too long.  Being too long will mean that it stands up too far towards the center line of the instrument.  Observe the fit through the endpin hole using a mirror to view the far side.  Take the post out and trim the points of contact off the ends.  This makes the post shorter, so it wil stand up farther from the center line.  As you keep repeating this process, the fit wil gradually improve and the post will gradually get shorter and move farther away from the center.  Stop when the post fits perfectly and is the the correct position.

 

I trim the ends with a knife.

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What Brad said.

I'll add that it's very difficult to produce a flat surface with a straight knife.  I use a curved knife for fitting bridge feet & posts.  Helps to dampen the post end you are working on for taking very fine end-grain shavings.  The knife really should be dead sharp (whatever that may mean).

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I wonder if we took a poll if everyone would find that fitting the sound post is the most irritating job associated with the violin?

 

One thing I have found is it helps starting with the post on the long side, as Brad said, and considering the process to be developmental.  Work the post down slowly enough to get familiar with what is happening.  Don't try to cut corners.  I think it's just one of those jobs that goes faster the slower you go.  Probably why a lot of shops—at least in the past— didn't cut very good posts for me.

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I feel I can get a perfect fit everytime because I do it the same everytime. I don't use a knife. I use a flat glass plate with 400 wet dry sandpaper to cut the angles. I use an angle finder to keep record and make adjustments. I use a dial caliper to keep tract of the length as I cut. And a starrett combination square to keep the ends square.

You will automatically get a feel for it after awhile. My lastest and greatest addition to fitting a perfect sound post is a Luthier Light. I used to think a mini maglight was sufficient until I bought one of these from Fiddle Doug. Get one trust me.

There is more to fitting it which I basicall do with a piece of business card and taking the post in and out. another great tool to have is a soundpost grabber. It makes things so much easier.

 

Here's my tools to fit a soundpost.

How do you respond to the anti sandpaper comments?

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I worked with a man who used to put a little dowel down through the top loop of the f hole, put his thumb nail where it came out, and took his starting length from that.

 

Another guy drew two circles divided into quarters with chalk on his bench, one for the top and one for the bottom. He marked where he needed to cut each time he tried the post, made the cuts, rubbed out the marks, and went again.

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Ok, thank you all that is a good amount of information to start with!

 

Definitely the worst part is to learn to cut the post with the knife  :wacko: and I confess in the end I used flat file.

 

Just one more question, looking through the end-pin hole its easy to state if the soundpost is straight widthwise, but how can you be sure it's straight "lenghtwise"? That can only be checked looking at the settled post from the f-hole?

 

Thank you!

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I'm thinking that sometimes there aren't going to be any special contours on the inside to accommodate the sound post.  That is, in the neighborhood of the sound post, the outside surfaces are pretty much parallel to the inside surfaces. 

 

Anyway, here is how I have fitted a SP for my cheap thick heavy student violin (Mendini MV400), assuming the inside surfaces were parallel to the outside ones.

 

I sand off the end of the SP at an angle such that the SP can stand upright on the top, above where it is to set on the inside.  For the angle on the other end of the SP, I turn the instrument on its belly and sand that end until the SP can stand upright on the outside of the back, opposite where the SP contacts the inside of the back.

 

Under what conditions does this assumption hold true: that, in the neighborhood of the sound post, the outside surfaces of the sound plates are pretty much parallel to the inside ones?

 

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I'm trying to adjust a new soundpost to my violin and it's becoming really difficult to perfectly adjust it to the top and back plates.

 

So far I've had no problems to chose the correct size of the post but can't achieve a perfect fit on both plates at the same time. Is there anything I could make to calculate the proper angles?

 

BTW I'm assuming the way to cut the post ends is with a very sharp knife?

 

Thank you!

 

If you're new at this, it is a difficult job to get right, and at first, it will take much effort and time, I find.

 

Yes, using a very sharp knife usually winds up being the technique that most people will use in order to trim the post, but any method to get wood from the trial post ends, in order to get it to fit properly, can and will work -  

 

As far as I know, there is no way or reason to "calculate" the angles, as there is simply a minuscule difference in angle from violin to violin and the only way to do it, or to arrive at the correct angle, where the post fits correctly, is by eye and by "feel".

 

So, as long as you know what the correct "fit" is composed of, and where the proper location is - the only way I know to get the fit right, is by practice.

 

Telling you how I do it is almost incidental. As, you'll eventually find a way to get the fit right if you do it (fitting sound posts, that is) often enough. If you only are going to fit a single post, then, your question is still appropriate - but my recommendation would be to either go ahead and work at it, until you manage to get it right, or, find a violin maker or repairman to do it for you. 

 

Good luck with this. Its a real accomplishment learning how to do this right! 

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You can also use the back of your chisel as a flat reference surface.

I use a very simple one piece jig to hold the soundpost.

 

1 On your table saw, cut a seasoned 2x4 pine stud to a length of about 7 cm. Do this by first adjusting the miter to about 7 degrees. So you will not be making a 90 degree crosscut, but one that is angled.

 

2. Repeat by making one these at 6 degrees, one at 5 , 4 and maybe 8. So you now have 5 different pieces of wood.

 

3. Using a drill press, drill into the end grain a 6 mm hole (use 1/4 inch). Or perhaps you should start with the next smaller drill size. The soundpost is going to be in this hole. So the hole is perpendicular to the surface of the block on one side and 7 degrees on the other.

 

4. Now you want to make a saw cut parallel with the hole and into the hole.

 

You place a C-clamp on it. With the sounpost inserted, you can tighten the clamp to hold the post. Now you can use a flat sharp chisel to trim the post accurately and repeatably.

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How do you respond to the anti sandpaper comments?

No need to comment. Results dictate and my posts fit perfectly. I will say not all sandpaper is created equal.

 

 I will agree with what ct said "Its a real accomplishment learning how to do this right! "

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