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Cello top and bottom block tear out


rgwebb6
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When I installed the top and bottom blocks on the cello I am making I encountered terrible tear out as I tried to shape them.  This also happened on the corner blocks.  Since they were already installed and since this is just a cello for me to see if I could make one, and one I have no intention of selling,I kept on going.  Now I am trying to install the neck and realize that I am having the same problem with the top block on the outside of it.  Duh...What a surprise.  I was a little concerned that the amount of tear out on the inside would weaken the top block to begin with, but now I am worried that too much tear out at the neck root area will be just too much.   When I saw the tear out start I first thought I could make a real amateur fix with plastic wood and then work with that.  But I see now that I need to go another 10mm past the rib and am worried that the tear out could really put me in deep trouble.  Does anyone out there have any suggestions on how I can deepen the cutout smoothly other than using chisels which just tear the wood apart?  I never encountered this with the six violins I have built.

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I obviously didn't think about grain direction when installing the blocks.  I thought I had the end grain at the top.  I must have cut the block with the bad side facing in and out and the good side to the sides of the block, if that makes sense.  I could fit a plug to the mortice with the grain facing the right way, but I would still have a lousy ragged gluing surface in the back of the mortice and most of the good hold depending on the sides and the button.   Would that be enough?  I even thought of cutting out the whole mortice between the top and bottom plates and seeing if I could fit a winged chalk-fitted replacement in through the hole that would have the wings to assist in holding it in place.  Does that sound feasible?

 

How would one go about routing out the mortice?

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I'm a little confused how your block is oriented. Here is a picture that will hopefully help us talk about which side is which.

Ideally you would have the end grain surface be "1."

I worked on a violin once which had the end grain on "2." It's not a good idea, and resetting the neck was a PITA. The block was made of maple, which was also inconvenient. (I ended up putting a normal upper block in.) If you've accidentally put the block in this way I think you will be okay leaving it, it will just be harder to work with.

If you have the end grain on "3" you need to replace the block.

-Michael

post-6731-0-50304100-1390885646_thumb.jpg

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I do have the end grain at 1. I don't really know much about wood grain, but it seem like I'm trying to work against it.  It's like when you try to plain the wrong direction and the plain chatters.  In this case the chisel, even when held almost perfectly flat against the wood, it catches under the grain and tears out a large chunk. 

 

Would that matter?  Is it possible to have a block in upside down? Where one direction would work smoothly and the other would tear out?    

 

Would the best solution be to just bite the bullet and take the top off and replace the end block? Or am I asking for trouble trying that?

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I made this trapezoidal sanding stick with metal sandpaper specifically for 'flattening' and 'adjusting' the neck mortice.  It works well on 'odd' types of wood especially if the grain is not oriented properly.  There are two sizes ... the smaller one is used first until the mortice is enlarged.

 

 

i am also having difficulty viewing recently attached images... some will open and some won't. Any ideas why?

 

post-24376-0-48291200-1390921070_thumb.jpg

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I think you've just had a great lesson on why it's better to split out your block material and the value of payingclose attention to grain direction. If you had turned your block 180 cutting the mortise would be easier/possible.

I fully agree.  But why in the world is something that important not emphasized or even mentioned in the several violin making books I have read over the years.  At least I don't remember reading it.  And none of the threads in MN that I can remember since joining in 2004.  Has nobody ever made this mistake before?  Am I the only dufus that would not know there is an up and a down to the block material? :wacko:  I guess I do remember something about splitting the wood for the blocks, but I just thought that was to ensure the grain was straight.  I always figured if I bought the wood from the reputable dealer I always buy from and it was bought as block wood, I could trust them the grain was straight.  But you are right I have learned a very PITA lesson and still am not sure how to solve the problem.  Do I assume then that if I had split it from the wrong end it would tear out and the right end would split smoothly, thus telling me which end is up?  Obviously I'm confused.

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Sizing with thin hide glue would firm things up. I did a chalk fit fill wedge on an oversize mortice that worked well.

I think that is my next attempt.  I will size it, go deeper than required, and chalk fit a fill-wedge of correctly oriented material that I can then "smoothly" chisel to the right depth/angle.  If that fails (I fail to do it successfully) I will take the top off and try to replace the whole block.  So near and yet so far from finishing this cello up.  I am really having to control myself from just rushing into it and possibly ruining the whole thing. 

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Everyone has glued their blocks with the split running the wrong way. I wouldn't replace the block, and I might hesitate before filling the mortise with a wedge, because you still have to work the block to get a good surface to glue the wedge to. I think that sanding sticks are your answer. It is slower than a chisel, but can be great. Make up one for the back of the mortise, with angled sides so it fits nicely into the corners, and one for the sides that matches the angle of the side of your neck. I like to use spray adhesive and 150 grit for sanding sticks.

Don't worry! It will be fine!

Michael

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Everyone has glued their blocks with the split running the wrong way. I wouldn't replace the block, and I might hesitate before filling the mortise with a wedge, because you still have to work the block to get a good surface to glue the wedge to. I think that sanding sticks are your answer. It is slower than a chisel, but can be great. Make up one for the back of the mortise, with angled sides so it fits nicely into the corners, and one for the sides that matches the angle of the side of your neck. I like to use spray adhesive and 150 grit for sanding sticks.

Don't worry! It will be fine!

Michael

Thanks.  It just seems like trying to remove 9mm of mortise depth with sandpaper is a really long project.  But I like the idea of not taking the top off.  And the idea of having a smooth mortise back to glue to.  So now Plan A is now to try to sand the surface back.  Would 80 or 100 grit work faster and then finish up with 150, or is that too coarse to keep it from continuing to tear out?  Easu enough to check out I guess.

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You might have better luck using skew chisels and rasps/files. The skew chisels will allow you to work somewhat to the side of the grain with a paring cut rather than straight in which will dig in and split.

Thanks.  I'll try both /all three.  Sandpaper, rasps and skew chisel.

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Finally, I'm on the move again.  The skewed chisel took it down to almost the deepest tear out with minimal additional.  Then I used a rasp and sandpaper to get it fairly flat and smooth, just to see if I could.  I now have the bottom corner of the root touching the button and the fingerboard lined up with the centerline.  I feel good.  I have more to do to get the tilt of the fb up to 80-81mm at the bridge (right now it's about 75mm) and to flatten the bottom of the root to the button.  But I am feeling like I am of the way.

 

Thank you all again for all the help.

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