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I am currently making my first violin I have completed the garland and I am currently working on the plates. I prepared the joint for the plates using a very long (about 90cm) wooden jointer plane which was carefully flattened, before using it on jointing the plates.

The joints came out very straight and I could see no light through them whatsoever. And I believe me I really tried to see if any light was visible at all by holding them on top of a very bright led panel. 

I was going to use a rub joint without any clamps, mainly  because the clamps I own are cheap/flexible  and dont apply the pressure perpendicularly to the joint but rather at an angle, plus I don't really think there is a need for them when using hot hide glue.

So long story short I was going to do the back first for the following reason. Due to lack of experience I was expecting to get a gap in the first try, so I would rather if it would be on the back instead of the top which is under a lot more stress. I was right to do so the center joint for the top has zero gap but the back is a different story

The back has a gap at the end of the front face and another gap at the opposite end of the other face. These gaps dont go all the way through to the other side. I have a theory as to why this happened. As i did the rub joint for the back i slightly twisted the one side of the plate after the glue had started to "bite". So when i twisted it back into place (so that both the pieced of the back rest on the same "plane") the glue had already gelled and some part of it was pushed out of the joint. But I could be wrong as I have no experience at all so hence the post :) 

Is there anyway to close the gap? should I even worry about it? I cant do the join again because I have removed quite a bit of wood. If I remove any more wood from the side of the back to do the joint again, due to the tapered shape of the wood there will be no material left for proper arching height. Thanks in advance for your help  :D Pictures are worth a thousand words, so here are some.

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2 minutes ago, Bodacious Cowboy said:

You say you can't redo the joint because you don't have enough thickness at the center. How thick is it?

about 17 mm and i still need to flatten the plate at the back doesnt need a lot of work but still a mm will probably be removed. I am aiming for 16mm arching height (i am using the templates from the Stradivari Titian poster) so i am already way too close to the final height. Is it necessary to redo the joint? I am asking because the gap isnt on the whole joint but only at the ends? Thanks

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5 minutes ago, Nestorvass said:

about 17 mm and i still need to flatten the plate at the back doesnt need a lot of work but still a mm will probably be removed. I am aiming for 16mm arching height (i am using the templates from the Stradivari Titian poster) so i am already way too close to the final height. Is it necessary to redo the joint? I am asking because the gap isnt on the whole joint but only at the ends? Thanks

You can make a perfectly respectable violin with a 15mm back, or even less. in fact 16mm is a bit on the high side to me. But I can understand you wanting to stick to your original plan.

If the gap is only at the ends, can you work things out so that they don't appear in the final outline? Although I'm sure you will have checked that, and the answer will be "no" :)

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18 minutes ago, Bodacious Cowboy said:

You can make a perfectly respectable violin with a 15mm back, or even less. in fact 16mm is a bit on the high side to me. But I can understand you wanting to stick to your original plan.

If the gap is only at the ends, can you work things out so that they don't appear in the final outline? Although I'm sure you will have checked that, and the answer will be "no" :)

I was hoping that this would be the case (that the final outline doesnt include the regions where the gaps are). If that where the top it would be fine but due  to the fact that the back is a bit longer since it has the neck button as well, the gap does appear. Only thing that i should decide if I cant cloese the gaps is whether i want the gap to be at the neck button or the bottom of the back. Thinking the first choice is the better one.

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I would cut them and re-join. 14 - 16 mm arch keeps you in the "normal" arch height range. There are some good threads on joining plates that describe how to leave a slight concave shape along the joint line. Swelling along the joint is more pronounced toward the center than the ends, which is possible how your gaps occurred.

-Jim

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What Jim said.

I do find it much better to leave a very slight gap in the center. I also like to clamp the joint, although many folks manage fine without. You don't need particularly heavy duty clamps, but it's a good idea to shape the clamping surfaces of the wood to ensure that the clamping force goes through the center of the joint. Otherwise the clamps can act to pull the join apart on one side or the other, which is a bit counter-productive.:)

One other thing i'd suggest is to be ruthless about eliminating "rock" in the joint. With one half in the vise, rest the other on top, and pull down *hard" on one end of the upper piece, and then the other. If you see any movement of the upper piece at all, then your work is not yet done. 

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19 minutes ago, Jim Bress said:

I would cut them and re-join. 14 - 16 mm arch keeps you in the "normal" arch height range. There are some good threads on joining plates that describe how to leave a slight concave shape along the joint line. Swelling along the joint is more pronounced toward the center than the ends, which is possible how your gaps occurred.

-Jim

Redoing the joint is probably not an option for me having this little material left for fine tuning. I still havent flattened the back and i am really trying to stick to the templates given to me by the strad poster as I dont have the experience to figure out how the arching is shaped if it is lower than 16mm. Is this gap such a problem that i would really have to do the joint again? I am asking because its not over the whole back but located only where the neck button is.  Cant I put some thinned hide glue in the crack and close it with a clamp or something like that? 

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2 minutes ago, Bodacious Cowboy said:

What Jim said.

I do find it much better to leave a very slight gap in the center. I also like to clamp the joint, although many folks manage fine without. You don't need particularly heavy duty clamps, but it's a good idea to shape the clamping surfaces of the wood to ensure that the clamping force goes through the center of the joint. Otherwise the clamps can act to pull the join apart on one side or the other, which is a bit counter-productive.:)

One other thing i'd suggest is to be ruthless about eliminating "rock" in the joint. With one half in the vise, rest the other on top, and pull down *hard" on one end of the upper piece, and then the other. If you see any movement of the upper piece at all, then your work is not yet done. 

I didn't really find the need of clamps to be honest with you. The top came out perfect without any clamps. Its only the back that doesn't want to behave :D For the reasons I mentioned above and due to lack of experience i dont want to mess with the arching height which will inevitably happen if i do the joint again. So really my two options are either leave it as is , since the gap doesnt occupy the whole joint or find a way to close it without taking the joint apart. 

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1 minute ago, Nestorvass said:

Cant I put some thinned hide glue in the crack and close it with a clamp or something like that? 

I wouldn't want to try that.  Even if it did work, it would take a lot of force to close a gap like that, and those forces might remain in the wood and cause it to open up in the future.

If I really HAD to use a back plate with a gap like that, I would prefer that the button have the non-gap, since that is one of the most critical areas for keeping the neck in place.  For the gap at the bottom block, if it was bad, I'd splice in a sliver of wood.  I'd really, really rather cut and re-do the joint, with the only consideration being if the plate becomes too narrow.  I would not worry about arching height.  And even with width problems, maybe I'd use the plate later for a small model, and start over with another set.  It depends on what you intend for this violin, if it's just for you, or what.

For future reference:  maple tends to be more porous than spruce, particularly if the cut is slightly off-quarter and/or if the flame has any sideways squiggle.  So it will suck up glue and swell much more than spruce, and give problems.  I prefer to glue-size the maple and let it dry, then very lightly use a scraper to smooth out the surface.  Usually there is no need to re-plane the joint, but of course check it before going on.

Personally, I prefer to do a rub joint without clamping.  I have had no issues with it, and clamping can put forces on the glue joint that might tend to open it... if the clamping isn't done exactly perfectly.

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4 minutes ago, Don Noon said:

 

Personally, I prefer to do a rub joint without clamping.  I have had no issues with it, and clamping can put forces on the glue joint that might tend to open it... if the clamping isn't done exactly perfectly.

I'm sure you're right. I've just always used clamps, and old habits die hard. I'd be nervous about doing an unclamped cello joint, however.

(my clamping is, of course, always done exactly perfectly :D)

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14 minutes ago, Don Noon said:

I wouldn't want to try that.  Even if it did work, it would take a lot of force to close a gap like that, and those forces might remain in the wood and cause it to open up in the future.

If I really HAD to use a back plate with a gap like that, I would prefer that the button have the non-gap, since that is one of the most critical areas for keeping the neck in place.  For the gap at the bottom block, if it was bad, I'd splice in a sliver of wood.  I'd really, really rather cut and re-do the joint, with the only consideration being if the plate becomes too narrow.  I would not worry about arching height.  And even with width problems, maybe I'd use the plate later for a small model, and start over with another set.  It depends on what you intend for this violin, if it's just for you, or what.

For future reference:  maple tends to be more porous than spruce, particularly if the cut is slightly off-quarter and/or if the flame has any sideways squiggle.  So it will suck up glue and swell much more than spruce, and give problems.  I prefer to glue-size the maple and let it dry, then very lightly use a scraper to smooth out the surface.  Usually there is no need to re-plane the joint, but of course check it before going on.

Personally, I prefer to do a rub joint without clamping.  I have had no issues with it, and clamping can put forces on the glue joint that might tend to open it... if the clamping isn't done exactly perfectly.

Thank you  for the reply :). Maybe I will try it then since I dont have a width problem at all I can take centimeteres and still have enough material to make the outline. How would I proceed in seperating the joint? I have a bandsaw but i would have to make the cut freehand since the edges are not parallel to the joint and if the fence was used the cut wouldnt be straight. I also have a ryoba japanese pull saw. 

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You could try brushing hot water on both sides of the seam, let it soak in and repeat until the seam is weak enough to pop open. 
I've had to do this before.  It takes a little patience but you should be able to get back to your starting point without losing material. 
 

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I am totally new to this forum and have only made 7 violins and am self trained.  Jointing the top has always been easy for me and the back has been my nemesis.  I admire those of you who do a rub joint without any problems.   Although I usually end up with a good joint, I can list my failures more than my successes: 

1.  Plane blade not sharp enough. Until I went to 3000 grit sandpaper on glass and then a leather strop, I didn't appreciate how sharp a blade can be.  

2.  Trying to cut a final perfect joint with a single sweep of the plane.  I learned from a Paul Sellers video how to finely plane just the portion that is out of true.  

3.  Trying a power jointer planer (I know....)

4. Over-clamping to try to fix a poor joint....squeezes out the glue so much the joint fails, and you can't clamp tight enough to fix a bad joint anyway.  

3.  Clamping with uneven pressure on the joint due to the wedge shape of the wood.  One side looks great and the other side has a gap.  

My last one turned out well with a rub joint plus gentle clamping.  I think I will try Don's glue sizing idea on the next one, and maybe even a rub joint with no clamping if I am feeling brave.  I am using inexpensive wood until I can justify hacking away at a really nice back.  

Don:  do you glue size with a regular mix of glue or thin?  

--Jay

 

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52 minutes ago, Jluthier said:

Don:  do you glue size with a regular mix of glue or thin?  

Either one should be better than none, but I use regular mix and wipe the excess off with a plastic scraper or finger.  I don't want the glue to get too far into the wood and create a glue ghost along the center during varnishing.

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2 hours ago, Nestorvass said:

Thank you  for the reply :). Maybe I will try it then since I dont have a width problem at all I can take centimeteres and still have enough material to make the outline. How would I proceed in seperating the joint? I have a bandsaw but i would have to make the cut freehand since the edges are not parallel to the joint and if the fence was used the cut wouldnt be straight. I also have a ryoba japanese pull saw. 

Since you say you have a lot of width margin, I'd use the bandsaw.

For later, after you plane:  not only check the gap for light passing through, but look on the inside and outside of the plates for visible gaps.  You could have a slight twist in the planed surfaces that would not let light thru, but still have gaps on one side or the other.  If there's any doubt, you could also use chalk on one half and see how it transfers to the other.

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1 hour ago, Don Noon said:

Since you say you have a lot of width margin, I'd use the bandsaw.

For later, after you plane:  not only check the gap for light passing through, but look on the inside and outside of the plates for visible gaps.  You could have a slight twist in the planed surfaces that would not let light thru, but still have gaps on one side or the other.  If there's any doubt, you could also use chalk on one half and see how it transfers to the other.

So I tried to take the joint apart with warm water and with a hairdryer. I am definetely convinced that a rub joint is the strongest thing in the world. I was for over an hour putting water and heating it the joint barely opened i put every bit of strength i had in me to open it it was impossible. Even tried a heat gun nothing... Even with so much heat and water and strength the joint didnt move. I had to take it to the bandsaw to make the cut. I don't see how clamping could improve such a strong joint. I was amazed.

Anyway back to the point I did the joint again, only this time i followed your advice and I sized the joint with glue. I will let it dry until tomorrow and then, I will do a pass on the jointer plane to take the glue off and flatten it again. Then I will take my block plane and take a few thin shavings in the middle to make it slightly concave. I have my block plane set up with a 45 degree bevel on the iron and it takes shavings which are about 10 to 20  microns thin.

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36 minutes ago, Davide Sora said:

Am I the only one who can't see the photos of the first post? I see all white with no entry signs in the center.

They do appear to me when I log out and when i visit the link from my phone, so they should probably be visible I am not sure though :unsure:

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37 minutes ago, Davide Sora said:

Am I the only one who can't see the photos of the first post? I see all white with no entry signs in the center.

I saw the pics initially, and thought I also saw openings near the ends of the top plate as well. However, when I went to look at them again the pictures were all blank. 

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14 minutes ago, Jim Bress said:

I saw the pics initially, and thought I also saw openings near the ends of the top plate as well. However, when I went to look at them again the pictures were all blank. 

You probably mean the back plate the top plate had no gaps. I will upload the photos again hopefully they will be visible 

3.jpg

1.jpg

2.jpg

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