Violin Forum/Message Board

[jethro]

Here was my mistake-I think ... Joined my highly figured back using my new expensive plane. Had about 3/4 inch at each end making contact and
the remaining part in the middle had the spring. Glued- let dry about a week. Cut the outer surfaces of the joint with plane on both sides to inspect joint quality. Looked as perfect as I could expect-no seams visible
on either side.
Cut the perrimeter out and proceeded to cut down the front. I've got the front side about 80 % cut. I have the edge at the bottom and top down to about 6 mm. Then the next day I noticed a crack opened in the center
joint at the botton - about 3/4 inch long. I have tried wetting and swelling the joint with heat twice. That brings the joint back together but
1/2 hour later when it dehydrates the crack is back. Either the glue there
isn't holding or thee is too much tension on it.
I think my mistake was when I cut the perrimeter out I may have cut inboard of the ends too much leaving the new ends in the area of the joint which was under pressure from the spring .

I am considering making a saw cut across the end of the plate - across the crack area- and then sliding a piece of side maple into the cut slot
like a biscut. The idea is that the strip might hold compression tension
to keep the crack "clamped" . It should only show edgeways on the
bottom of the plate.

Is this a good fix???????
Don't want to trash ANOTGER expensive plate !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Help please !!!!!!!!!!! Pulling hair out - ect !

Tim

[Jeffrey Holmes]

[actonern]

I'm sure you know your glueing process well, but it occurs to me that you may have either worked too slow in clamping up the middle sprung section or the wood was too cold when the glue was brushed on... either way if it gelled up before clamping pressure was applied a bad joint is inevitable. I find it critical, especially on long cello plate joints to warm the wood so as to increase working time.

Can you separate the plate and try again?

[jethro]

I was carefull to heat the wood well before applying the hot glue and I think I got the surfaces together and rubbing stoped within about 15-20
secconds- so that part I felt OK about.
I did try to rub some more glue into the joint before I tried steaming/swelling it closed but the carck was pretty thin then. Later
(1-2 hours ) it opened up even wider after it dehydrated, now I can slip
typing paper down it about 3/4 inch. But now that is has spread open I might be able to sork some better ammounts of glue into it . I have white
glued 4 oak blocks about an inch on either side of the crack on both sides to form a huge cleat to c-clamp across to try to get some closing pressure.
Tried hyde glue but it popped.

Now that you mention humidity.......
I am in Orlando near the wild fires and we have had Very low humidity
for the last month or so- way less than when I joined the plates.
If that is the culprit should I humidify the plates ??????????

we are nornaly at 60% to 100 % ---- now we are 15-20% or something like that!

Will try reglueing again when I think the blocks have dried enough !

Thanks, Tim

[jethro]

My understanding of the geometry of the "spring" is the joint was that
when the plate was cut out arround the perrimeter that the non sprung
ends (3/4 inch or so) should be at the ends of the joint so that later the
ends are not under tension to seperate- and that the middle parts may have some tension but none at the ends where a crack propigation might
start. But I wonder if when I cut the plate out I may have cut too far in
and cut across the joint INBOARD of those nonstresses ends so I may have been left with the end of the plate being in the central tensioned area. Maybe this and the massively low humidity bay have conspired
it to crack. What if I put the plate in a big tupperware box with some water in the bottom (not on the plate) to bring the environment back up
to higher humidity ????????????????????????????????????????????????
Might this close the crack part way ??????

Tim

[Jeffrey Holmes]

Hi Jethro;

As mentioned in previous threads, when I produce a spring joint in a maple plate, the "hollow" is very, very small (did I say "very" enough times?)... just enough to see a hint of light through if a strong lamp is shined onto the face of the plates. I set the spring evenly from one end of the plate to the other. The "tension" produced is little-to-none once the plates are glued (in other words, not worth even considering). The spring simply ensures that the ends stay in good contact during the gluing process and a slight suction is produced (that closes the center). Some makers do not plane in any hollow... many do.

In other words, unless your hollow was too large and/or unevenly applied, any theory of a spring joint is really not an issue here. There is something else going on. You should be able to cut into a good joint at any point and not compromise it.

An anomaly in the joint, inadequate seasoning, weak glue or drastic humidity change sound like more plausible explanations to me.

I'd avoid the tubs of water... but you may want to try "dry" clamping the joint closed (I'd apply blocks on both sides of the plate so you can get even pressure) and raise the humidity (humidifier) in the room to see if if things improve for you. If they do, maybe you can re-glue the section.

Another option: As was mentioned earlier, if you didn't cut your outline too close to finish, you may have enough room to open and carefully re-join the plates.
_________________
Jeffrey

http://holmesviolins.com

[Chet Bishop]

I had a similar mishap two days ago-- the very end of a completed plate (already installed, but in the white) began to let go. I put hot hide glue on the seam, and repeatedly mushed it in with the ball of my thumb, adding more glue, until I was sure the glue was all the way through the joint. ( I do not believe it would have simply "soaked" in.)

Then I wetted the outer perimeter of the plate, along both edges, hoping the swelling at the edges would help clamp the joint. I washed off the extra glue, but did no further deliberate wetting of the joint.

The results are good so far-- the joint is closed, the glue is dry and holding. But today is supposed to hit 95 degrees, so I guess we will see what happens.

Chet

[jethro]

Thanks JH,
I think I had as little spring as you refer to - less than 1/2 mill - could just
see a hint using a 150 watt spotlight 12 inches behind. It went together
seemingly easily and I just clamped it lightly in the center. I don't know the history of the wood as far as cureing out as I ordered it from a place
in the state of Md, (whose name I probably should not mention here) but
the last several backs I have gotten from them seemed to have some warpage going- like it's still shrinking and moving. Should I change
suppliers after seeing this ? I think either the wood has moved from
warping or the huge humidity change is working on it or maybe both !
If the raw plates show cupping across and twist after I recieve them does
this suggest not cured out wood ?????????????????????????????????????
I don't want to invest time and money on raw materials which lead to
trash can fodder !

I took some brass shim stock about .001 and wiped some hot hyde glue
inside the crack untill it was loaded and let it set a few moments, then
wiped the clean shim through the crack to the the excess from between
the plates hopefully leaving some clinging to wach side so the joint can close when I push on it later and steam or wet or however I activate it
and squeeze it. Hopefully the big cleats will not pop before the crack compresses. I was hoping by raising the humidity of the wood I might
reduce the distance the blocks had to push to get closure.

Thanks chet, that's about what I tried too, pushed it in with a fingertip
over and over to fill it up . I didn't have a way to hold it closed untill the
glue came to cure.

Will keep you all posted.

Jeffry - do you think I need better wood quality ?

Tim

[Chet Bishop]

Twice I have taken plates from home (northwest Oregon), where they had been stable for years, and went to Tucson for a workshop, where the maple proceeded to do its best imitation of a manta ray, the outer wings drifting upward in a distressing curve. The first time it happened, I was sure my plate was ruined. The teacher shrugged and said "...it will flatten out when you clamp it." He was right.

This time, though, when I had graduated it carefully, and it looked terrible (because the arching had been lost in the warp, or cup, or whatever you call it), I wetted the outside of the plate with warm water, and in minutes it returned to its normal shape. I clamped it in my work cradle, and left it overnight, and it stayed in the correct shape when dry.

Now it is installed on a violin, and has caused no problems. I hope that the varnish will seal it well enough to eliminate some of this nonsense.

[Jeffrey Holmes]

[jethro]

JH:

The current back wood gives me the impression it was pretty new and not
cured rearly long enough. The piece before was just as bad if not worse
and I may scrap it (?) ( I tried multiple times to re-join but never could get a good joint in the end) That back was sent as a replacement for the previous one which after sitting on my shelf about 6 months developed a crack running about 3/4 the length of the plate. It was a radial crack (looking on-end at the tree) - I sent it back for a replacment-
the one I may scrap. So there is a pattern of troublesome wood. My
first 2 instruments gave no such problem at all. I really don't want to
down talk the supplier because they seem to be a good companny and give good quality service and are interested and helpfull generaly! ( and
a family business- which I like ) I'm thinking I will continue to use tham
but I may experiment with another supplie for back wood (maybe Leif )

Thanks, TB

[kubasa]

Jethro,

I just sent you a PM. I'm not sure how you get notified on this system so I wanted to mention it here.

Thanks,
Kubasa

[jethro]

The top in question continued to crack. The existing crack on the bottom grew from about 3/4 inch to about 1.5 inches. Also (in one day) a crack
started at the back button (the glue joint) and propigated down to about the center of the plate. I grabbed the the top on either side of the seam
and started wiggleing and after some firm flexing the rest of the joint poped loose- seperaating the halves. I inspected the look of the faces
that were glued and they are as slick and perfect as when I planned them.
When I put the faces together and look at the joint - it touches in the middle and the seam tapers open towards the top and bottom. The gap
at the top and bottom is about 1/8 to 3/32 inch. The curve is very even
and "regular" geometricly. It had a "perfect" spring whan it was glued.
I am going to leave the 2 pieces to dry out (cure?) for a while and watch
the gaps to see if they gradualy go away.
My intuition tells me that the wood was not cured enough.
However I also have some suspicion about the hyde glue - I will post that
question as a new topic.

I have several sources for back wood I will explore this week.
(including Leif ! )

Tim