Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Question re typical pinblock separation in a vertical

Nice clamp Joev.. Thanks for the explanation & pics I would have replaced all the screws by bolts in that case, feel safer..
Those kind of problems are noticed when looking at the back of the piano.

Nice job Joe. Sometimes the separations never close up all the way. After tuning I am sure the client will be elated.

Smaller uprights usually have no board or felt covering this area, but some seem to have a fake top that makes the structure seem more substantial than it really is. Anyway, Mark, you can get a good idea if the pin block has separated by swinging the action out. If it hangs up on the studs, there is probably something wrong.

Mark, most European pianos have the back half of the hinged top securely glued to the top of the pin block, the back posts and the blocking, This creates a "box" with additional strength to hold the pin block in place. But is also makes it more difficult to diagnose a separation in its beginning stages (when you want to catch it!)

Many old and tall N. American uprights have this "back lid" screwed onto the top, with the screw heads hidden under wooden or dubber knobs. It is easier to remove the top and to inspect the pin block from above.

Many more recent studio and console pianos have the top of the pin block either uncovered or only covered with felt, as the one in this thread.

I was said you can diagnose a separation if you can insert a business card between the block and the case (or a thin ruler)

The bck is also bowing then, but certainly th first stages may pass unnoticed unless there is a serious pitch drop

Thanks for the kind words. They are much appreciated.

I'll let you know how things turn out.

-Joe

Hi Isaac,

I also thought of that. But then, I thought back to when I was a student. I asked back then and was told that it's usually best to try to keep some of the original screws if possible. Those specific type of screws in those holes is how the piano was originally designed.

I think ideally, instead of hex head bolts, it would be best to have countersunk screw heads on the bolts. But then, the angles, diameter, etc. would have to match fairly closely the hole from which they were removed.

Yes you are right, a screw tighten more the block than theaded rods. It was a baad idea, probably the 3 bolts are enough to stop the block , indeed the screws have a different role.

We did so on an open block mounting because it ws easy and it allowed to closer better the gap.

Hi Issac,

You are also right. The job requires whatever number of bolts it requires.

Mark,
I just got back from finishing up abd tuning that piano. I did not take any more pics. I was there for quite a while finishing up the job, tuning, and doing some other stuff. It;s not my home and I didn't want to overstay my welcome.

The glue gaps closed about 30% or so more since I was there on Tuesday. It's probably a combination of evaporation of the water in the glue, and the glue being absorbed into the wood. Maybe also the wood itself expanding as the glue was absorbed into it, and the wood itself being held in position by the bolts or clamp. Edit: So, the wood had nowhere else to expand to except inwards towards the gap.

As for drilling the hole through the plate...
This is a spinet piano made by the "Grand Piano Co." I would have been much more hesitant to drill a new hole through the plate if this was a valuable piano.

If you recall, the was one glue joint where I was not able to place a bolt in an optimal position. A s I was driving out today, I considered installing a screw from the back through the backpost into part of the pinblock. After I arrived and looked over the glue joint and saw that it actually closed up more, I felt fairly confident that this would have been unnecessary.

I hack-sawed off the excess from the bolts, filed off any remaining stubs and sharp areas, and refelted the top.

I brought the piano up to 440 and tuned it. There were no problems and the tuning seemed solid.

You mention the gaps closed up "30% more", which means that there were and still are gaps. Evaporative glue (Tightbond etc) is not meant to fill gaps, and it does not have real strength there. That is where epoxy comes in handy and it is the best choice for a gap filling job or for gluing parts that do not mate well.

This is not to criticize your work, but to inform others who read this and need to do a similar repair. I am sure the bolts are doing most of the holding and the piano will be just fine.

Epoxy is fine and appropriate. I like epoxy for this job.

I wanted something that would be very slow drying. These gaps were huge and stubborn. I wanted time to be able to close the gap a little, let the wood relax, close it some more, let the wood relax, etc. I'm also sure that some of the hide glue has managed to work its way somewhat around the sides of the backposts because of the amount of glue I had to use.

Hide glue is used in player work, often to attach the striker pneumatics to the valve board. Those glue joints take a beating. Yet, hide glue will fill some large gaps (when you take things down to scale) and the joints do not separate. In fact, they even maintain their seal.

Also, if that day should ever come when even Grand spinets are valuable because they are made from real wood, the bolts are not epoxied into position. The hide glue can be easily removed.

Also, hide glue was used on most of the old uprights, and many of them are still around.

One reason I think that liquid hide glue has gotten a bad rep is because not everyone is aware that you MUST use fresh liquid hide glue, the earlier from the expiration date the better.

Just keep in mind that you are gluing it with Jello when you use hide glue.

Blech! Jello... Ugh!

Not even the Cos could get me interested in that stuff.

Hi all - I'm working on a write-up for this procedure ( "Repairing the Separated Back")and would like feedback before I finalize it. I've done probably no more than a dozen of these repairs over the years, and want to know if I'm making any serious errors of omission, or if the procedures as I describe them are off base.

Not concerned at this point with proofreading errors. Will proofread myself, and will send it off to my editor who will spot any remaining mistakes. Just more concerned with content. Oh, and if anyone has an idea for a better title - what I have seems lame, but can't put my finger on a better one. Thanks, Chuck Behm

Looks good to me.

Chuck, your articles are always highly informative, easy to understand and well illustrated. I have very much enjoyed every one I have read so far. Thank-you!

Hi Chuck,

I have a question, not a criticism

On page 5
"Once the clamps are removed and before the tension is returned to the strings)the original bolts may be returned (after plugging and retapping the holes)... For a more reliable repair, however, the bolt holes may be drilled all the way through the back of the piano so that threaded rods with nuts and washers on either end might be inserted."
I was wondering if you do decide to go with bolts or all-thread rather than the original screws, if there was some reason you would not want to also use the bolts to help close the gap, rather than waiting until after the glue has set up. Too much tension on one part of the plate? Maybe the holes won't line up as well if drilled at this early stage?

Thanks,
-Joe

Chuck,

Another question: you wrote that the separation is pulled back together until beads of glue are squeezed out. Is it advisable to stop at this point (which really depends on the amount of glue inserted), or to continue and close the separation as far as possible?

Epoxy has good gap-filling properties - in fact, I've read in several epoxy instructions that one should be careful not to over-clamp an epoxied joint, as this may starve the joint of glue. Other glues, however, have weaker gap-filling properties, e.g. all the PVA glues...

That's a great question Joe - thanks for asking.

I see two reasons for not drilling the holes at least until the gap is closed, if not later after the glue has set. The first reason is as you mentioned - the holes won't line up well. If the pinblock is tilted forward to begin with, and you drill your hole perpendicular to the plate, the drill bit is going to follow that line as it goes through the back assembly. When you begin to close the gap, the orientation of the front part of the hole (through the pinblock) and the back part of the hole (through the back assembly) is going to change, so that it's no longer a straight line. It's going to end up with the back part of the hole tilted up from the front part. If you've inserted your threaded rod right after drilling, it's going to bind and prevent the gap from closing. Does that make sense?

Secondly, the 1/2" drill produces lots of wood chips as the hole is drilled. The last thing you would want is for chips to get down in the gap before you try to close it.

To me, it seems safest to drill the holes last. Since the clamps I use are pretty much in the way while they're still in place, I don't do the drilling until the glue has cured and the clamps are removed.

However, that being said, I'll try to do some rewording of the promo to allow for variations in methods here. The audience of the article is not the technician after all (this is not meant to be an instructional article). The audience of the promos I write is the customer of the technician. The last thing I want is to have made things too specific, so that the technician's customer questions him as to why he is doing things one way when the written material he provided said he would be doing it another.

Where various methods are used for a particular repair, I try to be vague enough (or else I mention various possible techniques that might be used) so that the technician doesn't have to explain himself to his customer for having a different technique than I happen to use myself.

Returning to your original question, with the number of clamps that I use, I honestly see no reason to use the bolts and washers as a clamping mechanism. However, I'll try to do a bit of rewording so that if a person did want to use a combination of clamps along with the bolts to tighten up the gap it would fit with what's described in the promo. (If for no other reason, this might be important to the technician who doesn't own a lot of clamps!)

I'll work on revising and post the new copy here for you to check out when I'm done. Thanks again. Chuck

Mark - another good question. When I'm turning down my clamps, I'm getting them as tight as I can, but I'm using Titebond. With the piano in the photographs I put in a lot of glue (using a piece of veneer to work it in) and when the clamps were set I had a running bead of glue showing along the top, but not nearly enough that I was worried that there wasn't enough glue left in the joint to hold.

I'm unfamiliar with how epoxy works for this repair, not having used it ever, I can see your point about not wanting to starve the joint of glue. I'll try to do a bit more rewording of the promo to leave it open as to glue and methods you might chose to use.

Again, keep in mind that this is not meant to be an instructive piece, but more a way for the technician to give his/ her customer enough information to give them the confidence in the procedure to hire the technician to do the job. Chuck