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

Chuck, you are right about the holes not lining but more about the chips, but I have bring back a block by drilling the original screw hole farther, then installing 2 long rods + washers, and it seemm to work fine (without glue in that case, we had not enough time nor the correct glue, but it can be done later). The separation was local, also (only last treble section).


No particular slip when tuning, later.

I understand I would not sell that as a "repair".

In case the 2 holes are not perfectly lining, up to some point, the rod simply bend, probably (not with an 1/2 inch separation).

Hi chuck,
PVA wood glues like Titebond have cold creep meaning that they can move over time if subjected to prolonged stress, especially if the glue joint is not tight. For that reason I would always replace the screws with bolts to maintain stability of the repair.

As for epoxy, its one of the only adhesives that needs to have some space in the glue joint. Too light a joint can weaken the bond. It is also subject to cold creep so the same procedure as above is recommended.

Thanks for the comment, Bill. I agree 100% - personally, I always bolt with threaded 1/2" rod with nuts and washers on either side. If it's just a hairline crack, I'll advise the owner of the potential problem, and mark a line across it marked on either side at exactly 1" so I can keep an eye on it to make sure it doesn't start spreading.

Again, this write-up is for technicians to give to their customers, and since each promo currently goes out to more than 200 technicians around the country, I try to allow for some "wiggle room" in the details so that technicians don't feel as if they are painted into a corner so to speak.

It's a given that various technicians are going to have their own procedures and specific tools. I'm trying to just give the gist of the repair so that the owner of the piano with potential repair work to be done is satisfied that (1). his piano has a problem which needs to be fixed and (2). the repair proposed is a legitimate one.

In the case of this particular problem and repair, the idea is to be able to give the owner a write-up which legitimatizes the fact that the technician is going to (1).(possibly) pry off the back half of the split lid (which can be easy or very difficult), hopefully not breaking it in the process, (2.) let off nearly all the tension on the strings, thus destroying the tuning, (3.) clamp the wayward plate / pinblock / back assembly together with the sincere hope that nothing breaks (such as the plate!), (4).drill a half dozen or so large holes completely through the back of his piano, (5.) insert large bolts that would look more at home if used on a farm implement and not a musical instrument and (6.) deal with the fact that the piano will probably be in sincere need of a regulation job when the work on the back is completed.

I remember well the first time I proposed this particular job to a customer. I was in my early 20's at the time, the customer in question was a college professor who probably had his fill of young kids my age, and when I tried to explain the work I wanted to do he look at me as if I was suggesting that his wife was a Martian. (He had me do the work eventually, but only after he had called several experience technicians around the area and learned that it was a bona-fide procedure.)

I would have loved to have a well-written explanation of the job complete with photos so that he would have seen that I wasn't just making it up - it was a real repair. It would have made things a lot simpler.

Anyway, I digress. Thanks again, Bill.

Hi Chuck,

Thanks for the response

"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. "

I do see the logic of drilling last. But, I think there are circumstances where it may make some sense to drill first, in such cases as the piano in this thread... where only the backposts have worked out of position, but the rest of the glue joints have held.

You make a very, very good point about wood chips. I think that in the future, if I must drill first, i will have a vacuum running as I drill to try to pick up the chips before they even fall into the crack. A very good point!

While we are on the subject of clamps, I was wondering if you, or anyone else here, had any firm opinions re the maximum amount of torque, foot-pounds or inch-pounds, that could safely be applied with the individual clamps, or individual bolts, without cracking the plate.

Thanks

The plate if going back to its previous condition is probably not crack..

Unless it decides to

Bill,

To my knowledge, it is mainly quick-set epoxy that is subject to creep. Slow-set forms more and better cross-links, and creeps much less.

Be that as it may, if all aforementioned adhesives (including epoxy) are subject to creep, then why use adhesive for a separated pinblock at all? Is it only an interim solution, to get the drilling done, and the bolts in place?

Isaac - I'm not sure about that. I'm no expert as to properties of various metals, but I don't believe cast iron has any "spring" to it. When it is deflected by the tension of the strings, and remains in that deflected position for a length of time, I don't sense that it necessarily wants to go back to its previous condition, as you say.

Could someone with more expertise comment on this? I haven't broken a plate myself with this repair, but I've seen a piano "repaired" by another technician where the plate was in fact cracked at the left strut. I was called in to see what I could do. Nothing at that point that I could see.

Again, as far as my write-up of the repair, the cautionary note concerning the risk of cracking is meant to provide some protection to the technician in case the worst happens. It's the same as warning a customer before a pitch-up that strings could potentially break. I would rather warn them and not have it happen, then not say anything until after the fact.

Joe, to answer your previous question, as long as the plate does return to its former orientation, and as long as you have a method of spreading out the pressure from the clamps (note picture in write up - I use scraps of pinblock material) I think you would have a hard time tightening your clamps by hand to reach a pressure that would break the plate. I don't have any way of measuring inch-pounds of pressure on my clamps, but I tighten them until the crank won't turn by hand any further. Chuck

Mark,
As you say, slow-set epoxies creep less, but they are still subject to some creep. The type of epoxy and the type of filler used will have an impact on its ability to resist creep. The surface area is also important. A high quality epoxy with a large surface area will have essentially no creep. A rough rule of thumb is the harder the epoxy sets, the more it will resist creep.

You can read more about epoxy/creep on West Systems' web site. They have an article about testing their products.

There are adhesives that do not creep... hide glue, plastic resin glue, polyurethane glues, and even super glues. Non of these adhesives are gap filling so you need to have a tight joint.

The other problem with pinblock separation repair is there is no way to properly clean the surfaces before applying the glue. Most of these separations are adhesive failures so the joint is full of old glue. The only glue that truly rebonds to itself is hide glue. But hide glue is not that easy to work with in someone's home.

I usually use Epoxy for this repair. I'll apply the epoxy, camp everything closed, drill out the old screw holes and insert new bolts. I try to get a bolt through each back post usually by adding extra bolts as needed.

Hi Isaac,

Though there has been some debate on this subject at PW before, I still believe that a plate can warp if it is kept out of its original position. Again, going back to when I was a student taking a grand rebuilding course, (and that's going way back LOL! So my memory may be flawed), I believe we were taught not to overtighten the screws when we initially install the plate. We were to let the plate settle a bit and then tighten the screws up a little at a time over several days, IF I remember I think that a bowed plate could possibly be persuaded back to it's original position if done gradually enough. We can "re-warp" it back to it's correct shape.

Unfortunately, I guess you are correct. You know you used too much force after the plate cracks. Or, the plate had an inherent hidden defect and the project was doomed from the start. I just wondered if there might be some sort of standardization as to optimal and maximum torque values. I guess this is one of those areas where you just have to use your own best judgment. Mine has been to observe how the nuts/washers are sinking into the wood on the back.

Chuck, thanks again for the advice. Many, many clamps; baby steps while tightening. It makes good sense!

Btw, this looks like you are doing another excellent professional presentation. Well written and great photography. Very classy!

Thanks,
-Joe

Bill,

Thanks for the detailed reply.



I've been wondering about the adhesion of other glues to hide glue residues. Reblitz, for one, warns us that PVA glues (carpenter's glue) make a jelly-like mess when applied over old hide glue.

And whether it's someone else's home or my own, my biggest concern with using hide glue would be its short open time. I'd hate to rush the clamping step.

Hello again, everyone. Based on comments made in this thread, I've done some revision on the write-up I've been working on, and would appreciate comments before I go to press with it. Check out here: "Repairing the Separated Back."

Please keep in mind that the intended audience is not the technician, but the technician's customer, to provide reassurance that the repair is needed and legitimate.

A couple of years ago I went to the dentist and was told that I needed a root canal. Not having had this procedure before, I was uneasy about the prospect. The dentist had a brochure to give me to take home. Reading it over at least took away the fear of the unknown. I wasn't looking forward to it, but I found I was much more relaxed about the idea knowing what to expect.

That, basically, is what this type of write-up is for--to take away the fear of the unknown for the owner of the piano. This is what the piano needs to have done, and this is how I will get it done.

Thanks in advance for any further suggestions before I finalize the copy to the write-up before publication. Chuck

Hi Chuck,

Great write-up.

Since this is for non-techs, my only suggestion would be to slightly expand upon the first paragraph somewhat... so the customers will understand why they need to have the separation repaired and help sell the job. Maybe just a little more on how the separation will affect things like tuning stability, etc. if left uncorrected. Possibly another sentence or so.

Of course, maybe you don't want to get into that much detail so as to just open the door for the tech to begin the conversation with the client?

Thanks for the suggestion, Joe. I'll try to do a bit more reworking of the opening paragraph or two and will post the revision when I'm done.

You are right about the importance of starting a conversation, however. When a customer feels he knows a bit about the topic at hand, I believe he is more open to talking about it. No one likes to feel completely stupid about a subject, so if you the technician can give them material to bring them up to speed,so to speak, it makes a conversation easier. Chuck

To Joe, Isaac, Bill, Ando and anyone else who has taken the time to look over my rough drafts - thanks. Here's the last (or close to it) version with some modification of the first page (according to your suggestions, Joe). I would welcome any last comments. The draft (Repairing the Separated Back - Final Revision) has been sent off to my editor for proofreading and hopefully it will be ready for distribution on the first of March.

In appreciation for your help, anyone who has pitched in with comments, or taken the trouble to read my material over, please accept my special invitation to receive a complimentary promo - your choice of topics. Thanks so much! Chuck Behm

Thank you for your very kind offer. I have decided to ask for the C/A promo.

Thanks Chuck!
Much appreciated.

-Joe

Joe - Check your email - I've sent the complimentary promo set over the topic you asked for. I hope you're able to put it to good use.

Thanks again for your suggestions (and the suggestions of others). When you're doing a technical write-up it's very helpful to get other opinions on the topic at hand - I appreciate the collective wisdom of everyone who posts here. I have my own methods of doing repairs, but for most repair jobs there are alternatives. It's helpful to hear about those alternatives so that I can do my write-up making an allowance for differing techniques.

If anyone else who has taken the time to read over the drafts of the separated back repair would like a complimentary promo set, here are the available topics. Pick out whichever one you would like. Thanks, Chuck

Beautifully done !

Thanks Chuck!
-Joe

So Chuck you have now Int recognizing as I forwarded it on the French PW forum

Piano owners are always amazed with the number of possible things on old pianos, and delighted to have a good global information on what can be done to repair.

But technicians of course also, thanks !

Comment from a friend : "blind" nut would be more nice looking (less easy to find may be, more expensive also)

Those long shiny screws for piano plates are expensive, I wonder if the American wood screws have different threading than European ones ?

Isaac - Thanks for the idea. I guess I've seen those in the past, but it never occured to me to consider making use of them for this repair. I would think from the back side in particular they would be useful. The big protruding bolts and nuts aren't particularly attractive when the back of the piano is exposed. I'm not sure going into the plate if they would work, but maybe so.

I'll check my local hardware store as to their availability. I'm sure I could order online as well, but whenever possible, I try to buy local.

Thanks again, and thanks for forwarding the post! Chuck

For the back I would try to make a deeper hole if possible, have the bolt embedded, I believe the front part is more where those large nuts and bolts could look a little surprising

when doing the job on site it may be a good idea to use a "martyr" (wooden plank) and not to make a hole in the wall behind the piano