Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum FAQ - Tuner-Technicians Forum inner and outer rims bent seperately vs. simultaneously

Steinway and Haessler ( by Bluthner ) bend their inner and outer rims together. Steinway claims that this is the best and most expensive way to build a piano. Bluthner claims that this is one of the reasons a Haessler is less expensive than a Bluthner. They say it is easier, faster, and less expensive to bend the rims together.
I could be mistaken, but every other major manufacturer, low end to high end bends their rims separately.
Also, if anyone wants to comment on the relative merits of rims being continuous ( Steinway, M&H, Steingraeber etc.) vs. sectional ( Bluthner, Bosendorfer, old Bechsteins, I don't know if the new Bechsteins have sectional or continuous rims)

I am very interested to hear everyone's opinions on this subject. I know rim materials have been covered. If this is a redundant topic, I apologize.

If one believes that a single piece of laminate retains any tension at all after it is bent then the sectioned rim's tensionless structure would be a benefit.

It seems to me an additional benefit in separate rim construction would be to give the maker an opportunity to make sure the inner rim/ soundboard relationship is right before the outer rim is joined.

Another issue with the Steinway belly assembly is their uses of pre-fab bracing that is laid into the rim after it is pressed. Many German makers intergrate the bracing with the inner rim before the outer rim is joined.

Keith,Baldwin artist grands also utilize a one-piece continuous bent rim.The use of two piece sectional rims makes it easier to notch bridges with the outer rim out of the way,if the manufacturer is notching bridges with the board glued to the inner rim.The one piece continuous rim is believed to be stronger than the sectionals,and acoustically superior.I believe there is'nt really any acoustical advantage,but a way to incorporate a cost reduction for the manufacturer.

The one-step rim lay-up has long been a selling feature for both Steinway and Baldwin. Both tout the supposed advantages in structural integrity gained by this construction technique. But, consider — in the end what is it that holds the two rim sections together when both are glued together as a single unit? It’s the glue joint between the outer laminae of the inner rim and the inner laminae of the outer rim. And what is it that holds the to segments of the separate inner and outer rim sections together when they are glued up separately and assembled at some later stage of construction? It’s the glue joint between the outer laminae of the inner rim and the inner laminae of the outer rim.

So, which is superior? In theory both will have essentially the same strength and structural integrity. In practice, however, I believe the prize has to go to the latter. I have several reasons for saying this, all of them based on practical building experience with both types of rim construction. The biggest problem with the one-step lay-up process is that the veneers must be exactly the right thickness — all the time, every time. If the inner rim veneers run even slightly thick there will be excessive glue squeeze-out, introducing the possibility of a “dry” glue joint. As well, there will be a tendency to buckle the outer rim veneers just above the inner rim. (Bunches of excess glue is forced up there and, with no place to go, the hydraulic pressure forces a bulge in the inside laminae of the outer rim.) If the veneers are running just a bit thin the glue joints won’t receive the right amount of pressure and the glue joints will be too thick. Because the adhesives commonly used for this task are not particularly good gap-fillers the glue joints will be weakened. You can see the effect of this on certain old Steinway (and similar) rims that have developed separations between the two rim sections.

Another difficulty sometimes seen with the one-step lay-up is their propensity to twist. This can often be seen in older Steinway (and similar) pianos by standing back and sighting across the top of the stretcher and the back of the outer rim and checking to see how close the two are to being exactly parallel. You can very often see a certain amount of twist to the rim. If there is a twist it will usually be in the counter-clockwise direction. I rarely see this twist in sectional rims. (Note: this doesn’t seem to cause any particular trouble — it’s just there.)

Also, from a purely practical standpoint, pressing the two rims separately and building the piano up on the inner rim makes it possible to fit the bellyrail and bracing system more easily and — at least potentially — more accurately. It’s much more efficient to build the piano this way. And, also from experience, I’ve long since concluded that the easier it is to accomplish any manufacturing step the more likely it is that it will be done correctly and accurately.

When all is said and done, though, in the real world of piano building both systems have a long and successful history.

As to your last question, our own upcoming grand piano will be built up on a separate inner and outer rim. It will also be a three-piece sectional rim. The bass and treble sides will be straight with a bent laminate section defining the back and tenor side. Among other things, this construction gives the designer better control over the shape of the soundboard. Obviously, then, I consider this to be superior. So why did I design the Walter 190 to use a continuous bent rim? (As does the upcoming Walter 175.) The continuous bent rim is a manufacturing expediency; it is easier to build in production. And, though I believe the sectional rim to offer (at least potentially) superior acoustics, the differences are not great.

Much is made about the great strength of the continuous bent-laminate grand piano rim. In reality, however, this great strength is mostly overkill — the rim assembly doesn’t really have all that much to do. It is not called on to carry much, often none, of the string tension load. Nor, contrary to the claims of some, does it play any significant roll in supporting soundboard crown. Basically, all it has to do is hold the plate in position, provide a parameter mounting structure for the soundboard and look pretty. Unless they are made of some really ridiculous Select Hardwood, both the continuous bent rim and the sectional rim will accomplish their assigned tasks with relative ease.

Del

Del,

Thank-you for your very thoughtful reply.

Thank-you to Alex and Curry, too.

Del, having you here is really a lot of fun. Great post.

Half-way through Del's post I was wondering what his credentials were as he basically dimissed the idea of the continuous rim being any better than a sectional one, and then I got to the bottom and found out.

I guess this is like the Pianist section of the forum having a Concert Pianst

There was one other thing about bending both rims simultaneously which was mentioned in one of the books about Steinways that I have. When Steinway first started doing it, they had a lot of rims that split after being glued up. They found that while they had been able to use different types of wood, maple on the outside and poplar in the center, in the laminations when bending the rims separately, the difference in drying characteristics caused the rims to crack when gluing them simultaneously. So they glued them out of solid maple.

As is usual with different manufacturing techniques, it made no difference to the consumer.

Interesting. Do you remember which book? I thought I'd read most of that stuff but I missed that completely.

Baldwin has used maple inner rims with poplar outer rims for some time with not particular problems that I'm aware of. (Though I think they are now back to all maple.) Walter successfully uses a combination of European birch and northern hard maple. There are other combinations used as well. I wonder what was going wrong with the Steinway rims.

It does take a longer period of time to dry and stabilize the one-piece pressing. Steinway uses something like six months. Baldwin uses a combination of heat and a shorter period of time. Just because the glue has kicked over doesn't mean the wood has taken a set and the whole mass has stopped squirreling around.

Del

You made me go downstairs and look it up. Lieberman, pp.139-140. New glues may eliminate the problem.

Thanks. Now I'll have to try to find it.

Possibly a glue problem but I suspect it was more likely a wood drying problem. There is a lot of evidence this was not always handled very well. If the two woods were at different moisture contents when glued up their shrinkage rate while the rim was drying/conditioning would be quite different.

Del

Del