Plastic jack warp

Dear All

Greetings from Hong Kong, where today marks the halfway point of my first post-COVID Asian harpsichord maintenance tour.

Here is a good example for those in the past who extolled the convenience and stability of modern plastics for use in harpsichord actions instead of having to deal with the fickle nature of wood!

I have never seen any jack warp quite as badly as this one! It’s from an inexpensive mid-1980’s virginal by Xavier Leigh-Flanders. This jack was irredeemable, and required replacement.



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I don’t think there are any souls remaining who advocate plastic jacks now. A bad historical dead end. [I know you are referring to past makers, but still.]

But pray tell how did you replace this? Surely impossible to come by?

Dear Carey,

Certainly this would not have happened with pearwood!

Let me add, however, for the benefits of those who have “plastic” jacks and may worry, that not all are made equal.

The black Delrin jacks Hubbard provided with my kit in 1973 (finished assembly March 1975) , after 50 years (!), with the instrument having been played through that time, are as straight today as they were when the kit was assembled.

There is no doubt, of course, of the superiority of pearwood or similar.



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My nearly 50 year old white Delrin Dowd jacks have shown no signs of warping either. From time to time, I have heard rumors of the superiority of old Delrin (some have referred to the “original” block of Delrin). Carey, do you have any knowledge of this?

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I don’t know what causes warping of plastic beams but I seem to recall there is some art in moulding engineering to take care of stress relief. I don’t think Delrin is inherently prone to warping - after all it is commonly used in precision machine gears, for one - but that the example in question was badly moulded to start with.

Well, here’s the info!

No doubt more subtle problems of this type may take many years to show up.

I have had two double manual Dowds with delrin jacks, which have exhibited no warping whatsoever in 50 years. Also no embrittlement of the tongues.

I have had pearwood jacks on other harpsichords which have not warped. However, about a half dozen have broken ears from (IMO) normal handling which had to be replaced.

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8 posts were merged into an existing topic: 3D printed jacks

So it’s clear from experience that Dowd had pretty good plastics moulding engineers!

Would be a good choice.


Looks like a cheap Injection molding process to me. Inappropriate cooling cycle resulting in residual stresses.


Which is what I was suggesting.

Dear All

My above warped jack example is extreme. This particular jack from a forty-year old instrument has only attained this unusable distortion since my last visit here in 2019.

However, the jacks in this instrument were doomed from the beginning, the English maker roughly moulding both jacks and tongues from an original of the first Zuckermann tapered variety, with corresponding lack of detail. But that meant to get this virginal playing again, I could easily move the top jack down to #14 and fit a brown Zuckermann jack to the top note.

There are many reasons why plastic can deteriorate, not only due to problems during the moulding process. Have you seen the exposed top part of plastic jacks go chalky and fall apart from UV exposure? And we all know about wispy plastic moulded springs (Hubbard, Herz, Goble…) losing their push.

Particular makes including Dowd, I’m sorry to say, may not be immune. Here is a video of me correcting warping of jacks from a 1963 Dowd four-choir French Double:
Correcting warped plastic harpsichord jacks

PEEK is a wonderful spring material, with a long-lasting snap comparable to real bristle, and far better than the rubbery result from nylon monofilament fishing line used by some in the past.

Any component or complete instrument is a combination of D, M & W: Design, Materials & Workmanship. Good wooden jacks are better than plastic; bad wooden jacks—and there are plenty of those around—not necessarily.



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I have had the same experience with my 1976 Dowd.

Ditto. My Hubbard 1973 kit black delrin jacks have not warped at all.