Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Reducing Hammer Density

I have a set of rock hard Chinese hammers that are on a clients piano (someone elses job). He would like me to work on them and see how they turn out. If, after I have worked on them, they do not produce a satisfactory sound, then he would like me to fit a new set of Abel natural felt hammers onto his piano mechanism.

This is the route that he would like to take, though he may pay more in the end if he is not satisfied.

This is a set of hammers that I would like to use the compass point needling technique on but apart from that I would like to reduce the hammer density.

I am wondering, are there any other ways of reducing hammer density apart from needling the shoulders?

Thank you,

first low and very low on the hammers to try to free the shoulders , then the shoulders, then the top.

you can work with one long needle not too thin and go along from 16:00 to 14:00 until you feel you have a less packed felt.

If you begin to be at ease use 2 needles

then put back in the piano and try.

if you do not have any FFF it is useless to work on the crown or to soften with moisture, in my opinion.

SOmetime the hammer felt seem to be glued and need many jabs at +- the same location to begin to move.

If they are impregnated really you will discover it as the needles will be hard to extract.

For the underside you may need a somewhat heavy tool so you can make your jab from 15 -20 cm high.

With a hard support under the shanks it is better, , on an upright first tighten all screws tight, then you can try holding one hammer , eventually 2 in front of the piano, for the underside, and make the upper side on a table with a wooden support.
Or on the keyboard with a sort of "comb" layed on the keys (must be the good height and not too large.

The shoulders and top of the felt if "glued", can be massaged with heavy parallel pliers, not on the flat side but with a rolling motion using your thumb as a fulcrum. It can help and make some breaking in of the shoulders.

all the tips on or near the crown, are not long lasting or desesperate ones . for lazy tech needling a little deep near the crown cut directly in the attack harshness but will not install much dynamics (spring)

Crown can be hard, that is how it is sustained that matters.

Bad felt with short glued fibers gives no much good results, but it is a good opportunity to work on first needling so to get an idea of the job that was common some decades ago, when hammers where more packed and dense than today.
The same voicing is done today, hopefully less and with better results.
Wear earplugs eventually, as you need to listen to FFF playing and get out of saturation there. Then you can voice.

If you can reduce density and find some springiness at the same time, the job is done

Hope that helps.

Other than needling, the only method that worked for me was forcing expansion/contraction of hammer felt with repeated and very conservative treatments of isopropyl alcohol. Success is predicated upon the piano being in a tuning/service cycle until the desired result is achieved. If the hammers have been lacquered to death, other methods are available - none of which are 100% and completely hammer safe, in my view.

Yes it may work, certainly, but does not install any "differncial" , I mean if the hammer get a little umpacked, its springiness will attain, say 5 mm in the height of the hammer, then all the felt under that zone will not be used for tone.

As a friend told after hearing the "compas point" treatment : "no tone" (no need to make phrases


Possibly isopropyl treatment can provide a hammer that can be voiced. then there is also some shrinkeage of the felt that is done with alcohol exposure, so I am unsure of the final structure.

Thanks, Isaac. Agreed. It is efficacious for both, but inasmuch as no "differential" (if I understand your meaning) is introduced, such is not necessarily permanent. Again, if I understand the OP correctly, the search is for a method other than needling. The procedure - when done correctly - can achieve result.

Thanks for the posts folks,

So, softening the hammer felt, increasing the resiliency, is the only way to reduce the density?

Filing the hammer felt is reducing the weight but not reducing the density. So, filing is out.

Yep, filing exposé even harder felt to the strings

Thank you Isaac

I had good success last week with a Samick grand with very hard hammers. I sprayed the hammers quite liberally with 50/50 isopropyl/water solution in an atomiser spray bottle. Less in the treble, more in the bass. Then I left it a couple of days to dry. Came back and whereas before it was almost impossible to penetrate the hammers with needles, now they go in quite nicely. The process causes the hammers to swell a little, so filing is necessary to restore the original shape. The hammers are just that little bit less dense now. It really rounded out the tone, got rid of the harsh overtones. I went a bit too far on some of them and they lost some sparkle, scorching the strike point with a hot iron restored that. Needled some notes that still stuck out.

Remains to be seen how permanent it is, but I and the customer were very pleased with the results.

My first time doing such work, done with that understood by the client. A little bit nerve wracking but it certainly paid off.

This is very similar to the method I have used. I preferred the common isopropyl alcohol 70/30. It is possible that 50/50 would have worked even better. Alcohol is really for penetration. It is the water the works the magic. Individual hammer "dosage," and the frequency thereof, subject to many variables. The last treble octave almost never treated.

You have been given some good suggestions for making the best of what is a bad set of hammers.

Additionally, I'd like to suggest that it is not unreasonable to suggest that the customer get new hammers. It's like tires on a car -- maybe the manufacturer didn't put on the highest quality tires and if the car isn't handling correctly high quality tires can make a big difference.

I mention this because, unlike the automotive world, people in the piano world somehow seem to think of hammers as a structural element of the instrument that should perform well even if that is where the manufacturer shaved corners.

I (and others) have a good number of happy customers who threw away their stock hammers and installed good ones.

To make the best of the existing set, feel free to PM me for a copy of my article on voicing.

Thanks for the run down Phil

I am glad that job worked out for you.

A word of caution :
avoid moistening up to the underfelt , as it may loose the inner tension (as when impregnating hammers) .

Energy storage, in a hammer, is installed as in a soundboard, by the sliding in force of one material along another, then glued.
The sliding of felt around the moulding is not that large (and probably sometime nil) then if any exists it sound as a good precaution to leave it untouched.

It would be difficult to prove but I believe that the use of hide (skin) glue for gluing the felts on some know brand, add some natural rebound at FFF, may be just because of the retraction of the glue when it sets.

Good point, Isaac. Micro-dropper is best. To either sides of the strike point. Never bathe the hammers.

Yes, there was a bit of luck involved, considering I only really dosed it once. And yes, I think if I were to do it again, I wouldn't do the top octave. I had to reharden most of those hammers.

Thanks to all who have contributed so far,

I think that I have been asking a silly question. But due to the simplicity or the complexity of the question, I am fumbling around in my own mind as to what the answer may be.

The question I asked initially was incorrectly worded, and should have been the following,

Are there any other ways of reducing hammer density without reducing hammer weight?

I am thinking that the answer is, "Absolutely not. Silly question Mark. Move on.".

If you can plan a way to reduce both the weight and the density by swelling the hammers up with diluted water-and then shaping them to produce a good pear shape-you have a plan that will improve both dynamic range, tone color, sustain, and durability.

With all tone regulation keep in mind that the ideal felt density will vary across the compass in a similar way that a frequency chart does. When you hit 1K HZ. and above things become exponential. Hammer 1 and hammer 20 can be almost identical. Hammer 55 and hammer 65 will be quite different. Hammer weight from note 55 to 88 must decrease dramatically to get good tone. Remove weight from the hammers everywhere except the wearing dimension.

Thank you very much Ed

Yes, but they will be bigger. The hard rock imported piano hammers I have seen don't needle out to a very resilient product, I think the felt is too brittle. I have had the best results with steam on the shoulders and just a faint pass across the crowns. The hammer will get bigger as the outer tension is lessened, but that will allow a file to get a decent shape to them.
Regards,

Thanks for that Ed

I have been thinking that these hammers are not a very resilient product.

I will have to dig up your procedure for steaming. It is somewhere on my old computer.

Regards,