How do you assess the "bump" in a grand action?

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Withindale
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How do you assess the "bump" in a grand action?

Post by Withindale » 23 Apr 2013, 18:04

In the Understanding Regulation thread Otto said, " ... and a load of tension taken off the repeat springs. (No I don't know why they were originally adjusted to be so fierce, either)."

Is there a simple way to assess whether "bump" resistance is too much or about right?

If it's too much, as it seems to be in my action, should I start by lubricating the rollers or adjusting the repetition springs? There is no jack adjustment and the drop occurs around set off.

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Re: How do you assess the "bump" in a grand action?

Post by Barrie Heaton » 23 Apr 2013, 18:57

The Bump is called after touch or drop. Now the Yank like a lot of Bump
The golden rule is what ever the set off is the drip should be the same so 1.5 mm set off the drop should be 1.5 (after touch bump)

the little screw behind the flange screw on the hammer alters the drop

one Other factor for a strong after touch are the rollers they have been put on back to front


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Re: How do you assess the "bump" in a grand action?

Post by Withindale » 24 Apr 2013, 00:14

Thanks, Barrie. I'll take a closer look at those rollers.

I measured the down weight on a typical key, or should I say up weight. About 66 g depresses it down to the point of "bump" resistance and an extra 100 g is needed to take it down past the bump to the cushion.

PS As it happens, Fred Sturm, University of New Mexico, went a long way to answering my question in a PTG post last year. He wrote This thread started (I believe) asking about how much weight should be used when setting dip. Personally, I use the sense of touch: I try to feel precisely when the key has touched the punching, and hold the block with that finger in that position. I think we need to cultivate this degree of sensitivity in regulation. It is necessary for feeling when the wippen hits the drop screw, and for feeling whether the jack tail hits at the same time.

But I suppose a weighted block could be useful, as a check. It needs to be heavy enough to drop the key, which means at least 50 grams or so (depending on down weight), plus enough to overcome the repetition spring. Since down weight and repetition spring strength both vary, this will actually yield inconsistent results, piano to piano, whatever actual weight is chosen. A quibble, but maybe not an unimportant one. I would think that 150 gm makes more sense than 400 gm, though.

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Re: How do you assess the "bump" in a grand action?

Post by Barrie Heaton » 24 Apr 2013, 20:36

Withindale wrote:Thanks, Barrie. I'll take a closer look at those rollers.

I measured the down weight on a typical key, or should I say up weight. About 66 g depresses it down to the point of "bump" resistance and an extra 100 g is needed to take it down past the bump to the cushion.
First of all have you got the sutain pedel presed down when trying the down weight as it need to be, second the down weight meserment is only taken on the first part of the cycle, up to set off not pased it Wile 66g is Ok for Bottom A on a concert grand its a tad hevey for top C But again a lot depends on the up weight

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Re: How do you assess the "bump" in a grand action?

Post by Withindale » 25 Apr 2013, 00:36

With the pedal depressed the range of down weights across the keyboard is 47g (C8) to 67g (C1) and the range of up weights is from about 20g (C8) to 40g (C1).

The bump is rather abrupt on most keys. Given that Fred Sturm's allowance of 100g to overcome the repetition spring is the same as my measurement, I imagine that less friction between jacks and rollers will reduce the jolt.

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Re: How do you assess the "bump" in a grand action?

Post by Colin Nicholson » 25 Apr 2013, 11:28

Withindale wrote:The bump is rather abrupt on most keys. .
Depending on the design and shape of the rep springs, some are wish bone shaped (like a wish bone on a chicken breast) .... or a wish bone with a hook on the end that attaches to a loop on the jack... similar to the Schwander action. I find the latter easier to adjust with the rep spring screw adjuster.... however, if (like Steinway), the rep spring does not have a hook & loop (but attaches itself to the base of the jack via a slot), occasionally you find grease/ corrosion etc building up in the recess areas, on the underside of the rep lever & inside the jack slot. The springs may need to be dislocated.... an/or replaced, and the appropriate bushings replaced. I prefer a DRY lubricant so everything works dry & smooth.... but for old actions, some liquid graphite (superslide paint) may help. Sometimes the springs tend to embed themselves too deep into the bushing recess, thus adjustments are difficult. Personally.... I would replace the whole lot, new springs, re-pinned & new bushings/ loops etc. Springs may need to be re-profiled & shaped.

The hook & loop versions I find are an "easier ride" though and generally easier to maintain.
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Re: How do you assess the "bump" in a grand action?

Post by Barrie Heaton » 25 Apr 2013, 15:27

Withindale wrote:With the pedal depressed the range of down weights across the keyboard is 47g (C8) to 67g (C1) and the range of up weights is from about 20g (C8) to 40g (C1).

The bump is rather abrupt on most keys. Given that Fred Sturm's allowance of 100g to overcome the repetition spring is the same as my measurement, I imagine that less friction between jacks and rollers will reduce the jolt.
on 47g would be looking at 23 -25g up so you do have a lot of friction. have you looked at the hammer swing. also what was the drop in mm

Colin has pointed out the rep spring but I would test first

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Re: How do you assess the "bump" in a grand action?

Post by Withindale » 30 Apr 2013, 00:12

Barrie Heaton wrote: ..one other factor for a strong after touch are the rollers they have been put on back to front
I think they may have been. It's easier to smooth the nap in the opposite direction to the movement of the jack as you depress the key.
Barrie Heaton wrote:... you do have a lot of friction. have you looked at the hammer swing. also what was the drop in mm. Colin has pointed out the rep spring but I would test first
4-5 swings on the hammer I looked at. I don't find it easy to measure the drop under the dampers but I'd estimate about 3 mm looking along the strings.

I've found that reducing after touch to about 0.5 mm makes the "bump" less noticeable. Smoothing the roller and some teflon also helped on a couple of test keys and I'll do that on the rest.

When I have the time I'll rebush the keys, level them precisely, and go through the action paying attention to the repetition springs as you suggest, Colin.

Thank you for your most helpful advice.

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Re: How do you assess the "bump" in a grand action?

Post by Barrie Heaton » 30 Apr 2013, 19:49

Withindale wrote:
Barrie Heaton wrote:... you do have a lot of friction. have you looked at the hammer swing. also what was the drop in mm. Colin has pointed out the rep spring but I would test first
4-5 swings on the hammer I looked at. I don't find it easy to measure the drop under the dampers but I'd estimate about 3 mm looking along the strings.

I've found that reducing after touch to about 0.5 mm makes the "bump" less noticeable. Smoothing the roller and some teflon also helped on a couple of test keys and I'll do that on the rest.
4.-5 swings is fine. It’s much easier to look and set the drop when the action is on the bench. I would work the Teflon into the rollers also put some on the set off pads.
May be a bit of CPL on the whippens and jacks
When you have done you keys put some Pro-tec on the Balance and front touch pins
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Re: How do you assess the "bump" in a grand action?

Post by pianotechman » 27 Oct 2013, 10:01

Have you checked the possitioning of the jack under the rollers to begin with? That will also make a difference to the touch/correct working of the action.
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Re: How do you assess the "bump" in a grand action?

Post by Withindale » 27 Oct 2013, 17:23

Thanks for a timely reminder, David, I still need to go through the action on a bench.

There is no jack adjustment on this action, other than the felt in the slot or a shim on the back of the jack. The rollers were replaced quite recently, but not entirely consistently. I shall have to see whether the differences were to compensate for the relative position of the jack. Possibly not, I suspect.

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Re: How do you assess the "bump" in a grand action?

Post by pianotechman » 28 Oct 2013, 20:08

Yeah, Old Steinway grand actions use the felt pads, so after years they compress and the jack top goes further under the roller than it should. I note that their modern actions are now fitted with an adjuster the same as Brooks!
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