Author Topic: Adjusting touchweight  (Read 294 times)

Offline David Aubke

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Adjusting touchweight
« on: April 18, 2017, 12:03:32 PM »
Has anyone ever concerned themselves with the key touchweight of a Rhodes? The first few hits on Google say standard acoustic piano touchweight is between 50 and 60 grams. I'm currently working on a late 70s with factory pedestal bumps and its action is about as light as any Rhodes. But the keys all require substantially more than 60 grams to depress.

I've begun adding weights to the fronts of the keys and sure enough, they feel very light. My main concern is I'm reducing the keys' ability to return quickly to upright. I think I'm going to have to wait until it's finished before I can decide whether this was a mistake.
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Offline Ben Bove

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Re: Adjusting touchweight
« Reply #1 on: April 18, 2017, 01:58:41 PM »
It would've been great if the service manual worked with a touchweight system to regulate the action, like in the acoustic piano world.  This would put a measurement to it.  I thought about experimenting with it, but because the Rhodes action has a number of different variations between models and how the key pedestal interacts with the rounded hammer curve, you might have to get era-specific.  That may be why they didn't, or perhaps it wasn't as big of a concern. 

On early pianos with no bump, I do not believe the tipping point would be linear while the hammer rolls over the pedestal, and more weight may need to be applied to get the key all the way down.  Perhaps on other pianos with a factory bump mod, the most force is required at initial key strike to get the hammer moving, and then it's very light after that.  I could imagine an aftermarket bump mod kit would have some real adjustments needed.

I'd be interested in what you come up with.
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Offline David Aubke

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Re: Adjusting touchweight
« Reply #2 on: April 18, 2017, 02:16:39 PM »
On early pianos with no bump, I do not believe the tipping point would be linear while the hammer rolls over the pedestal, and more weight may need to be applied to get the key all the way down.  Perhaps on other pianos with a factory bump mod, the most force is required at initial key strike to get the hammer moving, and then it's very light after that.  I could imagine an aftermarket bump mod kit would have some real adjustments needed.

I'm afraid I don't completely understand this paragraph. Seems like you're saying early pianos require non-linear force but also late pianos require non-linear force.

To me, the curved cam and no bump means early pianos do require linear force. And this is primarily why I dislike playing them. Even after a bump mod, they still feel slow to me. I much prefer the angled cam of later models where there's an initial push followed by much lighter resistance.

When I'm testing the touchweight, I help the key past that initial movement and only test the remaining 80% of travel. If I insisted on moving the key entirely by 60 grams, I think I'd have to add too much weight.

If this works OK, I'll be very interested in what I could do with an early Rhodes. I really don't like playing them that much as they are. On the other hand, if this ruins my piano, I'll have a whole bunch of holes to fill.
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Offline Ben Bove

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Re: Adjusting touchweight
« Reply #3 on: April 18, 2017, 02:45:51 PM »
Sorry about that, sometimes it can be sort of difficult to convey the concepts via text only.

I've always felt that with the hybrid hammer pianos and no bump-mod, where the hammer curve is more rounded, that the key gets heavier towards the bottom of the keystroke.  So, a player may need to apply an increasing amount of force to reach the end of the key stroke, rather than a constant.  This would mean when applying weights, perhaps the key might be floating in the middle and you'd have to keep adding weight until you finally bottomed the key out?  Not sure if that would be difficult to measure or check.

As you mentioned with the factory bump mod pianos with all-plastic hammers, and that sharper hammer curve, I'd believe that after the initial attack it would be much more of a constant weight.  Probably much easier to measure.  However, is the weight a player feels based off of that initial felt-dragging on the attack?  I can't say for sure and might not matter as much.
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Offline David Aubke

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Re: Adjusting touchweight
« Reply #4 on: April 18, 2017, 03:01:46 PM »
However, is the weight a player feels based off of that initial felt-dragging on the attack?  I can't say for sure and might not matter as much.

This concerns me a little bit. I think, with an angled cam, almost all of the force occurs right at the beginning. The first few millimeters flings the hammer upwards and the rest of the distance is just about getting the pedestal in position to catch the hammer. So, what I'm doing is kind of missing the point.

Basically, I'm just making the action feel very light. We'll see if that's a good thing.
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Offline Ben Bove

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Re: Adjusting touchweight
« Reply #5 on: April 18, 2017, 05:54:50 PM »
I forgot to mention that there is a slight increase in tension as you push a key down - the damper arm is tied directly to the hammer, and the damper is basically spring-loaded to recoil on release.  How much of that you could feel or is measurable, not sure.
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Offline David Aubke

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Re: Adjusting touchweight
« Reply #6 on: April 18, 2017, 06:02:53 PM »
Just started the third octave. About halfway through the second, several of the keys needed no weight at all, which was a comfort to me. I'm not especially interested in lightening the action, I only wanted to know what it would feel like "in spec".
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Offline David Aubke

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Re: Adjusting touchweight
« Reply #7 on: April 18, 2017, 06:30:46 PM »
It may have taken me twenty minutes but I got there!

I forgot to mention that there is a slight increase in tension as you push a key down - the damper arm is tied directly to the hammer, and the damper is basically spring-loaded to recoil on release.  How much of that you could feel or is measurable, not sure.

This, of course, explains why I stopped needing so much weight. The change occurred right at the breakpoint between the mid-range damper arms and the treble arms. These arms have the largest cutouts near their bases.
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Offline Ben Bove

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Re: Adjusting touchweight
« Reply #8 on: April 19, 2017, 01:30:28 PM »
That's interesting :)
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Offline David Aubke

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Re: Adjusting touchweight
« Reply #9 on: April 20, 2017, 02:41:44 PM »
A few observations so far.

I started at middle C and headed upward. I worried that I was doing nothing but lightening the action and that's not really what I set out to do. When I got up to the lighter damper arms, things changed and I've even found myself adding weight to the rear of a few keys making them feel heavier. By the same mechanics, the bass keys are going to require quite a bit of weight (relatively speaking) at their fronts. The upshot is, I'm now more hopeful that I'm balancing the touchweight across the keyboard and not just lightening everything.

What I said earlier about helping the key past its starting point before taking a real measurement isn't really true. Once I got a better feel for what I was doing, it became more straightforward and I chose and located weights until my reference weight simply caused the key to sink from start to finish at a slow, consistent rate.

I hope I'm doing it right. I have drill bits in 1/64" increments (checked again, not true) but nothing that matches the diameter of the weights perfectly. Also, the weights are irregular. Some fit tightly while others leave all kinds of gaps I'm basically backfilling with wood glue. I bought weights in three sizes but I'm afraid to use the largest as I'd have to compromise the structural integrity of the key to install them.

It'll be a while before I can really test this. The harp is still in hundreds of pieces.
« Last Edit: April 21, 2017, 07:00:09 AM by David Aubke »
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Offline pnoboy

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Re: Adjusting touchweight
« Reply #10 on: April 22, 2017, 08:35:10 AM »
Key weight in acoustic pianos, called up weight and down weight, are always measured with the sustain pedal depressed.  Also, the feel of the action will depend very strongly on the moment of inertia of the action.  My Rhodes feels so much lighter than my acoustic piano that I suspect the Rhodes moment of inertia is much less.  In acoustic pianos, down weight is measured by adding weights to a key until you've added just enough for the key to slowly drop to the point of letoff.  Up weight is measured by starting with the key depressed and putting weights on the key until it can raise slowly to its up position.  (down weight - up weight)/2 = friction.

Offline pianotuner steveo

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Re: Adjusting touchweight
« Reply #11 on: April 22, 2017, 10:58:06 AM »
Why would you only measure down weight with the pedal depressed? I've never heard of that and it's been discussed at PTG meetings. We were always shown measuring with gram weights but nobody ever said to depress the pedal. That would make it lighter than it actually is. Maybe comparing with the pedal pressed and not pressed would be a good thing to do, but we've never been taught to do it with just the pedal down.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
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1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
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Online Peter Hayes

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Re: Adjusting touchweight
« Reply #12 on: April 22, 2017, 12:46:22 PM »
Here's a detail loaded piece on this subject.

http://www.pianofinders.com/educational/touchweight.htm
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Offline David Aubke

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Re: Adjusting touchweight
« Reply #13 on: April 22, 2017, 12:57:53 PM »
Here's a detail loaded piece on this subject.

http://www.pianofinders.com/educational/touchweight.htm

Thanks Peter. I think I skimmed that one as part of my research.

"Lead weights will indeed counterbalance a heavy hammer, but will also add inertia: actions with a large quantity of lead in the keys feel sluggish, especially when trying to play fast repeated notes, trills or in any other situation where the key has to move quickly."

This may be where I'm headed. We'll see. I've got another late 70s here (albeit with bump-modded flat pedestals) so I should be able to do A/B testing. If I can't tell immediately, I may try to find some local pianists to provide an opinion.
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Offline pnoboy

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Re: Adjusting touchweight
« Reply #14 on: April 23, 2017, 12:35:56 PM »
Why would you only measure down weight with the pedal depressed? I've never heard of that and it's been discussed at PTG meetings. We were always shown measuring with gram weights but nobody ever said to depress the pedal. That would make it lighter than it actually is. Maybe comparing with the pedal pressed and not pressed would be a good thing to do, but we've never been taught to do it with just the pedal down.

I've never heard of anyone measuring touch weight without the sustain pedal depressed, and the link from Peter Hayes confirms my belief.  Releasing the sustain pedal and measuring touch weight will certainly reveal how much extra force the damper action is adding, but it won't tell you how much of that force is due to spring force and how much is due to the weight of the damper arm and damper.

Offline pnoboy

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Re: Adjusting touchweight
« Reply #15 on: April 23, 2017, 12:38:05 PM »
Here's a detail loaded piece on this subject.

http://www.pianofinders.com/educational/touchweight.htm

Thanks Peter. I think I skimmed that one as part of my research.

"Lead weights will indeed counterbalance a heavy hammer, but will also add inertia: actions with a large quantity of lead in the keys feel sluggish, especially when trying to play fast repeated notes, trills or in any other situation where the key has to move quickly."

This may be where I'm headed. We'll see. I've got another late 70s here (albeit with bump-modded flat pedestals) so I should be able to do A/B testing. If I can't tell immediately, I may try to find some local pianists to provide an opinion.

As it turns out, lots of lead in the keys is more of a symptom than a problem.  The lead is needed when the action ratio or hammer mass to too large.  That's what really causes the sluggishness.

Offline pianotuner steveo

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Re: Adjusting touchweight
« Reply #16 on: April 23, 2017, 03:53:18 PM »
And I've never heard of anyone measuring down weight only with the sustain pedal pressed.
It will always be lighter with the pedal down. Most people I know want to know the measurement with the dampers in play too. But again, it doesn't hurt to measure both ways and compare the difference... Maybe it's just the way my PTG chapter teaches how to do this.
I don't remember learning this anywhere else.
I was just always under the impression that not pressing the pedal gives the "true" reading.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline pianotuner steveo

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Re: Adjusting touchweight
« Reply #17 on: April 25, 2017, 07:31:55 AM »
We had a PTG meeting last night and I asked the guys how they measure down weight. Unfortunately, it was a very small turnout and the guy who taught the class on it was not there. Anyway, two guys (one taught the other when he was a beginner) said that they always press the pedal, and one guy said he does it my way, checking with the pedal down and without. The others guys were either noobs, or had no experience with down weight measuring, so they didn't chime in.
All 3 guys that chimed in are RPT's , but that doesn't really mean much to me. I've known at least 2 other RPT's that are pretty much noobs, with very little experience.
1960 Wurlitzer model 700 EP
1968 Gibson G101 Combo organ
1975 Rhodes Piano Bass
1979 Wurlitzer 206A EP
1980 Wurlitzer 200A EP
1980 Wurlitzer 270 Butterfly Grand
2000 Yamaha acoustic piano
2004 Hammond XK3
2009 73A Rhodes Mark 7
2009 Korg SV-1 73
....and a few guitars...

Offline David Aubke

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Re: Adjusting touchweight
« Reply #18 on: May 13, 2017, 08:33:42 AM »
Just got my harp assembled. Everything feels pretty good so far.

Except I didn't account for the way the tines push the damper arms down and relieve the bridle straps a little bit.

Doh!

I expect to be able to drill out some lead to remedy this.
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