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Key Pressure!?


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#1 conzertino

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Posted 03 August 2017 - 06:19 AM

I noticed that the pressure to actually press down a key differs a lot from instrument to instrument and - unfortunately - often even within one instrument.

So I made myself a usesful little device to measure that pressure. By bending the springs the pressure can be adjusted...

 

KP.jpg

 

On some of my favourite players the pressure is as low as 40 g, on some others well above 100 g.

If the pressure is to low, the tightness suffers, if it is too high, it is no fun to play.

 

Any ideas or experiences?? Is there a diffrence between ES and anglo?? If so, why?



#2 Geoff Wooff

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Posted 03 August 2017 - 09:39 AM

I have a similar gauge  ( bought at  an antique/ junk tools  dealer  in a flea market)   and modified it with  a  small block of cork  fixed to the lever, so as not to scratch anything  being tested.  I like    a button pressure  of  between 60 and 70 g. on my EC's  though  I also have one where  the buttons need   100 g. to start depression.  I do  not  have any problems  with this change  of pressure  on my EC's.

 

With an English  Concertina  the  fulcrum  points of  the  action levers  are   reasonably    in a central position, length wise...  so the downward  force  on the pallet  will be similar  to that needed to press the key...  but some levers on Anglos  and Duets  can have their  pivot points  a long way from the central  position  which might affect  the   spring pressure requirements.

 

I have  measured  the button pressure on two accordions  that I play regularly  ,   both have very constant spring pressure over their range...  but one instrument will start  opening  its pallets  at  50 g  and  the other takes 100g....  changing from one to the other  is not a problem  generally , only  where  rapid ornamentation  practiced at one return pressure  is transfered  to the other box!


Edited by Geoff Wooff, 03 August 2017 - 09:42 AM.


#3 Bruce McCaskey

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Posted 03 August 2017 - 02:26 PM

I have an interest in being able to measure button pressure.

It seems to me that you want more than just sufficient pressure to keep the pad from leaking. A little extra pressure makes the difference between a soft close and an abrupt interruption of air flow. The latter, in my opinion, is essential to supporting crisp cuts and other ornamentation. On the other hand, too much button pressure and it's more of a challenge (when playing fast) to depress the button sufficiently to ensure that the reed actually sounds.

How about some more information about this pressure messing device? What is it called if one were to go looking to purchase such a thing?

#4 Chris Ghent

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Posted 03 August 2017 - 05:58 PM

I have an identical device to the one in the picture though my vertical return is a little different. I'm away from home so can't tell you the brand but they are expensive. You can make a cheap device which will do the same in many ways. The easiest I have heard, suggested by David Hornett recently, is to put the end on an electronic scale and push the button slowly while watching the readout. Another, suggested by Geoff Crabb some time ago, is to get a longish bolt weighing less than your target weight and a bunch of washers. Hold the bolt vertically on the button and let slip the washers one at a time until the button moves. Bolt weight plus washer weight x number of washers = button pressure.

#5 Chris Ghent

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Posted 03 August 2017 - 06:01 PM

Might just add, I find the minimum button pressure can be found by starting on the longest lever and finding what weight will hold it's pad closed under reasonable bellows pressure. Shorter levers should all have less trouble staying shut.

Minimum pressure is not everyone's favourite, someone was telling me it makes for a slow returning button, limiting your playing speed.

#6 Geoff Wooff

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Posted 04 August 2017 - 12:20 AM

Bruce,

 

I think the  device  I use, very similar to  the one shown in   Robbie's  picture,  is a hand held   progressive spring  pressure  indicator  used for  setting   mechanical Relays  or the like.  Perhaps  these are not  used  much these  days  as I'd imagine  electronic   switches  replace  the old fashioned  leaf spring  Relays .  As Chris  says, they may be expensive tools to purchase  new  but   can be found    at government  'surplus'  sales  and the like.  Perhaps every  telephone engineer  had one in their tool kit?

 

Mine has the  black 'crackle' finish paint on the all metal body  and the  maker's name   CARPO ( made in France)  on the dial and came in  a small wooden box.  It reads from 0- 175 grames.  If I see another , whilst I scour the flea markets  for useful  items, I will  surely  liberate it.

 

PS ;  a quick search  on a  classified adverts  website  and I found another, which goes from  0 - 50g,  the seller says it is used for setting the springs in a typewriter....  for sale in its box   for 15 euros!  Another  that  will measure to 150g  , the seller says it is for weighing  letters, for 20 euros.

 

PPS;  found at least  3  for sale on line ( in France)  that will  measure  0- 150 grams....  prices range from 15 to 30 euros  plus  postage.  I'm sure you will find  these  locally.


Edited by Geoff Wooff, 04 August 2017 - 12:42 AM.


#7 Don Taylor

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Posted 04 August 2017 - 08:27 AM

Somebody in China is making new ones that look very much like the one in Robbie's picture. There are several sellers on eBay listing the 0-100gm version for about us$35.

For example: http://www.ebay.com/itm/262699247208

If this is what Robbie's bought then perhaps he could comment on its quality and accuracy.

#8 conzertino

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Posted 05 August 2017 - 01:47 AM

Don, this is exactly the one, which I ordered from China. It does a good job.

I have found some buttons with a higher pressure than 100g, but as I set them to about 60g, it works!

I had experimented with other contraptions before using two tubes and a spring or metal bars with different weights, but this one works best. 

The holes at the ends are useful as they hold the keys in position when ends are off.


Edited by conzertino, 05 August 2017 - 01:48 AM.


#9 Chris Ghent

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Posted 05 August 2017 - 09:48 PM

Cheap! About a quarter of what I paid for mine. Very similar looking so maybe a knockoff?

#10 Bruce McCaskey

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Posted 08 August 2017 - 07:06 PM

I've found a few "Force Gauges" online that are similar. Thanks for the insights.

#11 alex_holden

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Posted 09 August 2017 - 01:13 AM

I just picked up this Swiss one made by Correx. It has a handy second needle that records the peak force. The 125g reading is from a heavily-sprung cheap German instrument that happens to be sitting on my desk at the moment.

correx_force_gauge.jpg




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