I think it is about time to summarize the measurements and findings so far.
My hypothesis is Topre keys stiffen over time and use.
I measured actuation forces of 33 keys "QWERTYUIOP[]ASDFGHJKL;'ZXCVBNM,./" on my HHKB.
Here is how you read my results:
weight tested - number of keys actuated(number of additional keys actuated - list of keys actuated
Results from 5-year-old(manufactured on Aug 2006) HHKB used for 5 years. Lubricated using RO-59 and Krytox GPL100.
55g - 1 - '
57.5g - 3(+2) - [ ' m
60g - 7(+4) - [] k ' nm,
62.5g - 12(+5) - [] hjk ;' nm,./
65g - 26(+14) - qw rtyuiop[] asd ghjkl;' nm,./
67.5g - 33(+7) - qwertyuiop[] asdfghjkl;' zxcvbnm,./
Average actuation force 63.78g
Results from three-year-old(manufactured on Feb 2009 HHKB) in like new condition:
50g - 2 - []
52.5g - 3(+1) - [] '
55g - 9(+6) - ert [] s ' c n
57.5g - 28(+19) - qwertyu [] asdfghjkl;' zxcvbnm,
60g - 33(+5) - qwertyuiop[] asdfghjkl;' zxcvbnm,./
Average actuation force is 56.81g
This is the weight system I used.
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Whenever I increase the weight by 2.5g(this is how much each US penny weighs), I test the 33 keys. I put the weight two to three times on different points of key face if it doesn't drop in the first try. So this measurement is somewhat downward biased, but I chose to introduce such small bias in exchange of reducing uncertainties on the measurement. Also this downward bias work against my hypothesis of stiffening of keys.
Aranair was kind enough to post his measurment on his new HHKB (produced on Nov 2011):
source45g - 3
52.5g - 7(+4)
55g - 9(+2)
57.5g - 23(+14)
60g - 33(+10)
Average actuation force is 56.36g. This is pretty similar to my like-new HHKB.
Ripster provided some measurements, but I am not really sure what he means by measurement of 50g. I initially thought he meant putting 50g on a key would actuate the key, but his own picture here shows otherwise. All theee keys in the picture is not actuated when he puts on 50g.
This is his measurement on 14 Mar 2012, which shows 50g was NOT enough to actuate but 52g was enough.
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measurements and photos are from hereAlthough Ripster keeps saying that
1. he doesn't feel anything changed over time for this Realforce 87U keyboard
2. he gets same measurement
this is in contrast to his own finding. When a self-proclaimed scientist relies on feeling rather than measurements and even misinterpret measurements, I say something is fishy.
There were only three people who participated and actually post their measurements. I obtained full measurements of 3 HHKBs(one heavily used and two like-new), one suspicious measurement from ripster. This lack of providing measurement could be due to incentive for users conceal negative information on the products they use or love. They are incentivised to act that way for possibly two reasons. 1. they fear the resale value is negatively affected, 2. they don't like to hear bad things about what they love. However, I cannot really rule out that they don't really care.
So far, from what I observe, I tentatively conclude that
1. using HHKB for a while will stiffen the switches.
2. storing it in cool and dry place and not using it will not change key feel that much.
3. Topre's specification of 45g +/- 15g generally works but we only see measurement towards +15g. (This is shame on Topre, because they are selling 45g and 55g boards separately, but it turns out 45g board will be likely to actuate close to 55g range.)
This conclusion is from a small number of observations which may or may not represent true population of HHKB or Topre switches. If you have any other information that says otherwise, I am open to revise my conclusion and say I was unlucky one.