Substitute for spring (no. 20) for HP-97 printer

[AndiGer]

Today I realized that one spring - marked no. 20 in the service manual - in my HP-97 printer is weak, is out of shape (lengthend) and hasn't the strength of the spring on the other side.
When I push the paper feed pressure shaft forward toward the rubber rollers paper advance is ok. The rubber rollers have one visible flattened spot.
Has anybody encountered this problem and has found a substitute for that springs?
I was looking on the website of a spring producing company here in Germany but I am not sure if the force of those springs is suitable.
Dimensions could fit the printer.
Force 1.19N: https://www.febrotec.de/content.php?lang...ails=16665
Force 1.67N: https://www.febrotec.de/content.php?lang...ails=16670
Any suggestions or experience?
Andi

[Giancarlo]

Hello, i can’t help you specifically on hp97 but what i can see is that the two springs you selected are very different in terms of wire size (0,2 vs 0,18 mm).
This lead to a ‘c’ parameter which is one the double of the other.

Do you have a caliper (1/100mm precision) or a micrometer to measure the wire size correctly?

I can suggest, if your spring is not too damaged to hang a small (and known weight) to measure yourself the displacement (travel) of the spring and then calculate your ‘c’ as ratio between the change in lenght and the weight?

Otherwise i suggest to buy both and verify.

Sorry if i can’t help more.

Giancarlo

[AndiGer]

Thank you for the hint to determine the spring constant c. Long forgotten this is important ;-)
Measured on the other side, spring there is still ok.
Came across with about 85 g weight displacement is about 0.75 mm which will lead to c about something more than 1.
Wire thickness is around 0.3 mm.
So should be more like that one:
https://www.febrotec.de/content.php?lang...ails=16719
Andi

[ignazio]

Hi Andi,
you have a PM.