increasing spiral spring tension

[cass]

good day all. I am trying to isolate the leaks on my 1950s frontalini. the "drop test" results are about 45-50 seconds for the bass end to fall and about 15 seconds for the treble end to settle. based on that I thought it was likely leaking past the pallets. I have a pressurization jig set up using an old CPAP blower. The treble end is essentially air tight but I can see several of the bass pallets lifting slightly when pressure is applied. I am thinking that increasing the return spring tension would force the pallets tight against the plate. Does anyone have experience increasing the spring tension? could it be as simple as removing a turn or two and remaking a new hook? I did find a very entertaining you tube video on making springs () and it appears doable but dealing with the springs I have would be simpler. hope I posted the link correctly.
as always, thanks for assistance.

 

[JKJ]

cass,

That is indeed an entertaining video! Thanks.

I have several sizes of spring wire, have made a few springs, and modified plenty of existing springs (but none on an accordion). The hardest thing about making a new spring is to find the right wire. I can’t really answer your question about the bass springs since I don’t have experience with those in the accordion, but in general shortening a tension spring should make it pull a bit stronger. Prob best to try changing a very little at a time. But are all the springs in the bass section the same? If so, could you compare the tension of one that’s not working correctly with one that is? Maybe swap them and see if anything changes?

But if some springs are weaker, why? If due to fatigue then modifying some existing springs might not be a long-term solution. Any evidence of rust inside?

BTW, I like to buy bulk spring assortments when I find them and salvage springs from things I take apart, so I’ve ended up with a huge variety and can usually find one that will do what I need or can be easily modified. But not always - just a few days ago I found myself with the need to modify a strong compression spring to make a repair - it this case I had to anneal the end of the spring a little in order to bend it, something usually not needed with most smaller springs. (I had to try with two different springs to make one do what I needed!)

JKJ

 

[debra]

good day all. I am trying to isolate the leaks on my 1950s frontalini. the "drop test" results are about 45-50 seconds for the bass end to fall and about 15 seconds for the treble end to settle. based on that I thought it was likely leaking past the pallets. ...

The best way to test whether you have leaky pallets (due to either a weak spring or some misalignment) is with a cigarette paper. Put a cigarette e paper under the pallet and check how easy or hard it is to pull it out. The amount of pulling force you need to remove the paper should be roughly the same on all pallets.

 

[boxplayer4000]

What a good video of an area of engineering which is largely off the radar. Thanks for posting.
A torsion spring is simply a long cylinder of metal under torsion. To increase its strength it should be shortened (a few spirals removed) and a new end loop/eye formed.
Springs do not loose their strength with age or use provided they are designed to operate within the metal’s elastic limits (as all properly designed springs are.)
As mentioned in the video I have found using ‘music’ wire (I take that to mean piano wire) a good start for making replacements.
This thread has already moved to pallet air leakage and as already it’s been suggested the cause of air leakage is likely to be from something else other than weakened springs. Pallet air leakage is already well covered elsewhere on this site.

 

[cass]

thanks for the responses. I should have said that I did do the paper pull test and the bright light test to ensure that the felt pads I installed are correct thickness, flat against the plate and centered. Was MUCH more careful on the re-do following first attempt. when installing the return springs, it was obvious some were stronger than others. at the time, I thought it would not be significant but turns out it is. when I pressurize the bass end, I can see some of the pallets lift and can confirm leakage at those pallets with a stethoscope. I will redo a paper pull test to compare the pallet springs and will likely be modifying or remaking springs. with a bit of luck, I should end up with a tight instrument.

 

[boxplayer4000]

when installing the return springs, it was obvious some were stronger than others. at the time,

Cass: We're all trying to visualise your accordion at a distance so forgive me please if my question(s) seem frivolous.
Personally I would need to measure carefully, with proper equipment, individual springs to know if one was stronger than another.
Viewers on this site cannot see your bass end assembly. It is normal for there to be 12 bass pallets and 12 chord pallets. The pallets, between the two groups, usually vary in size as well as having differences in levers and pivots operating the two groups.
Is there any chance that the springs serving the two groups might be different in strength, to cope with the differences in pallet size etc., and that at some stage of your repair and dismantling may have got mixed up?
A further condition which can aggravate the situation, particularly on older accordions, is that reed blocks often become deformed and the air seal between them and their sounding board becomes imperfect. Often a sign of this leakage is a discolouration of the leather gasket which becomes "dirty' where there is air leakage. This leakage along the reed block puts the pallet under greater pressure.

 

[cass]

hi boxplayer. yup, there is every chance I mixed up the springs. the perils of disassembly when you don't know what you are doing. I do have 12 note and 12 chord pallets. they are indeed different sizes, in length and in the thickness the pallet lever rests on. those I have not mixed up. I tried to sort through the springs when reassembling but didn't come up with 12 shorter or longer. I will revisit that before I start twisting and bobbing the springs.
I also discovered a significant leak due to a non-flat bass reed blocks. after a little research here, I glued a piece of sandpaper to a sheet of glass, used a pencil to cover the base of the block in graphite and gingerly sanded until the reed block is flat. The leather gasket looks good and I roughed it up the a bit with a toothbrush and tried the accordion revival feeler gauge method to judge improvement. pretty confident that leak is gone but after rereading your last line, I will reassess my sanding job.
thanks for taking the time to respond. all hints, suggestions and comments are valuable.

 

[henry d]

A pretty reliable and quick way of checking for leaking pallets- LH or RH- is to open the instrument, pull the block over the suspected leakers, place a strip of thin paper over the ports of the pallets which are suspected of being the culprits (piece of paper cut to the same dimensions as the base of the removed block), reinsert the block over the strip of paper, re-pin the bellows and test. If no change, then it's really unlikely to be those pallets that are leaking, if it gets better- then the obverse.

A badly warped plate or block base could give sketchy results with this method- but it'd have to be pretty bad and with a warped base some notes would leak, the rest seal really tightly. The leaks from a warped block base would only manifest themselves when playing.

You could use a good readily removable masking tap vice paper but if the adhesive is too strong I suppose you might damage the seating area nap on the foundation plate covering.

As above- work on the RH and LH. Old LMMH non cassotto instruments frequently have minor seepage along those long four port RH pallets which individualy are negligible but cumulatively leak like sin. LH not so much but of course still possible.

This method is great for an instrument that has an unidentifiable slow leak. At least you can narrow it down to case fittings or bellows (and the sealing strip twixt bellows and case).

Good luck- leaks can be really annoying to find and fix.

Henry

 

[Glug]

You could use a good readily removable masking tap vice paper but if the adhesive is too strong I suppose you might damage the seating area nap on the foundation plate covering.

When I do this I stick the masking tape to the bottom of the reed block, therefore no sticky hits the nap.
Also handy if you want to only cover one side of the block - measuring tuning for example.

I've used the same masking tape to seal off the entire foundation plate with all reed blocks removed (checking basic joints).
I found masking tape does leak air slightly so had to use 3 or 4 layers, but if you're replacing the reed block it should be fine - much smaller area of tape for air to leak through.

 

[henry d]

When I do this I stick the masking tape to the bottom of the reed block, therefore no sticky hits the nap.

Wow- what a simply great idea when using tape vice paper. My thanks- H