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Author Topic: detecting and fixing pallet leaks  (Read 302 times)

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Mark Leue

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detecting and fixing pallet leaks
« on: May 17, 2019, 11:00:38 PM »

I recently refaced the  treble pallets on an old Pokerwork with Charlie Marshall's Persian leather/felt material. There is still some leakage around the pallets (I can feel air movement on my cheek)
It gets me wondering if there is a foolproof way of pinning down exactly where leaks are occurring, perhaps holding a stick of burning incense near the pallets and working the bellows? 
Then of course I need to tweak the position of the errant pallets.  I have a feeling there is either a very slight twist to some of therm, or in some cases I am wondering if the springs are tired... All the buttons are sitting about right in the fingerboard, and they center well on the holes.  I have already restricted  the action.
Suggestions appreciated.
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Jesse Smith

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Re: detecting and fixing pallet leaks
« Reply #1 on: May 17, 2019, 11:03:06 PM »

One technique that works well is to obtain a stethoscope and remove the resonator at the bottom so you've just got the tubing and the earpieces. It makes it easy to hear the rushing of air at the point of the leak.
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Mark Leue

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Re: detecting and fixing pallet leaks
« Reply #2 on: May 17, 2019, 11:06:56 PM »

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Mark Leue

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Re: detecting and fixing pallet leaks
« Reply #3 on: May 17, 2019, 11:08:08 PM »

I guess untwisting can be done with two sets of pliers... what about that notion of weakish springs? is this common?
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Winston Smith

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Re: detecting and fixing pallet leaks
« Reply #4 on: May 17, 2019, 11:29:27 PM »

It looks (to me) as if most of the pallets on the outer (left) row are not sitting squarely, according to the picture. Some look more skewed than others. If they aren't actually sitting flat, I'd sort that before looking elsewhere.
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Steve_freereeder

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Re: detecting and fixing pallet leaks
« Reply #5 on: May 17, 2019, 11:36:10 PM »

A good way to detect where a pallet is leaking from is to use a sliver of cigarette paper (e.g. Rizla or similar) as a very fine and sensitive feeler gauge.
Cut a wedge-shaped piece the full length of the cigarette paper about 10 mm wide at one end tapering to about 5 mm at the other. Lift each pallet in turn and slide the thin end of the paper under the facing, then release the pallet so the spring 'grabs' the paper.

Try to gently pull the paper out. If the seal is good, the pallet will grab the paper. If there is a leak the paper will slide out easily. Test the pallet all round the sides and mark the pallet faintly with a soft pencil where the least grab is. That will be the zone where you need to gently bend the pallet closed.

The cigarette paper method is a well-known test among woodwind instrument repairers to detect leaks around tone hole pads.
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playandteach

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Re: detecting and fixing pallet leaks
« Reply #6 on: May 17, 2019, 11:38:39 PM »

It gets me wondering if there is a foolproof way of pinning down exactly where leaks are occurring, perhaps holding a stick of burning incense near the pallets and working the bellows? 
Suggestions appreciated.
You could try an LED light inside the bellows, and look from above in the dark (obviously no reed blocks in). The other thing that works for clarinet pads is a long sliver of Rizzla Cigarette paper (just tear a strip off - not the glue side). Hold this under each corner of each pallet and pull gently. If the paper pulls too easily then there's a leak.
I'm always a little wary of offering advice here where there are really skilled workers, but this did work for me.
EDIT Ah, Steve got there first.
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boxcall

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Re: detecting and fixing pallet leaks
« Reply #7 on: May 18, 2019, 02:53:08 AM »

I recently refaced the  treble pallets on an old Pokerwork with Charlie Marshall's Persian leather/felt material. There is still some leakage around the pallets (I can feel air movement on my cheek)
It gets me wondering if there is a foolproof way of pinning down exactly where leaks are occurring, perhaps holding a stick of burning incense near the pallets and working the bellows? 
Then of course I need to tweak the position of the errant pallets.  I have a feeling there is either a very slight twist to some of therm, or in some cases I am wondering if the springs are tired... All the buttons are sitting about right in the fingerboard, and they center well on the holes.  I have already restricted  the action.
Suggestions appreciated.
Hmm, did you follow lester’s pallet resurfacing video? If so , I’d think that they would be sitting as flat and tight as possible. And buttons sitting at the proper height.
I ‘d probably take offending ones off and reposition if possible rather than chase down exactly where on the pallet its leaking. Might be easier than trying to tweak back to correct position.
Could be springs also , did you resurface because it was leaking before or just to quiet things?
« Last Edit: May 18, 2019, 02:57:21 AM by boxcall »
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RogerT

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Re: detecting and fixing pallet leaks
« Reply #8 on: May 18, 2019, 06:51:23 AM »

Um...it may be down to your method. I’d start again. Remove the pallets and put them back on..if they are very tight on the arms ream out the slots a tiny bit so the pallets have a better chance of laying flat. Reposition the pallets *but don’t glue them on*. Hold the assembly up infront of bright light (the sun is very good for this). You will see any misaligned pallets. Assemble and try for leaks..but without the reed blocks in situ. Keep tweaking the pallets until it is leak free. And *finally* glue/fix them. This works for me 100% of the time. I doubt very much if it’s the springs. The only time I ever get issues with a spring is when it breaks...and you'll know about that.
« Last Edit: May 18, 2019, 07:12:11 AM by RogerT »
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Winston Smith

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Re: detecting and fixing pallet leaks
« Reply #9 on: May 18, 2019, 07:22:30 AM »

"(the sun is very good for this)"

That's if you can catch it!!!!!
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Mark Leue

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Re: detecting and fixing pallet leaks
« Reply #10 on: May 18, 2019, 12:32:49 PM »

Thanks for the advice.  Yes, I think I need to reposition some errant pallets!
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Eshed

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Re: detecting and fixing pallet leaks
« Reply #11 on: May 18, 2019, 12:34:45 PM »

That's if you can catch it!!!!!
Consider moving the workshop to Egypt, there's more sunshine in this part of the world :)
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diatonix

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Re: detecting and fixing pallet leaks
« Reply #12 on: May 18, 2019, 01:10:53 PM »

When it comes to pallet refacing, it is important to follow the correct procedure  from the very beginning. Had you done that, there wouldn't be any leaks. Locating and fixing these afterwards isn't easy and usually not 100% successful.
« Last Edit: May 18, 2019, 02:21:47 PM by diatonix »
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