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Lachenal Cranked Arms


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Its happened, another Lachenal with a severely worn arm/ pivot post due to the arm being cranked to get around other elements of the action. This arm was bad, there was nothing to loose by trying plan 'C'. The action arm/pivot was already a write off. So much so that the arm was rotated by 45 degrees, it fouled an adjacent button, its own button was about 1.5 mm low, and the pad face was all but sheared off.

 

But (Smugly he writes) I have now a simple repair that recovers both the pivot post and the arm, buying a life extension of a good many years. It anyone is interested, I will do some sketches.

 

It surely is grand when it all works out, SPANKING!! as they say in some parts of Yorkshire.... oops, nothing to do with the less polite side of some peoples lives, I assure you.

 

modestly

 

Dave

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Its happened, another Lachenal with a severely worn arm/ pivot post due to the arm being cranked to get around other elements of the action. This arm was bad, there was nothing to loose by trying plan 'C'. The action arm/pivot was already a write off. So much so that the arm was rotated by 45 degrees, it fouled an adjacent button, its own button was about 1.5 mm low, and the pad face was all but sheared off.

 

But (Smugly he writes) I have now a simple repair that recovers both the pivot post and the arm, buying a life extension of a good many years. It anyone is interested, I will do some sketches.

 

It surely is grand when it all works out, SPANKING!! as they say in some parts of Yorkshire.... oops, nothing to do with the less polite side of some peoples lives, I assure you.

 

modestly

 

Dave

 

I'm interested.

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I'm interested too.

 

A fix would be greatly appreciated.

 

On mine the arm twists so much that after a few presses of the button the pad gets stuck at an angle in the hole, thus allowing air to pass permanently.

 

Ian

 

 

The button also drops too low as well? Lachenal Cranked Arm Syndrome (LCAS)

 

1. remove the pad from the arm, unclip the spring, and unthread the arm trhrough the 'window' in the pivot post, you may well need to take out a couple of adjacent keys so that you can do this.

 

2. examine the arm and you will see two areas of wear on the arm flanks (at the pivot position) one by the notch that hooks into the pivot post and one diagonally opposite accross the section, the worst will probably be the area round the notch.

 

3. extract the pivot post from the pad board (good grip with pliers and pull, like a dentist) Examine the window and spot the wear halfway down one side of the slot.

 

4. Take the arm , pick the worst flank, lightly abraide it, and 'tin' it with solder. take a bit of 0.020-0.030 brass shim, I actually used part of a broken brass (bronze) reed tongue, tin that, and solder it onto the pre-tinned arm flank to form a thicker arm section with a local wear pad.

 

5 lightly dress out the wear on the arm flank that has not been soldered to.

 

6. re-file the notch and wear pad to the correct profile.

 

7 offer up the arm to the pivot, but the now thicker part of the reinforced arm will not enter the pivot post window.

 

8 file the window to widen it, but only take metal from the side with the wear in it. By the time the arm enters the window evenly, the bulk of the window wear will have been removed, the arm will now sit square in the pivot post window and move evenly in a vertical plane.

 

9 re assemble and glow with satisfaction

 

10 have a pint!

 

Start to finsh, around 35-40 minutes. some (many) years down the line the wear pad may wear through, if so re-solder a new one on......

 

Dave

 

I will try some sketches later

 

D

Edited by d.elliott
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  • 2 years later...

I note that Wim Wakker (Concertina Connection) offers a service to completely replace Lachenal cranks with a proper riveted action: maybe he has a bin full of Lachenal cranks and posts many perfectly useable for one off repairs.

Inventor.

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