Need advice. Arm lever not staying in Crabb

[seanc]

Need some advice.

one of the arms/ levers popped out. I put it back. But as soon as the spring is reattached the post pops out. This is a crabb. The post is a V shape, going into the board. It does not appear to be glued.

 

what is the process for keeping it in there? Tap with hammer? Glue?

 

[d.elliott]

Originally the pivot post tangs were driven into the action plate, the tangs of the pivot posts had 'serrations' for better grip. Looking at the photos I suspect you have replacement springs (strong) fitted, which may have contributed to the backing out problem. Certainly the locator part of the springs seems to be into drilled holes rather than being pushed into the wood as the original springs would have been.

 

When faced with the issue of a backed out pivot post tang, I unhook the spring, put a dab of super glue gel onto the tang and push the post down into place using fine nosed pliers. I then give the glue an hour or so to cure before re-connecting the spring. Before setting aside to cure, just be sure that the pivot post has not distorted and that the pad coverage of the hole, and the arm penetration of the cross bush in the key are as before.

[SteveS]

It does look as though the springs have forced the pivot post to back out - as Dave says above.

My repair is to ensure the tangs on the pivot post will grip, then to partially fill the hole with a small piece of sycamore.

Then press the pivot post into the hole (I use an arbor press) - do not hammer since this may cause the button board to crack.

[seanc]

as my sycamore stash is incredibly low...

 

I will give the super glue a try.

it does not look like the post is bent at all. It looks like it just popped out. I was using that button and all of sudden the button just popped out and I noticed this when I opened it up.

 

[Shayfogs]

I would not use super glue in case the post had to be removed eg. in the case of a lever breaking. I would insert a small sliver of wood into the post hole and tap it gently back into the action board. Perhaps put an extra serration or two in the foot of the post to improve grip.

[Alex West]

A couple of other suggestions, depending on how far you want to go, similar to and expanding on Shayfogs' suggestions.

 

It doesn't have to be sycamore to fill (or partially fill) the lever pivot hole.  A matchstick will do, glued in with woodworking glue.

 

You can recreate the serrations on the side of the brass lever post by gently (but firmly) squeezing the corners of the post in a pair of pliers - not so hard as to cut the post in two, just enough to crimp the edges a little.  This should deform them enough that there's some "teeth" to grip into the wood in the hole

 

Alex West

[seanc]

the hole is so small and the post is wedge shaped. With the upward force of the spring, it is going to be tough to have enough downward pressure to keep it seated.

 

What about wood filler? Does anybody think this would creat enough grip on the wedge to keep it seated? At least with superglue, This should create enough of a bond on the metal and the wood to keep it in place. 

 

if the post was cylinrical or square, I could see using the stick method to create enough fill to keep the post in place. But, here it is V shaped, I am not seeing how filling overcomes the issue of wider at the top and smaller at the bottom to hold it in place with the upward spring pressure.

 

[seanc]

For reference. A pic of the assembly

[wunks]

To transfer a bit of "Tech" from the timberman's lore:  A shallow angled wedge of that shape will hold extremely well presumably because it spreads rather than cuts the wood fibers when driven in creating immense side pressure on the wedge.  Attach a ring and you can skid logs with it.  I'm guessing the hole was drilled small and the post pressed in and now matches the shape of the post.  I'd try a slim piece of hard wood to shim the hole on one tapered side or the other,  pro'lly no need to glue it.

[SteveS]

The original hole was smaller than it is now - as the post was *pressed* into the hole during manufacture, the hole size increased.

Friction between the wood fibres and the brass post was what kept it in place.

 

Here's how you fix it:

 

1) using a piece of hard wood (I use sycamore which is what the original button board is usually made from) and fashion a small filler piece.  Leave a small hole to accept and locate the pivot post when refitting.

2) fit the filler piece into the button board - glue the filler in place with PVA glue (or a tiny dab of super glue - this is one of the few cases I'd suggest using super glue on a concertina).  Allow the glue to set thoroughly - at least 24 hours.

3) Make a few serrations on the tang of the pivot post using the sharp edge of a medium file - this is to help increase the friction between tang and wood (don't over do it).

4) *Press* the post into the hole you created/left in 1) above.

I hope this helps.

Edited December 7, 2023 by SteveS

[Theo]

Steve’s advice above is absolutely spot on.  Using superglue (or any other glue) alone is definitely second best. 

[seanc]

this hole is tiny...

Any shim is likely to be the width of a hair. I am guessing maybe a wooden match stick shaved down would work?

 

And Would I do a shim on both sides (glue those in), or just one? And then a tiny drop od super glue on the post? or just press that in?

 

 

[d.elliott]

The only issue I have with using a wooden hole filler as an alternative to super glue, and this is not a favourite glue of mine, is the risk of bending / distorting the tang if you use the gel, then it is gap filling and there is minimal risk to the pivot post. In the unlikely event that the same action assembly suffers an arm/ rivet failure you will have plenty of room to take out the pivot, and replace the action parts. 

 

Please note I am suggesting the gel, not the ordinary glue, I cannot say that I have ever had a repeat failure. 

[seanc]

21 minutes ago, d.elliott said:

The only issue I have with using a wooden hole filler as an alternative to super glue, and this is not a favourite glue of mine, is the risk of bending / distorting the tang if you use the gel, then it is gap filling and there is minimal risk to the pivot post. In the unlikely event that the same action assembly suffers an arm/ rivet failure you will have plenty of room to take out the pivot, and replace the action parts. 

 

Please note I am suggesting the gel, not the ordinary glue, I cannot say that I have ever had a repeat failure. 

Just so I am clear.. Your suggestion is to use the superglue (gel) only. And NOT add any sort of wood into the hole?

 

I am inclined to the option. As I am not sure i have the skills to make a wooden shim this small, then glue it into the hole. Then similtaneously glue the post into the hole and also have the ability to press/ seat the post into the hole with sufficient pressue and accuracy to make sure everything lines up and the pad still entirely cover the hole.

 

[d.elliott]

I am suggesting that you apply super glue gel to the pivot tang then us fine nosed plier to push it back into place. Whilst the other suggestions are all valid, not everyone has the skill and tools to add fine wooden shims, or plug the square and tapered hole and then drift the pivot post back into position. I would suggest you give the tang a scrape over with abrasive paper, to scuff the surface and improve the glue's bond. If you decide not to glue the post back, then I would drill out the existing square hole, plug it with fine grained hardwood like beech or sycamore, then pilot drill where the post is to sit. Then drive/ drift the pivot into place. This process I find is easier than the other packing out suggestions. However, but unless you are replacing a full action arm assembly from a donor instrument, it is just not necessary. If the arm comes loose again, then revert to plan B, but it is not likely.