Broken bow screw advice?

[M Alpert]

I wonder if anyone has a great idea for getting the broken tip of this screw out of the eyelet (short of milling out the eyelet through the frog, ugh no fun). It's stuck in the eyelet threads inside, preventing removal of the frog.

Some way to get the screw tip to turn inwards, out of the eyelet? Magic tricks, anyone?!

 

[Guido]

If you have a thin walled steel tube with the inside diameter to fit the screw, and the screw hole in the stick has some wear so you get the steel tube in there, you could form one end into a cutter, which might last long enough to cut away the soft brass eyelet.

Alternatively, you could use a drill bit coming in from the back. Put some tape around it to protect the screw hole in the stick. I don’t think you can drill out the screw tip this way; but on a slow turn the drill bit might catch and give rotation to the broken off screw piece.

[Brad Dorsey]

4 hours ago, Guido said:

…on a slow turn the drill bit might catch and give rotation to the broken off screw piece.

I have heard that the piece of the screw that is still attached to the button can sometimes be used in the same way.  If you are lucky, the two broken ends of the screw have irregularities that will interlock well enough so that you can turn the piece that is still in the bow with the piece that is attached to the button.  You should cut the hair, pull the frog as close as you can to the butt end of the stick, stick the piece of the screw attached to the button through the end hole in the stick and turn the button in the direction that you would to tighten the hair.  If you are lucky, you will be able to turn the piece of the screw that is still in the bow all the way through the eyelet, freeing the frog.  The big problem in doing this is aligning the two pieces of the screw to each other.  This will be easy if the screw broke in the eyelet, and it will be very difficult if it broke elsewhere.  And it also requires that the screw pilot not be stuck in the inner hole of the stick, and that the screw not be stuck in the eyelet.  I have never attempted this.

I don’t think that Guido’s tube idea will work.  Whenever I file eyelets, they seem pretty hard.

I think that cutting the hair; removing the ferrule, pearl slide, plug and hair from the frog; and milling out the eyelet is the best way to go here.

[M Alpert]

Hey,  thank you guys for the support, I feel better about approaching this already! I am also skeptical of the tube idea, even if I could manage it.

The hope that the two halves of the screw will line up gives me some reason for optimism!

I don't yet have the bow in hand; it belongs to a customer who is currently abroad. I just rehaired it a couple of weeks ago and hope to retain the new hair.

I'll update after I solve it! Thanks again.

[Brad Dorsey]

57 minutes ago, M Alpert said:

...I...hope to retain the new hair...

Not a chance.

[Brad Dorsey]

Another idea -- better than any of the other suggestions:  After you cut the hair, you may be able to slide the frog far enough toward the butt end of the stick that the screw pilot will be out of the inner hole.  Then you would probably be able to simply remove the frog from the stick.

[edi malinaric]

Hello M Alpert - my most tricky bow "resurrection" was after someone tried to drill out the broken screw. The drill slipped to side and drilled alongside the screw. While rebuilding the stick around a Tufnol bushing I gave some thought how I might have carried out work.

 1.0 Drill Guide

- chuck a piece of 6mm dia. steel rod in a lathe - protrusion - Depth of hole + 10mm

-face end and centre drill

- drill a 1mm dia. hole down its centre.  Depth of hole + 10mm

- turn the OD down to a slip-fit into the  stick. Length 1mm less than the depth of the hole.

- part off at Depth of hole + 10mm

2.0 Attack

- clamp stick vertically

-"peck" drill a 1mm hole for 4-6mm using a hand drill and patience - you now have a pilot hole

- measure  the diameter of the broken screw  and buy a drill about 0.2 mm larger in dia.

- drill away the screw and the threads of the brass eyelet

Good Luck - edi

 

 

[Brad Dorsey]

edi,  I'm trying to understand your proposed method.

When you say, "depth of hole," do you mean the end hole of the stick?  If yes, where are you measuring the depth to?  To the eyelet mortise?  To the broken-off screw?

Apparently, your drill guide is inserted through the end hole of the stick.  It seems that the accuracy of the location of the hole drilled with your guide requires the end hole to be unworn and concentric with the broken screw in the eyelet.  Do I understand this correctly?

 

[edi malinaric]

Hi Brad - Dammit - a word to the wise - avoid strokes, retirement and old age!

Yes - the depth of hole is measured from the end of the stick, down the screw-hole, until you hit the broken end of the screw.  The odds are that the screw broke very close to the eyelet.

Yes - the drill guide is inserted into the end of the stick. The reason for trimming the guide 1mm short is to ensure adequate chip clearance  and reduce the chance of breaking the drill. Ditto "peck" drilling  and drilling using a hand drill.

Worn holes and dubious concentricity are a given.   

The use of a drilling guide gives you a fighting chance  to keep the drill more or less lined up with the screw.

- use of shavings between the drill guide and worn hole will help with centreing

- wrapping the end of stick/drill guide with a few layers of masking tape and a small jubilee clamp will keep things quiet

- as will a few layers of masking tape to immobilise the frog to the  stick.

cheers edi

[fiddlecollector]

11 hours ago, Brad Dorsey said:

I have heard that the piece of the screw that is still attached to the button can sometimes be used in the same way.  If you are lucky, the two broken ends of the screw have irregularities that will interlock well enough so that you can turn the piece that is still in the bow with the piece that is attached to the button.  You should cut the hair, pull the frog as close as you can to the butt end of the stick, stick the piece of the screw attached to the button through the end hole in the stick and turn the button in the direction that you would to tighten the hair.  If you are lucky, you will be able to turn the piece of the screw that is still in the bow all the way through the eyelet, freeing the frog.  The big problem in doing this is aligning the two pieces of the screw to each other.  This will be easy if the screw broke in the eyelet, and it will be very difficult if it broke elsewhere.  And it also requires that the screw pilot not be stuck in the inner hole of the stick, and that the screw not be stuck in the eyelet.  I have never attempted this.

I don’t think that Guido’s tube idea will work.  Whenever I file eyelets, they seem pretty hard.

I think that cutting the hair; removing the ferrule, pearl slide, plug and hair from the frog; and milling out the eyelet is the best way to go here.

Ive used Guido suggestion once or twice using a cutter made from O1 steel and hardened on the teeth end .I used the screw itself as a guide . But they were both bows with worn screw holes. It does work occasionally and ive had no problem cutting through the eyelet.The tube has to have the same inside diameter as  the  outside diameter of the screw  and very thin walled to avoid cutting up the underslide. Also go slowly and keep backing the tube cutter out.

I had one a few weeks back that had broken off flush with the nipple  and the hole wasnt worn so i had to mill out the eyelet from inside the frog mortice.

Also used a similar tube cutter on a Pajeot button where the screw had broken off flush with the collar on the button. Obviously have to bush them afterwards.

[FiddleDoug]

" I just rehaired it a couple of weeks ago and hope to retain the new hair. "

Did you clean and lube the screw when you had it in for the rehair? That's something that I always do.

[M Alpert]

Thanks @edi malinaric for the guide idea, and in-depth description. 

And to @fiddlecollector for comping @Guido on the tube saw idea, I am starting to see the promise.

I'm still hoping I'll get lucky,  and perhaps I can avoid the more surgery-like operations.

Yes, @FiddleDoug I nearly always clean and lube the screw. If I remember correctly, this one was snug but not unusually so; I was very surprised to hear of the break.

In fact it's only the second broken screw I can remember in 7 years of doing mostly bow repairs. The other one had broken off at the eyelet so that the tip was loose inside.

I've replaced tens, possibly hundreds of worn-out eyelets but only 2 broken screws. The brass is clearly softer, which is a good argument for the hole-saw idea...

[M Alpert]

On 8/24/2024 at 2:59 PM, Brad Dorsey said:

If you are lucky, the two broken ends of the screw have irregularities that will interlock well enough so that you can turn the piece that is still in the bow with the piece that is attached to the button.  You should cut the hair, pull the frog as close as you can to the butt end of the stick, stick the piece of the screw attached to the button through the end hole in the stick and turn the button in the direction that you would to tighten the hair.  If you are lucky, you will be able to turn the piece of the screw that is still in the bow all the way through the eyelet, freeing the frog.  The big problem in doing this is aligning the two pieces of the screw to each other.

 

Update:

I got lucky,  thank you Brad, your suggested method worked. With the hair tension off, I got the screw butt to match up with the broken bit inside, and screwed it in until the frog came out. Yes!!

Next problem

I have to get the broken screw butt out of the button, but it is VERY stubborn. Have tried heating it with a soldering iron, "whacking it" (with the broken screw part in a vise, a board with a hole so the force touches only the inner/screw-side surface of the button.

No movement.

Help?? I tried trolling MN for suggestions on this, no dice. Please, do one of you know a great way to do this?!!

[edi malinaric]

1 hour ago, M Alpert said:

 

Update:

I got lucky,  thank you Brad, your suggested method worked. With the hair tension off, I got the screw butt to match up with the broken bit inside, and screwed it in until the frog came out. Yes!!

Next problem

I have to get the broken screw butt out of the button, but it is VERY stubborn. Have tried heating it with a soldering iron, "whacking it" (with the broken screw part in a vise, a board with a hole so the force touches only the inner/screw-side surface of the button.

No movement.

Help?? I tried trolling MN for suggestions on this, no dice. Please, do one of you know a great way to do this?!!

 

1 hour ago, M Alpert said:

 

Update:

I got lucky,  thank you Brad, your suggested method worked. With the hair tension off, I got the screw butt to match up with the broken bit inside, and screwed it in until the frog came out. Yes!!

Next problem

I have to get the broken screw butt out of the button, but it is VERY stubborn. Have tried heating it with a soldering iron, "whacking it" (with the broken screw part in a vise, a board with a hole so the force touches only the inner/screw-side surface of the button.

No movement.

Help?? I tried trolling MN for suggestions on this, no dice. Please, do one of you know a great way to do this?!!

Hi M Alpert - when luck runs with you go and buy a lottery ticket. 

You have the right method - just exchange the soldering iron with a gas flame. As a safety measure wrap the button in a wet cloth.

Good Luck edi

[Brad Dorsey]

4 hours ago, M Alpert said:

... I got the screw butt to match up with the broken bit inside, and screwed it in until the frog came out...

Great!  I have never done this, or even tried to.  It's just something I have read about on this forum.  I wasn't sure that it was even possible.

 

4 hours ago, M Alpert said:

...I have to get the broken screw...out of the button...

Occasionally, a screw is screwed into the button.  Look closely at the screw where it goes into the button.  If you see threads, try clamping the screw in a vise and unscrewing the button from it.  I have been told that these threads are always right-handed; i. e. normal.

Are there any threads left on the piece of the screw that is stuck in the button?  If there are, I would find an eyelet that fits these threads.  (You could possibly unscrew the one that is in the frog, if you don't have another one available.)  Then find a scrap of wood with a thickness somewhat bigger than the unthreaded length of the screw piece in the button.  Drill a hole the size of the screw diameter in the wood.  Put the screw through the hole.  Put a washer over the screw.  Turn the eyelet onto the screw up to the washer.  Continue turning the eyelet, with pliers if necessary, and it will probably pull the screw out of the button.

The other thing that might happen, if the screw is stuck very tightly in the button, is that the screw will strip the eyelet threads.  But I have never had this happen.  To minimize the chance of this happening, you should try to find an eyelet whose threads have a tight engagement with the screw threads.

[fiddlecollector]

Or an alternative to Brads, which i used untl someone on here mentioned the clever idea of using a cheap hand pop riveter. You have to put something to protect the delicate collar of the button,here i usually use a piece of aluminium sheet with a 4mm hole in it. But in the photo i just used the slot in an old stanley knife blade.

As Brad says you have to watch for screwed in buttons.

https://www.toolstation.com/draper-expert-hand-riveter/p64135?store=JD&utm_source=googleshopping&utm_medium=feed&utm_campaign=googleshoppingfeed&mkwid=_dc&pcrid=null&pkw=null&pmt=null&gad_source=1&gclid=EAIaIQobChMIgraDmeS9iAMV45VQBh048jdQEAQYBSABEgI1BPD_BwE&gclsrc=aw.ds

 

 

[M Alpert]

Hey, great suggestions, especially like the pop-riveter, I have one already...

Seriously, what would I do without MN and all you beautiful people

Would be a much sadder world...

 

Btw, any way to know for sure it's not screwed into the button? I mean, obviously I can't see any sign of threads...

It's from a Finkel cello bow, in case anyone happens to know that Finkels do or do not screw their screws (sic)

Thanks a million!

 

[Brad Dorsey]

Normally, when a screw is screwed into the button, there will be some threads visible right where the screw goes in.  But I suppose it’s possible to have a screw screwed into the button such that all the threads are invisible because they’re inside the button.  In that case, the only way to know that that screw is screwed in would be to pull it out so that the threads are visible.  It is possible to pull out screwed-in screws, but they don’t come out easily.  I know this because I’ve done it when I forgot to look for the threads at the button.

I forgot about the pop rivet gun.  I have pulled out screws with one, and it works great.  I don’t like to use the gun because it damages the screw threads, so I only pull a screw out this way if I know I don’t want to re-use it.  Since your screw is broken, there’s no reason not to use a gun.

[fiddlecollector]

Brad i havent noticed any damage before with them, maybe its just the soft cheapy screws you get on some bows.

[Brad Dorsey]

If you haven't noticed any screw damage, I think my problem is likely related to the mechanism of my rivet gun.  Mine has a serrated part, probably made of hardened steel, that clamps on the screw threads when it pulls the screw out.  It is inevitable that the serrations will damage the screw threads.  I assumed the same would be true of any rivet gun, but your experience suggests that I should find one of a different design that won't damage the threads, because it is a very easy and simple way to pull a screw out of a button.

[fiddlecollector]

I think they all have that sort of serated jaw mechanism but i have found i have to use very little pressure on the handles to get a screw out and i think the jaws start off nearer the button so dont really put any force on the threaded part of the screw.(though all screwsare different with some threaded full length)

I suppose with these riveters  being found on ebay for very little money ,you could easily dismantle the riveter and replace the jaws with something similar made on a lathe out of nylon 6.6 rod or similar ,i would think it would still work for bow screws .

[edi malinaric]

8 minutes ago, fiddlecollector said:

I think they all have that sort of serated jaw mechanism but i have found i have to use very little pressure on the handles to get a screw out and i think the jaws start off nearer the button so dont really put any force on the threaded part of the screw.(though all screwsare different with some threaded full length)

I suppose with these riveters  being found on ebay for very little money ,you could easily dismantle the riveter and replace the jaws with something similar made on a lathe out of nylon 6.6 rod or similar ,i would think it would still work for bow screws .

Hi Fiddlecollector - brilliant! - and here's me with both the pliers and lazy tong type pop riverters sitting on the shelf.

Just itching in excitement to try this out.  While I wait I'll make a set of copper or brass jaws for the pliers.

Thank you - edi

 

[fiddlecollector]

2 hours ago, edi malinaric said:

Hi Fiddlecollector - brilliant! - and here's me with both the pliers and lazy tong type pop riverters sitting on the shelf.

Just itching in excitement to try this out.  While I wait I'll make a set of copper or brass jaws for the pliers.

Thank you - edi

 

Just spent 1/2 hour (most of it trying to reassemble the riveter) making a rough one out of black delrin. I followed the basic design of the originals but didnt even put any serations in the jaws,just filed a v slot in them. Delrin is quite slippery so i though it may not grip .Anyway it worked first time . Original jaws in the photo but a bit out of focus.

Added another photo of the original jaws and piece of rectangular section steel that fell out whilst dismantling ,i cant figure where it came from .

 

 

[M Alpert]

An update:

The screw was threaded into the button! Not a hint of threads visible, but the riveter worked like a charm, pulled it right out, threads and all. Very lucky the square butt of the screw I had fit well into the hole that was left. Tanged and glued, it all worked out!

Thanks all for your input, it was very helpful!!