Bow repair question.

[Joe Swenson]

Got a bow in for repair and re-hair from the local music shop.  The wood of the bow I just discovered is cracked and the eyelet, which is slightly undersized has such thin walls that it does not hold when tensioning the bow hair.  An new eyelet of the correct thread will not tread into the frog because the stem is also undersized by 0.2 mm.  Easy enough (yes?) to drill out the frog to the right dimension for the new eyelet.  A 7/64 drill bit worked well on a tes piece of ebony.  But the width of the new eyelet needs to be filed down to fit the bow slow but at least 0.2 mm.  Depth is OK so I can leave the height if the eyelet alone which is where the old eyelet failed.

So my main question is is the bow crack an issue that needs to be addressed any other way that gluing with hide glue?  Or would you use white glue?

The store told me this was a $600 bow.  I am reminded of the Pink Panther when Inspector Clouseau destroys this grand piano and the butler reminds him that is a "Priceless Steinway"... and Clouseau responds "Not any more"... 

 

[FenwickG]

The crack in the bow can be repaired with a butt bushing  used to reinforce the glued crack. I use H2 epoxy as an adhesive, others use super glue for this type of repair. 

[Conor Russell]

In a student bow like this I'd take the liberty to widen the mortice to a size that accepts an eyelet that will work properly. I'd glue the crack with super thin superglue and put in a carbon fibre ring.

[Joe Swenson]

2 hours ago, FenwickG said:

The crack in the bow can be repaired with a butt bushing  used to reinforce the glued crack. I use H2 epoxy as an adhesive, others use super glue for this type of repair. 

Thanks for the response.  A ring to support the glued crack makes sense.  I found this example which requires a special cutter which I don't have to recess the ring.

http://www.fineviolinbows.com/Repair-blindring.htm

In the absence of the proper bushing channel cutter tool.  Would you recommend just gluing the crack as well as the remaining eyelet repair and referring them to a bow maker to get a bushing installed?

Thanks,

Joe

[Joe Swenson]

9 minutes ago, Conor Russell said:

In a student bow like this I'd take the liberty to widen the mortice to a size that accepts an eyelet that will work properly. I'd glue the crack with super thin superglue and put in a carbon fibre ring.

Is this carbon fiber ring hidden in a cut slot like the repair in the link I posted?

Thanks,
Joe

[Conor Russell]

Yes it's exactly the same. If you have a lathe you can make the cutters in a few minutes. I use the stock end of drills. 

I showed the repair in a thread maybe six months ago.

[Joe Swenson]

 

8 hours ago, Conor Russell said:

Yes it's exactly the same. If you have a lathe you can make the cutters in a few minutes. I use the stock end of drills. 

I showed the repair in a thread maybe six months ago.

Unfortunate I don't have a lathe to make my own tool.  On my wish list.  That and with access to a milling machine, I could make almost anything. 

The bow owner was fine with the extent of the repairs - minus the support ring.  There should be no stress on the crack unless the bow is dropped again.  Which is probably how it broke in the first place...  The crack was pretty safe to begin with and the bow still quite strong, as it took a bit of pressure to separate the seam enough to get the glue permeating the crack.  I suggested, if he wanted the bushing installed, to take it to a bow repair shop. 

Once glued (with cyanocrylate) and wrapped with string to clamp, the crack is almost invisible.

The eyelet repair also went very well.  Did a test drill on a piece of ebony with 7/64" drill bit and could firmly screw in the new eyelet.  So enlarging the eyelet hole by 0.2 mm was really simple.  I only had to then narrow the eyelet "box"  by 0.15 mm clean out the channel slightly for a nice slip fit. All that is left now is to rehair the bow.

Thanks for the help!

Joe

[bengreen]

What worries me is that if the crack was deep enough to extend into the adjuster shaft, gluing may not be enough. When the bow is under tension, the hair will be trying to pivot the frog, and that force will ultimately pull down on the adjuster rod, stressing the crack.

A bushing would be the ideal.

But a collar is good insurance. If you're not set up do a buried collar, there's actually a cheap and simple alternative. The only trouble is, if the store is trying to hide the damage and sell it as unblemished, this one is visible.

It simply involves wrapping the butt end of the stick (behind the frog at its furthest back travel) with polyester thread, exactly as if you were doing a silk winding. Saturate the the thread with thin CA glue and sand to whatever level of gloss appeals to you. If it's black or brown thread, you can make it appear just like leather. And it's very strong.

 

[nathan slobodkin]

If you don't have the tools to do the job properly perhaps better to let a more experienced repairman handle it. Most of these repairs are made much more difficult if they have been done before and the repair failed.

[Joe Swenson]

16 hours ago, bengreen said:

What worries me is that if the crack was deep enough to extend into the adjuster shaft, gluing may not be enough. When the bow is under tension, the hair will be trying to pivot the frog, and that force will ultimately pull down on the adjuster rod, stressing the crack.

A bushing would be the ideal.

But a collar is good insurance. If you're not set up do a buried collar, there's actually a cheap and simple alternative. The only trouble is, if the store is trying to hide the damage and sell it as unblemished, this one is visible.

It simply involves wrapping the butt end of the stick (behind the frog at its furthest back travel) with polyester thread, exactly as if you were doing a silk winding. Saturate the the thread with thin CA glue and sand to whatever level of gloss appeals to you. If it's black or brown thread, you can make it appear just like leather. And it's very strong.

 

I like that idea about winding something around the nipple.  The good thing is the bow even with the crack was still pretty stable and rigid.  The crack was relatively difficult to open up for gluing.  The bow owner is aware of the damage and I asked the shop owner to recommend  to the bow owner that he take it to a bow repair shop to have a collar installed.

15 hours ago, nathan slobodkin said:

If you don't have the tools to do the job properly perhaps better to let a more experienced repairman handle it. Most of these repairs are made much more difficult if they have been done before and the repair failed.

I confirmed with the shop they wanted to proceed with the repair in spite of not being able to install the collar.  But I totally understand and agree with your concern.

Thanks all for the input!

Cheers,

Joe