Bow head mortise crack repair

[Northerner]

Dear community,

 

How would you go about glueing a cracked mortice like this one? Could it be clamped tight and then glued with CA glue from the inside of the mortice?

Your advice would be greatly appreciated!

 

[Brad Dorsey]

Before answering your question, I have two of my own:  1. Is the wood cracked at the wide end of the mortise, or just the ivory?  2.  What is the distance between the narrow end of the mortise and the frog end of the head?

[Blank face]

18 minutes ago, Brad Dorsey said:

Before answering your question, I have two of my own:  1. Is the wood cracked at the wide end of the mortise, or just the ivory?  2.  What is the distance between the narrow end of the mortise and the frog end of the head?

Agree on this, and before taking any action it’s absolutely necessary to remove hair, ivory plate and liner.

[HoGo]

I would not ry to remove plate and liner on such cracked tip. It could lead to more damage than there is now if not done with tip held in a clamping jig or vice of some kind that will prevent further developing of cracks.

[Brad Dorsey]

Yes, I think I would glue any cracks before removing the face place and the liner, for fear of breaking off bits of the bow during removal, assuming that I could get the cracks to close.  It would be safer to remove the plate and liner after gluing the cracks(s).

[Blank face]

I’ve done this several times before without causing further damage, it might depend of the right technique.

 I rather doubt that it is possible to get a really close glue joint without removing irregular split plates, liners and cleaning the crack.

[fiddlecollector]

How would you glue that crack shut without removing the ebony liner and faceplate (especially if its still glued on or has been loose at onetime and reglued). Trying to force that crack shut witht he faceplate in place would possibly  put stress on the sides of the head causing a possible cheek crack.

[Brad Dorsey]

As I said, I wouldn't do it if I couldn't close the crack.  I should have added "with reasonable force."  A previous regluing attempt would complicate the repair.

[Northerner]

Thank you all for your replies!

I have carefully removed the faceplate and the liner and this is what I am left with.

What do you think be the best way to clean the crack and glue it if I’d go the CA way?

[Brad Dorsey]

Can you press the crack closed with a thumb and a finger?

[Northerner]

54 minutes ago, Brad Dorsey said:

Can you press the crack closed with a thumb and a finger?

Yes I can, but it’s still slightly visible when pressed together.

The first two photos are of the open crack, and the last three when I press it together

[Northerner]

On 6/28/2024 at 1:49 PM, Brad Dorsey said:

Before answering your question, I have two of my own:  1. Is the wood cracked at the wide end of the mortise, or just the ivory?  2.  What is the distance between the narrow end of the mortise and the frog end of the head?

Sorry Brad, missed this one.

1. It was just the head plate 

2. Approximately 3mm

[David Burgess]

1 hour ago, Northerner said:

What do you think be the best way to clean the crack and glue it if I’d go the CA way?

Using CA can be a bit of a challenge. If you clamp the crack closed before applying the CA, there's a good chance that the CA won't wick in all the way, producing a bond on only part of the crack.

If the CA is applied prior to clamping the break, there's a good chance that it will start to set up prior to clamping, resulting in the two sides not coming together completely.

[fiddlecollector]

What i usually do is put the head in a vice with leather pads ,apply gentle pressure to see if it closes ok, (pressure from vice very gentle). I back off the vice jaws so the crack opens a tiny amount. Then i apply very thin CA (been using starbond from the USA reecntly,wicks very well). I then rapidly open and close the crack with the vice 2-3 times finishing with it (the crack) closed . Seems to work fine.

If it was an expensive bow i would probably put a re-enforcement in as well but i usually use a milling machine to cut that.

This is the glue.

[David Burgess]

Fiddlecollector, that gives me a great idea. I should probably add the text "high-performance, premium" to my instrument labels. Time to discard my old fuddy-duddy ways.

[fiddlecollector]

[Brad Dorsey]

46 minutes ago, fiddlecollector said:

What i usually do is put the head in a vice with leather pads ,apply gentle pressure to see if it closes ok, (pressure from vice very gentle). I back off the vice jaws so the crack opens a tiny amount. Then i apply very thin CA (been using starbond from the USA reecntly,wicks very well). I then rapidly open and close the crack with the vice 2-3 times finishing with it (the crack) closed . Seems to work fine…

That sounds good.  But if the crack closes easily with finger pressure, I think that using fingers rather than the vise would work fine, too.

[Brad Dorsey]

49 minutes ago, fiddlecollector said:

…If it was an expensive bow i would probably put a re-enforcement in as well but i usually use a milling machine…

I would reinforce this even if it’s not expensive.  It probably split because the wall thickness is only 3 millimeters.  So I would thicken the wall by gluing in a bit of pernambuco, with its grain running perpendicular to the stick, before gluing on the face plate.

[fiddlecollector]

11 minutes ago, Brad Dorsey said:

That sounds good.  But if the crack closes easily with finger pressure, I think that using fingers rather than the vise would work fine, too.

I prefer the vice as i like to go and do other things,also i know CA is supposed to dry fast but i like to just leave it for an hour or two to be on the safe side.

[fiddlecollector]

On the bow in question the mortice doesnt seem especially long  compared to the ruler. I suppose its good practice to strengthen the wall regardless of bows value.

Heres a photo off the web  showing the type of re-enforcement i assume we are talking about.

 

[Josep Pampidó]

Is not better epoxi? A lot of time to ensure the crack is aligned after glueing and perhaps stronger than CA. (Amateur with no experience on the subject)

[Brad Dorsey]

7 hours ago, fiddlecollector said:

…the type of re-enforcement i assume we are talking about.…

That’s not the type of re-enforcement that I’ve been doing, but I really like the looks of it.  I assume the its grain runs perpendicular to the grain of the stick?  And that you cut the slot for it with an end mill on a milling machine?

I have been gluing a cross-grain re-enforcement to the inside wall of the mortise.  If the crack is somewhere close to the middle of the mortise, this reinforces the crack as it adds extra thickness to the mortise wall.  With the new face plate ties everything together, this makes this mortise wall stronger than it was when the bow was new.

The crack shown above is a bit different, because it is at the corner of the mortise rather than being in the center of the wall.  So the wood that I have been adding, even though it adds thickness to the wall, wouldn’t re-enforce the crack.  Which is why I like your method.

How do you mount the bow head in the milling vise?  Do you cut your slot with one full-depth pass, or do you make several passes, increasing the depth each time?  The mill to cut your slot has such a small diameter that it must be rather fragile.  What sort of mill do you use?  I have broken a few small carbide end mills working on bows.  I think my feed rate is pretty slow, but maybe I should be feeding slower, or taking shallower cuts, or perhaps carbide mills are too brittle.  Have you got any suggestions?

[LCF]

8 hours ago, Brad Dorsey said:

... Do you cut your slot with one full-depth pass, or do you make several passes, increasing the depth each time?  The mill to cut your slot has such a small diameter that it must be rather fragile.  What sort of mill do you use?  I have broken a few small carbide end mills working on bows.  I think my feed rate is pretty slow, but maybe I should be feeding slower, or taking shallower cuts, or perhaps carbide mills are too brittle.  Have you got any suggestions?

Brad, fwiw I don't work on bows but I do use 0.8mm ( 1/32") carbide cutters to make bridges. I bought some 0.5mm cutters that broke almost as soon as you looked at them! With the 0.8 I only use them via cnc which gives a very steady feed and take typically no more than 0.5mm deep cuts so ten passes to get through a bridge blank. (The .8mm cutters originally only had 4mm flutes so I carefully ground them up a bit with a diamond wheel  to clear 6mm.) I have a manual bench micro mill but I don't think I'd use those tiny cutters with hand feed. 

[fiddlecollector]

11 hours ago, Brad Dorsey said:

That’s not the type of re-enforcement that I’ve been doing, but I really like the looks of it.  I assume the its grain runs perpendicular to the grain of the stick?  And that you cut the slot for it with an end mill on a milling machine?

I have been gluing a cross-grain re-enforcement to the inside wall of the mortise.  If the crack is somewhere close to the middle of the mortise, this reinforces the crack as it adds extra thickness to the mortise wall.  With the new face plate ties everything together, this makes this mortise wall stronger than it was when the bow was new.

The crack shown above is a bit different, because it is at the corner of the mortise rather than being in the center of the wall.  So the wood that I have been adding, even though it adds thickness to the wall, wouldn’t re-enforce the crack.  Which is why I like your method.

How do you mount the bow head in the milling vise?  Do you cut your slot with one full-depth pass, or do you make several passes, increasing the depth each time?  The mill to cut your slot has such a small diameter that it must be rather fragile.  What sort of mill do you use?  I have broken a few small carbide end mills working on bows.  I think my feed rate is pretty slow, but maybe I should be feeding slower, or taking shallower cuts, or perhaps carbide mills are too brittle.  Have you got any suggestions?

The i usually have the grain perpendicular for the insert somepeople use a ply madeup of 2 or more pieces glued together.

(the photo i showed is not mine ,it was just to show what itcan look like. ) I usually prefer a thicker insert than what is shown there.

Yes the corner crack like this would be best repaired using the insert extending either side of the mortice. But i dont see a problem for your method for cracks that are in the middle. But for high value bows id always use the milled extended insert when possible.

I clamp the bow head using several methods but often just 1/2" packing foam glued to a wooden backing. (see photo,i tighten the vice quite alot but so that the head comes just short of touching the wooden backing pieces. It seems totally stable and doesnt move. Butive also used that hot water mouldable plastic ,leather andallsorts of stuff in the past.

I tend to avoid carbide cutters for something like this , but i usually use 2-3mm HSS good quality cutters. When carbide breaks off in a hole   its almost impossible to get it out withoit drastic action.

The milling machine i use for bow work is just a Proxxon mf70 micromill ,though i do have a chinese based mini mill (similar to a Teig and a much larger machine that is like a basically an English made Deckel copy. (i generally use this when doing things like chevals that require bigger round nosed cutters.)The Alexander Toolmaker machine just mentioned can cut at any angle conceivable.

A good illustration of similar repairs on an FX Tourte bow with similar corner crack to the OP's bow is shown in this link ,carried out by Pete Oxley. He appears to be using something like a 5mm mill on a cello head. The repair is alot more involved due to the valiueof the head but alot is relevant . Along with the carefully  soaking in water locally  to close a crack.

http://oxleytourte.oberlinbowrestoration.com/

Afew photos showing the very small Proxxon mill i use for most stuff and one of the simple ways i clamp the head using foam.

 

[Brad Dorsey]

18 hours ago, Josep Pampidó said:

Is not better epoxi? A lot of time to ensure the crack is aligned after glueing and perhaps stronger than CA...

As I see it, CA has three advantages over epoxy in this situation:

CA can be applied to the outside of the crack, and it will flow all the way into the crack by itself or assisted by the crack being pressed together several times.  Epoxy will not flow into the crack as well.  It might require some sort of thin tool (spatula) to work it deep into the crack.  The spatula would probably gouge the wood fibers in the crack, making the crack wider and making the fit worse.

CA leaves a thinner glue line -- practically none at all.

Much faster set time.  After a few minutes, one can go on to the next step.

In this situation, there is no need to do anything to align the crack.  The sides are automatically aligned, because they are attached to each other at the bottom.