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Hill Bow Tip Repair options


HullGuitars
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This will be the second Hill bow I have repaired, with 6 years between them.

This is a very nice bow weighing in at 57.3 grams. Very close to the previous hill bow.

I have since sold my vertical mill, and the new one is still on its crate. SO... I will set up to preform the repair with my standard mill and a slitting saw. The last repair was done using a .030 blade and veneer of pernambuco. I'm wondering if that is sufficient or maybe I should step it up to .040 or .050?

Also curious on the general consensus of retouching the tip? I want it to be easily identifiable that this tip has been repaired, but on the other hand its standard to hide all repairs as well as possible. With the tolerances Im working with and the clean break,.... I could make it invisible. But then it would be easy for the new owner to mislead a buyer into buying a repaired bow.

Will upload some photos in a few minutes.

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I think you're talking about the spline repair.(Inserting a piece of hardwood vertically in the head).

 

It's not much about the thickness,because the total glue surface is about same whether it's .30 or .40.(Thickness makes a negligible difference.)

 

Main point is the location of the crack,if the crack is higher than the mid point of the head(including the stick),it may not hold well.(But I'm not a bow specialist,I'd like to hear from bow guys.)

 

I would use ebony because it's stronger.(For the spline,hiding crack is less of a concern than the workability.)

 

KY

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I would be hesitant to recommend ebony, or any other oily wood for a spline repair. For valuable bows I think I would only use pernambuco, despite the natural oil. The success of this repair is based entirely on the quality of the glue bond, so it makes sense to use a hardwood that accepts glue readily. I've repaired 2 or 3 broken heads using very thin model aircraft plywood. It's 3 plies with a total thickness of .050". It can be dyed dark after to blend in with the bow stick.

 

I clean out the kerf for the spline well using laquer thinner to remove any residual oil from the pernambuco, and then glue up using Industrial Formulators G2 Epoxy.

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This will be the second Hill bow I have repaired, with 6 years between them.

This is a very nice bow weighing in at 57.3 grams. Very close to the previous hill bow.

I have since sold my vertical mill, and the new one is still on its crate. SO... I will set up to preform the repair with my standard mill and a slitting saw. The last repair was done using a .030 blade and veneer of pernambuco. I'm wondering if that is sufficient or maybe I should step it up to .040 or .050?

Also curious on the general consensus of retouching the tip? I want it to be easily identifiable that this tip has been repaired, but on the other hand its standard to hide all repairs as well as possible. With the tolerances Im working with and the clean break,.... I could make it invisible. But then it would be easy for the new owner to mislead a buyer into buying a repaired bow.

Will upload some photos in a few minutes.

Ghull07,

- I believe about .8 mm is good, I don't know the English equivalent.

- Use cross grained penumbucco, no need to worry about making it too invisible, you will not when it is cross grained.

- Do not cut the slot past the line of the back of the head, doing this will put your spline right into the most flexible part of the stick changing the feel. There is also no need as the strength comes from the crown portion.

- I have not had a spline come loose, even when the break is directly along the stick with very little glue surface using cyanoacrylate, but I have had to redo splines that were done elsewhere with epoxy.

- Use very fresh high quality cyanoacrylate, Hot Stuff Red has come out on top in tests.

- Clean spline and slot with alcohol, and hash mark spline to aid in glue dispersion before adhesion.

- Line up the crack like your left thumb depended on it.

Jp

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Thanks for the replies. I have been wondering what type of glue to use and have always leaned toward epoxies when doing permanent repairs. I like the 2 hour stuff because it seems to remain more flexible and become less brittle over time.

CA glue is a new one on me! I use it all the time in guitar work but could not imagine using it on something like this!!! I'm not saying its a bad Idea or questioning your methods, but it seams like it should share the same strength as epoxy,.... BUT if things go wrong it happens SO FAST!

 

Also never thought of using cross grained wood. I will have to think on that one.

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HERES THE PHOTOS.

I know they aren't great but didn't feel like setting up my real camera and lights.

 

The tip tests out at 18kt gold.... But no makers mark that I can see other than the three pins. (in strange relation to each other) the pins are gold as well.

There is however a capital letter (or roman numeral?) "V" just behind the grip on the belly of the bow. If anyone has any insight into the markings I would love to hear it.

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Yes but not normally on once valuable bows. As specified in the first post I've always used a .03 blade therefor a .03 spline or "veneer". But I've seen so much of varying information come across the forums in the past three or four years that I thought I would start a discussion myself.

The oily wood and the different choices in adhesive really interest and concern me.

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Just to be sure: 0.03 inch? That is 0.76mm, should be fine.

Your veneer should be good long grain wood, with fibres running in line with the surface, no runout.

Cross grain means that you orientate the veneer cross grain in relation to the grain in the head. The fibres should be running parallel to the front line of the head.

Epoxy glue needs a glue gap between surfaces to guarantee its strength, whereas superglue prefers as little gap as possible.

It is difficult to get epoxy between all surfaces in a small inaccessible gap like this. Warming up the epoxy and all pieces helps. Once glued, warm again and apply some more epoxy to the edges to help saturation. Superglue is probably safer, make sure the veneer fits super well, with a very little bit of friction but not pushing the saw line open. No gaps anywhere.

Install the veneer, then apply superglue to the edges. The very runny zapp glue works for me, Jerrys is probably even better, it's no available here.

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Hull, it looks like you have already glued the tip into place.  What glue did you use?  You are now committed to using a spline.

 

In my experience, CA glue works for violin bows but will not hold for cello bows.  I have had 100% success using G-2 epoxy, and now I use it for all bow repairs. 

 

I would have suggested avoiding the spline repair since it is possible to make the repair invisible by inserting reinforcement internally at the tensile axis of the break.  Some people use broken coping saw blades for this, but I use small diameter carbon fiber rod from the hobby store. 

 

I would never make a "moral" decision on hiding a repair so that some unscrupulus owner could sell it a perfect, in the future.  I would always go for an invisible repair.

 

Mike D

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On the face plate I see two circles, just behind the mortise, one sort of touching the mortise. Are these definitely pins rather than embossed marks?

If they're embossed marks, then you most likely have a Hill bow with a stick made by Arthur Scarbrow. If they're pins, then in my opinion the face plate is a replacement or the bow isn't a Hill.

Between these ?pins and set further back in the face, direction of the frog, there seems to be a further mark. Or am I imagining this? Or is this a third pin?

Is the frog showing the same quality of gold?

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On the face plate I see two circles, just behind the mortise, one sort of touching the mortise. Are these definitely pins rather than embossed marks?

If they're embossed marks, then you most likely have a Hill bow with a stick made by Arthur Scarbrow. If they're pins, then in my opinion the face plate is a replacement or the bow isn't a Hill.

Between these ?pins and set further back in the face, direction of the frog, there seems to be a further mark. Or am I imagining this? Or is this a third pin?

Is the frog showing the same quality of gold?

What bothers me is i cant seem to see any trace of the other pining in the tip plate . They usually are easily to spot with age of the bow and seeing as the tip plate appears to be lifting from the ebony in areas id expect to see the two pins in front(towards the tip) of the mortice. One explanation of pins running into the mortice is if the mortice has been enlarged but in this case the two visible are too far over already for this to be the case.

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There have been many "innovative" methods to repair heads through the ages. Maybe Josh will post a couple of examples of doozies he has collected.

Thanks for the email Jerry. Yes, I do have a collection of photos (and even some of the actual bows) exhibiting some of the more steampunk kind of ingenuity in their repairs. It has been a few years since I have posted some of these, and there are a few new ones in here, so I post the following for your viewing pleasure—and as examples of WHAT NOT TO DO!

post-25151-0-17545100-1416582902_thumb.jpg   post-25151-0-12464700-1416582903_thumb.jpg   post-25151-0-94208700-1416582903_thumb.jpg

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post-25151-0-93742900-1416582971_thumb.jpg   post-25151-0-98736400-1416582972_thumb.jpg

 

And for those who have a preference for butt-ends, here is one for you:

post-25151-0-06436500-1416582967_thumb.jpg

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