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JPherson

Cello frog eyelet adjustment issue

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Hi all,

I’m trying to replace an eyelet on a cello bow. Got the eyelet screwed in and Its too tight. I back off 1/2 turn and it’s too loose then I turn it 1/2 revolution and it’s now too tight for the frog to slid. With no middle ground. 
is there a trick to do a 1/4 turn ? 
 

thanks

 

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If you can find one, an eyelet with a finer thread on the shaft permits a finer adjustment.

Check to see that the screw holes are not worn and that the screw is running parallel to the central frog-seating facet of the butt of the stick.  The way I check for parallelism is to turn the screw so that the frog moves all the way from one end of its range of motion to the other end.  If the screw is not running parallel, the frog will be tighter to the stick at one end than at the other.  Also check that they eyelet shaft is not bent and that the eyelet hole goes into the frog squarely.  Any of these can cause or exacerbate screw/eyelet problems.

If all of these things are OK, you might try experimenting with what might be a stupid idea that I have just come up with and which I have not tried:

Using precision (i.e., capable of measurements to .001 inch or .1 millimeter) calipers measure the distance across the frog and eyelet when the eyelet is 1/4 turn too loose and again when it's 1/4 turn too tight.  The average of these two readings is what you want to achieve.  Take the eyelet out of the frog.  Using your number drill set, gradually enlarge the hole in the frog.  You want to cut away the threads in the hole until you can, with some effort, just move the eyelet shaft axially into and out of the hole without turning it.  Position the eyelet in the hole so that the measurement across the eyelet and frog is the average that you previously calculated and the eyelet screw hole is running parallel to the length of the frog.  Put a drop of thin superglue at the spot where the eyelet shaft enters the frog.  It will wick into the hole around the eyelet shaft.  The idea is that the glue, when it dries, will form a new thread in the hole that will be 1/4 turn out of phase with the old thread.

Will this idea work?  I don't know.  I just conjured it up as a thought experiment.  I do know that occasionally I have had an eyelet that's a bit too loose in the frog, and I have run a drop of glue into the hole, and this has tightened up the fit.  There is a possible risk that the eyelet would become permanently glued in the hole and it would break if you tried to turn it.  But whenever I have run a drop of glue in like this, I have found that I could turn the eyelet.  I think that the glue never bonded very well to the eyelet threads because they were corroded or dirty or they had a thin coating of oil/grease/wax.  So you could lightly oil or wax the threads to prevent the glue from bonding to them.  The other risk is that the glue would not bond to the inside of the hole strongly enough, the eyelet would pull out of the frog and the frog would require an eyelet hole bushing.

Consider this as an untested experimental procedure.  You should try it first on a junk frog or by screwing a spare eyelet into some scrap wood and trying to pull it out.  I don't recommend that you try it if you don't have a lot of experience working on bows.  I will try this idea on a junk bow the first chance I get, because I run into the same problem myself, and now I wonder if this could be a solution.   I will report the results here.

Also note that you need a set of number drill bits, because the increments between the drill diameters are very small -- several thousandths of an inch.  The increments in a fractional inch set are 1/64 inch (about .016 inch) -- much too big.

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3 hours ago, Brad Dorsey said:

If you can find one, an eyelet with a finer thread on the shaft permits a finer adjustment.

Check to see that the screw holes are not worn and that the screw is running parallel to the central frog-seating facet of the butt of the stick.  The way I check for parallelism is to turn the screw so that the frog moves all the way from one end of its range of motion to the other end.  If the screw is not running parallel, the frog will be tighter to the stick at one end than at the other.  Also check that they eyelet shaft is not bent and that the eyelet hole goes into the frog squarely.  Any of these can cause or exacerbate screw/eyelet problems.

If all of these things are OK, you might try experimenting with what might be a stupid idea that I have just come up with but which I have not tried:

Using precision (i.e., capable of measurements to .001 inch or .1 millimeter) calipers measure the distance across the frog and eyelet when the eyelet is 1/4 turn too loose and again when it's 1/4 turn too tight.  The average of these two readings is what you want to achieve.  Take the eyelet out of the frog.  Using your number drill set, gradually enlarge the hole in the frog.  You want to cut away the threads in the hole until you can, with some effort, just move the eyelet shaft axially into and out of the hole without turning it.  Position the eyelet in the hole so that the measurement across the eyelet and frog is the average that you previously calculated and the eyelet screw hole is running parallel to the length of the frog.  Put a drop of thin superglue at the spot where the eyelet shaft enters the frog.  It will wick into the hole around the eyelet shaft.  The idea is that the glue, when it dries, will form a new thread in the hole that will be 1/4 turn out of phase with the old thread.

Will this idea work?  I don't know.  I just conjured it up as a thought experiment.  I do know that occasionally I have had an eyelet that's a bit too loose in the frog, and I have run a drop of glue into the hole, and this has tightened up the fit.  There is a possible risk that the eyelet would become permanently glued in the hole and it would break if you tried to turn it.  But whenever I have run a drop of glue in like this, I have found that I could turn the eyelet.  I think that the glue never bonded very well to the eyelet threads because they were corroded or dirty or they had a thin coating of oil/grease/wax.  So you could lightly oil or wax the threads to prevent the glue from bonding to them.  The other risk is that the glue would not bond to the inside of the hole strongly enough, the eyelet would pull out of the frog and the frog would require an eyelet hole bushing.

Consider this as an untested experimental procedure.  You should try it first on a junk frog or by screwing a spare eyelet into some scrap wood and trying to pull it out.  I don't recommend that you try it if you don't have a lot of experience working on bows.  I will try this idea on a junk bow the first chance I get, because I run into the same problem myself, and now I wonder if this could be a solution.   I will report the results here.

Also note that you need a set of number drill bits, because the increments between the drill diameters are very small -- several thousandths of an inch.  The increments in a fractional inch set are 1/64 inch (about .016 inch) -- much too big.

Thanks! The experiment does sound promising. I’ll have a go at it with a practice frog. 
 

Jesse 

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After experimenting with my idea this afternoon, I concluded that it is possible to use thin superglue form a new internal thread in the eyelet hole of a frog that will be 1/4 turn out of phase with the old thread, and that this could be a safe and effective eyelet adjustment technique.  Here's what I did:

I found a used brass eyelet.  The major diameter of the thread on the shaft was 0.116".  The thread looked fine (as opposed to coarse).  I drilled a hole in a piece of scrap ebony with my #32 drill (0.116" diameter).  As I screwed the eyelet in it felt right -- neither too tight nor too loose.

P1100951.thumb.JPG.401aad56da7ea0cf5048f5fe5c5936ed.JPG

In this picture you can see my handy eyelet pliers that I made by sawing off and filing the jaws of a cheap pair of pliers.

I screwed the eyelet most of the way in until only about two or three threads could be seen.  With my calipers I measured across the eyelet and the ebony and got a reading of 1.095".  I screwed the eyelet  in half a turn and got a reading of 1.087" (meaning that the thread pitch is 0.016", equivalent to 62.5 threads per inch).  This means that my goal was to form a new thread in the hole with superglue that would yield a reading of 1.091".

P1100952.thumb.JPG.7d31679a438ee0b64c42e9226d47c60e.JPG

I screwed the eyelet out of the hole and drilled out the hole with my next biggest drill, which was a #31 with a diameter of 0.120".  Putting the eyelet back in, I found that the hole was much too big.  I could move the eyelet axially in the hole with no resistance, and the eyelet would fall out of the hole under its own weight if I held the ebony with the eyelet straight down.  Using the caliper, I pushed the eyelet into the hole until the dial read the desired 1.091".  Doing my best not to change the position of the eyelet in the hole, I carefully placed a couple of drops of thin superglue where the eyelet shaft entered the hole.  The glue wicked into the hole.  After the glue set, I turned the eyelet a little both ways, measured across the eyelet and the ebony and got a reading of 1.090" -- pretty good, only 0.001" off what I was aiming for.  In forming the new thread in the hole with the glue, I had effectively rotated the eyelet 1/4 turn.

I had been worried about two things.  The first was that I would glue the eyelet in the hole permanently, making it impossible to turn without breaking it.  This didn't happen.  The eyelet turned easily and smoothly.  Before starting the whole thing, I wiped the threads gently with a paper towel, but I did not clean them with any solvent.  The threads on the shaft were not visibly corroded.  I did not apply anything to the threads to prevent glue adhesion.  I conclude that there's no danger of gluing the eyelet immovably in the ebony.

The other thing that I had worried out was that the new threads formed from glue would be too weak, allowing the eyelet to pull out.  To test the thread strength, I ran a cord through the eyelet screw hole, tied it around the handle of a 5-gallon plastic bucket and suspended the bucket from the eyelet.

P1100953.thumb.JPG.cfa04dd20bb0d60431580e44f6b7b23d.JPG

My plan was to gradually put sand in the bucket until the threads failed and the eyelet pulled out of the ebony then weigh the sand.  But I filled the bucket without pulling the eyelet out.  The weight of the bucket full of sand was 66 3/4 pounds.  I conclude that the glue threads are strong enough.

There are several variables that my experiment did not consider:  eyelet shaft diameter, eyelet shaft thread pitch, depth of insertion of the eyelet shaft into the ebony and the characteristics of the ebony.

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3 hours ago, Brad Dorsey said:

After experimenting with my idea this afternoon, I concluded that it is possible to use thin superglue form a new internal thread in the eyelet hole of a frog that will be 1/4 turn out of phase with the old thread, and that this could be a safe and effective eyelet adjustment technique.  Here's what I did:

I found a used brass eyelet.  The major diameter of the thread on the shaft was 0.116".  The thread looked fine (as opposed to coarse).  I drilled a hole in a piece of scrap ebony with my #32 drill (0.116" diameter).  As I screwed the eyelet in it felt right -- neither too tight nor too loose.

P1100951.thumb.JPG.401aad56da7ea0cf5048f5fe5c5936ed.JPG

In this picture you can see my handy eyelet pliers that I made by sawing off and filing the jaws of a cheap pair of pliers.

I screwed the eyelet most of the way in until only about two or three threads could be seen.  With my calipers I measured across the eyelet and the ebony and got a reading of 1.095".  I screwed the eyelet  in half a turn and got a reading of 1.087" (meaning that the thread pitch is 0.016", equivalent to 62.5 threads per inch).  This means that my goal was to form a new thread in the hole with superglue that would yield a reading of 1.091".

P1100952.thumb.JPG.7d31679a438ee0b64c42e9226d47c60e.JPG

I screwed the eyelet out of the hole and drilled out the hole with my next biggest drill, which was a #31 with a diameter of 0.120".  Putting the eyelet back in, I found that the hole was much too big.  I could move the eyelet axially in the hole with no resistance, and the eyelet would fall out of the hole under its own weight if I held the ebony with the eyelet straight down.  Using the caliper, I pushed the eyelet into the hole until the dial read the desired 1.091".  Doing my best not to change the position of the eyelet in the hole, I carefully placed a couple of drops of thin superglue where the eyelet shaft entered the hole.  The glue wicked into the hole.  After the glue set, I turned the eyelet a little both ways, measured across the eyelet and the ebony and got a reading of 1.090" -- pretty good, only 0.001" off what I was aiming for.  In forming the new thread in the hole with the glue, I had effectively rotated the eyelet 1/4 turn.

I had been worried about two things.  The first was that I would glue the eyelet in the hole permanently, making it impossible to turn without breaking it.  This didn't happen.  The eyelet turned easily and smoothly.  Before starting the whole thing, I wiped the threads gently with a paper towel, but I did not clean them with any solvent.  The threads on the shaft were not visibly corroded.  I did not apply anything to the threads to prevent glue adhesion.  I conclude that there's no danger of gluing the eyelet immovably in the ebony.

The other thing that I had worried out was that the new threads formed from glue would be too weak, allowing the eyelet to pull out.  To test the thread strength, I ran a cord through the eyelet screw hole, tied it around the handle of a 5-gallon plastic bucket and suspended the bucket from the eyelet.

P1100953.thumb.JPG.cfa04dd20bb0d60431580e44f6b7b23d.JPG

My plan was to gradually put sand in the bucket until the threads failed and the eyelet pulled out of the ebony then weigh the sand.  But I filled the bucket without pulling the eyelet out.  The weight of the bucket full of sand was 66 3/4 pounds.  I conclude that the glue threads are strong enough.

There are several variables that my experiment did not consider:  eyelet shaft diameter, eyelet shaft thread pitch, depth of insertion of the eyelet shaft into the ebony and the characteristics of the ebony.

Wow that’s fantastic! Even if some of the remaining variables need to be tested it’s a very promising way to achieve the 1/4 turn that I need in the ebony frog. 
 In the 2 min of thought since reading your findings. It seems that thread pitch could very well derail the holding strength if not sharp enough. Don’t know how different the thread pitch’s are between the eyelets though. Also would other materials work equally as well as the ebony I wonder. 
 

Jesse 

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Jesse, something else to check.  Many times on a cheaper bow, the eyelet will not be perpendicular to the screw.  With the frog out of the bow, I install the screw, and push (lightly) up, and then down to check #1: how much play in the eyelet #2: how parallel the eyelet is.  I have had the same problem as you, and found that "another " 1/2 turn brings it in line.  Doesn't make sense in a perfect world if everything is right,  but if the screw is not in line, it will actually "sometimes" work.  Obviously, in a good bow, just plug the hole and redrill, correctly, the eyelet hole.  Much of Luthier/Archetier work is on cheaper stuff when you just need to get it to work.  Nice thoughts Brad.  I'll try that sometime.  It scared me a bit at first.

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1 hour ago, Jeff White said:

Jesse, something else to check.  Many times on a cheaper bow, the eyelet will not be perpendicular to the screw.  With the frog out of the bow, I install the screw, and push (lightly) up, and then down to check #1: how much play in the eyelet #2: how parallel the eyelet is.  I have had the same problem as you, and found that "another " 1/2 turn brings it in line.  Doesn't make sense in a perfect world if everything is right,  but if the screw is not in line, it will actually "sometimes" work.  Obviously, in a good bow, just plug the hole and redrill, correctly, the eyelet hole.  Much of Luthier/Archetier work is on cheaper stuff when you just need to get it to work.  Nice thoughts Brad.  I'll try that sometime.  It scared me a bit at first.

Hi Jeff,

that does seem counter intuitive lol. Though I can just barley see it in my minds eye. Thanks for the tip. And yeah most of what I work on is not the type where I can tell the customer to spend more than the bow is worth in repairs. 
 

Jesse 

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There was a bowmaker in Detroit who, rather than threading the eyelet directly into the frog, used a separate threaded insert, into which the eyelet was screwed. This threaded insert could be rotated via a screwdriver slot to any degree needed, to provide infinite micro-adjustment to the height of the eyelet.

I thought this was a brilliant idea. However, it probably wouldn't be a great idea to retrofit this into an existing frog by another maker.

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11 hours ago, David Burgess said:

There was a bowmaker in Detroit who, rather than threading the eyelet directly into the frog, used a separate threaded insert, into which the eyelet was screwed. This threaded insert could be rotated via a screwdriver slot to any degree needed, to provide infinite micro-adjustment to the height of the eyelet.

I thought this was a brilliant idea. However, it probably wouldn't be a great idea to retrofit this into an existing frog by another maker.

Halvorson?

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17 hours ago, David Burgess said:

There was a bowmaker in Detroit who, rather than threading the eyelet directly into the frog, used a separate threaded insert, into which the eyelet was screwed. This threaded insert could be rotated via a screwdriver slot to any degree needed, to provide infinite micro-adjustment to the height of the eyelet.

I thought this was a brilliant idea. However, it probably wouldn't be a great idea to retrofit this into an existing frog by another maker.

That's a cool idea.  Just to be clear, it'll only work if the insert's outer thread is a different (probably coarser) thread pitch than the eyelet's (and the insert's interior) thread pitch.

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It doesn't matter if one is reverse-threaded or not, and the thread pitches don't matter.  As long as the eyelet screws into the insert and the insert screws into the frog, the eyelet projection from the frog will be adjustable in nearly infinitely fine increments. 

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It does sound like a good idea.  The threaded insert would be a larger diameter and would have less tendency to tear out of the frog as well.  I know I have had frustrations with eyelets in the past where I just needed to get the frog down on the stick and I was thousands of miles from my bow guy.  

Hope you all are well during this situation.

Best,

DLB

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Clever idea Brad.  I have a couple of bows right now with this issue.   The problem though is that the top of the frog slopes down a little toward the back - this would make it very hard to get the measuring calipers at exactly the same place each time.  We are dealing with very small adjustments here.

I remember hearing an idea from Rodney Mohr at one of the VSA meetings.  He suggested opening up the eyelet hole just enough to let the eyelet stem move up or down.  Then putting the screw and eyelet in place in the stick and putting a little epoxy putty in the frog.  Then you could press the frog into position down tightly on the stick.  When the epoxy had cured the frog would be in just the right place.  Whether he did this or whether it was just an idea, I don't know.

I also like the insert idea.  I'm going to try it out.

Ed

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I have done a lot of model and high power rocketry and using very thin CA glue to harden wood or even cardboard to hold threads is a pretty common practice.  It helps in a lot of situations.  That said it is really easy to turn a small problem into a big mess in nothing flat!

 

DLB

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4 hours ago, Ed Shillitoe said:

...The problem though is that the top of the frog slopes down a little toward the back - this would make it very hard to get the measuring calipers at exactly the same place each time...

I don't think this is a problem.  When I was making my measurements, I moved the caliper jaw on the frog a little until it was at the spot the gave the smallest reading.  If you do this, the jaw would be the same point every time you measured.  Or, if you prefer, you could mark the spot with a pencil or a piece of tape to be sure you're always measuring at the same point.

It seems like Rodney's idea would work, but you would first have to be sure that the screw were correctly aligned -- centered sideways and running parallel to the central frog-mounting facet.

 

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2 hours ago, Dwight Brown said:

...it is really easy to turn a small problem into a big mess in nothing flat!...

I've had plenty of practice doing that.

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