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Ed Shillitoe

Bow bushing

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When bushing an old bow where the screw holes have become really worn, what is the best method for drilling the small hole accurately?  The placement of this hole is critical, because if it is too high or too low, the frog will be loose or will bind at one end of its travel.  

The way I do it is to drill the large hole first, then put the frog in place and drill the small hole with a long drill that passes through the eyelet.  This works well if the eyelet is screwed into just the correct depth.  But if it is just one turn too high or too low then the small hole will not be placed correctly and the frog will bind.  But, how to find if the eyelet is the right height, without doing it wrong the first time and repeating the bushing?

I do have a Bow Badger and it works quite well on a new bow, but for an old worn-down bow it is not so good.  Any suggestions?

Thanks!

Ed 

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Hi Ed.

If you're happy with your large hole placement, you can buy (very pricey) or make a step drill to extend that lineup to the small hole.. It doesn't have to be very fancy to drill such a slight amount of wood. A "D" drill head works fine.

You start with a length of drill rod the diameter of the larger hole.

Turn the end of it on a lathe to the diameter and length you wish for the smaller hole.

File the business end to a round shape.

Then file across the length of the narrow portion, using a caliper for measurement, until you're left with a "D" cross section exactly half the thickness of it's starting diameter.

The larger diameter serves as a guide to position the smaller drilling head when it's inserted in the large hole you already drilled.

It works quite well. No need to harden or even be all that smooth in your filing. Though being centered is no guarantee the frog's going to track perfectly. You still may have to tweak. A length of drill rod with the end filed at an angle to give you a cylindrical chisel is useful (you can give it a bit of a burr to if you like).

If you don't have a lathe let me know. It just takes a moment to turn the end. I can send it to you and you can do the filing.

If the large hole alignment is the issue because the bow doesn't work with your jig, you can always make a spade bit which you can steer as you're drilling.

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On a related topic...

I had two bows here in the last while with screws broken in the middle of the threads. Both had seemed to fine until the screws went. 

In both bows the tips of the old screws were pointed. When I fitted new ones with untapered tips, they wouldn't start into the inside holes which were too high. So the old screws, when they were in, held the frogs nicely in place, but were always slightly bent, and with constant turning, they broke at the eyelets.

I often see frogs tightened up with a turn or two of the eyelet, when repairers don't think it necessary to bush the inner hole, or don't position the new one correctly,  but it can lead to problems.

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Thanks everyone!  Nice to hear from you Ben!

Maybe I didn't explain the question too well.  I do have a lathe, but by itself it does not drill the inner hole exactly in the right place n the  bushing.  With a traditional bit there is the probability of the tip wandering a little before it bites and starts to drill in.  Even if it didn't wander there is still the possibility that the eyelet is not placed quite correctly in a lateral direction in the existing frog.  Also the inner hole has to be exactly on a line that is parallel with the upper facet of the bow.  If it is not, then the frog will get too tight or too loose as it travels back and forth.  

One way to help might be to use a guide such as shown in Fig 8.9 of John Stagg's book.  But that would still not help to get the screw exactly parallel to the top facet of the bow.  I think the only way to line up the drill (whether a step drill or a conventional drill) exactly, would be to seat the frog exactly in place and use the eyelet to guide the drill.  But -that requires having the eyelet extending exactly the right amount from the frog and I'm not sure how to arrange that.

Of course in making a new bow the situation is much easier - the stick is an exact octagon and there is also some trimming of the stick left to do, and that can help to seat the frog.  On an old bow the stick can have all sorts of distortions and peculiarities and the frog can have its own little quirks as well.

 

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I spent a long time pondering this same question, and here's the solution I have come up with:

Make sure that the eyelet can travel the full length of the stick mortise without sticking or binding.  If necessary, file the eyelet (preferable) or enlarge the mortise.

After you get the outer hole drilled, hold the frog on the stick, with one hand, as close to the butt end of the stick as the eyelet will allow.  Insert the screw into the outer hole and screw it a few turns into the eyelet.  Try to wiggle the frog side to side on the stick.  If the frog seems too loose, remove it from the stick and screw the eyelet further into the frog.  (If you couldn't get the screw into the eyelet, this means that the eyelet is screwed too far into the frog, so you have to take the frog off the stick and unscrew the eyelet.)  Keep screwing or unscrewing the eyelet as necessary until you find the eyelet extension that makes the frog just the right tightness on the stick.  Since you have done this with the frog as close to the butt end of the stick as the eyelet will allow,  this is the eyelet extension that will allow the frog to run parallel to the upper facet of the stick.

Now go to your number drill set, select the largest drill that will pass through the eyelet and mount it in whatever you're using as a bow drill.  Hold the frog on the stick, with one hand, as close to the head of the bow as the eyelet will allow.  Run the drill bit though the outer hole of the stick and through the eyelet and drill into the far end of the mortise with the other hand.  Only drill in about two millimeters, because you only want drill deep enough to establish the center of the inner hole.  Pull the stick off the drill.  Measure the diameter of the screw pilot, select the corresponding drill size, mount it in your drill and drill the inner hole to full depth starting in the previously established center hole.

Try the screw in the holes without the frog.  If the screw feels too tight when you turn it, re-drill the inner hole with the next largest size number drill and try the screw again.  When the screw feels right by itself,  try the frog on the stick with the screw..  If the screw feels too tight when you turn it, re-drill the inner hole again with the next largest size drill.

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I have a jig that Alberti Design made which was a prototype. It aligns the hole parallel with the bottom facet as well as centering it in the stick. I also have a Bow Badger which works well but the Alberti jig I feel is more precise, especially on old worn sticks. Check with John Alberti at Alberti Design to see if he is selling this jig commercially.

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17 hours ago, Brad Dorsey said:

I spent a long time pondering this same question, and here's the solution I have come up with:

Make sure that the eyelet can travel the full length of the stick mortise without sticking or binding.  If necessary, file the eyelet (preferable) or enlarge the mortise.

After you get the outer hole drilled, hold the frog on the stick, with one hand, as close to the butt end of the stick as the eyelet will allow.  Insert the screw into the outer hole and screw it a few turns into the eyelet.  Try to wiggle the frog side to side on the stick.  If the frog seems too loose, remove it from the stick and screw the eyelet further into the frog.  (If you couldn't get the screw into the eyelet, this means that the eyelet is screwed too far into the frog, so you have to take the frog off the stick and unscrew the eyelet.)  Keep screwing or unscrewing the eyelet as necessary until you find the eyelet extension that makes the frog just the right tightness on the stick.  Since you have done this with the frog as close to the butt end of the stick as the eyelet will allow,  this is the eyelet extension that will allow the frog to run parallel to the upper facet of the stick.

Now go to your number drill set, select the largest drill that will pass through the eyelet and mount it in whatever you're using as a bow drill.  Hold the frog on the stick, with one hand, as close to the head of the bow as the eyelet will allow.  Run the drill bit though the outer hole of the stick and through the eyelet and drill into the far end of the mortise with the other hand.  Only drill in about two millimeters, because you only want drill deep enough to establish the center of the inner hole.  Pull the stick off the drill.  Measure the diameter of the screw pilot, select the corresponding drill size, mount it in your drill and drill the inner hole to full depth starting in the previously established center hole.

Try the screw in the holes without the frog.  If the screw feels too tight when you turn it, re-drill the inner hole with the next largest size number drill and try the screw again.  When the screw feels right by itself,  try the frog on the stick with the screw..  If the screw feels too tight when you turn it, re-drill the inner hole again with the next largest size drill.

Thanks Brad.  That's exactly what I was looking for. 

And thanks FenwickG.  I'll look up the Alberti solution, but I think the way Brad does it is probably the most accurate.    The stick I am working with is not only old and worn, but some previous repairer has filed away at the facets in an effort to fit a commercial frog.  I doubt if any jig is going to help a lot.  

 

 

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