Repairing a Split-out Lower Screw Hole

Another fairly common repair on bows is repairing a split in the stick at the lower screw hole. A bow can be cracked and damaged at the lower screw hole if it is dropped on the button, and the shock transferred into the lower part of the stick.

The repair that I describe on this page is called a "blind ring repair" because after gluing the break, a small ring is inserted into the stick to reinforce the strength at the end of the bow and prevent the end from future cracking. When the repair is completed, the internal ring will not be visible.

I recommend this blind ring repair for bows that are less expensive or do not have significant value. For bows of historical significance and value, I prefer the time-honored repair of enlarging and bushing the cracked screw hole. To see an example of this repair, please see the Sartory restoration.

 

When a bow splits out at the lower screw hole, there are typically at least two cracks--sometimes more. This bow came in with two cracks on opposite sides of the stick.


Cracks at the lower screw hole.

The fist step in making a strong repair is to clean out any foreign material from the cracks. Because there are often lubricants used on the frog lining and at the screw, there is often grease in the cracks. To remove any lubrication, rosin, varnish, dirt, etc. I will soak the end of the bow in a small amount of acetone to clean and dissolve any of these things that would prevent the glue from adhering.


Bow soaking in acetone for cleaning and preparation for gluing the cracks.

Once the cracks are clean, I glue them with an industrial grade of cyanoacrylate glue, and use a string winding for holding the cracks closed.


Cracks glued and "clamped" with string.

The reason this repair is called a "blind ring repair" is because I use a specially-made cutter to cut a channel into the end of the stick. The cutter has a centering pin that fits into the lower screw hole to keep it centered while the cutter fits over the stick nipple. The brass tubing in the picture below is the same diameter as the cutter, and is what I use to make the ring that fits inside of the channel.


The cutter and tubing for the blind ring.

I prefer to use this cutter in my bowmaker's foray (hand-operated bench drill) because of the control and the low speed operation. I normally leave the string winding on the bow for the cutting operation, but I've removed it for these photos.


The cutter mounted in the drill, with the bow ready for cutting the ring channel. I cut the channel to a depth of approximately 2.5 to 3 millimeters deep into the stick. Note the piece of paper below the bow to catch the dust from the cutting operation. This dust will be used later in the repair.


The channel for the blind ring in the end of the stick.


The stick showing the channel, the cutter, and the ring that will be inserted into the stick. The length of the ring is about 2 millimeters.


I insert the ring into the channel in the end of the stick without any glue, and press it to the bottom with the point of a knife.


Once the ring is in place, I use thin cyanoacrylate glue to penetrate around the ring in the channel, and then back-fill the channel with the dust that I saved from the cutting process.

Once the filler has dried, I use another specialized tool to work down the excess filler and to reestablish the surface on the end of the stick. One could use a file for this step, but this tool is far more accurate. This is a tool that I made to cut a nipple on a new bow as I make it. Like the ring cutter above, this tool has a centering pin, but the cutting surface is large enough to reface the surface that the button turns against.


Nipple cutter--used to resurface the end of the stick.


The end of the stick has been resurfaced smooth for easy turning of the screw button.

The final step is to lightly file away the excess glue away from the facets on the stick, and then finish off the repair by polishing or varnishing the butt-end of the stick.

The finished "blind ring" repair.


The finished repair.

 


Just for a comparison, I've included a picture from another bow that has had an old-fashioned repair for a similar break in the lower screw hole area. On this bow, the repairer has filed away part of the end of the stick and installed a ring from an old screw button on the outside of the stick. This is a structurally sound repair, but the ring is very obvious and will forever devalue the bow.

 

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