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Bridge Reglue Clamping Caul

3.8 1963 gibson b 25 new bridge plate.jpg 1.8 martin dm bridge reglue clamping cauls.jpg
1. Inside the Box. The braces under the bridge on an acoustic guitar get in the way of fully supporting a bridge with a simple caul when gluing down a bridge. 2. Clamping Cauls.The aluminum caul in the bottom of the photo is a widely available outside caul. The one in the top of the photo is an inside caul I fabricated. The grooves accommodate the cross and finger braces and the small outer sections are raised to make up for the thickness of the bridge plate.
1.0 bridge reglue inside clamping caul fabrication.JPG 1.1 bridge reglue inside clamping caul fabrication.JPG
3. Preparing the Stock. I’ve flattened both faces of some scrap poplar and thicknessed it to 1 1/8″. Now I’m squaring one side. I’ll cut and plane the caul to final shape after I’ve done my groove lay-out. 4. Layout can be done in a number of ways. If you have the plans for the guitar’s top bracing you can base your lay out on that. If not, you can sometimes light up the inside of the guitar with an inspection light and draw yourself a little map based upon the shadows of the braces as seen through the top. I don’t have the plans for this Guild and the top is too thick to safely light up so I did a little trial and error with some scrap pine to find the foot print of the bridge plate and cross braces beneath the bridge.
1.2 bridge reglue inside clamping caul fabrication.JPG 1.4 bridge reglue inside clamping caul fabrication.JPG
5. Final Shaping of the Caul. With the layout complete, I can now cut and plane the caul to it’s final dimensions. It’s pretty important to first determine where the E strings’ pin-holes will fall on the caul. This ensures that your making your final dimensions in such a way that the caul will properly support the bridge. 6. Marking the Depth of Cut for the grooves with a marking guage. Next, I’ll use a square to transfer the cut lines down the side of the caul.
1.5 bridge reglue inside clamping caul fabrication.JPG 1.6 bridge reglue inside clamping caul fabrication.JPG
7. Cutting the Grooves with a dovetail saw is quick and accurate. I’m using a Japanese pull saw. 8. Clearing out the Grooves with a bevel edged socket chisel and mallet.
1.7 bridge reglue inside clamping caul fabrication.JPG 1.8 bridge reglue inside clamping caul fabrication.JPG
9. Chopping the Waste to accommodate the lower face brace and finger braces is done by alternating between downward and angled inward chisel cuts. 10. Accommodating the Bridge Plate is most easily done by raising the outer ends of the caul. I thickness sanded and planed some scrap maple to .100″ thick then glued it to the outer caul surfaces with hot hide glue. Now I’m paring away the waste with a chisel. Next, I’ll sand the raised surfaces to a 28′ radius in a hollow form to approximate the arching of the top.
1.9 bridge reglue inside clamping caul fabrication.JPG 2.0 bridge reglue inside clamping caul fabrication.JPG
11. All Done. I chose poplar for this particular caul because it’s easy to work with hand tools and because this caul probably won’t see heavy use. When I make an inside caul for a more common guitar such as the more popular Martin and Taylor models, I’ll use a denser wood such as oak or rosewood either as a backing for softer hardwoods such as cherry and poplar or for the entire caul.These denser hardwoods aren’t as likely to get indentations from my clamping during the bridge gluing process. 12. Labeling Cauls is a good idea. It makes it a lot faster to find the right caul when you have drawers full of them.