Back Plate Preparation

Tools and Supplies:

24″ Aluminum Level
Adhesive Sandpaper 220 Grit
Guitar Plate Jointing Jig
Titebond Glue
2-Part Epoxy Glue
Dremel Moto Tool 4000:
Portable Block Sander

Upon arrival the back/side sets to your shop, they should have a chance to acclimate to your shop atmosphere for several days or several weeks – longer is better. So if possible, order the wood for the instrument(s) well ahead of time. The main reason for this acclimation process is to allow for the wood to make adjustments to the shop humidity. It is likely that the wood had been stored in a outdoor covered storage area or an unheated storage building. The atmosphere of your shop will be considerably different. Check our our article on Shop Humidity.

The wood usually arrives in a rough sawn state and is rarely sanded. Most luthier supply houses will finish sand or finish plane the top and back plates at an additional cost. This is something to be considered as thinning plates is a very difficult operation to complete properly without the proper tools. If this service is not offered or you already have the tonewood purchased, see the article on Proper Thickness Sanding Guitar Plates for instruction to complete this operation without the aid of a shop planer or other stationary thicknessing device.

The next important step is to prepare the wood for gluing of the center joint.

Use A Level With Sandpaper On One Edge To Sand The Back Joint

Use A Level With Sandpaper On One Edge To Sand The Back Joint

Lay out the top halves of the plate so they are Bookmatched. If there is any Runout, make sure it is at the outside edges of the plate. If the center joint is terribly crooked it will need to be planed reasonably straight for the purposes of the next operation.

Place one half of one plate on top of the other and slightly overhang the top plate as shown in the photo. Place a Jointer Plane on its side and make long light strokes the full length of the joint until it is straight. Repeat this with the other plate half.

Place 220 self-adhered sandpaper to one edge of the 24″ Metal Level and burnish it so it is tightly set. In an operation similar to the planing operation, overlap the top plate and make long, slow strokes with the Level. After about 50 strokes, lighten the pressure on the strokes until the level is barely touching the joint.
Repeat the process with the second plate.

Place the plates together at the join,t and hold both halves up to a bright light. You should not see any light coming through the joint. If you do, repeat the jointing process using the Level and use lighter strokes. Check again, and you should be good to go.

Gluing the plate halves together is easiest and best completed with the Georgia Luthier Supply Plate Joint Jig.

Plate Joining Jig

Plate Joining Jig

Position the plates on the jig and adjust the fence so it snugs up against the plate very lightly.

Do a dry run of the glue-up. Place the joint hold-down over the joint on the plates and lightly snug it up. Now tighten up the cams about half way and check that everything is tight. Tighten the Joint hold down more and adjust the cams all the way. If everything checks out you are good to glue.

If you purchased an exotic hardwood such as one of the Rosewoods, Cocobolo, Koa or other aromatic wood, you will need to remove the resin with Acetone. Don some rubber gloves, a respirator, and grab a rag with a liberal amount of Acetone on it an rub on both joint surface until no more color shows up on the rag.

For exotic woods I would recommend the use of an instrument quality 2-part epoxy. Other hardwood such as Mahogany, Birch, Maple or Walnut can be glued with Titebond. Apply a small amount of glue on each edge of the joint. Do this with an index finger and gently run it along each joint. Make sure ALL surfaces are covered and there is no dry wood. This should just be a thin layer, not a liberal layer as you will be dealing with too much squeeze-out.

Place in the Guitar Plate Joining Jig. Rub the two pieces of wood together in a back and forth motion to  evenly distribute the glue along the joint. Next, tighten the jig just as was done during the dry fitting. This time remember to place a strip of waxed paper over the top of the joint as well.

Potential Concerns:

Too much downward pressure on the top joint hold-down fixture of the Plate Joining Jig will prevent adequate joint clamping due to the friction. Use only minimum downward pressure.

Do not place much cam action on the side cams. The way you can usually see this if the plate buckles between the cam and the joint hold-down. If you feel you need this much pressure, use heavy weights to hold down the buckling.

Leave a Reply

Copyright © 2015 Georgia Luthier Supply