Archive for February, 2008

Joining the Back and Top

The first step for me is to join the back and sides. Most of the techniques I use are detailed in Cumpiano’s splendid book Guitarmaking with a couple of exceptions, most notably the power jointer.  I decide which sides I’m going to join, trim them to align the grain if needed or desired using a band saw or my table saw, square them up against the fence of the joiner and then tape the board to keep them from moving.  I then run both sides through the jointer so they’re straight.  They don’t need to be parallel.  This keeps the ends I’m going to cut flush when they’re put into the shooting board (the second photo).

Squaring Edges Shooting Board Jointer Plane Candling

The power jointer creates a long straight cut but it’s not as smooth as it could be.  The spinning blades create tiny gaps which just aren’t good enough for luthiery.  I use a long Lie-Nielsen jointing plane to clean up the cut from the jointer.  I try to get it ready for joining using as few passes as possible since you can run out of wood pretty quickly.  Also, the more passes I make the more “wavy” the edge begins to get–the blade of the plane takes varying amounts of wood as the grain of the piece changes direction along the joint.  If I can’t get it right in three passes with the Lie-Nielsen I put it back on the power jointer and start over again.  The power jointer takes off 1/64″ per pass.

The fourth photo shows me “candling” the joint i.e., holding the joint up to a light source to look for gaps.  It works really well.  A joint can look absolutely perfect until you hold it up to a window or bright light (or candle) and a .001″ gap shows up.  If the joint here is really tight the likelihood of the joint failing is really small.  After the glue dries the joint is stronger than the surrounding wood.

Joining jig Glue up Glue Cleanup laying protecting newspaper strip Tapping in Wedges

The jig I use for gluing is really simple and came from Cumpiano’s design shop.  I put the dry pieces in place, slide a piece of newspaper underneath (important) clamp little blocks of wood in place on the side using c-clamps and then glue the side using Titebond.  I then push the sides together, clean up the squeeze-out and lay another strip of newspaper on top.  Over that goes a heavy straight-edge and then sand bags to keep the joint from popping up when clamped.  I use little wedges I made from some ebony scrap and gently tap them between the side and the blocks.  Not a lot of force is needed. 

After an hour or so (if I’m gluing more than one set and need the jig) I’ll remove the wood from the jig and set aside to dry overnight.  I always undo the clamps before I remove the weight to keep the thing from popping in the middle and making me swear a lot.

One of the luxuries of working by myself is that when I make a mistake I can swear and no one can hear me.  When I was learning carpentry back in the mid 80s I was working with a friend of mine who had been in the business for 15 years.  I goofed up something and said an expletive.  He said, “Shhh!  Don’t swear!”  I was surprised by his prurience and asked him why.  He told me that if you don’t swear the client won’t know you’ve screwed up. That was pretty good advice. No one wants to hear their heart surgeon say, “damn!”

Anyway, these photos show the top being joined but the back is identical.

The next step is thicknessing which I do on a drum sander.  I’m going on vacation for a week so it may be a few days before my next update.   If you have any questions feel free to post them or email me.

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