Tuesday, May 29, 2012

Building a Mountain Banjo: Marking the Neck

This is a continuation of my series of posts that are following my construction of a mountain banjo.  If you missed the first post it is available here, Building a Mountain Banjo: The Pot.

Here are some basic tools that I used to measure out my neck because I couldn't get a hold of full size plans.  
      Before I could begin measuring out the neck, I head to find suitable material for the neck.  If you look at the profile of the neck on the plans (courtesy of bluestem strings) you will notice that the angled headstock makes it necessary to use a large block of wood if you want to cut the neck from a block of wood rather than joining a headstock onto a smaller piece of wood.  Some people get away with joining a headstock (I myself have used the method to construct a cigar box guitar), but a neck cut out of block of wood is stronger and looks nicer.  That does not mean the block of wood has to be solid.  Roughing out this neck from a block (laminated or solid) of wood requires the block to be at least 25 1/4" long x 2"wide (not accounting for the width of the headstock) x 2"deep (accounting for the angled head stock).  These are the bare minimum measurements with no extra room.  I found it easier to use a 3" x 3" block.  However, a neck is best made out of hardwood, and a 3" x 3" block can be expensive.  So, I laminated 3, 1" x 3" pieces of poplar together to form a block that was 26" x 3" x 3".  All I had to do was cut the poplar to length, dampen the sides to be joined, apply gorilla glue and clamp the pieces tight overnight.  I should also point out that I followed some advice I found on both the Banjo Hangout and the Bluestem Strings websites that said to try and book match the grain.  I'm not sure if I did this correctly, but I'll describe what I did.  I had two slab sawn pieces (quarter sawn would be better but this is a homemade banjo that I'm not investing much money in it) with curves in the grain (when viewed from the end of the board) and one without curves.  I put the one without curves in the middle and laminated the others on the side so their curves were convex to the middle piece.  Hopefully these crude drawings will clarify things.

This is what the grains on a cross section of my wood block look like.  Of course, I exaggerated everything to make it easier to draw.
Here, the cross section of my neck is shown in relation to the cross section of my wood block.
      After the glue dried, I had to mark the block so I could rough cut it.  My local print shop wasn't able to print a full scale version of the plans for me so I resorted to manually making all the measurements rather than tracing the shape of the neck.  It was a little more time consuming, but not too hard.  (Note, I did not use this helpful page because I did not know it existed at the time, but if you are following my steps you may want to check this page out instead.  It should save some time).  First I measured out the total length of the neck being sure to include the little piece of the neck that fits between the top and bottom parts of the pot.  Then I established wear the nut was.  I also drew a center line down the entire length of the block.
This shows the centerline, the edge of what will become the headstock (left line), marks where the nut will be positioned (double lines on the right) and a reference line (tick mark on the right) that would later be used to create the side profile of the neck.
      Using the center line, I measured out the dimensions on the plan.  Not every little measurement is on the plan, but I used some simple arithmetic to figure out most of them.  Also, once you get past the fifth fret on the neck, you can't just divide the width in half to find out how far to measure from the center line.  Past this point, the centerline doesn't actually run down the center of the neck.  I really don't know why I have even been calling it a center line (I could have called it the "fingerboard longitudinal reference line, but that is quite a lot to handle).  However, the total width and the number of pixels (or the distance on your screen if you don't have a pixel counter) are proportional.  So you can solve for the distances using the following formula below where X = the distance from the centerline to the edge of the banjo.  Once you find the distance from the centerline to one edge, it is only a matter of subtracting this from the total width to find the distance from the centerline to the other edge.

(X/Total distance indicated on the plan) = (Pixels from centerline to edge/Pixels from edge to edge)

      I know this looks confusing, but it's really not.  It's just a simple proportion.  You probably learned about them in 6th or 7th grade.  If you don't have a pixel counter, just measure the distance on your computer screen with a ruler.  Be careful not to scratch your screen.  Anyway, it would be much easier to just get full size plans and trace them.  Unfortunately the guy at my local print shop (Pak 'n Fax) tried to print scale drawings for about an hour and then failed.  I wasn't upset until he said it was possible, but it would just take too much time.  He didn't think there would be a net gain for the store, because his wages would not be outweighed by the $3 I would pay.  Unfortunately for the store he failed to consider the possibility of return business which they will not get from me.  Anyway, I am ranting now.  I'll get back on topic.
Measuring the width of the neck.  The distance from the centerline to both edges is equal until you get past the fifth fret (where the bulge in the center of the picture is).  The extra string added at this point changes causes the centerline to not really be in the center.  I really don't know why I have been calling it a centerline.  A square is useful for this step.
      Once you have the top (fingerboard) of the neck marked out you can move on to marking the side profile.  It is pretty easy.  Just measure the appropriate distance from the nut (as indicated on the plans) and then measure the correct depth of the neck at that point.  Make a few of these measurements and then connect the dots.  Again, it would be easier to trace from a full size plan.

I marked the side profile on one side.  It was hard to get an image of the whole profile, but this shows what will later become the angled headstock.  At this point I was really glad that I was cutting the whole neck out of a wood block instead of gluing a separate headstock on.
       At this stage (before you rough cut the neck) I had to decide if I wanted to make a fretless banjo or not.  If I was going to add frets (which I did not) it would have been much easier to measure them and cut slots for them while the edge of my neck block was still square.  I decided not to add frets, but I still took advantage of the square neck blank to measure out where the frets would be and then burn some markers into my neck.  This way, I could still have a fretless instrument but I would have some sort of visual aid to help me get a feel for a fretless instrument.  You can add frets to your banjo if you want, but they require precise measurements from the nut (if I had to guess I would say at least 1/64", but don't quote me on that) and they all need to be level on the plane that is parallel to the fingerboard (or you can get a buzz).  Adding frets is beyond the scope of this article, but there is plenty of other information online.  I didn't want to fret about all the extra trouble, so I just went fretless.

Using a square and a wood burner to put marks instead of frets on the neck.  Doing this step before  rough cutting the neck allowed me to utilize the edge of the wood block and the square.
      There really isn't much to preparing the neck for rough cutting.  It did require a lot of measuring though.  This could be reduced by using this helpful page or just tracing the layout from full size plans.  I have since rough cut my neck and I am now awaiting final shaping.  I'll keep updating as I do more and have time to write.  Oh yeah, I have now spent $17 dollars on my banjo.  I bought screws (used later), poplar, and gorilla glue (which will surely be used for other projects as well).  By the time I finished marking the neck I had probably spent about 5 hours on the banjo, most of which was measuring and re-measuring.  I also met a guy at a bluegrass festival who made his own banjo and has some leftover goat skin.  I think I know what I'll use for my head.

Looking down what will soon be the fingerboard on my banjo neck.

No comments:

Post a Comment