Drilling Spars and the Optical Center Punch

 With all the layout work done, I'm ready to start drilling bolt holes in the spars.
The first task is to make sure the table is perpendicular (square) to the drill bit.  I'm using the ShopSmith to do this because I can adjust squareness and drill speed better.  I start by getting a long drill to use as a reference to measure how square the table is.  Rotate it by hand to make sure it's not bent.  A piece of rod would work if it's straight.
I used the drafting triangle to check squareness in several directions around the drill.  Because of it's size, using it also saved re-positioning the table when I was done.

 I set up the rollers to hold the spar flat while drilling.

 The ShopSmith drill bits have a unique shape which cuts wood well.  The little skirts on the side also help me later when aligning the drill in a template or part to assure multiple holes match between the part and the spar.

 Working with Wood always makes me crazy when center punching holes.  The punch wants to move over to be in the soft wood between growth rings.  The solution is an Optical Center Punch.  The one I'm using is the H5781 by Grizzly Industrial.

 It has a holder base for the center punch with cork on the bottom so you can keep the punch in position without sliding into the soft wood.
To locate it you use an Eyepiece with a Reticle on the bottom end.  This one comes with a Cross Hair reticle and a Point reticle.  I generally prefer the cross hairs because I normally layout crossed center lines, which I find it easier to align with.
It also has a prick punch, the pointy one, and a punch for standard twist drills.  I'm using the prick punch with the ShopSmith drill bits.

 You put the eyepiece in the holder and then align the reticle with your hole location marks.  I find it real easy to see getting it aligned.

 Hold the base tight to the spar.  Remove the eyepiece and insert the punch in the same hole.  An appropriately light tap with a hammer and you've got your mark.

 When the part I'm going to install has multiple holes I prefer to drill the first hole using the center punch and then use the part or template to locate the added holes.

A bolt in the first hole allows the template to be held Accurately in position.  The skirts on the ShopSmith drill bit make it real easy to align the added hole to the drill.  With a regular twist drill I just raise the part or template with some washers under it at each hole.  With the ShopSmith drill bit I put a center punch mark a little deeper for clearance of the tip when I'm using a thin template.  It's easier than fooling with washers.

 I always remove the template before drilling.  Bad things can happen otherwise.

The holes drilled and the part fits perfect.  I this case I wouldn't need the table perfectly square since the part goes on the side we're drilling from.  For the welded strut fittings the holes have to match on both sides so they really need to be square.

Time to keep drilling.