Sunday, February 16, 2020

Spar Drilling Done - Slight Issues with Wider Front Spars

 With the wider front spars the the long 5/16" drill bit won't drill all the way through, after drilling the 1/4" hole.  The quill on the headstock doesn't travel that far.

I've been using a short 5/16" bit to get a more centered start to the hole.  I found if I drill it 3/4" to 1" deep, then start the long bit near the bottom of that hole, it goes all the way through in one pass.  I use a lot of short in and out strokes to keep chips cleared.

 My last step has been to use a "P" drill to open the hole a few thousandths.  The holes wandered just enough, from each end, to still leave the hole slightly tight in the middle.  I found that if I gently tapped the 5/16" chain saw file through the hole it cleared the slight bend and the 5/16" bit, being used as a gauge, fits perfect.  It can't have taken off much.

All the holes are drilled.  On to routing the spars.

Saturday, February 15, 2020

More - Wing Attachment Bolt Holes in Spars

 The Roller stands do take a bit of time to get level with the table each time the table has to be moved up or down.  The rear spars are 1 1/4" thick and the front spars 1" thick, so the table had to move up for the front spars.

It takes a little wiggling to get that long spar aligned tight to the fence, but it gets there.

 For the front spars I used a 3/8" drill bit as a gauge to set the table depth.  I could have used a 1/2" bit for the 1 1/4" spars.

It got me thinking I cut a scrap piece of 1 1/8" tubing as a gauge for the distance to the end of the spar.  I started measuring sockets and found the 13/16" socket was also 1 1/8" in diameter.

 I found that I needed 2 clamps on the end stop so it didn't move.  The end swung out, changing the stop position.

I also found it easier to work with the spars If I clamped them to the table once aligned.
All lined up ready to drill. 

Back to drilling spars.

Thursday, February 13, 2020

Wing Attachment Bolt Holes in Spars

The upper wings attach to the cabane struts, and the lower wings attach to "L" shaped brackets on the sides of the fuselage.  The 5/16" bolts run through the spars from top to bottom.  You could drill these by hand, good luck.  Fortunately I have a ShopSmith and it is perfect for drilling these holes using the Horizontal Drill Press.

 As with the other bolt holes the first step is to get everything aligned and positioned.  Drilling is the easy part.

The headstock rails are back down to their horizontal positon and the table is back in the normal, flat, position.  I'm using the long drill bit again to align things.  Use a back light to level the table to the drill bit.  As you adjust the table "zero stop" you can look at the light coming through the gap under the drill to see when the table is aligned to the bit. 

I discovered the center section of the table is slightly lower than the outer sections.  We'll drill with the spar resting on the outer section.

 Next square the fence to the the drill bit.  It has adjustment screws, which is why I love the Shopsmith.  Everything on it is adjustable.
 I put in a 1/4" drill and used 1 1/8" of gauge blocks to position the stop for the end of the spar.  My wife was a die maker.  This gets the center of the hole 1 1/4" from the end of the spar.  When the root rib is installed the hole will be 1 1/2" from the end of the wing.

Double check with the vernier.

 The height of the table was set to 5/8" with a 1/2" gauge block under the 1/4" drill.  Check with the center punch to see that the height is correct.
 I drilled past 1/2 way from each side of my test piece.

A piece of threaded rod went right through the hole.

 I'm going to drill all the way through with the long 5/16" drill bit.  To make sure it starts out nicely centered on the 1/4" hole, I'm using a shorter bit for about 1/2".  Then I finished the through hole with the long bit.  There is a backing block to make sure I don't drill into the fence.

 The last step is to open the hole a few thousandths with a "P" size bit ( 0.323" ).  I use an "F" bit ( 0.257" ) on 1/4" holes, and a "V" bit  ( 0.377" ) on 3/8" holes.  The bolts fit easier and come out easier if needed some day.
 A perfect hole.  How cool is that?

Time to go drill the spars.

Wednesday, February 12, 2020

I Ruined a Spar

 The bottom of the holes, where the drill bit comes out, has some wood fiber burrs, even with a sharp drill bit.  The factory ignored it.  I'm to nutty to ignore it.  A 30 degree break-away knife works great to clean up the holes.  I normally just use a backup board to prevent this but I couldn't get it as flat and square as just using the table.
 The first spar I drilled got ruined because I started drilling a hole in the wrong place for the strut/brace wire fitting.  I had the template upside down, tall wire end pointing at the tip instead of the root.  It was the result of how I made the templates for the fittings and not checking the fitting outline I drew on the spar.  Fortunately Aircraft Spruce hadn't shipped the other spar material so they were good about adding another spar blank to that order.

This all started because of how I made the templates.  I made the holes for the 1/4" hole and the .377" hole using the Whitney punch.  It doesn't make holes as big as 3/8".  I could have made the holes actual size because I have 3/8" and 1/4" duplicating punches.  I like the shorter centering nib on the Whitney punches, rather than the duplicating punches, because you don't need as thick a spacer under the template to get the punch to set completely in the template hole.  This all worked perfect for making the fittings.

 I could have used the actual fittings to locate the holes in the spars but they're all welded and painted and a tight fit to the spars.  So I used the original templates.  After ruining the first spar I decided I needed a better process so this didn't happen again.  I also wanted to use the original templates for better accuracy.

I start by drilling the 3/8" hole first.  I bought a bag of small bushings at Oshkosh some years back and regularly find uses for them.  This one is 3/8" O.D and 1/4" I.D.  It allows me to use a 1/4" bolt in the original template hole to position the template for the next hole.

 For the 1/4" hole I aligned the 3/16" drill bit in the template hole.  While holding the spar so it didn't move, I changed to the 1/4" bit and drilled the hole.

I made a bushing for the 1/4" hole from a piece of 1/4" aluminum tubing.  It allowed me to use a 3/16" bolt for this hole in the template.

 With the first 2 bolts in the 3/16" bit was aligned to one of the holes, the template removed and the hole drilled.

The same was done for the 4th hole.

 A truly tortured process, but it worked very well.  All 4 bolts fit perfectly.  Because the table is so square, they also fit perfectly on the backside of the 1 1/4" thick spar.  Not bad.

Sunday, February 9, 2020

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.